Effects of season and bread of sire on incidence of estrus and ovulation rate in sheep.
The effects of season and breed of sire on estrous activity and ovulation rate were estimated in 50 mature ewes, 10 each sired by North Country Cheviot, Dorset, Finnsheep, Romney and Suffolk rams and born from Suffolk dams. Estrus was checked with vasectomized rams from July 1979 through December 1980. From May through December of 1980, ovulation rate was determined by the counting of corpora lutea (CL) during laparoscopic examinations of ovaries. A breed X month interaction (p less than .01) was found for incidence of estrus. Finnsheep-sired ewes were slower to enter anestrus and had the shortest anestrus period. Cheviot-sired ewes had the longest anestrus period. Ovulation rate, measured as the number of CL/ewe examined per month from August through December of 1980, was highest (P less than .05) in October and November. Finnsheep-sired ewes tended to have higher ovulation rates (2.04) per ewe ovulating than did Romney-or Cheviot-sired ewes (1.48). Suffolk- and Dorset-sired ewes were intermediate. Ovulation rate, measured as the number of CL/ewe available per month from May through December of 1980, was highest (P less than .05) in September, October and November. Suffolk-, Finnsheep- and Dorset-sired ewes had higher (P less than .10) ovulation rates (.95) per ewe available than did Romney- and Cheviot-sired ewes (.67). Monthly repeatability of ovulation rate from August through December of 1980 was .41 +/- .25.
D000704:Analysis of Variance; D000818:Animals; D004971:Estrus; D005260:Female; D010535:Laparoscopy / Q000662:veterinary; D008297:Male; D010060:Ovulation; D011247:Pregnancy; D012621:Seasons; D012756:Sheep / Q000235:genetics / Q000502:physiology*