CIRCANNUAL ESTROUS VARIATIONS AND OVULATION RATE IN PELIBUEY EWES

Abstract

Twelve cycling, mature ewes were kept with two vasectomized rams under constant nutrition maintenance conditions to study annual estrous activity and ovulation. Mean ovulation rate per month was 1.2 corpora lutea (CL)/ewe and 1.72 CL/ewe ovulating, mean proportion of ewes ovulating per month was 69\%; proportions of ewes ovulating varied significantly (P<0.001) among months. The month with lowest number of CL/ewe and proportion of ewes ovulating was April (0.2 and 20\%). Months with highest values were May (1.86 and 86\%) and July (1.83 and 83\%). Annual mean ovulation rate per ewe and per ewe in estrus were 1.19 and 1.72 CL, respectively. Monthly proportions of observed estrus (OE) over expected estrus (EE) {[}O/E] differed significantly (P<0.001), and April (24\%) and August (97\%) were the lowest highest months (P<0.025), respectively. On a trimester basis, proportions also differed (P<0.001), being higher during the two trimesters from July through December. Estrous cycles were divided into short (<12 d), regular (13-20 d) or long (>22 d), proportions for each class were 4, 70 and 26\%, respectively. Results indicated that Pelibuey ewes exhibit estrous cycles regularly from May through December, and the frequency of estrous cycles declines significantly from February through April, due perhaps to factors such as temperature or humidity.