Embryo production by repeated superovulation of commercial donor cows

Mature beef cows of 13 major and several minor breeds were repeatedly superovulated by injections of follicle stimulating hormone (FSH) and prostaglandin F2 alpha (PGF). Embryos were collected nonsurgically 6 to 8 days after artificial insemination. The average number of transferable embryos per collection was measured on the basis of all cows started on superovulation. Within groups of cows superovulated from two to ten times, embryo production per collection declined with repeated collections. This decline was not apparent in the pooled data when the mean number of embryos per collection the first through the tenth collection was 5.6, 5.1, 4.9, 5.0, 4.3, 5.1, 5.0, 5.0, 5.4, and 5.6 embryos, respectively. Embryo production at the first collection was one of the criteria for selecting cows for repeated superovulation. Cows superovulated more than three times had the highest embryo production at the first collection. The decline in embryo production with repeated superovulation could not be corrected by increasing the FSH dose. The number of embryos per collection was significantly correlated in cows superovulated repeated times. The correlation coefficients varied from 0.32 in cows superovulated twice to 0.35 in cows superovulated 10 times. The predictability of embryo production from cows that were selected to remain in the embryo transplant program, and were superovulated more and more times, did not increase. Some cows continued to produce embryos after 20 repeated superovulations. The results indicated that a cow should be superovulated two or three times before being discarded as a poor embryo producer.