Jackson, A., Ellis, K.A., McGoldrick, J., Jonsson, N.N., Stear, M.J. and Forbes, A.B. (2017) Targeted anthelmintic treatment of parasitic gastroenteritis in first grazing season dairy calves using daily live weight gain as an indicator. Veterinary Parasitology, 244, pp. 8590.(doi:10.1016/j.vetpar.2017.07.023) This is the author’s final accepted version. There may be differences between this version and the published version. You are advised to consult the publisher’s version if you wish to cite from it. http://eprints.gla.ac.uk/146317/ Deposited on: 21 August 2017 Enlighten – Research publications by members of the University of Glasgow http://eprints.gla.ac.uk33640 Revised Manuscript with changes marked Click here to view linked References 1 1 Targeted anthelmintic treatment of parasitic gastroenteritis in first 2 grazing season dairy calves using daily live weight gain as an indicator 3 4 A. Jackson1, K.A. Ellis1. J. McGoldrick1, N.N. Jonsson2, M.J.Stear3, A.B. 5 Forbes1 6 7 1 8 Veterinary Medicine, College of Veterinary and Life Sciences; University of 9 Glasgow, Bearsden, Glasgow, G61 1Q Scottish Centre for Production Animal Health and Food Safety, School of 10 2 11 of Veterinary and Life Sciences; University of Glasgow, Bearsden, Glasgow, 12 G61 1Q 13 3 Institute of Biodiversity, Animal Health and Comparative Medicine, College La Trobe University, Animal, Plant and Soil Sciences, Melbourne, Australia. 14 15 Corresponding author: A.B. Forbes: Telephone +44(0)7712738530; email 16 andrew.forbes@glasgow.ac.uk 17 18 A. Jackson’s current address is: Merial New Zealand, Level 3, Merial 19 Building, 2 Osterley Way, Auckland 2104, New Zealand 20 21 ABSTRACT 22 23 Control of parasitic gastroenteritis in cattle is typically based on group 24 treatments with appropriate anthelmintics, complemented by grazing 25 management, where feasible. However, the almost inevitable evolution of 2 26 resistance in parasitic nematodes to anthelmintics over time necessitates a 27 reappraisal of their use in order to reduce selection pressure. One such 28 approach is targeted selective treatment (TST), in which only individual 29 animals that will most benefit are treated, rather than whole groups of at- 30 risk cattle. This study was designed to assess the feasibility of implementing 31 TST on three commercial farms, two of which were organic. A total of 104 32 first-grazing season (FGS), weaned dairy calves were enrolled in the study; 33 each was. All animals were weighed at monthly intervals from the start of 34 the grazing season using scales or weigh-bands. A; at the same time dung 35 and blood samples were collected in order to measure faecal egg counts 36 (FEC) and plasma pepsinogen, respectively. A pre-determined threshhold 37 weight gain of less than 0.75 kg/day was used to determine those animals 38 that would be treated; t. The anthelmintic used was eprinomectin. , which 39 has persistent efficacy of 3 weeks against Cooperia oncophora and 4 weeks 40 against Ostertagia ostertagi. No individual animal received more than one 41 treatment during the grazing season and all treatments were given in July 42 or August; five animals were not treated at all because their growth rates 43 consistently exceeded the threshold. Mean daily live weight gain over the 44 entire grazing season ranged between 0.69 and 0.82 kg/day on the three 45 farms. On the two organic farms, these growth rates exceeded those 46 recorded during the preceding grazing season. Neither FEC nor pepsinogen 47 values were significantly associated with live weight gain and therefore are 48 unsuitable markers for performance-based TST. Implementation of TST at 49 farm level requires regular (monthly) handling of the animals and the use of 50 weigh scales or tape, but can be integrated into farm management 3 51 practices. This study has shown that acceptable growth rates can be 52 achieved in young FGS cattle with modest levels of treatment and 53 correspondingly 54 anthelmintics, which should mitigate selection pressure for resistance by 55 increasing the size of the refugia in the both hosts and on pasture. less exposure of their nematode populations to 56 57 Key words: Targeted selective treatment, TST, parasitic gastroenteritis, 58 PGE, cattle, eprinomectin, organic 59 60 1. INTRODUCTION 61 The spectre of aAnthelmintic resistance (AR) hangs like a malevolent cloud 62 over many popular methods of parasite control and consequently resistance 63 has become a major driver for parasitology research and in tailoring advice 64 on parasite controlto farmers. In northern temperate Europe there are 65 currently only three classes of anthelmintic that are licensed for the control 66 of 67 tetrahydropyrimidines (levamisole)s and macrocyclic lactones (MLs), none of 68 which are available in combination with each other. The most commonly 69 reported cases of resistance in bovine nematode parasites in Europe have 70 been in Cooperia species, in which the efficacy of MLs has been shown to be 71 sub-optimal (Geurden et al., 2015). Given that Cooperia spp. are commonly 72 dose-limiting in for the several MLs (Vercruysse and Rew, 2002), accurate 73 weighing of animals and dose administration of the correct dose is essential 74 for efficacy and reports of resistance in which these basic criteria have not 75 be fulfilled should be treated circumspectly. In addition there is some parasitic gastroenteritis (PGE) in cattle: benzimidazoles, 4 76 evidence for ML-resistant Ostertagia ostertagi in Europe, which has also 77 been observed in other regions of the world (Sutherland and Leathwick, 78 2011; Waghorn et al., 2016). For these reasons it is paramount that 79 practices that reduce selection pressure for resistance and conserve the 80 longevity of the current array of cattle anthelmintics are adopted. 81 82 In New Zealand, the emergence of ML-resistant Cooperia was associated 83 with high frequency (every 3-4 weeks) administration over periods of six 84 months or longer each year in young cattle grazed intensively (Jackson et 85 al., 2006). There is little evidence for similar use patterns in Europe, where 86 specific risk factors for AR in cattle have not been determined. Early season 87 strategic anthelmintic treatments have been well established in Europe and 88 shown to provide effective control of parasitic gastroenteritis (PGE) 89 particularly in set-stocked, weaned first grazing season (FGS) cattle (Shaw 90 et al., 1998), but also in the second year at grass (Taylor et al., 1995). The 91 primary objective of strategic approaches is to limit concentrations of 92 infective larvae in the herbage throughout the grazing season by minimising 93 worm egg output and autore-infection, so strategic treatments create low 94 challenge pastures with correspondingly low refugia; this has the potential 95 to increase the speed of selection for anthelmintic resistance (Martin et al., 96 1981). 