animal
Animal (2014), 8:7, pp 1191–1200 © The Animal Consortium 2014
doi:10.1017/S1751731114000998
Grazing increases the concentration of CLA in dairy cow milka
M. N. Lahlou1, R. Kanneganti1, L. J. Massingill1, G. A. Broderick1, Y. Park2, M. W. Pariza3,
J. D. Ferguson4 and Z. Wu4†
1
US Dairy Forage Research Center, USDA-ARS, Madison, WI 53706, USA; 2Department of Food Science, University of Massachusetts, Amherst, MA 01003, USA;
Food Research Institute, University of Wisconsin, Madison, WI 53706, USA; 4New Bolton Center, University of Pennsylvania, Kennett Square, PA 19348, USA
3
(Received 18 June 2013; Accepted 17 March 2014; First published online 30 April 2014)
An experiment was conducted to examine whether increased CLA in milk of dairy cows fed fresh pasture compared with alfalfa
and corn silages was because of ruminal or endogenous synthesis. Eight Holsteins were fed a total mixed ration using alfalfa and
corn silages as the forage source in confinement or grazed in a replicated crossover design. The proportion of total fatty acids
as CLA (primarily c9, t11-18:2) in g/100 g was 0.44 v. 0.28 in ruminal digesta, 0.89 v. 0.53 in omasal digesta and 0.71 v. 1.06
in milk during confinement feeding and grazing, respectively. Blood plasma CLA was 0.54 v. 1.05 mg/l for the two treatments,
respectively. The increased concentration of CLA in milk with grazing likely resulted from increased synthesis through desaturation
of t11-18:1 in the mammary gland.
Keywords: CLA, pasture, milk fatty acids, dairy cow
Implications
CLA c9, t11-18:2 has been shown to be beneficial to human
health, and its concentration in milk of dairy cows was
increased when cows were grazed on fresh pasture compared with receiving conserved feeds. The increase was not
explained by more production in the rumen, but likely
because of increased synthesis in the mammary gland.
Introduction
C9, t11-18:2 is the most abundant isomer of CLA in milk of
dairy cows, and because of its health benefits to humans,
various feeding strategies have been studied for their effect on
the content of the fatty acid in milk (Palmquist et al., 2005).
Grazing (Kelly et al., 1998; Dhiman et al., 1999; Schroeder
et al., 2003) is one of the most effective approaches identified
for increasing CLA, compared with feeding stored feeds, the
most common practice in the modern dairy industry.
Understanding the origin of milk CLA is important, and
sources include both ruminal synthesis and endogenous
contributions (Palmquist et al., 2005). Ruminal synthesis is
a result of partial biohydrogenation of 18:2n-6 and 18:3n-3.
a
Trade names and the names of commercial companies are used in this report to
provide specific information. Mention of a trade name or manufacturer does not
constitute a guarantee or warranty of the product by the USDA or an endorsement over products not mentioned.
†
E-mail: zwu@vet.upenn.edu
The biohydrogenation of 18:2n-6 initiates with isomerization of
c9, c12-18:2 into c9, t11-18:2, the primary isomer of CLA, as the
first intermediate (Kepler et al., 1966). The subsequent step is
reduction of the cis-9 double bond, resulting in t11-18:1 as the
second intermediate. The final step is another reduction,
resulting in 18:0. The rumen bacterium Butyrivibrio fibrisolvens
is the primary species that carries out the isomerization and
the first reduction step (Kepler et al., 1966). Bacteria that carry
out the last reduction are separate species, including some
Fusocillus and Ruminococcus strains (Kemp et al., 1975). Formation of intermediates during biohydrogenation of 18:3n-3 is
not well understood. The biohydrogenation pathway begins
with isomerization of the double bond at carbon 12, forming a
conjugated cis-9, trans-11, cis-15 triene (Kim et al., 2009).
Hydrogen is subsequently added to the double bonds, likely
in the order of carbon positions 9, 15 and 11 (Dawson and
Kemp, 1970). Loor et al. (2002) reported distinct increases in
t11, c15-18:2 in blood plasma and milk when cows were grazed
compared with being fed a total mixed ration. However, no
typical CLA would be formed with this 9 > 15 > 11 preference
order (Jenkins et al., 2008). Other preference scenarios are
9 > 11 > 15 and 15 > 9 > 11, with the latter being the one that
would yield c9, t11-18:2 as an intermediate. However, such a
preference order has not been documented (Dawson and Kemp,
1970; Destaillats et al., 2005). Observed increases in milk CLA
when cows are grazed have not been well explained by ruminal
biohydrogenation because the main fatty acid in grasses and
clovers is 18:3n-3 (Palmquist, 1988).
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Lahlou, Kanneganti, Massingill, Broderick, Park, Pariza, Ferguson and Wu
Table 1 Ingredients and composition of the total mixed ration, supplement and pasture forage
Item
Ingredient
Alfalfa silage
Corn silage
Shelled corn
Soybean meal
Expeller soybean meal2
Blood meal
CaCO3
CaHPO4
MgO
NaHCO3
Salt
Trace mineral and vitamin mix3
Chemical composition
CP
NDF
ADF
Total mixed ration
(g/kg of dry matter)
Supplement
(g/kg of dry matter)1
Pasture forage
(g/kg of dry matter)
190
270
350
40
110
10
5
7
2
6
8
2
–
–
825
–
100
20
15
10
5
10
10
5
–
–
–
–
–
–
–
–
–
–
–
–
175
236
156
149
93
33
180
398
288
1
The supplement was offered to grazing cows at 10 kg/day (dry matter).
SoyPlus (West Central Coop; Ralston, IA, USA).
Each kilogram contained 0.32 g of Se, 0.43 g of Co, 1.03 g of I, 13.35 g of Cu, 23.99 g of Fe, 51.00 g of Mn, 62.01 g of Zn, 7,000,000 IU of
vitamin A, 2,222,000 IU of vitamin D and 17,630 IU of vitamin E.
