Synchronization and Artificial Insemination Strategies in Beef Cattle
Synchronization and Artificial Insemination Strategies in Beef Cattle
Synchronization and Artificial Insemination Strategies in Beef Cattle
Artificial Insemination
Strategies in Beef Cattle
a, b
Graham Clifford Lamb, PhD *, Vitor R.G. Mercadante, PhD
KEYWORDS
Estrus synchronization Artificial insemination Beef cattle Economics
KEY POINTS
Development of fixed-time artificial insemination (TAI) estrus-synchronization protocols
limit animal handling and eliminate detection of estrus to provide users an opportunity
to more readily incorporate artificial insemination (AI) into their herds.
Annually, the Beef Reproduction Task Force (http://beefrepro.unl.edu) updates recom-
mended estrus-synchronization protocols for beef cows and heifers.
The development of the AI Cowculator economic decision-aid tool allows producers an
opportunity to determine whether they should consider AI rather than purchasing herd
sires.
As a result of continued use of intensive reproductive management tools, such as estrus
synchronization and AI, producers will note a benefit in calving distribution, enhanced
pregnancy rates, and increased subsequent calf value.
INTRODUCTION
Currently only 7.6% of beef operations in the United Sates use AI as a reproductive
management tool,2 whereas 72.5% of all pregnancies in dairy females are the result
of AI.3 When queried as to their reluctance to use AI, more than 53% of operations
cited labor concerns or complicated estrous synchronization protocols as primary
reasons for not implementing this reproductive technology.2 During the past decade,
TAI protocols have been developed that eliminate detecting estrus and yield satisfac-
tory pregnancy rates. Most of these TAI protocols depend largely on the use of exog-
enous progesterone (P4), gonadotropin-release hormone (GnRH) to induce ovulation,
and luteolysis via administration of prostaglandin F2a (PGF).4,5
Later, the inclusion of P4, supplemented by a controlled internal drug release (CIDR)
device, to prevent ovulation before PGF injection was extensively investigated.4,15–17
Comparing conception rates between protocols with or without exogenous sources of
P4 indicated that fertility was improved when the device was applied (7-day CO-
Synch 1 CIDR protocol).4,15,18 In addition, pregnancy rates of anestrus cows synchro-
nized with the CIDR were similar to cyclic cows.15,16,19 However, follicles that fail to
ovulate to the first GnRH in the 7-day CO-Synch 1 CIDR protocol4,18 may become
persistent during the 7-day period in which the CIDR is present, thereby reducing
fertility to TAI. The proestrus phase in the 7-day CO-Synch 1 CIDR protocol may be
defined as the interval from the administration of PGF to the second injection of
GnRH, which may have a duration of 60 to 72 hours.4,15,17 Recently, in an attempt
to improve fertility, research focused on increasing the length of the proestrus in
estrous synchronization protocols from 66 hours (7-day CO-Synch 1 CIDR) to
72 hours (5-day CO-Synch 1 CIDR).17,20,21
Synchronization and AI Strategies in Beef Cattle 337
Extensive research has been done and is still being conducted by several research
groups to enhance the understanding of physiologic processes involved in the estrous
cycle and to enhance fertility and pregnancy success of TAI protocols. In an effort to
combine expertise in reproductive physiology and estrous synchronization and
encourage research cooperation across the United States, the Beef Reproduction
Task Force (BRTF) was formed in 2002. The BRTF is a multistate team of reproductive
physiology experts from 7 to 9 universities across the United States (http://beefrepro.
unl.edu/). The objectives of the BRTF are as follows:
Improve the understanding of the physiologic processes of the estrous cycle, the
procedures available to synchronize estrus and ovulation, and the proper appli-
cation of these systems.
Improve the understanding of methods to assess male fertility and how it affects
the success of AI programs.
Every year the BRTF releases an updated chart of recommended estrous synchro-
nization and TAI protocols that have been tested and are proven to be effective for
beef cows and heifers, including different protocols for Bos taurus and Bos indicus
cattle (Figs. 1 and 2). These charts are an excellent source of information and serve
as a guideline for beef producers and industry leaders in the United States.
Follicle Development
Several ovulation-synchronization protocols use GnRH at the time of CIDR insertion
to induce ovulation and reset follicular waves to improve pregnancy outcomes.5
338 Lamb & Mercadante
Fig. 1. BRTF chart of recommended estrous synchronization and TAI protocols for beef cows.
a
The time listed for “Fixed-time AI” should be considered as the approximate average time
of insemination. This should be based on the number of cows to inseminate, labor, and fa-
cilities. (Courtesy of Beef Reproduction Task Force, University of Nebraska-Lincoln, Lincoln,
NB; with permission.)