97 98 Irrespective of the possible risk factors for AR in cattle nematodes, 99 practices that reduce anthelmintic usage are likely to limit selection 100 pressure on parasite populations. One such approach is targeted selective 5 101 treatment (TST) in which, rather than the more typical, synchronous group 102 anthelmintic treatments, individual animals are treated on the basis of a 103 marker or markers that indicate that they will benefit from removal of their 104 parasite burdens. Targeted selective anthelmintic treatments (TST) were 105 initially studied in small ruminants (Kenyon et al., 2009), in which proof of 106 concept 107 performance could be maintained with TST at a level comparable to that 108 seen in animals that were treated more intensively. Equally important was 109 the demonstration that TST applied over successive years led to lower 110 selection for resistance compared to that in lambs treated at 4-week 111 intervals over the grazing season (Kenyon et al., 2013). was demonstrated insofar as disease control and animal 112 113 There is limited published literature regarding the use of performance- 114 based TST approaches in cattle in the field (Charlier et al., 2014; Kenyon 115 and Jackson, 2012). Analysis of published trial data using reporter operating 116 curve (ROC) analysis suggested that an appropriate threshold for daily live 117 weight gain (DLWG) in a TST regime in young cattle would be 0.75 kg/day 118 (Hoglund et al., 2009). This figure coincides with growth rates that are 119 required for replacement dairy heifers to reach minimal breeding weight at 120 15 months in order to calve at two years of age (Froidmont et al., 2013; 121 Zanton and Heinrichs, 2005), thus, DLWGs of ~0.75kg are consistent with 122 commercial targets and farmer aspirations . Weight-gain based TST 123 approaches have provided similar results to those reported in sheep, that is 124 to say acceptable weight gains have been maintained and the number of 125 anthelmintic treatments has been reduced compared to routine, whole 6 126 group treatments (Greer et al., 2010; Hoglund et al., 2013; McAnulty et al., 127 2011). It should be noted that to date, TST has only been shown to be 128 effective in the management of PGE, furthermore, if, for example, 129 lungworm (Dictyocaulus viviparus) is present and has not been controlled 130 through vaccination, then parasitic bronchitis can thwart efforts to control 131 PGE through TST (O'Shaughnessy et al., 2015). 132 133 A series of studies were conducted to extend the scientific evidence base 134 for TST in cattle and to determine its on-farm feasibility (Jackson, 2012). 135 Included in this work was an assessment of various biomarkers as potential 136 indicators for TST, an evaluation of the accuracy and utility of weigh bands 137 for farms that do not have access to weigh scales and implementation of a 138 weight gain-based TST. The objective of the study described in this paper 139 was to determine the feasibility of a weight-gain based TST in first season 140 dairy-bred calves on three livestock farms, two of which were organic. 141 142 2. MATERIALS AND METHODS 143 144 This TST study was approved by the Ethics and Welfare Committee of the 145 School of Veterinary Medicine, University of Glasgow. 146 147 2.1. Participating Farms 148 Three dairy farms located in central and south-west Scotland were recruited 149 into the study: two organic and one conventional (Farm O1, Farm O2 and 150 Farm C3). The three farms were a sub-set of the six farms that were 7 151 involved in a monitoring study of gastrointestinal parasitism the previous 152 year (Jackson, 2012). 153 154 2.1.1 Organic Farm 1 (O1) 155 Organic dairy farm 1 comprised a mixed breed milking herd, predominantly 156 of Friesians and Ayrshires, with some Brown Swiss and Jersey crosses, 157 calving all-year-round and grazing over 93 hectares (ha) of semi-improved 158 grassland from April to October. All FGS cattle in the study were vaccinated 159 against lungworm prior to turnout in late April, when the calves grazed a 160 small paddock near the farm and were given supplementary feed. Two 161 weeks later the calves were moved onto another pasture and subsequently 162 were rotated every two weeks around seven different paddocks in an 163 extensive grazing system. The previous year these fields were grazed by 164 FGS, second season grazers (SGS) or adult dairy cattle. 165 166 In the year prior to the TST study, faecal egg counts (FEC) were taken in 167 June and September and only calves with a FEC of ≥200 eggs per gram (epg) 168 were treated with fenbendazole (Panacur® 10% oral suspension, MSD). The 169 farmer had used this method of anthelmintic treatment over the previous 170 two grazing seasons. The average DLWG in FGS calves during the year that 171 preceded the TST study was 0.46 kg/day. 172 173 2.1.2. Organic Farm 2 (O2) 174 Organic dairy farm 2 covered 344 ha which supported a milking herd of 135 175 Ayrshire and Ayrshire cross cows; some Aberdeen Angus suckler cows and 8 176 sheep were also kept on the farm. Approximately forty per cent of the dairy 177 herd calved between November and December, the rest calved year-round; 178 heifers calved between February and April. The FGS were turned out in 179 early May as a group of sixty calves, which were rotationally grazed over 180 three fields, each of ~20 ha. The year before the TST study, based on faecal 181 egg counts, all FGS were treated with fenbendazole drench in mid-July; the 182 treatment was repeated again at housing in late November. The average 183 DLWG in FGS calves during the year that preceded the TST study was 0.57 184 kg/day. 185 186 2.1.3. Conventional Farm 3 (C3) 187 The conventional dairy farm milked a herd of eighty five Holstein-Friesian 188 cows and there were also beef and sheep enterprises on the farm. Calving in 189 the dairy herd was year round and both heifer replacements and beef x 190 dairy calves were grazed together. The previous year, the FGS animals were 191 not turned out until mid-July because herbage regrowth after early sheep 192 grazing was insufficient; they were set-stocked on four hectares of land and 193 treated with moxidectin injection (Cydectintm 10%, Zoetis) at turnout. The 194 average DLWG in FGS calves during the year that preceded the TST study 195 was 0.93 kg/day. 196 197 2.2 Experimental Animals 198 199 All first season grazers (FGS) on-farm were included in the study (Farm O1 n 200 = 20, Farm O2 n = 41, Farm C3 n = 43). All animals on Farms O1 and C3 were 9 201 vaccinated against D. viviparus (Bovilis HuskvacTM, MSD) before turnout to 202 control lungworm disease. 203 204 2.3. Experimental Design 205 206 Farms were visited in late April and early May 2010, just prior to turnout 207 from housing onto pasture and then at 28-day intervals until housing in the 208 autumn, except for September, when two of the farmers were unable to 209 gather the cattle because of other farming activities. At visit 1 on all farms, 210 each FGS animal had its live weight calculated by weigh-band (Coburn® 211 weigh tape). On Farm C3, all FGS were also weighed on Ritchie® mechanical 212 weigh-scales. At visit 3 in July, eight to ten weeks post-turnout, the girth of 213 all FGS calves were measured using the weigh-band and their live weight 214 gain from turnout calculated. If the live weight gain of an individual animal 215 was < 0.75 kg/day they were treated with eprinomectin (EprinexTM pour-on, 216 Merial). At visit 4 in August, the live weight gain of the FGS over the 217 previous four weeks was calculated. Animals that had not been treated 218 previously and were growing < 0.75 kg/day were treated with eprinomectin. 219 220 Because eEprinomectin has persistent activity of twenty-eight days against 221 O. ostertagi and 21 days against C. oncophora (Cramer et al., 2000), the 222 two most common species contributing to PGE in FGS in northern Europe. 223 Thus, following treatment, FECs would be expected to be minimal for 6-7 224 weeks, this being the sum of persistent activity and a typical pre-patent 225 period of ~3 weeks for O. ostertagi and C. oncophora. For this reason, 10 226 animals previously treated at visit 3 were not treated again at visit 4, 227 irrespective of their DLWG in the interim, as this would have meant treating 228 within the effective pre-patent period and this can potentially exert a high 229 selection pressure for AR. As farmers had requested a month off from 230 sampling in September on farms O1 and O2, no treatments were given on 231 this visit (5) on Farm C3. No treatment was planned for visit 6 at housing. 