The basic program is the "Ovsynch" regimen. Numerous variations have been tested and developed. These synchronization programs are the best that are currently available. They have not been able to overcome the consequences of lowered fertility associated with high levels of milk yield, forms of nutrition and environmental factors like heat stress that have profound effects on the physiology and metabolism of the high producing dairy cow.
Abstract Synchronization programs have become standard components in the current breeding management of cows in the dairy herds of most dairy industries. Cows should be inseminated near the end of standing heat see section on timing of artificial insemination for maximum conception to provide enough time for the sperm to undergo a process called capacitation, which gives sperm the ability to fertilize the egg, before they encounter the egg.
Cows ovulate approximately 4 to 16 hours after the end of standing heat. If no problems occur during pregnancy, the embryo develops into a fetus that is born as a calf about days after the egg was fertilized as shown in Table 2. Federal law restricts the majority of reproductive hormones to use by or on the order of a licensed veterinarian.
Therefore, contact your veterinarian for specific recommendations and products before initiating an estrus synchronization program. Recommended protocols are updated frequently and provide a comparison of both cost and labor resources to help beef producers select the appropriate estrus synchronization protocol for their operations.
Figure 2. Timing of artificial insemination for maximum conception. Figure 2 shows general guidelines for timing of AI based on observed standing heat, or estrus.
Actual times will vary depending on the length of standing heat, but the goal is to inseminate near the end of a heat period. Inseminating near the end of heat provides time for the sperm to undergo capacitation, which gives sperm the ability to fertilize, before they encounter the egg. In general, it is better to have the sperm waiting for the egg, rather than the egg waiting for the sperm, because the egg has a shorter lifespan.
Estrus synchronization and AI are reproductive tools that when used properly ultimately enhance the profitability of a well-managed beef cattle operation. The most common failure of estrus synchronization and AI programs is poor attention to detail. Neglecting crucial management practices, such as nutrition, record keeping, AI technician proficiency, good heat detection, and proper timing of estrus synchronization protocols, generates poor results.
Therefore, attention to detail is the key to having a successful estrus synchronization and AI program. The number of days necessary to observe the herd for signs of heat such as standing to be mounted is reduced, which ultimately allows for closer observation.
The hormones administered can also cause stronger heats that have more noticeable signs of estrus. The breeding season is shorter and more concentrated, which allows for more efficient labor management during the breeding season and ultimately during the resulting calving season. Artificial insemination can result in less stressful calving seasons by allowing the use of calving ease sires resulting in fewer dystocias. Table 1. Figure 1. Cyclicity—the normal day cycle.
Estrus Synchronization Programs. Once removed, the cow or heifer typically comes into heat in 1 to 3 days. However, a heifer is subfertile during the first heat following MGA treatment due to ovulation of an older egg oocyte , so the heifer should be bred on a subsequent, synchronized heat. Gonadotropin-releasing hormone GnRH injections promote and synchronize follicle growth and induce ovulation.
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