Beyond the Abstract: Single Injection of Prostaglandin for Natural Service Mating
The phrase “estrus synchronization” often recalls trips through a working facility, numerous hormones to administer at the correct dose, timing, and route, and artificial insemination. Despite this association, estrus synchronization, as its name implies, is a method for synchronizing the expression of estrus (heat) in cattle. While estrus synchronization can be paired with artificial insemination, substantial benefits can be realized with exceptionally simple protocols and natural service.
Research reported in 2009 by Daniel Larson, University of Nebraska-Lincoln and others sought to determine the efficacy of a single injection of prostaglandin F2α (PGF), a simple protocol requiring only one trip through the chute. Data was collected on March-calving cows three years and older at the Gudmundsen Sandhills Laboratory near Whitman, Neb. Cows were unsynchronized between 1999 and 2005 (n = 2073) and synchronized in 2006 and 2007 (n = 518). In their protocol, cows were exposed to fertile breeding bulls 108 hours prior to being administered PGF. Following the injection, bulls remained with cows for 45 days with a minimum ratio of 1 bull:25 cows. In years when cows were unsynchronized, the breeding season lasted 60 days. The corpus luteum is unresponsive to PGF for around 96 hours post-ovulation, but will lyse if ovulation occurred more than 96 hours before PGF injection, causing cows to restart the estrus cycle. Thus, cows bred before PGF administration may still obtain pregnancy.
n their results, cows synchronized using the single injection PGF protocol had 11% more calves born in the first 21 days of the calving season. However, average birth date did not differ between synchronized and unsynchronized cows, likely because synchronized cows that did not obtain pregnancy in their first cycle after receiving PGF were bred approximately 21 days later. Despite having a shorter breeding season, pregnancy rate did not differ between synchronized and unsynchronized cows. Finally, weaning weights were not statistically different, although synchronized cows had an 18-pound numerical advantage.
In summary, the single injection PGF protocol with natural service increased the proportion of calves born at the beginning of the calving season. On the ranch, “front-loading” the calving distribution could lead to several direct benefits, including labor efficiency during calving, improved calf crop uniformity, and potentially, greater weaning weights due to increased age at marketing. With relatively low labor and cost requirements, estrus synchronization is practical to implement—and not adopting can be an expensive missed opportunity.
To learn more, visit https://digitalcommons.unl.edu/animalscinbcr/527
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Nebraska Extension is a Division of the Institute of Agriculture and Natural Resources at the University of Nebraska–Lincoln