232 233 2.3.1. Laboratory Analysis 234 235 Each calf had a blood sample taken by jugular or coccygeal venepuncture 236 into an EDTA tube for serum pepsinogen analysis (all visits) and a faecal 237 sample taken per rectum obtained at visits 2, 3, 4, 5 and 6 for faecal egg 238 count, lungworm and liver fluke monitoring. Larval culture was performed 239 on faeces collected during visit 3. Further details of the standard laboratory 240 techniques used can be found in a companion previously published paper 241 (Ellis et al., 2011). 242 243 2.3.2. Statistical Analysis 244 245 The Spearman’s rank correlation test was used on non-normally distributed 246 data to investigate any associations with live weight gain. Statistical analysis 247 of the data was performed using Excel, Minitab 16 for Windows and SAS 248 University edition (SAS Institute, Cary, N. Carolina). The association of 249 bodyweight or growth rate with faecal egg count (FEC) or pepsinogenaemia 250 (Pep) was assessed by repeated measures variance analysis. The proc mixed 11 251 procedure in SAS was used and the model fitted the effects of farm, sample 252 date, test variable (FEC or Pep) and the interaction between sample date 253 and test variable. Several variance structures were tested including 254 unstructured, compound symmetry and heterogeneous autoregressive of 255 order 1. The best fitting model was chosen using four criteria: residual log 256 likelihood, Akaike’s information criterion (AIC), the finite-population 257 corrected AIC and Bayes Information criterion (BIC). For both faecal egg 258 count 259 autoregressive structure provided the best fit. and plasma pepsinogen concentration, a heterogeneous 260 3. RESULTS 263 3.1. Live weight Gain 264 Mean live weight gains (± Standard Deviation) over the grazing season for all 265 FGS animals in the study were: 261 262 266  Farm O1 0.69 ± 0.28 kg/day (weighband) 267  Farm O2 0.82 ± 0.13 kg/day (weighband) 268  Farm C3 0.75 ± 0.23 kg/day (weigh scale) 269 The cattle on the conventional farm were heavier (277 kg) at turnout than 270 those on the organic farms (190 and 167 kg), but the growth curves of cattle 271 on all three farms were similar and DLWG was distributed normally amongst 272 all the animals (Figure 1). 273 274 3.2. Faecal Egg Count 12 275 No results are available from tThe faecal samples taken from the cattle on 276 the organic farms on visit 6 as they were stored incorrectlypoiled after 277 collection in the laboratory. The majority of faecal egg counts on all farms 278 over the grazing season were less than 200 epg (Figure 2), though at the 279 July sampling a peak individual count of 1200 epg was observed on one of 280 the organic farms (O1). There were significant differences among the farms 281 (p=0.007). Consistent with results on the same farms sampled the previous 282 year, faecal egg counts showed no significant association with growth rate 283 (p=0.605) and there was no interaction between FEC and sample date 284 (p=0.177). 285 286 3.3 Larval Culture 287 Using standard techniques and keys (MAFF, 1986; van Wyk et al., 2004), 288 lLarval culture and speciation identification was undertaken on dung 289 samples collected at visit 3 in July, corresponding to the middle of the 290 grazing season before anthelmintic treatment. The results are tabulated in 291 Table 1. The majority of larvae cultured were C. oncophora, the remainder 292 were O. ostertagi. 293 294 3.4. Pepsinogen 295 Plasma pepsinogen concentrations were at baseline on visit I prior to 296 turnout; thereafter concentrations increased on all farms over the grazing 297 season, though the majority of values remained at ≤2 IU (Figure 3). The 298 differences among farms in the mean pepsinogen response were not 299 significant (p=0.051), although cattle farm O1 had high plasma pepsinogen 13 300 concentrations at housing (3.2 ± 1.7 iu/l). Consistent with results on the 301 same farms sampled the previous year, plasma pepsinogen concentrations 302 showed no association with growth rate (p=0.409) and there was no 303 interaction between pepsinogen and sample date (p=0.131). 304 305 3.5. Targeted Selective Anthelmintic Treatment 306 None of the animals on any farm were treated more than once over the 307 grazing season; all the treatments were administered in either July or 308 August according to individual DLWG over the preceding 28 days. 309  Farm O1 18 in July; 1 in August; 1 animal not treated at all 310  Farm O2 29 in July; 8 in August; 4 animals not treated at all 311  Farm C3 18 in July; 25 in August 312 313 5.4. DISCUSSION 314 315 The basic premise for DLWG-based TST is that, providing nutrition is not 316 limiting and that no other identifiable causes of ill-health are present, then 317 the individual growth rate of weaned calves (or lambs) at pasture is linearly 318 and consistently related to the impact of gastrointestinal parasitism (Greer 319 et al., 2009) through its effect on appetite, feed intake, protein metabolism 320 and nutrient partitioning (Forbes et al., 2000; Fox, 1997). In order to 321 incorporate the quality and quantity of the herbage available into the 322 implementation of TST, in sheep systems an algorithm named the Happy 323 FactorTM has been developed (Greer et al., 2009), which. This adjusts the 324 target DLWG to the availability and quality of the herbage. This approach 14 325 has not yet been used in cattle TST, where the assessment of pasture is 326 typically undertaken either subjectively by observation, or quantitatively 327 through the use of standard techniques to measurements of herbage mass 328 and/or sward height (Lambert et al., 2004). Individual DLWG alone was used 329 as the determinant for treatment in this study, though samples were also 330 taken for parasitological examination in order to gain further knowledge of 331 their interrelationships. 332 333 5.1. Biomarkers 334 335 Faecal egg counts and plasma pepsinogen concentrations were analysed 336 throughout the grazing season and an evaluation of their correlation with 337 live weight gain was undertaken as both have been advocated for use in 338 targeted selective anthelmintic regimes (Charlier et al., 2014). 339 340 5.1.1. Faecal Egg Counts 341 As in the preceding year (Jackson, 2012), there were no significant 342 associations between FEC and DLWG. This result is not surprising, given that 343 FECs in young cattle in temperate regions with an Ostertagia/Cooperia 344 dominant nematode fauna, whether in experimental infections or under 345 field conditions, have shown no consistent or linear relationship with worm 346 burdens or animal performance (Brunsdon, 1969, 1971; Michel, 1969). 347 348 An analysis was performed of the number of calves that would have been 349 treated with anthelmintic at visit 3 if FECs were used as an indicator using 15 350 an arbitrary threshold of ≥250 epg. The results show only ten FGS had FEC of 351 ≥250 epg, all on Farm O1. Overall, 54 calves, growing <0.75 kg/day would 352 not have been treated with anthelmintic had FEC been used as an indicator. 353 354 5.1.2 Larval culture 355 Cooperia spp. larvae predominated in the faecal cultures conducted in July, 356 but these results do not necessarily reflect the worm burdens in the animals 357 at the time (Brunsdon, 1968, 1971). The results of the pepsinogen assays 358 suggest that O. ostertagi nematodes waswere having a greater impact over 359 the second half of the grazing season. 