2
3
Endogenous synthesis is a result of Δ9 desaturation of
t11-18:1 (Griinari et al., 2000; Morales et al., 2000). T11-18:1,
derived from the rumen during biohydrogenation of 18:2n-6, as
discussed above, can be desaturated as a result of the action of
Δ9-desaturase (Palmquist et al., 2005; Mosley et al., 2006),
forming c9, t11-18:2. The enzyme acts on the bond at carbon 9
in 16:0, 18:0 as well as t11-18:1 in the presence of NADPH,
flavin and ferrous ion (Moore and Christie, 1979).
The most recent studies have shown that endogenous
synthesis contributes a large proportion of total CLA in milk,
with estimates including 64 (Griinari et al., 2000), 78 (Corl
et al., 2001), 94 (Kay et al., 2004) and 93% to 97% (Piperova
et al., 2002; Mohammed et al., 2009), depending on diet
composition, oil supplementation and grazing. However,
reasons for increased synthesis with regimens that are
known to be effective in increasing milk CLA remain unclear.
The objective of this study was to determine the concentration of CLA in ruminal and omasal contents and in milk of
cows fed conserved forages or pasture to gain insights into
the mechanism of observed increases in milk CLA.
Material and methods
The experimental protocol was approved by the Institutional
Animal Care and Use Committee of the College of Agricultural and Life Sciences, University of Wisconsin, Madison,
United States of America.
Animals and dietary treatments
Eight ruminally cannulated multiparous Holsteins were
paired based on milk yield and days in milk (ranging from 16
to 290) and utilized in a replicated crossover design in June
1192
to July. Cows within a pair were fed a total mixed ration
consisting of alfalfa silage, corn silage and a concentrate mix
(Table 1) or grazed for 21 days, and then switched to the
other regimen for 21 more days. In each period, the first
14 days served as adaptation and the last 7 days for sample
collection. Grazed cows were also offered a supplement mix
at 10 kg/day (dry matter basis) using ingredients similar to
those included in the concentrate portion of the total mixed
ration for the other group of cows. The allowance was used
to provide 40% of the total feed intake, assuming that
animals would obtain 60% of their intake from the pasture
based on previous season estimates (Wu et al., 2001).
The use of these values before the commencement of the
experiment was necessary, but as reported below, the actual
amount of the supplement consumed was less than offered.
Cows in the total mixed ration group were housed in tie
stalls and offered the diet at 0830 h daily for ad libitum
consumption (5% to 10% refusal). Actual amounts of feed
offered and refused by individual animals were recorded
daily to obtain net intake. Cows in the pasture group grazed
continuously except for ∼ 6 h/day when taken to the milking
parlor and then tie stalls to receive the supplement. Refusals
of the supplement were recorded.
The pasture was about 20 ha in size, divided into 0.4 to
0.8 ha paddocks by electric fences. It was routinely fertilized
with 56 kg/ha of nitrogen in two applications annually, one
in June and one in August. The June application for the year
the experiment was conducted fell 2 weeks before the
beginning of the trial and the August application occurred
after the trial. Determined as described below, the pasture
used for this experiment contained grasses (bluegrass 35%,
quackgrass 28%, timothy grass 16%, and bromegrass,
CLA in milk
orchardgrass and unidentified species 21%) and clovers (red
clover 70%, white clover 30%) at ∼55 : 45, as well as some
dead matter (∼10%, dry matter basis). A new paddock was
allocated every 3 days, and the stocking rate was estimated
to be ∼6 cows/ha. Rotation length was 28 days, and grazed
forages were a result of re-growth, thus similar in phenological stage between the two periods. Water was available
all times in paddocks.
Sampling and analysis
Cows were milked at 0600 and 1700 h, with milk weights
recorded each time. Milk samples were collected at milking
on days 16 and 20 of each period and analyzed for fat,
protein, lactose and solid-not-fat (AgSource Milk Analysis
Laboratory, Menomonie, WI, USA). An aliquot of the milk
samples was pooled, extracted for fat with hexane and
analyzed for fatty acids upon methylation with 1.097 M
methanolic HCl (Chin et al., 1992) using a gas chromatograph (Hewlett-Packard model 5890 Series II; HewlettPackard, Brookfield, WI, USA) fitted with a flame ionization
detector and a 3396 A auto-integrator. The analysis used a
fused silica capillary column (60 m × 0.32 mm i.d., 0.25 μm
film thickness; Supelco, Inc., Bellefonte, PA, USA). A mixture
of known fatty acids was used as a standard (Nu-Chek Prep,
Inc., Elysian, MN, USA). The peaks identified for CLA included
a major one for c9, t11-18:2 and a minor one for t10, c1218:2. Because the minor peak was identified for only some
samples, the two were combined when identified in calculating the proportion of total CLA. Likewise, other isomers
such as t7, c9-18:2 and t8, c10-18:2 were not separated from
these peaks, and were included in total CLA.
Blood was sampled (10 ml) 3 h after feeding on day 19 in
each period from the coccygeal vessels into heparinized
vacutainers, and centrifuged at 2200 × g for 15 min. Plasma
was kept at − 20°C before analysis for CLA (c9, t11-18:2)
(Chin et al., 1992) using HPLC (Beckman 125/166; Beckman
Instruments, Inc., Palo Alto, CA, USA).
Alfalfa silage, corn silage and refusals were sampled daily
and kept frozen to generate weekly composites. Corn, soybean
meal and blood meal were sampled weekly. All weekly
samples were determined for dry matter by oven-drying at
60°C for 48 h. Refusals were used only for net intake calculations. Pasture forage was sampled before grazing from
alternate paddocks for botanical and nutrient (CP, NDF, ADF)
composition analysis; a total of four paddocks were sampled in
each period. For botanical analysis, herbage from 10 randomly
selected strips (0.01 × 1.0 m each) in each of the sampling
paddocks was cut at ground level and separated into plant
species by hand; the species profile was determined on the dry
weight of samples (60°C oven-dried). For nutrient analysis,
herbage from a second randomly selected area was cut at 9 cm
above the ground to obtain 0.5 kg of wet material. Ten such
areas were cut in each of the sampling paddocks. The collected
herbage was subsampled, oven-dried (60oC), and pooled
within paddock to generate four composites for each period.
