Lamb and milk production of a flock of dairy ewes under an accelerated breeding regime

Abstract

SummaryThe management of an experimental flock of dairy sheep was changed from a onceyearly to a frequent-lambing regime. Results are reported on the performance of the flock under the new regime in the course of 3 years. There were 53 and 160, 46 and 242, and 70 and 237 Awassi and Assaf (East-Friesian x Awassi) ewes, respectively, in the flock at the beginning of the 3 consecutive years. A breeding calendar was adopted to produce four mating seasons each year, namely June–July; September–October; December–January; March–April.Average annual production was 1·16 ± 0·24 lambs and 209±9 kg milk for Awassi ewes, and 2·07 ± 0·20 lambs and 287 ± 19 kg milk for Assaf ewes. Hoggets of the same breeds produced 0·61 ± 0·14 and 1·23 ± 0·10 lambs and 99 ± 37 and 220 ± 21 kg of milk, respectively.Following the February-March lambing, conception rates of hormone-treated ewes weaned 2 or 70 days post-partum were 57·1 and 48·8% respectively (P < 0·10). There were no differences in the length of the post-partum interval to conception between low and high milk-yielding ewes. Fertility was highest in the September–October and December–January mating periods, intermediate in June–July and lowest in March–April.Twenty-seven per cent of the original 126 mature Assaf ewes and 15% of the original 46 mature Awassis remained in the flock at the end of 3 years for further breeding. Thirty-one per cent of the mature Assaf population (mixed ages) and 21% of the hoggets were culled in the course of 3 years due to failure to conceive within 6 months post-partum. With Awassi ewes the rate of failure was much higher.Ewes which had lambed twice and completed, on average, 1·5 lactations in a year, produced 30% more milk per year than those which lambed only once during the same period. The more frequent lambing resulted in shorter lactations (156 days) and lower average daily milk yields (1·27 kg) compared with the 182 days and 1·41 kg in the less frequently lambing groups. Pregnancy during early stages of lactation had a small but significant (P < 0·05) effect on the concurrent lactation. Shortening the breeding interval had a much more marked effect on the subsequent lactation. Ewes that conceived, on average, 120 days post-partum, in the subsequent lactations produced 17% more milk than those conceiving 60 days post-partum (P <0·02).Ewes gaining weight at a rate of 5–7 kg during the first 2 months of pregnancy produced, on average, 0·27 kg less milk per day than those which either lost or maintained their weight in that period (P < 0·01).