360 361 5.1.3 Pepsinogen 362 Consistent with results from the preceding year (Jackson, 2012), there were 363 no significant correlations between plasma pepsinogen concentrations and 364 DLWG. Pepsinogen provides a direct measure of abomasal dysfunction and is 365 closely associated with abomasal pathology and intra-luminal O. ostertagi 366 populations (Michel et al., 1978). It is perhaps surprising that it is not more 367 closely correlated with growth rate, but this hwas also been observed in 368 other field studies in temperate regions (Brunsdon, 1969, 1971, 1972) and 369 may be due to co-infection with the intestinal species of Cooperia in FGS 370 calves, which can also impact growth rate, singly (Armour et al., 1987) or in 371 combination with O. ostertagi (Parkins et al., 1990), but Cooperia spp. do 372 not typically provoke an increase in pepsinogen. 373 374 45.2. Performance-based Targeted Selective Anthelmintic Treatment 16 375 5.2.1. Growth rate 376 The current trial was primarily a feasibility study for TST on commercial 377 farms, so there are no contemporary comparisons were possible, however 378 cattle growth rates from the previous year are available for each farm and 379 these provide a basis on which to assess the impact of TST. Despite some 380 concurrent (non-parasitic) respiratory disease, the mean growth rate of the 381 FGS cattle on the conventional farm C3 was ≥0.75 kg/day over the grazing 382 season, which was the target, though less than the previous year when, 383 using a long-acting anthelmintic and over a shortened grazing season, the 384 growth rate was 0.93 kg/day. On the organic farm O2 the average growth 385 rate under the TST regimen exceeded 0.75 kg/day and this was considerably 386 higher than in the previous year (0.57 kg/day). Although the growth rate on 387 organic farm O1 was less than target, at 0.69 kg/day it was again higher 388 than that of the previous grazing season when it was 0.46 kg/day. On 389 neither of the organic farms were there any major changes in nutritional or 390 grazing management between years. 391 392 5.2.2. Anthelmintic use 393 The number of animals treated (all) on the conventional farm was the same 394 using TST as it was the previous year, but the potential exposure to 395 discriminating doses of anthelmintic was reduced with TST through the 396 asynchronous, mid/late season administration of eprinomectin, which has 397 persistent activity of 28 days against O. ostertagi, compared to moxidectin 398 10%, which has 120 days of persistent activity against this species. On 399 organic farm O2, all FGS calves were treated once in July the previous year 17 400 with fenbendazole, which has no persistent activity, whereas under the TST 401 regimen, all bar four animals were treated in July or August, with 402 eprinomectin, so arguably the anthelmintic selection pressure could have 403 increased under TST. Similarly, oOn organic farm O1, only two calves were 404 treated the previous year with fenbendazole, while 19/20 animals were 405 treated with eprinomectin under TST, however, on both organic farms, the 406 FGS growth rates were higher under the TST regime. 407 408 In order to assess the effect of TST in satisfying the joint objectives of 409 achieving satisfactory growth rates while limiting selection pressure for 410 anthelmintic resistance, modellers have introduced a factor named ‘benefit 411 per R’, abbreviated to BPR (Laurenson et al., 2016). This is calculated from 412 a ratio between the average weight gain benefit (AWGB) arising from 413 whatever control measures have been used and the increase in anthelmintic 414 resistance allele frequency (IRAF) under that system; both are calculated 415 over the duration of the grazing season. This approach was used initially in 416 sheep and has subsequently extrapolated to cattle (Berk et al., 2016), in 417 which it was shown that the use of a DLWG threshold as an indicator for 418 anthelmintic treatments in TST was the approach that optimised BPR. 419 420 45.3. Concluding remarks 421 422 Applying a performance-based TST in the field was shown to be feasible 423 through the use of weigh bands, albeit this measurement requires adequate 424 restraint of animals. Gathering and handling young stock can be a critical 18 425 factor in commercial dairy herds, where replacement heifers are often 426 grazed on pastures away from the main farm and where handling facilities 427 may be rudimentary and inadequate for monthly individual animal 428 assessments. Wider adoption of some of the technologies that are already 429 used by some sheep farmers, such as electronic identification (EID), weigh- 430 scales with integrated software and automatic shedding gates (McBean et 431 al., 2016) would all facilitate the adoption of TST in cattle. Faecal egg 432 count and plasma pepsinogen concentration were found to have no 433 significant association with live weight gain and showed high levels of 434 variability amongst individuals within the management groups, so cannot be 435 recommended if one of the primary objectives for parasite control in 436 youngstock is to maintain growth rates that are commensurate with farm 437 objectives and industry standards. 438 439 On the organic farms, where anthelmintic treatment was already minimal, 440 DLWG was increased compared to the previous grazing season to rates that 441 are considered to be more compatible with optimum life-time performance 442 in heifer replacements (Wathes et al., 2014). Although organic principles 443 eschew the priority of performance in medication decisions, poor growth is 444 virtually a universal indicator of illness in young animals, commonly through 445 mechanisms that include anorexia (Exton, 1997; Hart, 1990), then it seems 446 that monitoring DLWG should be compatible with the organic ethos in 447 promoting animal welfare. 448 449 ACKNOWLEDGEMENTS 19 450 The authors would like to thank the participating farmers and farm staff for 451 their assistance with animal handling and sample collection. Merial 452 Animal Health is acknowledged for its support of this project. Abigail 453 Jackson was supported by the Crawford Endowment. 454 455 REFERENCES 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 Armour, J., Bairden, K., Holmes, P.H., Parkins, J.J., Ploeger, H., Salman, S.K., McWilliam, P.N., 1987. 