Ruminal samples were collected every 2 h on day 19 of
each period, beginning at 0830 h, until six samples were
collected, representing 0, 2, 4, 6, 8 and 10 h after feeding.
This schedule did not include night times, and thus could
result in biases if changes in rumen contents over time were
different between the dietary treatments. Samples were
strained through two layers of cheesecloth. The liquid was
measured for pH (Corning® pH Meter 360i; Corning, Inc.,
Corning, NY, USA) and kept at − 20°C until analyzed for
NH3-N (Broderick and Kang, 1980) using an auto analyzer
(Technicon Auto Analyzer II; Technicon Instruments Corp.,
Tarrytown, NY, USA) and for volatile fatty acids (Brotz
and Schaefer, 1987) using GLC (Varian Vista 6000; Varian
Instrument Group, Walnut Creek, CA, USA). The solids were
pooled within animal and period and lyophilized.
Omasal samples were obtained at 0830 and 1530 h during
days 16 and 19 in each period. A one-hand opening and
closing flip-top vial (35 ml; www.capitol-dairy-solutions.
com) was held in the left hand with the cap closed and
inserted through the rumen cannula into the omasum. The
cap then was opened using the thumb to allow the vial to be
filled with digesta. The vial was then closed and withdrawn.
Two vials of samples were obtained at each sampling time.
The samples (16 vials) were pooled within cow and period
and lyophilized.
Dried samples of feeds (including pasture forage), ruminal
contents and omasal contents were ground through a Wiley mill
using a 1-mm screen (Arthur H. Thomas, Philadelphia, PA, USA).
Ground feed samples were analyzed for dry matter (105°C),
CP (LECO FP-2000 Nitrogen Analyzer; Leco Instruments, Inc.,
St. Joseph, MI, USA) and NDF (using heat stable α-amylase
and Na2SO3) plus ADF (Robertson and Van Soest, 1981)
using the ANKOM200 Fiber Analyzer (ANKOM Technology,
Fairport, NY, USA). Chemical analyses were expressed on a
dry matter basis (105°C). Nutrient content of the total mixed
ration and the supplement was computed from average analyses
of the ingredients over the experiment. Ground ruminal and
omasal samples were analyzed for fatty-acid concentration and
profile (Chin et al., 1992) using the same gas chromatograph
used for milk fatty-acid analysis described above. Heptadecanoic
acid was used as an internal standard, assuming sample content
of this acid was negligible. Peaks for c9, t11 and t10, c12 isomers
were detected for most of the digesta samples.
Statistical analysis
Data were processed for ANOVA using two models by the
GLMs procedure of SAS (2000). Model 1 was based on a
crossover design and used for all data except for ruminal pH,
volatile fatty acids and NH3-N, all of which were analyzed
with Model 2 according to a crossover split-plot design. The
two models were as follows:
Y ¼ μ + R + C ðRÞ + P + T + E
(Model 1)
Y ¼ μ + R + C ðRÞ + P + T + RT + H + RH + HC ðRÞ + HP
+ TH + RTH + E
ðModel 2Þ
where Y is the observation, μ the overall mean, R the replicate,
C(R) the cow within replicate, P the period, T the treatment,
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Lahlou, Kanneganti, Massingill, Broderick, Park, Pariza, Ferguson and Wu
E the error term, RT the interaction between replicate and
treatment, H the hour, RH the interaction between replicate
and hour, HC(R) the interaction between hour and cow within
replicate, HP the interaction between hour and period, TH
the interaction between treatment and hour and RTH the
interaction among replicate, treatment and hour. In Model 2,
replicate, cow within replicate, period and treatment were in
the main plot and the remaining terms were in the subplot.
Treatment effects were tested by replicate and treatment
interactions.
Results and discussion
One cow in the total mixed ration group during period 1 was
off feed before sample collection began and was removed
from the trial, leaving seven cows contributing to the data
analyzed. In addition, as mentioned above, some fatty acids
in some of the milk and digesta samples were not identified,
including those of 10 carbons or shorter, t10, c12-18:2 and
t11-18:1. We did not think it appropriate or meaningful to
assign a ‘0’ to these samples and then conduct a statistical analysis to compare treatment means. Instead, the
values for t10, c12-18:2, minor if detected, were combined
with c9, t11-18:2 and reported as ‘CLA.’ T11-18:1 was
detected in most of the milk and digesta samples and thus
reported separately.
Lactation performance and ruminal fermentation
Mean consumption of the supplement by grazing cows was
8.4 kg/day (dry matter; Table 2). Using the 40 : 60 split for
intake from the supplement and pasture and the nutrient
content of the feed sources (Table 1), the diet consumed by
grazing cows would contain 168, 276 and 186 g/kg CP, NDF
and NDF, respectively, compared with 175, 236 and 156 g/kg
for the total mixed ration (Table 1). Feed starch was not
analyzed, but the ration formulation showed 350 g/kg for the
total mixed ration and 620 g/kg for the supplement. These
values were relatively high because of the use of high
amounts of corn. Likewise, feed ingredients were not analyzed for fatty acids for this experiment, but forages from the
same pasture were analyzed in the previous season, and the
analysis showed 174 and 393 g/kg of the total fatty acids as
18:2n-6 and 18:3n-3, respectively (unpublished). Using these
values and values listed in the NRC guidelines (2001) for
Table 2 Feed intake and milk production of cows fed a total mixed ration or grazed
Item
Total mixed ration
Grazing
s.e.m.
P
20.3
8.41
–
–
35.2
32.2
1.138
28.2
0.979
48.5
1.691
85.1
146
28.4
32.0
0.907
27.6
0.776
47.2
1.335
83.1
136
1.4
0.9
0.047
0.4
0.045
0.4
0.052
0.5
28
0.02
0.89
0.02
0.34
0.02
0.05
0.01
0.03
0.79
Feed intake (kg/day)
Milk
Yield (kg/day)
Fat (g/kg)
Fat (kg/day)
Protein (g/kg)
Protein (kg/day)
Lactose (g/kg)
Lactose (g/day)
Solids-not-fat (g/kg)
Somatic cell count (1000/ml)
1
Supplement intake only; forage intake from pasture is not included.