Fig. 2. BRTF chart of recommended estrous synchronization and TAI protocols for beef
heifers. a The times listed for “Fixed-time AI” should be considered as the approximate
average time of insemination. This should be based on the number of heifers to inseminate,
labor, and facilities. (Courtesy of the Beef Reproduction Task Force, University of Nebraska-
Lincoln, Lincoln, NB; with permission.)
GnRH ranged from 10.7 to 15.7 mm in diameter.30 Nonetheless, recent studies inves-
tigating the effects of different follicle ages by manipulating the duration of proestrus
and comparing mature larger follicles with young smaller follicles in beef cows and
heifers determined that the age and maturity of the ovulatory follicle did not influence
pregnancy to TAI outcome.31,32
340 Lamb & Mercadante
The most desirable pregnancy outcomes indicated in the review41 were noted in
older, early calving cows in better body condition, and the poorest outcomes were
in primiparous, late-calving cows in the poorest body condition (Table 1). Progester-
one status at the onset of synchronization was not critical to pregnancy outcome in
multiparous cows, whereas pregnancy rate per AI was suppressed in primiparous
cows starting in a low-P4 environment (proestrus, metestrus, estrus, or anestrus), rein-
forcing the necessity of developing heifers adequately for early puberty to increase the
proportion that calve early in the calving season,43 which is related to their postpartum
reproductive performance.
Table 1
Influence of parity, days postpartum, and body condition score on resulting pregnancy rate
per artificial insemination in 8500 suckled beef cows exposed to variation of the CO-Synch
program
3. Each cow must produce a live calf every year and calve without assistance or they
will be culled
4. Every cow must provide the resources for the genetic potential of the calves and
each calf she produces must be genetically capable of performing
5. No supplemental feeding was offered to cows that failed to maintain body
condition
6. Any cow with an undesirable temperament or disposition was culled.
Initially, calving season length resulted in cows being inseminated in 3 TAI groups (in
the 2008 and 2009 breeding seasons), subsequently reduced to 2 TAI groups (in the
2010 and 2011 breeding seasons), and eventually to a single TAI group (in the 2012
and 2013 breeding seasons; Fig. 3). Following the initial TAI for each group, females
Fig. 3. Timeline of events and length of breeding seasons at the NFREC from 2006 to 2013.
344 Lamb & Mercadante
Fig. 4. Cumulative calving percentage during each calving season at the NFREC from 2006 to
2013.
were detected for estrus and inseminated artificially after an observed estrus until day
23 after TAI. On day 23 after TAI, bulls were introduced and cows were naturally mated
for the remainder of the breeding season. All bulls passed a breeding soundness ex-
amination before being introduced to females.
As a result of incorporating estrous synchronization and TAI, in addition to other
reproductive management practices, the breeding season was reduced from 120 to
70 days in the course of 5 years. Furthermore, currently almost all cows calve before
initiation of the subsequent breeding season and are exposed to a single TAI on the
first day of the breeding season. The effect of using estrous synchronization and
TAI on calving distribution can be observed in Fig. 4. In 2006 and 2007, before initia-
tion of the TAI program, it took 90 days for 50% of the calves to be born. In 2013, how-
ever, it took less than 30 days for 50% of the calves to be born. Mean calving date from
the first calf born during each calving season was reduced from 80.9 days from the
2007 breeding season to 38.7 days from the 2013 breeding season. In addition, overall
pregnancy rates, including AI and natural service, increased from 81% and 86% in the
2006 and 2007 breeding seasons, respectively, to 92% and 93% in 2012 and 2013,
respectively (Table 2).
Table 2
Breeding season length, final pregnancy rate, mean calving day, and change in calf value at
weaning, after initiation of an estrous synchronization and fixed-timed artificial insemination
program at the North Florida Research and Education Center
Assuming an average daily gain of 0.91 kg per day, a fixed calf value of $4.41/kg
across years, the mean value per calf increased by $87 per calf resulting from the
2008 breeding season to $169 per calf resulting from the 2013 season. Overall, the
net result of a more compact calving season with increased value of calves (in current
dollars) by $169 per calf resulted in an increased net result of $47,151.00 per year for
the 300-head herd and 94% pregnancy rate at the NFREC (see Table 2).
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