A NOTE ON THE EFFECT OF LEVEL OF NUTRITION AFTER WEANING ON THE RESUMPTION OF REPRODUCTIVE ACTIVITY BY EWES OF 2 SPANISH BREEDS LAMBING IN SPRING

Two experiments were carried out from April to September 1990 at Zaragoza, Spain. Fifty-three Rasa Aragonesa (RA) ewes, weaned in April, were studied in experiment 1, whilst 33 Salz (Sz) ewes, weaned in June, were studied in experiment 2. From weaning onwards, the animals were allocated to two groups receiving two planes of nutrition: high (H) and low (L). Mean time between weaning and the first detected oestrus was 113 (s.e. 2.7) and 52 (s.e. 3.0) days for RA and Sz ewes, without any significant effect of the plane of nutrition. Ewes of the H group showed a constantly higher ovulation rate than those of the L group with a significant effect of the plane of nutrition in the second fortnight of August (P < 0.05) and of September (P < 0.001) in RA ewes (1.68 v. 1.29 and 1.89 v. 1.38 corpora lutea for H and L groups, respectively) and in September (P < 0.01) in Sz ewes (2.53 v. 2.00 corpora lutea for H and L groups). In conclusion, a slightly higher plane of nutrition after weaning in these sheep breeds, lambing in spring, cannot advance either the reproductive resumption or increase the ovulation rate of the first cycle. The high plane of nutrition after weaning exerts a significant effect on the ovulation rate in the medium term, in the early breeding season.