Table 3 Ruminal pH, NH3-N concentration and volatile fatty-acid profile measured during a 10-h period after feeding in cows fed a total mixed ration
or grazed
P
Item
pH
NH3-N (mg/dl)
Volatile fatty acids (mM)
Proportion (mol/100 mol)
Acetate
Propionate
Isobutyrate
Butyrate
Isovalerate
Valerate
Acetate : propionate
1194
Total mixed ration
Grazing
s.e.m.
Diet
Diet × hour
5.94
7.6
56.9
5.84
12.1
64.4
0.03
0.3
1.6
0.09
0.07
0.01
0.002
0.11
0.22
62.0
23.4
0.84
10.8
1.56
1.41
2.75
63.1
20.7
1.06
11.9
1.68
1.60
3.25
0.9
0.6
0.02
0.2
0.04
0.09
0.11
0.52
0.17
0.05
0.18
0.05
0.50
0.04
1.00
0.99
0.01
0.91
0.02
0.42
0.94
CLA in milk
Table 4 Fatty acids in ruminal contents, omasal contents, blood plasma and milk fat of cows fed a total mixed ration or grazed
Fatty acid
Total mixed ration
Grazing
s.e.m.
P
29.9
33.9
0.7
0.1
0.13
0.53
14.91
0.09
49.13
8.40
4.75
17.07
0.44
3.42
0.11
0.45
14.51
0.10
45.64
9.63
7.07
17.18
0.28
4.94
0.01
0.04
0.21
0.01
1.82
0.93
0.86
1.44
0.04
0.46
0.05
0.22
0.22
0.21
0.23
0.39
0.11
0.67
0.02
0.06
31.4
34.0
1.3
1.9
0.14
0.62
15.73
0.09
48.77
8.96
6.39
16.83
0.89
1.50
0.54
0.09
0.48
14.52
0.09
46.51
9.67
9.32
17.28
0.53
1.47
1.05
0.01
0.03
0.09
0.01
1.67
0.46
0.30
1.18
0.08
0.05
0.16
0.01
0.02
0.01
0.78
0.38
0.32
0.01
0.80
0.03
0.66
0.07
0.80
0.55
0.15
2.05
3.38
12.49
36.29
1.43
14.09
2.06
21.66
4.37
0.71
0.92
0.24
0.84
0.61
0.14
1.74
2.54
9.50
29.18
1.76
14.96
3.57
29.51
4.69
1.06
1.12
0.10
0.07
0.03
0.04
0.18
0.18
0.55
0.90
0.06
0.65
0.27
1.02
0.15
0.07
0.03
0.06
0.68
0.17
0.80
0.28
0.02
0.01
0.01
0.01
0.38
0.01
0.01
0.17
0.02
0.01
0.16
Ruminal contents
Total fatty acids (g/kg of dry matter)
Fatty acid composition (g/100 g of total fatty acids)
12:0
14:0
16:0
c9-16:1
18:0
t11-18:1
c9-18:1
18:2n-6
CLA1
18:3n-3, n-6
Omasal contents
Total fatty acids (g/kg of dry matter)
Fatty acid composition (g/100 g of total fatty acids)
12:0
14:0
16:0
c9-16:1
18:0
t11-18:1
c9-18:1
18:2n-6
CLA1
18:3n-3, n-6
Blood plasma CLA (mg/l)1
Milk fatty acid composition (g/100 g of total fatty acids)
4:0
6:0
8:0
10:0
12:0
14:0
16:0
c9-16:1
18:0
t11-18:1
c9-18:1
18:2n-6
CLA1
18:3n-3, n-6
20:4n-6
1
Primarily c9, t11-18:2, including t10, c12-18:2, if any.
the other feed ingredients, as well as the 40 : 60 split for
supplement and pasture intake, the total mixed ration and
the diet consumed during grazing were calculated to contain
33 and 35 g/kg long-chain fatty acids, of which 48.1% and
32.4% were 18:2n-6 and 9.4% and 24.7% were 18:3n-3,
respectively. The estimated intake was 322 and 235 g/day for
18:2n-6 and 63 and 179 g/day for 18:3n-3, totaling 385
and 404 g/day, for the two regimens, respectively. These
estimates were consistent with observations that the predominant fatty acid is 18:2n-6 in cereal grains and 18:3n-3 in
grasses and clovers. The estimates also suggest that, because
both fatty acids are extensively biohydrogenated, combined
outflow of these fatty acids from the rumen would be similar
between the diets.
Milk yield was 6.8 kg/day lower (P < 0.05) for cows grazed
than fed the total mixed ration (Table 2). The concentrations
of milk fat were similar between the feeding systems, and
both were low, reflecting the estimated high dietary starch
content. The solids-not-fat proportion of milk of grazing
cows was reduced compared with those on the total mixed
ration (P < 0.05), largely because of a lower (P < 0.05) lactose concentration. Yield of milk protein also was lower
1195
Lahlou, Kanneganti, Massingill, Broderick, Park, Pariza, Ferguson and Wu
CLA
Total fatty-acid concentration in ruminal digesta was higher
(P < 0.01) for cows grazed than fed the total mixed ration
(Table 4). The concentration for c9-18:1 tended to be higher
(P < 0.01) in ruminal digesta of grazed cows than for those fed
the total mixed ration. Also, CLA concentration in ruminal
digesta was lower (P < 0.05) for grazing cows. Some small
decreases in 12:0, 14:0 and 16:0 were observed (P < 0.10) in
omasal digesta during grazing relative to total mixed ration
feeding. However, the concentration of c9-18:1 increased
(P < 0.01). The concentration of CLA in blood plasma was
higher (P < 0.10) for grazing than for the total mixed ration. The
CLA proportion of milk fatty acids was ∼50% higher (P < 0.05)
during grazing than during total mixed ration feeding (1.06 v.
