Some important factors affecting fertility in sheep

Abstract

Efficiency of sheep production is conditioned by fertility. According to some authors number of offspring obtained per lambing is more important than gain of weight. Genetic relationships involving reproductive traits were seldom studied. Reproductive traits have low heritabilities, a discrete phenotypic expression, and are expressed only in sexually mature ewes leading to low selection intensities and long generation intervals. Documentation of realized selection response is also often complicated by the low heritabilities of fertility traits. Existence of a major gene affecting prolificacy had been suggested and at that time there were many sceptics who strongly doubted that a trait as complex as reproduction could be profoundly influenced by a single gene. Major genes affecting prolificacy in sheep was founded. A mutation in the bone morphogenetic protein 15 gene (BMP15, also known as GDF9B) responsible for high prolificacy in Inverdale sheep had been discovered and evidence of segregating major genes was being reported from flocks around the world. Development of gene mapping techniques, and locating alleles that are responsible for the fertility of sheep began a new chapter in predicting and controlling the fertility of sheep. The beneficial effects of nutrition on reproduction in sheep are well known. This procedure is known as flushing. The effect of Body Condition Score (BCS), before mating, during mating and after mating period, on reproductive efficiency of different breeds of sheep in the different rearing systems were studied. The farm manager has the ability to control or at least to manipulate the factors that have an impact on fertility.

Genetic polymorphism in melatonin receptor 1A and arylalkylamine N-acetyltransferase and its impact on seasonal reproduction in Egyptian sheep breeds

“…Seasonal variation in fertility is an important factor limiting the efficiency of sheep production, resulting in the occurrence of births and milk production in specific periods of the year (Trecherel et al, 2010). The identification of polymor-phisms in genes affecting nonseasonal reproduction, such as the MTNR1A and AA-NAT genes, could open a new chapter in predicting and controlling the sexual activity of sheep (Petrovic et al, 2012). MTNR1A is thought to be the main receptor involved in the regulation of seasonal reproductive activities in mammals (Dubocovich et al, 2003).…”

“…Teyssier et al (2011) stated that changes in day length may act as a major factor controlling seasonal changes in estrous activity in sheep breeds with maximal reproductive activity during short days. The identification of quantitative trait loci (QTL) and the implementation of marker-assisted selection (MAS) could assist in selection schemes to shorten the anestrous season and open a new chapter in forecasting and controlling the fertility of sheep (Petrovic et al, 2012). Melatonin is called the "hormone of darkness" because its production is controlled by day and night alteration (Rosa and Bryant, 2003).…”

Corn-based or high linoleic acid flushing increases productivity of Morada Nova and Brazilian Somalis ewes

“…The mechanism of action for nutritional factors on productive and reproductive performance is a complex process. Many interactions exist between the availability of nutrients, weight, and body condition score of animals depending on their physiological state of the animal (PETROVIC et al, 2012;ROBINSON et al, 2006). Flushing is a nutritional management strategy widely practiced among researchers and Morada Nova and Brazilian Somalis ewes grazing native pasture.…”

Short-term under-nutrition affects feeding and sexual behaviour in oestrous-synchronized Saint Croix ewes (Ovis aries)

“…Nutritional stress could delay follicular development and the preovulatory surge of luteinizing hormone (LH), which would affect the fertility of the ewes (Daley et al 1999;Abecia et al 2006) mainly through irregular cycles and reduced ovulation rate (Petrovic et al 2012). In other species, Mani et al (1992) report that restricted feed intake in goats tends to delay the onset of oestrus.…”