干旱区生态环境知识资源中心

Prevailing sheep production systems in the region are based on continuous breeding throughout the year. Peak lambing, however, occurred in October-December and April-May. Twenty percent of ewes in the arid rangelands and 30% in the Nile Valley lambed twice a year. Breeding local ewes every 8 months increased number of lambs weaned per ewe annually by 54.2 and 41.9% in Ossimi and Rahmani breeds, respectively.

Fertility and prolificacy were consistently better in fall (September) than in winter (January) and spring (May) matings. Ovulation rate (OR) was highest in September and January, while ova wastage was lowest in September and highest in January and May matings. Introduction of rams to ewes for one week prior to mating in spring increased (by 27%) the percentage of ewes that demonstrated oestrus and were mated.

Applying artificial light in spring, to simulate autumn, increased percent of ewes in oestrus by 45% and of ewes ovulating by 30%. Continuous exposure to long days of July during the fall, decreased percentage of ewes in oestrus, especially in the more seasonal subtropical breeds.

Melatonin treatment increased percentage of ewes ovulating and ovulations per ewe from 3.0 in controls to 4.1. Progesterone (PMSG) treatment and immunization against androstenedione significantly increased OR, but was not converted into increasing litter size, due to high ova wastage. Season of lambing had little effect on age at puberty of subtropical ewe lambs. Reducing age at puberty of subtropical breeds seems to be hindered by their low growth rate.