0.71 g/100 g). The proportions for 4:0, 6:0 and 8:0 in milk fat
are listed in Table 4, but because not all of them were detected
in some of the samples, as indicated above, the values may
have been underestimated and could be biased. Low values
could be a result of loss of methyl esters during analysis or
extremely low concentrations that were below the sensitivity of
the flame ionization detector. The proportions for 12:0, 14:0
and 16:0 were lower (P < 0.05) for grazing cows than for those
fed the total mixed ration. In contrast, c9-16:1, t11-18:1, c1118:1 and 18:3n-3 and n-6 were present in higher (P < 0.05)
concentrations, along with CLA, in milk fat of grazing cows.
The increase in the concentration of CLA in milk during
grazing compared with feeding a total mixed ration observed
1196
in this experiment was in accordance with previous reports
(Kelly et al., 1998; Dhiman et al., 1999; Loor et al., 2002).
These studies showed that grazing can effectively increase
milk CLA, and the CLA concentration is somewhat proportional to the contribution of pasture to the total feed intake.
The origin of milk CLA has been ascribed to both ruminal
and endogenous syntheses. Rumen-based theories concerning
the mechanism of increased milk CLA synthesis when cows are
grazed include: (1) reduced digesta retention in the rumen,
which would increase the passage of biohydrogenation intermediates from the rumen to the small intestine (Kay et al.,
2004); (2) rapid release of fatty acids from grazed herbage in
the rumen, which would result in inhibited biohydrogenation at
the latter step, thus causing accumulation of intermediates
formed in the rumen (Noble et al., 1974; Kim et al., 2009);
(3) altered microbial populations and associated biohydrogenation pathways (Polan et al., 1964) and (4) decreased
ruminal pH (as shown in Table 3), which would result in shifts
in bacterial populations (Kim et al., 2002; Piperova et al., 2002;
Palmquist et al., 2005). None of these hypotheses is relevant
for the present study because grazing cows had ruminal and
omasal CLA concentrations that were only about 60% of the
cows fed the total mixed ration (Table 4), despite their higher
milk CLA concentrations. In addition, a plot (Figure 1) using
cows from both treatments reveals a trend for a negative
relationship between the proportion of CLA in milk fat and the
proportion in omasal fat; the CLA in milk would include isomers
that are usually present in higher amounts in milk than in the
rumen (such as t7, c9-18:2). These data suggest that increased
milk CLA during grazing observed in this experiment was not a
result of more production in the rumen. The observation is
consistent with the analysis of Mohammed et al. (2009) and
Halmemies-Beauchet-Filleau et al. (2013a and 2013b) for the
effect of grazing on milk CLA compared with feeding chopped
grass or hay.
Discussion should be made on several other factors that
could be related to increased milk CLA in this study. First,
while cows usually lose BW after taken onto a pasture,
the data on milk fatty acids for this short-term experiment
might not have been confounded by adipose mobilization, as
suggested by the similar low proportions of 18:0 in milk, a
pre-formed, major fatty acid in the adipose tissue, for both
1.4
Conjugated linoleic acid in milk
(g/100 g of fatty acid)
(P < 0.05) when cows were grazed than fed the total mixed
ration. A balance calculation showed that cows would
consume 7 kg/day forage from the pasture, in addition to the
8.4 kg/day from the supplement, to produce 28.4 kg/day milk
when their energy balance was zero and protein balance was
positive (180 g/day). The intake from the pasture would be
even lower if cows were in fact losing BW, which was likely
the case based on visual observations (cows were not
weighed). In contrast, cows fed the total mixed ration had
an energy balance of 21 MJ/day and a protein balance of
400 g/day with 35.2 kg/day milk. These estimates suggest
that the intake from the pasture was not sufficient to support
a higher milk yield above the energy maintenance requirement that usually substantially increases because of grazing
activities (NRC, 2001). Milk decreases are a common observation when cows are changed from a total mixed ration to
grazing, often accompanied with BW losses, and the change
is considered to result from insufficient intake from pasture
because of small bite sizes (Wu et al., 2001).
Mean ruminal pH, obtained from measurements taken
during a 10-h period after feeding, was low for both treatments (5.84 and 5.94 for grazing and total mixed ration,
respectively, P < 0.10; Table 3), reflecting the high starch
content of the diets. The NH3-N and total volatile fatty-acid
concentrations were higher (P < 0.10) for grazing, reflecting
more rapid fermentation and degradation of protein for fresh
herbage than conserved forages. Isobutyrate and isovalerate
were slightly higher (P < 0.05) for grazing cows, as was the
acetate to propionate ratio.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Conjugated linoleic acid in omasal digesta (g/100 g of fatty acid)
Figure 1 Concentration of CLA (primarily c9, t11-18:2, including t10,
c12-18:2, if any) in milk and omasal digesta when cows were fed
conserved forages (light markers) or grazed (dark markers).
15.0
g/100 g of fatty acid
g/100 g of fatty acid
CLA in milk
10.0
5.0
0.0
15.0
10.0
5.0
0.0
14:0
40.0
g/100 g of fatty acid
g/100 g of fatty acid
12:0
30.0
20.0
10.0
0.0
60.0
40.0
20.0
0.0
18:0
15.0
g/100 g of fatty acid
g/100 g of fatty acid
16:0
10.0
5.0
0.0
12.0
9.0
6.0
3.0
0.0
Trans 18:1n-7
20.0
g/100 g of fatty acid
g/100 g of fatty acid
Cis 18:1n-9
16.0
12.0
8.0
4.0
0.0
1.5
1.0
0.5
0.0
18:2+18:3
Omasal
CLA
Milk
Omasal
Milk
Figure 2 Omasal and milk fatty-acid proportions when cows were fed conserved forages (light bars) or grazed (dark bars).
feeding systems (Figure 2). These proportions were also
lower than those in the omasal contents, contrasting to those
for 12:0, 14:0 and 16:0 that can be synthesized in the
mammary gland. On the other hand, milk c9-18:1 was higher
for grazing, which would suggest increased adipose contribution, but its omasal concentration was also higher.
