AGE OF PUBERTY IN EWES WHICH DEVELOPED PRENATALLY WITH EITHER A RAM OR A EWE FETUS

This experiment was designed to compare time of first estrus and ovula tion in ewe lambs, which developed prenatally next to a female fetus ( 0M ewe), with ewe lambs which developed prenatally next to a male fetu s (1M ewe). Prenatal environment had no effect (P > 0.05) on weight of ewes during the experimental period (42 +/- 1 and 43 +/- 0.5 kg for 0 M and 1M ewes, respectively). Age at first estrus (29 +/- 0.8 weeks fo r 0M and 30 +/- 0.4 weeks for 1M ewes) did not differ (P > 0.05) betwe en groups. There was, however, more variability (P less than or equal to 0.05) in age at first estrus in 0M than in 1M ewes. The number of s hort estrous cycles, as determined by plasma concentrations of progest erone, was 1.5 +/- 1 and 1.6 +/- 0.6 in 0M and 1M ewes, respectively, and did not differ (P > 0.05) between groups. In conclusion, there was no effect of group on mean age at puberty or on mean number of short estrous cycles before puberty. Variability in age of puberty was sligh tly greater in 0M than in 1M ewes, but it is unlikely that this is a m ajor factor in variability in age of puberty. The implication is that it is not important to know the sex of the adjacent fetus during prena tal development when trying to predict age of puberty in twin-lambing ewes.