USMARC Twinning Herd Background
The USMARC created the Twinner herd to research multiple births in cattle in 1976 with research beginning fully in 1981 in order to explore the potential for increasing the output of calves relative to nutrient inputs for cow maintenance. Females that had previously produced multiple sets of twins were chosen for the herd, with no breed requirements.
Increasing the frequency of multiple births within the herd was one of the main objectives. The research team was very successful at increasing the occurrence of twins and triplets. When the research herd was dispersed starting in 2011, multiple births occurred 50 percent of the time, which was thought to be a nearly impossible feat when the herd was established, according to both Hays and Thallman.
Thallman explained that the center was able to increase the rate of multiple births by studying the ovulation rates of the females within the herd. By selecting the heifers that had released multiple eggs during an estrus cycle, they in turn were able to increase the occurrence of multiple births from those multiple ovulations. Studying the ovulation rate with the aid of ultrasound gave them the opportunity to examine many ovulations without having to wait for a confirmed multiple birth pregnancy.
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