Second, milk CLA was reported to increase when dietary
starch was increased from 150 to 250 g/kg (Cabrita et al.,
2007), but decreased when corn, a starchy feed source, was
increased from 365 to 588 g/kg of the diet (Griinari et al.,
1998), or remained unchanged when corn was replaced by
citrus pulp, a non-starch feed source (Solomon et al., 2000).
Regardless of the inconsistency of reports in the literature,
changes in milk CLA observed in these studies were extremely
small, especially compared with those caused by oil supplementation. Dietary starch in the present study would be within
the range of the amounts used in the above-cited studies.
Furthermore, the amounts would be similar between the
treatments based on formulation and milk fat concentrations.
It was unlikely that dietary starch caused a bias for the effect
of pasture v. conserved feeds on milk CLA. Lastly, red clover
contains polyphenol oxidase, which may have a protective
effect on lipids from ruminal metabolism, thus increasing the
transfer of polyunsaturated fatty acids from the forge to milk
(Lee et al., 2009). However, substituting red clover for grasses
in the diet had little effect on milk CLA (Lee et al., 2009)
or the formation of c9, t11-18:2 or t11-18:1 in the rumen
(Halmemies-Beauchet-Filleau et al., 2013c), although flows of
18:2n-6 and 18:3n-3 at the omasum showed some increases
(Halmemies-Beauchet-Filleau et al., 2013c).
From results of the present study, endogenous synthesis
was more likely responsible for increased milk CLA when
cows were fed pasture compared with conserved feeds. The
proportion of fatty acids as CLA increased in milk compared
with omasal contents for both regimens, as did the proportions for 12:0, 14:0 and 16:0 (Figure 2), all of which are
known to be synthesized entirely or partially in the mammary
gland. In addition, CLA was the only fatty-acid group that
had a lower concentration in omasal contents but a higher
concentration in milk during grazing than during total mixed
ration feeding. Lastly, the proportion of t11-18:1 was lower
in milk than in the digesta (Figure 2). While this was the case
for both treatments, the observation is consistent with the
understanding that CLA can be formed from t11-18:1 in
1197
1198
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
Omasal trans 18:1(n-7) (g/100 g of fatty acid)
Conjugated linoleic acid in milk
(g/100 g of fatty acid)
the mammary gland. More directly, calculated productto-substrate ratios for Δ9-desaturase (Perfield et al., 2002)
for grazed cows were 0.06, 1.97 and 0.30 for c9-16:1/16:0,
c9-18:1/18:0 and c9, t11-18:2/t11-18:1 in milk, respectively,
compared with 0.01, 0.20 and 0.05 in omasal contents;
the ratio for the c9, t11-18:2/t11-18:1 pair was sixfold
higher in milk than in omasal contents, and the difference
was 1.5 times that when cows were fed the total mixed
ration. Data from all these lines suggest that CLA in milk was
synthesized to a large extent at a post-absorptive stage and
the synthesis increased when cows were grazed. The results
are consistent with the report of Yang et al. (1999) that the
activity of Δ9-desaturase was higher in grazing beef cattle
than in feedlot cattle, and of Mohammed et al. (2009)
that ruminal concentration of CLA has little to do with its
final concentration in milk because of the involvement of de
novo synthesis.
There are several possible reasons for endogenous synthesis of CLA to increase when cows are grazed. First, greater
formation of t11-18:1 in the rumen could lead to more
c9, t11-18:2 synthesized in the mammary gland through
increased substrate availability (Halmemies-Beauchet-Filleau
et al., 2013a and 2013b). This mechanism may also offer
some explanations for increased production of CLA in milk
associated with 18:3n-3, whose classical biohydrogenation
pathway does not involve formation of c9, t11-18:2, as discussed above. Mohammed et al. (2009) also reported that
increased CLA cannot be fully explained by the outflow of
18:2n-6 and 18:3n-3 from the rumen and suggested that the
effect of these fatty acids on milk CLA is primarily through
formation of t11-18:1 during their biohydrogenation. However, no relationship was shown between omasal t11-18:1
proportion and milk CLA proportion in this experiment
(Figure 3). Piperova et al. (2002) also reported that duodenal
flow of t11-18:1 was larger than milk CLA output. Included
in Figure 3 also is a plot of milk CLA against omasal 18:2n-6
and 18:3n-3 concentrations, a measure that reflects the
intake, and more importantly, the metabolism of these
fatty acids in the rumen through biohydrogenation. The plot
shows no relationships between omasal and milk concentrations of these fatty acids, consistent with the report of
Mohammed et al. (2009). Second, the availability of the
essential cofactors involved in the desaturase activity could
increase when the forage source was grazed pasture. The
third possibility is related to milk fat liquidity. According to
Moore and Christie (1979), a liquid form is necessary for milk
fat droplets to move to the surface of the secretory cells to be
pinched off during milk fat secretion and for fat globules to
be suspended in milk. Normally, fat liquidity is assured by
acylation of short-chain fatty acids (low melting point) to
the sn-3 position of the glycerol moiety. In the absence of
short-chain fatty acids, c9-18:1, also low in melting point
(14°C), could be substituted. In the present study, fatty acids
of 10:0 to 16:0 carbons decreased from 52.2 to 43.0 g/100 g
in milk fat during grazing compared with total mixed ration
feeding (Table 4), consistent with the literature (Christie,
1979; Timmen and Patton, 1988; Kelly et al., 1998) that
Conjugated linoleic acid in milk
(g/100 g of fatty acid)
Lahlou, Kanneganti, Massingill, Broderick, Park, Pariza, Ferguson and Wu
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
Omasal 18:2 and 18:3 (g/100 g of fatty acid)
Figure 3 Relationship between the concentration of t11-18:1 and
polyunsaturated octadecenoic acids (18:2n-6 and 18:3n-3) in omasal
fatty acids and the concentration of CLA (primarily c9, t11-18:2, including
t10, c12-18:2, if any) in milk fatty acids when cows were fed conserved
forages (light markers) or grazed (dark markers).
short-and medium-chain fatty acids (C4–16) decrease when
cows receive their forage from pasture. In that case, CLA
synthesis may increase as a compensatory mechanism to
maintain milk fat liquidity, because t11-18:1 (melting point
44oC) does not exist in a liquid form at body temperature
and physicochemically resembles 18:0 (melting point 69oC)
rather than c9-18:1 (melting point 14oC). While plausible, the
liquidity theory is difficult to study. Toral et al. (2013) found
in a meta-analysis that the variability of the melting point of
milk fatty acids was narrower than the variability of milk
fatty-acid concentrations, suggesting that melting point may
be involved in the control of milk fatty-acid composition,
although the effect might be small.