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A comparative study of the effects of four treatment regimes on ivermectin efficacy, body weight and pasture contamination in lambs naturally infected with gastrointestinal nematodes in Scotland. Int J Parasitol Drugs Drug Resist 3, 77-84. Lambert, M.G., Clark, D.A., Litherland, A.J., 2004. Advances in pasture management for animal productivity and health. N Z Vet J 52, 311319. Laurenson, Y.C.S.M., Kahn, L.P., Bishop, S.C., Kyriazakis, I., 2016. Which is the best phenotypic trait for use in a targeted selective treatment strategy for growing lambs in temperate climates? Vet Parasitol 226, 174-188. MAFF, 1986. Manual of Veterinary Parasitological Laboratory Techniques. Her Majesty’s Stationary Office, London, 160 p. Martin, P.J., Le Jambre, L.F., Claxton, J.H., 1981. The impact of refugia on the development of thiabendazole resistance in Haemonchus contortus. Int J Parasitol 11, 35-41. McAnulty, R.W., Gibbs, S.J., Greer, A.W., 2011. Liveweight gain of grazing dairy calves in their first season subjected to a targeted selective anthelmintic treatment (TST) regime. Proc NZ Soc Anim Prod 71, 301303. McBean, D., Nath, M., Lambe, N., Morgan-Davies, C., Kenyon, F., 2016. Viability of the Happy Factor targeted selective treatment approach on several sheep farms in Scotland. Vet Parasitol 218, 22-30. Michel, J.F., 1969. Observations on the faecal egg count of calves naturally infected with Ostertagia ostertagi. Parasitology 59, 829-835. Michel, J.F., Lancaster, M.B., Hong, C., Berrett, S., 1978. Plasma pepsinogen levels in some experimental infections of Ostertagia ostertagi in cattle. Vet Rec 103, 370-373. O'Shaughnessy, J., Earley, B., Mee, J.F., Doherty, M.L., Crosson, P., Barrett, D., de Waal, T., 2015. Controlling nematodes in dairy calves using targeted selective treatments. Vet Parasitol 209, 221-228. Parkins, J.J., Taylor, L.M., Holmes, P.H., Bairden, K., Salman, S.K., Armour, J., 1990. Pathophysiological and parasitological studies on a concurrent infection of Ostertagia ostertagi and Cooperia oncophora in calves. Res Vet Sci 48, 201-208. Shaw, D.J., Vercruysse, J., Claerebout, E., Dorny, P., 1998. Gastrointestinal nematode infections of first-grazing season calves in Western Europe: general patterns and the effect of chemoprophylaxis. Vet Parasitol 75, 115-131. Sutherland, I.A., Leathwick, D.M., 2011. Anthelmintic resistance in nematode parasites of cattle: a global issue? Trends Parasitol 27, 176181. Taylor, S.M., McMullin, P.F., Mallon, T.R., Kelly, A., Grimshaw, W.T., 1995. Effects of treatment with topical ivermectin three and eight weeks after turnout on nematode control and the performance of secondseason beef suckler cattle. Vet Rec 136, 558-561. Formatted: French (France) 22 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 van Wyk, J.A., Cabaret, J., Michael, L.M., 2004. Morphological identification of nematode larvae of small ruminants and cattle simplified. Vet Parasitol 119, 277-306. Vercruysse, J., Rew, R.S. 2002. Macrocyclic lactones in antiparasitic therapy (United Kingdom and USA, CABI Publishing), p. 432. Waghorn, T.S., Miller, C.M., Leathwick, D.M., 2016. Confirmation of ivermectin resistance in Ostertagia ostertagi in cattle in New Zealand. Vet Parasitol 229, 139-143. Wathes, D.C., Pollott, G.E., Johnson, K.F., Richardson, H., Cooke, J.S., 2014. Heifer fertility and carry over consequences for life time production in dairy and beef cattle. Animal 8 Suppl 1, 91-104. Zanton, G.I., Heinrichs, A.J., 2005. Meta-Analysis to Assess Effect of Prepubertal Average Daily Gain of Holstein Heifers on First-Lactation Production. J Dairy Sci 88, 3860-3867. 23 611 Tables 612 613 Table 1. Percentage of O. ostertagi and C. oncophora larvae cultured from 614 faecal samples collected pre-treatment in July (visit 3) on each farm. 615 24 616 Figures 617 618  live weights of animals throughout study. 619 620  623 624 Figure 2. Skewed distribution (Kolmogorov-Smirnov test p<0.01) of individual faecal egg counts (FEC) throughout study. 621 622 Figure 1. Normal distribution (Kolmogorov-Smirnov test p>0.150) of  Figure 3. Skewed distribution (Kolmogorov-Smirnov test p<0.01) of individual plasma pepsinogen (PEP) throughout study. Revised Manuscript with NO changes marked (clean) Click here to view linked References 1 1 Targeted anthelmintic treatment of parasitic gastroenteritis in first 2 grazing season dairy calves using daily live weight gain as an indicator 3 4 A. Jackson1, K.A. Ellis1. J. McGoldrick1, N.N. Jonsson2, M.J.Stear3, A.B. 5 Forbes1 6 7 1 8 Veterinary Medicine, College of Veterinary and Life Sciences; University of 9 Glasgow, Bearsden, Glasgow, G61 1Q Scottish Centre for Production Animal Health and Food Safety, School of 10 2 11 of Veterinary and Life Sciences; University of Glasgow, Bearsden, Glasgow, 12 G61 1Q 13 3 Institute of Biodiversity, Animal Health and Comparative Medicine, College La Trobe University, Animal, Plant and Soil Sciences, Melbourne, Australia. 14 15 Corresponding author: A.B. Forbes: Telephone +44(0)7712738530; email 16 andrew.forbes@glasgow.ac.uk 17 18 A. Jackson’s current address is: Merial New Zealand, Level 3, Merial 19 Building, 2 Osterley Way, Auckland 2104, New Zealand 20 21 ABSTRACT 22 23 Control of parasitic gastroenteritis in cattle is typically based on group 24 treatments with anthelmintics, complemented by grazing management, 25 where feasible. However, the almost inevitable evolution of resistance in 2 26 parasitic nematodes to anthelmintics over time necessitates a reappraisal of 27 their use in order to reduce selection pressure. One such approach is 28 targeted selective treatment (TST), in which only individual animals that 29 will most benefit are treated, rather than whole groups of at-risk cattle. 30 This study was designed to assess the feasibility of implementing TST on 31 three commercial farms, two of which were organic. A total of 104 first- 32 grazing season (FGS), weaned dairy calves were enrolled in the study; each 33 was weighed at monthly intervals from the start of the grazing season using 34 scales or weigh-bands. At the same time dung and blood samples were 35 collected in order to measure faecal egg counts (FEC) and plasma 36 pepsinogen, respectively. A pre-determined threshhold weight gain of 0.75 37 kg/day was used to determine those animals that would be treated; the 38 anthelmintic used was eprinomectin. No individual animal received more 39 than one treatment during the grazing season and all 40 given in July or August; five animals were not treated at all because their 41 growth rates consistently exceeded the threshold. Mean daily live weight 42 gain over the entire grazing season ranged between 0.69 and 0.82 kg/day on 43 the three farms. Neither FEC nor pepsinogen values were significantly 44 associated with live weight gain. Implementation of TST at farm level 45 requires regular (monthly) handling of the animals and the use of weigh 46 scales or tape, but can be integrated into farm management practices. This 47 study has shown that acceptable growth rates can be achieved in FGS cattle 48 with modest levels of treatment and correspondingly less exposure of their 49 nematode populations to anthelmintics, which should mitigate selection treatments were 3 50 pressure for resistance by increasing the size of the refugia in both hosts 51 and pasture. 52 53 Key words: Targeted selective treatment, TST, parasitic gastroenteritis, 54 PGE, cattle, eprinomectin, 55 56 1. INTRODUCTION 57 Anthelmintic resistance (AR) has become a major driver for parasitology 58 research and in tailoring advice on parasite control. In northern temperate 59 Europe there are currently only three classes of anthelmintic that are 60 licensed for the control of parasitic gastroenteritis (PGE) in cattle: 61 benzimidazoles, 62 lactones (MLs), none of which are available in combination with each other. 