The widespread use of artificial insemination (AI) in beef
cattle is strictly dependent upon development of effective methods to control
estrus. Less than 10% of beef females in the United State are bred by AI.
Limiting factors include, but are not limited to, tradition, the
marketing system of the industry, the extensive low-input nature of many of our
beef production systems and the effectiveness of existing estrous control
methods. The economic advantages of
an effective AI program have been well-defined in the past and the movement of
the beef industry toward valued-based marketing has heightened the importance of
the use of AI.
The purpose of estrous synchronization is to control estrus
(heat) and ovulation in cycling females so that breeding can be completed in a
short period of time. The use of
synchronization can improve beef production but requires good management for
A major factor that has prevented the widespread use of AI
is that the process of twice-daily heat detection and insemination, moving and
sorting individuals or groups of cows and calves to the working facilities, etc.
is not practical for many beef producers. The
extensive nature of many cattle operations, lack of adequate facilities and
sufficient labor, the distant location of cattle from working facilities during
grazing rotation, and other related factors all impede the use of AI.
For most beef producers to implement an AI program, it is critical that
the process be reduced to a short period of AI during which an acceptable
proportion of the females become pregnant.
Expectations for an "Ideal" Estrus
Enhance reproductive performance of the cow herd in terms of interval to
conception in addition to grouping cows for breeding and calving.
Effective, within reason, cyclic and non-cyclic cows and heifers within
Greater than 50% of a well-managed herd should become pregnant to AI over
a maximum of 3 days or to a timed insemination protocol
Designed to minimize cattle handling, use treatments that are easy to
administer and be of reasonable cost while attaining the above goals.
Advantages of Successful Implementation of Estrus
Permits the use of AI through reducing time and labor needed for heat
detection in the absence of estrous control
Reduced days to conception, shorter breeding and calving seasons, and a
more uniform and valuable calf crop
Greater use of superior, proven sires with targeted and predictable
performance characteristics through AI
Reduced bull costs and costs/pregnancy in many cases
Requirements for Estrus Synchronization
Heifers and cows on adequate nutrition-management programs
High-quality semen and experienced inseminators
Concentrated labor at breeding and calving
Adequate facilities to perform AI
Estrous Synchronization Programs
The “ideal” system of estrous synchronization as defined earlier has not yet been developed. However, systems are currently available to producers which will provide acceptable results in many cases. The traditional systems that use PGF2a (Lutalysẻ, Estrumatẻ, etc.) are available and work well in the right situations. For heifers, the most effective system of estrous synchronization available at present is the use of MGẢ and PGF2a (Fig 1). The system outlined in Figure 1 has a 17 d interval between the end of MGẢ and the injection of PGF2a. Producers are having even greater success with this program by extending this interval to 19 days. The SYNCRO-MATE B̉ (SMB) system has been used extensively in heifers, however, this product is temporarily not available to producers.
For synchronization of estrus in postpartum cows, systems of estrous control that incorporate the use of GnRH (Cystorelin̉, Factrel̉, Fertagyl̉) and PGF2a are increasing in popularity (Fig 2). However, it is important to note that these products are currently not labeled for the uses described below. The base program involves the use of an injection of GnRH followed 7 days later by PGF2a with cows bred by AI 12 hours after detection of estrus (Select Sync). Addition of a second injection of GnRH two days after PGF2a (OvSync and CoSync) is designed to permit timed breeding. The OvSync and CoSync programs are the same, except in one case insemination occurs at the time of the second GnRH injection (CoSync) whereas with OvSync the cows are inseminated 16 hours after the second GnRH. Many opt for the CoSync approach to avoid bringing cows through the chute another time, however it is expected that conception rates may be slightly higher (5-8%) with an 8-16 hour interval between GnRH and insemination as in the OvSync program. Results in terms of pregnancy rate are expected to be highest with these systems when used on cows that are cycling or approaching the time that they will start to cycle again after calving. Exceptional results have been obtained when using mature cows that are at least 45 days postpartum. The addition of an SMB implant between the first GnRH injection and PGF2a has been shown to be beneficial for higher risk cattle (less than 45 days postpartum, 2 year-old cows, cows in poorer body condition) however as indicated above this implant is not available at present. The substitution of MGẢ during this time may be effective, however, this approach is still being investigated. The addition of 48 hour calf removal following PGF2a has also been shown to improve reproductive performance in higher risk animals.
In summary, as new approaches are developed and we learn more about reproduction in beef cows, we are increasingly becoming able to synchronize estrus in more females within a given herd. As new technologies become available and approaches are refined in the future, this capability will continue to increase. This paper briefly describes some of the approaches that are currently being used effectively in many situations. For further information, contact Mike Day or Steve Boyles, and consult the OSU Beef Team web page.
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