Conclusions
It has been amply demonstrated that grazing dairy cows
increases the CLA concentration in milk compared with
feeding stored feeds, and this was again shown in the current
study. In addition, this study showed that CLA accounted for
a smaller proportion of long-chain fatty acids in ruminal and
omasal digesta in pasture-fed cows than in cows fed stored
feeds, thus discounting increased ruminal formation as a
reason for increased CLA concentrations in milk. Rather,
increased endogenous synthesis via desaturation of t11-18:1
might be the primary mechanism for the increase. Current
hypotheses for increased endogenous synthesis include
increased substrate availability and compensation for deceased
short- and medium-chain fatty acids that are important for milk
fat liquidity.
CLA in milk
Acknowledgments
This study was supported in part by a grant from the American
Cancer Society, grant number IRG-58-41-10. The authors wish
to acknowledge the leadership Dr L. D. Satter played in the
project. In addition, J. E. Delahoy helped verify the identification
of fatty acids on the gas chromatograph.
References
Broderick GA and Kang JH 1980. Automated simultaneous determination of
ammonia and total amino acids in ruminal fluid and in vitro media. Journal of
Dairy Science 63, 64–75.
Brotz PG and Schaefer DM 1987. Simultaneous determination of lactic acid and
volatile fatty acids in microbial fermentation extracts by gas-liquid chromatography. Journal of Microbiological Methods 6, 139–144.
Cabrita ARJ, Bessa RJB, Alves SP, Dewhurst RJ and Fonseca AJM 2007. Effects of
dietary protein and starch on intake, milk production, and milk fatty acid profiles
of dairy cows fed corn silage-based diets. Journal of Dairy Science 90,
1429–1439.
Chin SF, Liu W, Storkson JM, Ha YL and Pariza MW 1992. Dietary sources of
conjugated linoleic acid, a newly recognized class of anticarcinogens. Journal of
Food Composition and Analysis 5, 185–197.
Christie WW 1979. The effect of diet and other factors on the lipid
composition of ruminant tissues and milk. Progress in Lipid Research 17,
245–277.
Corl BA, Baumgard LH, Dwyer DA, Griinari JM, Philipis BS and Bauman DE 2001.
The role of Δ9-desaturase in the production of cis-9, trans-11 CLA. The Journal
of Nutritional Biochemistry 12, 661–666.
Dawson RMC and Kemp P 1970. Biohydrogenation of dietary fats in ruminants.
In Physiology of digestion and metabolism in the ruminant (ed. AT Phillipson),
pp. 504–518. Oriel Press, Newcastle-upon-Tyne, England.
Destaillats F, Trottier JP, Galvez JMG and Angers P 2005. Analysis of α-linolenic
acid biohydrogenation intermediates in milk fat with emphasis on conjugated
linolenic acids. Journal of Dairy Science 88, 3231–3239.
Dhiman TR, Anada GR, Satter LD and Pariza MW 1999. Conjugated linoleic
acid content from cows fed different diets. Journal of Dairy Science 82,
2146–2156.
Griinari JM, Dwyer DA, McGuire MA, Bauman DE, Palmquist DL and Nurmela
KVV 1998. Trans-octadecenoic acids and milk fat depression in lactating
dairy cows. Journal of Dairy Science 81, 1251–1261.
Griinari JM, Corl BA, Lacy SH, Chouinard PY, Nurmela KVV and Bauman DE
2000. Conjugated linoleic acid is synthesized endogenously in lactating dairy
cows by Δ9-desaturase. Journal of Nutrition 130, 2285–2291.
Halmemies-Beauchet-Filleau A, Kairenius P, Ahvenjärvi S, Crosley LK, Muetzel S,
Huhtanen P, Vanhatalo A, Toivonen V, Wallace RJ and Shingfield KJ 2013a.
Effect of forage conservation method on ruminal lipid metabolism and microbial
ecology in lactating cows fed diets containing a 60:40 forage-to-concentrate ratio.
Journal of Dairy Science 96, 2428–2447.
Halmemies-Beauchet-Filleau A, Kairenius P, Ahvenjärvi S, Toivonen V,
Huhtanen P, Vanhatalo A, Givens DI and Shingfield KJ 2013b. Effect of forage
conservation method on plasma lipids, mammary lipogenesis, and milk fatty
acid composition in lactating cows fed diets containing a 60:40 forage-toconcentrate ratio. Journal of Dairy Science 96, 5267–5289.
Halmemies-Beauchet-Filleau A, Vanhatalo A, Toivonen V, Heikkilä T, Lee MRF
and Shingfield KJ 2013c. Effect of replacing grass silage with red clover
silage on ruminal lipid metabolism in lactating cows fed diets containing
a 60:40 forage-to-concentrate ratio. Journal of Dairy Science 96, 5882–5900.
Jenkins TC, Wallace RJ, Moate PJ and Mosley EE 2008. Board-invited
review: recent advances in biohydrogenation of unsaturated fatty acids
within the rumen microbial ecosystem. Journal of Animal Science 86,
397–412.
Kay JK, Mackle TR, Auldist MJ, Thompson NA and Bauman DE 2004. Endogenous synthesis of cis-9, trans-11 conjugated linoleic acid in dairy cows fed
fresh pasture. Journal of Dairy Science 87, 369–378.
Kelly ML, Kolver ES, Bauman DE, VanAmburgh ME and Muller LD 1998. Effect of
intake of pasture on concentration of conjugated linoleic acid in milk of
lactating cows. Journal of Dairy Science 81, 1630–1636.
