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 plodnošću. Prema nekim autorima broja potomaka dobijenih po jagnjenju je važnije od prirasta i mase tela. Genetski uticaji koji uključuju reproduktivne osobine se retko izučavaju. Plodnost ovaca ima nizak heritabilitiet, diskretnu fenotipsku ekspresiju, a izražena je samo u seksualno zrelih ovaca, što dovodi do niskog intenziteta selekcije i dugih generacijskih intervala. Otkriće major gena koji utiču na plodnost je u to vreme otkrilo mnogo skeptika koji su snažno sumnjali da takav kompleks reprodukcije može biti duboko pod uticajem jednog gena. Glavne geni utiču na plodnost kod ovaca i ovnova. Mutacija u koštanoj morfogenetsko proteina 15 gena (BMP15, takođe poznatom kao GDF9B) otkrivena je kod mnogih ovaca širom sveta, kao dokaz segregacije major gena. Razvojem tehnika mapiranja gena i lociranja alela koji su odgovorni za plodnost ovaca, počelo je novo poglavlje u predviđanju 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 različitih rasa ovaca u različitim podizanju sistema su takođe proučavali mnogi ovde pomenuti autori. Farmer putem menadžmenta ima mogućnost da kontroliše, ili bar da manipuliše faktorima koji imaju uticaj na plodnostovaca, a što je takođe predstavljeno u ovom preglednom radu.