The effect of being housed with adult female flock-mates on the age at puberty of autumn-born ewe-lambs.

Twenty-five ewe-lambs born in November were used to measure the effect of the presence of cyclic or non-cyclic adult ewes on the age at first fertile estrus. Lambs were weaned at 45 days of age and kept in a single flock until 3 Mar (4 months old), when they were assigned to one of the following three groups: Group CE (n = 8), housed with six cyclic adult ewes; Group NCE (n = 8), housed with three non-cyclic ovariectomized adult ewes, and Group ISO (n = 9), housed isolated from adult ewes. On 2nd May (6 months old), two rams were introduced into each group, until 31st Oct (12 months old), when rams were removed. Adult ewes in group CE were separated from rams and ewe-lambs by a metal fence, allowing visual, olfactory, and nose-to-nose contact between animals. Average earliest fertile estrus was significantly (P < 0.01) earlier in NCE ewe-lambs (8th Aug) than it was in ISO (9th Sep) and CE (17th Sep) ewe-lambs, they lambed about 35 d earlier (1st Jan) than did the other two groups (2nd Feb and 10th Feb, respectively) (P < 0.01), and at an earlier age (14 mo, 15.2 mo, and 15.3 mo, respectively; P < 0.01). In conclusion, the presence of non-ovulatory adult ewes advanced puberty in autumn-born ewe-lambs of a Mediterranean genotype. The factor(s) that delayed age at puberty in isolated females and those housed with estrous adult ewes remains to be elucidated.