ESTRUS CHARACTERIZATION IN SUPEROVULATED CATTLE

Based on frequent examinations per rectum and on external signs of estrus, the intensity of estrus was characterized in 107 superovulated dairy cows and heifers. Three intensity groups were defined: strong (n=57), moderate (n=34), and weak(n=16). Frequent blood samples were obtained for analyses of estradiol-17 beta and LH. The ovaries were exposed through surgery at various intervals after the time of prostaglandin administration, and ovarian findings (follicles, premature ovulations) were described. A total of 527 oocytes was recovered from 998 follicles aspirated, and, of these, 420 were processed for chromosomal evaluation of their nuclear maturational stage. The weak estrus intensity group differed from the strong and moderate groups in several ways. Cows and heifers in the weak intensity group had more frequent deviations in plasma hormonal patterns, a higher proportion of animals with only a few follicles, and more animals exhibiting premature ovulations. The mean oocyte recovery rate was lower in the weak group as compared with that of the other 2 groups, since more oocytes could not be accounted for in this group during the evaluation process, indicating a higher degree of oocyte fragility. Furthermore, a larger number of oocytes in the weak group displayed no identifiable chromosomes, than in the remaining 2 groups. However, apparently normal oocytes were also found in the weak group. It is concluded that accurate characterization of estrus in superovulated cattle can be a valuable tool for identifying donors with a high risk for inadequate oocyte maturation, which in turn could lead to inferior embryo yield.