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.Efikasnost proizvodnje ovaca je uslovljena plodnoscu. Prema nekim autorima broja potomaka dobijenih po jagnjenju je vaznije od prirasta i mase tela. Genetski uticaji koji ukljucuju reproduktivne osobine se retko izucavaju. Plodnost ovaca ima nizak heritabilitiet, diskretnu fenotipsku ekspresiju, a izrazena je samo u seksualno zrelih ovaca, sto dovodi do niskog intenziteta selekcije i dugih generacijskih intervala. Otkrice major gena koji uticu na plodnost je u to vreme otkrilo mnogo skeptika koji su snazno sumnjali da takav kompleks reprodukcije moze biti duboko pod uticajem jednog gena. Glavne geni uticu na plodnost kod ovaca i ovnova. Mutacija u kostanoj morfogenetsko proteina 15 gena (BMP15, takodje poznatom kao GDF9B) otkrivena je kod mnogih ovaca sirom sveta, kao dokaz segregacije major gena. Razvojem tehnika mapiranja gena i lociranja alela koji su odgovorni za plodnost ovaca, pocelo je novo poglavlje u predvidjanju i kontrolisanju plodnosti ovaca. Povoljni efekti ishrane na reprodukciju u ovaca su dobro poznati. Ovaj postupak je poznat kao flushing, pred oplodnju. Uticaj kondicije tela (BCS), pred parenje, tokom parenja i posle parenja na reproduktivnu efikasnost razlicitih rasa ovaca u razlicitim podizanju sistema su takodje proucavali mnogi ovde pomenuti autori. Farmer putem menadzmenta ima mogucnost da kontrolise, ili bar da manipulise faktorima koji imaju uticaj na plodnostovaca, a sto je takodje predstavljeno u ovom preglednom radu.