Age at Puberty in Fall-Born Ewe Lambs

Abstract

In a 4-year study age at puberty was determined in 189 grade Rambouillet and crossbred ewe lambs born in October and November each year. The average age at first estrus was 316 days with a range of 199 to 577 days. Breed or strain differences were not significant but year differences were. There were highly significant differences in the percentages of lambs coming into puberty in different months with approximately half of them exhibiting first estrus in either September or October. The average number of estrual periods was 3.5 with a range of 1 to 10. Dorset × Rambouillet and Hampshire × Rambouillet crossbreds had slightly longer breeding seasons than the Columbia × Rambouillet crosses and the grade Rambouillets. The average estrual period length was 1.78 checks (12-hr, intervals) or about 21 hours. Correlations of age at puberty with season of birth and with 120-day weight were insignificant.