Reproductive and productive performance in Chios ewes mated in spring or in autumn

One hundred and sixty adult ewes of the Chios breed were divided randomly i nto two groups. One group was used for bleeding in spring (S) and the other in autumn (A). In both groups oestrous behaviour was detected once a day. Ovulatory activity, 7 d after oestrus, fertility, prolificacy, embryo morta lity, birth weight of lambs and milk production were recorded. The percenta ge of ewes which exhibited oestrous behaviour was 92 and 100 % in S and A g roups, respectively, while fertility of mated ewes was 98 and 100 %. Ovulat ion rate was significantly lower in S than in A ewes (M +/- sd; 2.85 +/- 1. 07 versus 3.44 +/- 1.45, respectively, P < 0.0001). However, prolificacy di d not differ between the two groups (2.04 +/- 0.77 versus 2.13 +/- 0.85, fo r S and A ewes, respectively) as it did nor increase after an ovulation rat e of 4.0. There were no differences in birth weights (except for triplets) but rotal milk production was significantly higher in S ewes (257.5 +/- 100 .7 kg versus 153.0 +/- 51.9 kg, for S and A, respectively, P < 0.001). Thes e results suggest that despite a higher ovulation rate in autumn, higher em bryonic mortality at this time of the year leads to equivalent fertility, p rolificacy and birth weight in spring as in autumn. (C) Inra/Elsevier, Pari s.