63 The most commonly reported cases of resistance in bovine nematode 64 parasites in Europe have been in Cooperia species, in which the efficacy of 65 MLs has been shown to be sub-optimal (Geurden et al., 2015). Given that 66 Cooperia spp. are dose-limiting for several MLs (Vercruysse and Rew, 2002), 67 accurate weighing of animals and administration of the correct dose is 68 essential for efficacy and reports of resistance in which these basic criteria 69 have not be fulfilled should be treated circumspectly. In addition there is 70 some evidence for ML-resistant Ostertagia ostertagi in Europe, which has 71 also been observed in other regions of the world (Sutherland and Leathwick, 72 2011; Waghorn et al., 2016). For these reasons it is paramount that 73 practices that reduce selection pressure for resistance and conserve the 74 longevity of the current array of cattle anthelmintics are adopted. tetrahydropyrimidines (levamisole) and macrocyclic 4 75 76 In New Zealand, the emergence of ML-resistant Cooperia was associated 77 with high frequency (every 3-4 weeks) administration over periods of six 78 months or longer each year in young cattle grazed intensively (Jackson et 79 al., 2006). There is little evidence for similar use patterns in Europe, where 80 specific risk factors for AR in cattle have not been determined. Early season 81 strategic anthelmintic treatments have been well established in Europe and 82 shown to provide effective control of parasitic gastroenteritis (PGE) 83 particularly in set-stocked, weaned first grazing season (FGS) cattle (Shaw 84 et al., 1998), but also in the second year at grass (Taylor et al., 1995). The 85 primary objective of strategic approaches is to limit concentrations of 86 infective larvae in the herbage throughout the grazing season by minimising 87 worm egg output and re-infection, so strategic treatments create low 88 challenge pastures with correspondingly low refugia; this has the potential 89 to increase the speed of selection for anthelmintic resistance (Martin et al., 90 1981). 91 92 Irrespective of the possible risk factors for AR in cattle nematodes, 93 practices that reduce anthelmintic usage are likely to limit selection 94 pressure on parasite populations. One such approach is targeted selective 95 treatment (TST) in which, rather than the more typical, synchronous group 96 anthelmintic treatments, individual animals are treated on the basis of a 97 marker or markers that indicate that they will benefit from removal of their 98 parasite burdens. Targeted selective anthelmintic treatments (TST) were 99 initially studied in small ruminants (Kenyon et al., 2009), in which proof of 5 100 concept was demonstrated insofar as disease control and animal 101 performance could be maintained with TST at a level comparable to that 102 seen in animals that were treated more intensively. Equally important was 103 the demonstration that TST applied over successive years led to lower 104 selection for resistance compared to that in lambs treated at 4-week 105 intervals over the grazing season (Kenyon et al., 2013). 106 107 There is limited published literature regarding the use of performance- 108 based TST approaches in cattle in the field (Charlier et al., 2014; Kenyon 109 and Jackson, 2012). Analysis of published trial data using reporter operating 110 curve (ROC) analysis suggested that an appropriate threshold for daily live 111 weight gain (DLWG) in a TST regime in young cattle would be 0.75 kg/day 112 (Hoglund et al., 2009). This figure coincides with growth rates that are 113 required for replacement dairy heifers to reach minimal breeding weight at 114 15 months in order to calve at two years of age (Froidmont et al., 2013; 115 Zanton and Heinrichs, 2005). Weight-gain based TST approaches have 116 provided similar results to those reported in sheep, that is to say acceptable 117 weight gains have been maintained and the number of anthelmintic 118 treatments has been reduced compared to routine, whole group treatments 119 (Greer et al., 2010; Hoglund et al., 2013; McAnulty et al., 2011). It should 120 be noted that to date, TST has only been shown to be effective in the 121 management of PGE, furthermore, if, for example, lungworm (Dictyocaulus 122 viviparus) is present and has not been controlled through vaccination, then 123 parasitic bronchitis can thwart efforts to control PGE through TST 124 (O'Shaughnessy et al., 2015). 6 125 126 A series of studies were conducted to extend the scientific evidence base 127 for TST in cattle and to determine its on-farm feasibility (Jackson, 2012). 128 Included in this work was an assessment of various biomarkers as potential 129 indicators for TST, an evaluation of the accuracy and utility of weigh bands 130 for farms that do not have access to weigh scales and implementation of a 131 weight gain-based TST. The objective of the study described in this paper 132 was to determine the feasibility of a weight-gain based TST in first season 133 dairy-bred calves on three livestock farms, two of which were organic. 134 135 2. MATERIALS AND METHODS 136 137 This TST study was approved by the Ethics and Welfare Committee of the 138 School of Veterinary Medicine, University of Glasgow. 139 140 2.1. Participating Farms 141 Three dairy farms located in central and south-west Scotland were recruited 142 into the study: two organic and one conventional (Farm O1, Farm O2 and 143 Farm C3). The three farms were a sub-set of the six farms that were 144 involved in a monitoring study of gastrointestinal parasitism the previous 145 year (Jackson, 2012). 146 147 2.1.1 Organic Farm 1 (O1) 148 Organic dairy farm 1 comprised a mixed breed milking herd, predominantly 149 of Friesians and Ayrshires, with some Brown Swiss and Jersey crosses, 7 150 calving all-year-round and grazing over 93 hectares (ha) of semi-improved 151 grassland from April to October. All FGS cattle in the study were vaccinated 152 against lungworm prior to turnout in late April, when the calves grazed a 153 small paddock near the farm and were given supplementary feed. Two 154 weeks later the calves were moved onto another pasture and subsequently 155 were rotated every two weeks around seven different paddocks in an 156 extensive grazing system. The previous year these fields were grazed by 157 FGS, second season grazers (SGS) or adult dairy cattle. 158 159 In the year prior to the TST study, faecal egg counts (FEC) were taken in 160 June and September and only calves with a FEC of ≥200 eggs per gram (epg) 161 were treated with fenbendazole (Panacur® 10% oral suspension, MSD). The 162 farmer had used this method of anthelmintic treatment over the previous 163 two grazing seasons. The average DLWG in FGS calves during the year that 164 preceded the TST study was 0.46 kg/day. 165 166 2.1.2. Organic Farm 2 (O2) 167 Organic dairy farm 2 covered 344 ha which supported a milking herd of 135 168 Ayrshire and Ayrshire cross cows; some Aberdeen Angus suckler cows and 169 sheep were also kept on the farm. Approximately forty per cent of the dairy 170 herd calved between November and December, the rest calved year-round; 171 heifers calved between February and April. The FGS were turned out in 172 early May as a group of sixty calves, which were rotationally grazed over 173 three fields, each of ~20 ha. The year before the TST study, based on faecal 174 egg counts, all FGS were treated with fenbendazole drench in mid-July; the 8 175 treatment was repeated again at housing in late November. The average 176 DLWG in FGS calves during the year that preceded the TST study was 0.57 177 kg/day. 178 179 2.1.3. Conventional Farm 3 (C3) 180 The conventional dairy farm milked a herd of eighty five Holstein-Friesian 181 cows and there were also beef and sheep enterprises on the farm. Calving in 182 the dairy herd was year round and both heifer replacements and beef x 183 dairy calves were grazed together. The previous year, the FGS animals were 184 not turned out until mid-July because herbage regrowth after early sheep 185 grazing was insufficient; they were set-stocked on four hectares of land and 186 treated with moxidectin injection (Cydectin tm 10%, Zoetis) at turnout. The 187 average DLWG in FGS calves during the year that preceded the TST study 188 was 0.93 kg/day. 189 190 2.2 Experimental Animals 191 192 All first season grazers (FGS) on-farm were included in the study (Farm O1 n 193 = 20, Farm O2 n = 41, Farm C3 n = 43). All animals on Farms O1 and C3 were 194 vaccinated against D. viviparus (Bovilis HuskvacTM, MSD) before turnout to 195 control lungworm disease. 