Kemp P, White RW and Lander DJ 1975. Hydrogenation of unsaturated fatty
acids by five bacterial isolates from sheep rumen, including a new species.
Journal of General Microbiology 90, 100–114.
Kepler CR, Hirons KP, McNeill JJ and Tove SB 1966. Intermediates and products
of the biohydrogenation of linoleic acid by Butyrivibrio fibrisolvens. The Journal
of Biological Chemistry 241, 1350–1354.
Kim EJ, Huws SA, Lee MRF and Scollan ND 2009. Dietary transformation of lipid
in the rumen microbial ecosystem. Asia-Australian Journal of Animal Science 22,
1341–1350.
Kim YJ, Liu RH, Rychlik JL and Russell JB 2002. The enrichment of a
ruminal bacterium (Megasphaera elsdenii YJ-4) that produces the trans-10,
cis-12 isomer of conjugated linoleic acid. Journal of Applied Microbiology 92,
976–982.
Lee MRF, Theobald VJ, Tweed JKS, Winters AL and Scollan ND 2009.
Effect of feeding fresh or conditioned red clover on milk fatty acids and
nitrogen utilization in lactating dairy cows. Journal of Dairy Science 92,
1136–1147.
Loor JJ, Herbein JH and Polan CE 2002. Trans 18:1 and 18:2 isomers in blood
plasma and milk fat of grazing cows fed a grain supplement containing solventextracted or mechanically extracted soybean meal. Journal of Dairy Science 85,
1197–1207.
Mohammed R, Stanton CS, Kennelly JJ, Kramer JKG, Mee JF, Glimm DR,
O’Donovan M and Murphy JJ 2009. Grazing cows are more efficient than zerograzed and grass silage-fed cows in milk rumenic acid production. Journal of
Dairy Science 92, 3874–3893.
Moore JH and Christie WW 1979. Lipid metabolism in the mammary gland of
ruminant animals. Progress in Lipid Research 17, 347–395.
Morales MS, Palmquist DL and Weiss WP 2000. Effects of fat source and copper
on unsaturation of blood and milk triacylglycerol fatty acids in Holstein and
Jersey cows. Journal of Dairy Science 83, 2105–2111.
Mosley EE, Shafii B, Moate PJ and McGuire MA 2006. Cis-9, trans-11 conjugated
linoleic acid is synthesized directly from vaccenic acid in lactating dairy cattle.
Journal of Nutrition 136, 570–575.
Noble RC, Moore JH and Harfoot CG 1974. Observations on the pattern on
biohydrogenation of esterified and unesterified linoleic acid in the rumen. British
Journal of Nutrition 31, 99–108.
NRC 2001. Nutrient requirements of dairy cattle, 7th edition. National Academy
Press, Washington, DC, USA.
Palmquist DL 1988. The feeding value of fats. In Feed science (ed. ER Orskov),
World Animal Science B4, pp. 293–311. Elsevier Science Publishers, Amsterdam,
The Netherlands.
Palmquist DL, Lock AL, Shingfield KJ and Bauman DE 2005. Biosynthesis of
conjugated linoleic acid in ruminants and humans. Advances in Food Nutrition
Research 50, 179–217.
Perfield JW II, Bernal-Santos G, Overton TR and Bauman DE 2002. Effects
of dietary supplementation of rumen-protected conjugated linoleic acid
(CLA) in dairy cows during established lactation. Journal of Dairy Science 85,
2609–2617.
Piperova LS, Sampugna J, Teter BB, Kalscheur KF, Yurawecz MP, Ku Y,
Morehouse KM and Erdman RA 2002. Duodenal and milk trans octadecenoic
acid and conjugated linoleic acid (CLA) isomers indicate that postabsorptive
synthesis is the predominant source of cis-9-containing CLA in lactating
dairy cows. Journal of Nutrition 132, 1235–1241.
Polan CE, McNell JJ and Tove SB 1964. Biohydrogenation of unsaturated fatty
acids by rumen bacteria. Journal of Bacteriology 88, 1056–1064.
Robertson JB and Van Soest PJ 1981. The detergent system of analysis. In The
analysis of dietary fibre in food (ed. WPT Kames and O Theander), Chapter 9, pp.
123–158. Marcel Dekker Inc., New York, NY, USA.
SAS 2000. SAS® user’s guide, statistics, version 8. SAS Institute, Inc., Cary, NC,
USA.
Schroeder GF, Delahoy JE, Vidaurreta I, Bargo F, Gagliostro GA and Muller LD
2003. Milk fatty acid composition of cows fed a total mixed ration or pasture
plus concentrates replacing corn with fat. Journal of Dairy Science 86,
3237–3248.
Solomon R, Chase LE, Ben-Ghedalia D and Bauman DE 2000. The effect of
nonstructural carbohydrate and addition of full fat extruded soybeans on the
concentration of conjugated linoleic acid in the milk fat of dairy cows. Journal of
Dairy Science 83, 1322–1329.
1199
Lahlou, Kanneganti, Massingill, Broderick, Park, Pariza, Ferguson and Wu
Timmen H and Patton S 1988. Milk fat globules: fatty acid composition, size and
in vivo regulation of fat liquidity. Lipids 23, 685–689.
Toral PG, Bernard L, Chilliard Y and Glasser F 2013. Short communication: dietinduced variations in milk fatty acid composition have minor effects on the
estimated melting point of milk fat in cows, goats, and ewes: insights from a
meta-analysis. Journal of Dairy Science 96, 1232–1236.
1200
Wu Z, Kanneganti VR, Massingill LJ, Wiltbank MC, Walgenbach RP and Satter LD
2001. Milk production of fall-calving dairy cows during summer grazing of grass
pasture or grass-clover pastures. Journal of Dairy Science 84, 1166–1173.
Yang A, Larsen TW, Smith SB and Tume RK 1999. Δ-9 desaturase activity in
bovine subcutaneous adipose tissue of different fatty acid composition. Lipids
34, 971–997.