196 197 198 2.3. Experimental Design 9 199 Farms were visited in late April and early May 2010, just prior to turnout 200 from housing onto pasture and then at 28-day intervals until housing in the 201 autumn, except for September, when two of the farmers were unable to 202 gather the cattle because of other farming activities. At visit 1 on all farms, 203 each FGS animal had its live weight calculated by weigh-band (Coburn® 204 weigh tape). On Farm C3, all FGS were also weighed on Ritchie® mechanical 205 weigh-scales. At visit 3 in July, eight to ten weeks post-turnout, the girth of 206 all FGS calves were measured using the weigh-band and their live weight 207 gain from turnout calculated. If the live weight gain of an individual animal 208 was < 0.75 kg/day they were treated with eprinomectin (Eprinex TM pour-on, 209 Merial). At visit 4 in August, the live weight gain of the FGS over the 210 previous four weeks was calculated. Animals that had not been treated 211 previously and were growing < 0.75 kg/day were treated with eprinomectin. 212 213 Because eprinomectin has persistent activity of twenty-eight days against O. 214 ostertagi and 21 days against C. oncophora (Cramer et al., 2000), animals 215 previously treated at visit 3 were not treated again at visit 4, irrespective of 216 their DLWG in the interim, as this would have meant treating within the 217 effective pre-patent period and this can potentially exert a high selection 218 pressure for AR. As farmers had requested a month off from sampling in 219 September on farms O1 and O2, no treatments were given on this visit (5) 220 on Farm C3. No treatment was planned for visit 6 at housing. 221 222 223 2.3.1. Laboratory Analysis 10 224 Each calf had a blood sample taken by jugular or coccygeal venepuncture 225 into an EDTA tube for serum pepsinogen analysis (all visits) and a faecal 226 sample taken per rectum obtained at visits 2, 3, 4, 5 and 6 for faecal egg 227 count, lungworm and liver fluke monitoring. Larval culture was performed 228 on faeces collected during visit 3. Further details of the standard laboratory 229 techniques used can be found in a previously published paper (Ellis et al., 230 2011). 231 232 2.3.2. Statistical Analysis 233 234 The Spearman’s rank correlation test was used on non-normally distributed 235 data to investigate any associations with live weight gain. Statistical analysis 236 of the data was performed using Excel, Minitab 16 for Windows and SAS 237 University edition (SAS Institute, Cary, N. Carolina). The association of 238 bodyweight or growth rate with faecal egg count (FEC) or pepsinogenaemia 239 (Pep) was assessed by repeated measures variance analysis. The proc mixed 240 procedure in SAS was used and the model fitted the effects of farm, sample 241 date, test variable (FEC or Pep) and the interaction between sample date 242 and test variable. Several variance structures were tested including 243 unstructured, compound symmetry and heterogeneous autoregressive of 244 order 1. The best fitting model was chosen using four criteria: residual log 245 likelihood, Akaike’s information criterion (AIC), the finite-population 246 corrected AIC and Bayes Information criterion (BIC). For both faecal egg 247 count 248 autoregressive structure provided the best fit. and plasma pepsinogen concentration, a heterogeneous 11 249 3. RESULTS 252 3.1. Live weight Gain 253 Mean live weight gains (± Standard Deviation) over the grazing season for all 254 FGS animals in the study were: 250 251 255  Farm O1 0.69 ± 0.28 kg/day (weighband) 256  Farm O2 0.82 ± 0.13 kg/day (weighband) 257  Farm C3 0.75 ± 0.23 kg/day (weigh scale) 258 The cattle on the conventional farm were heavier (277 kg) at turnout than 259 those on the organic farms (190 and 167 kg), but the growth curves of cattle 260 on all three farms were similar and DLWG was distributed normally amongst 261 all the animals (Figure 1). 262 263 3.2. 264 No results are available from the faecal samples taken from the cattle on 265 the organic farms on visit 6 as they were stored incorrectly after collection. 266 The majority of faecal egg counts on all farms over the grazing season were 267 less than 200 epg (Figure 2), though at the July sampling a peak individual 268 count of 1200 epg was observed on one of the organic farms (O1). There 269 were significant differences among the farms (p=0.007). Consistent with 270 results on the same farms sampled the previous year, faecal egg counts 271 showed no significant association with growth rate (p=0.605) and there was 272 no interaction between FEC and sample date (p=0.177). 273 Faecal Egg Count 12 274 3.3 Larval Culture 275 Using standard techniques and keys (MAFF, 1986; van Wyk et al., 2004), 276 larval culture and identification was undertaken on dung samples collected 277 at visit 3 in July, corresponding to the middle of the grazing season before 278 anthelmintic treatment. The results are tabulated in Table 1. The majority 279 of larvae cultured were C. oncophora, the remainder were O. ostertagi. 280 281 3.4. Pepsinogen 282 Plasma pepsinogen concentrations were at baseline on visit I prior to 283 turnout; thereafter concentrations increased on all farms over the grazing 284 season, though the majority of values remained at ≤2 IU (Figure 3). The 285 differences among farms in the mean pepsinogen response were not 286 significant (p=0.051), although cattle farm O1 had high plasma pepsinogen 287 concentrations at housing (3.2 ± 1.7 iu/l). Consistent with results on the 288 same farms sampled the previous year, plasma pepsinogen concentrations 289 showed no association with growth rate (p=0.409) and there was no 290 interaction between pepsinogen and sample date (p=0.131). 291 292 3.5. Targeted Selective Anthelmintic Treatment 293 None of the animals on any farm were treated more than once over the 294 grazing season; all the treatments were administered in either July or 295 August according to individual DLWG over the preceding 28 days. 296  Farm O1 18 in July; 1 in August; 1 animal not treated at all 297  Farm O2 29 in July; 8 in August; 4 animals not treated at all 298  Farm C3 18 in July; 25 in August 13 299 300 4. DISCUSSION 301 302 The basic premise for DLWG-based TST is that, providing nutrition is not 303 limiting and that no other identifiable causes of ill-health are present, then 304 the individual growth rate of weaned calves (or lambs) at pasture is linearly 305 and consistently related to the impact of gastrointestinal parasitism (Greer 306 et al., 2009) through its effect on appetite, feed intake, protein metabolism 307 and nutrient partitioning (Forbes et al., 2000; Fox, 1997). In sheep systems 308 an algorithm named the Happy FactorTM has been developed (Greer et al., 309 2009), which adjusts the target DLWG to the availability and quality of the 310 herbage. This approach has not yet been used in cattle TST, where the 311 assessment of pasture is typically undertaken either subjectively by 312 observation, or quantitatively through the use of standard techniques to 313 measure herbage mass and/or sward height (Lambert et al., 2004). 314 Individual DLWG alone was used as the determinant for treatment in this 315 study, though samples were also taken for parasitological examination in 316 order to gain further knowledge of their interrelationships. 317 As in the preceding year (Jackson, 2012), there were no significant 318 associations between FEC and DLWG. This result is not surprising, given that 319 FECs in young cattle in temperate regions with an Ostertagia/Cooperia 320 dominant nematode fauna, whether in experimental infections or under 321 field conditions, have shown no consistent or linear relationship with worm 322 burdens or animal performance (Brunsdon, 1969, 1971; Michel, 1969). 323 14 324 An analysis was performed of the number of calves that would have been 325 treated with anthelmintic at visit 3 if FECs were used as an indicator using 326 an arbitrary threshold of ≥250 epg. The results show only ten FGS had FEC of 327 ≥250 epg, all on Farm O1. Overall, 54 calves, growing <0.75 kg/day would 328 not have been treated with anthelmintic had FEC been used as an indicator. 329 330 Cooperia spp. larvae predominated in the faecal cultures conducted in July, 331 but these results do not necessarily reflect the worm burdens in the animals 332 at the time (Brunsdon, 1968, 1971). The results of the pepsinogen assays 333 suggest that O. ostertagi was having a greater impact over the second half 334 of the grazing season. 335 336 Consistent with results from the preceding year (Jackson, 2012), there were 337 no significant correlations between plasma pepsinogen concentrations and 338 DLWG. Pepsinogen provides a direct measure of abomasal dysfunction and is 339 closely associated with abomasal pathology and intra-luminal O. ostertagi 340 populations (Michel et al., 1978). It is perhaps surprising that it is not more 341 closely correlated with growth rate, but this has also been observed in other 342 field studies in temperate regions (Brunsdon, 1969, 1971, 1972) and may be 343 due to co-infection with the intestinal species of Cooperia in FGS calves, 344 which can also impact growth rate, singly (Armour et al., 1987) or in 345 combination with O. ostertagi (Parkins et al., 1990), but Cooperia spp. do 346 not typically provoke an increase in pepsinogen. 347 348 4 15 349 The current trial was primarily a feasibility study for TST on commercial 350 farms, so no contemporary comparisons were possible, however cattle 351 growth rates from the previous year are available for each farm and these 352 provide a basis on which to assess the impact of TST. Despite some 353 concurrent (non-parasitic) respiratory disease, the mean growth rate of the 354 FGS cattle on the conventional farm C3 was ≥0.75 kg/day over the grazing 355 season, which was the target, though less than the previous year when, 356 using a long-acting anthelmintic and over a shortened grazing season, the 357 growth rate was 0.93 kg/day. On the organic farm O2 the average growth 358 rate under the TST regimen exceeded 0.75 kg/day and this was considerably 359 higher than in the previous year (0.57 kg/day). Although the growth rate on 360 organic farm O1 was less than target, at 0.69 kg/day it was again higher 361 than that of the previous grazing season when it was 0.46 kg/day. On 362 neither of the organic farms were there any major changes in nutritional or 363 grazing management between years. 364 365 The number of animals treated (all) on the conventional farm was the same 366 using TST as it was the previous year, but the potential exposure to 367 discriminating doses of anthelmintic was reduced with TST through the 368 asynchronous, mid/late season administration of eprinomectin, which has 369 persistent activity of 28 days against O. ostertagi, compared to moxidectin 370 10%, which has 120 days of persistent activity against this species. On 371 organic farm O2, all FGS calves were treated once in July the previous year 372 with fenbendazole, which has no persistent activity, whereas under the TST 373 regimen, all bar four animals were treated in July or August, with 16 374 eprinomectin, so arguably anthelmintic selection pressure could have 375 increased under TST. Similarly, on organic farm O1, only two calves were 376 treated the previous year with fenbendazole, while 19/20 animals were 377 treated with eprinomectin under TST, however on both organic farms the 378 FGS growth rates were higher under the TST regime. 379 380 In order to assess the effect of TST in satisfying the joint objectives of 381 achieving satisfactory growth rates while limiting selection pressure for 382 anthelmintic resistance, modellers have introduced a factor named ‘benefit 383 per R’, abbreviated to BPR (Laurenson et al., 2016). This is calculated from 384 a ratio between the average weight gain benefit (AWGB) arising from 385 whatever control measures have been used and the increase in anthelmintic 386 resistance allele frequency (IRAF) under that system; both are calculated 387 over the duration of the grazing season. This approach was used initially in 388 sheep and has subsequently extrapolated to cattle (Berk et al., 2016), in 389 which it was shown that the use of a DLWG threshold as an indicator for 390 anthelmintic treatments in TST was the approach that optimised BPR. 391 392 4.3. Concluding remarks 393 394 Applying a performance-based TST in the field was shown to be feasible 395 through the use of weigh bands, albeit this measurement requires adequate 396 restraint of animals. Gathering and handling young stock can be a critical 397 factor in commercial dairy herds, where replacement heifers are often 398 grazed on pastures away from the main farm and where handling facilities 17 399 may be rudimentary and inadequate for monthly individual animal 400 assessments. Wider adoption of some of the technologies that are already 401 used by some sheep farmers, such as electronic identification (EID), weigh- 402 scales with integrated software and automatic shedding gates (McBean et 403 al., 2016) would all facilitate the adoption of TST in cattle. Faecal egg 404 count and plasma pepsinogen concentration were found to have no 405 significant association with live weight gain and showed high levels of 406 variability amongst individuals within the management groups, so cannot be 407 recommended if one of the primary objectives for parasite control in 408 youngstock is to maintain growth rates that are commensurate with farm 409 objectives and industry standards. 410 411 On the organic farms, where anthelmintic treatment was already minimal, 412 DLWG was increased compared to the previous grazing season to rates that 413 are considered to be more compatible with optimum life-time performance 414 in heifer replacements (Wathes et al., 2014). 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Percentage of O. ostertagi and C. oncophora larvae cultured from 586 faecal samples collected pre-treatment in July (visit 3) on each farm. 587 23 588 Figures 589 590  live weights of animals throughout study. 591 592  595 596 Figure 2. Skewed distribution (Kolmogorov-Smirnov test p<0.01) of individual faecal egg counts (FEC) throughout study. 593 594 Figure 1. Normal distribution (Kolmogorov-Smirnov test p>0.150) of  Figure 3. Skewed distribution (Kolmogorov-Smirnov test p<0.01) of individual plasma pepsinogen (PEP) throughout study. Table Table 1. Percentage of O. ostertagi and C. oncophora larvae cultured from faecal samples collected pre-treatment in July (visit 3) on each farm. Farm O. ostertagi C. oncophora C3 18% 82% O1 21% 79% O2 4% 96% Figure Figure 1. Normal distribution (Kolmogorov-Smirnov test p>0.150) of live weights of animals throughout study  Figure 2. Skewed distribution (Kolmogorov-Smirnov test p<0.01) of individual faecal egg counts (FEC) throughout study.  Figure 3. Skewed distribution (Kolmogorov-Smirnov test p<0.01) of individual plasma pepsinogen (PEP) throughout study.