An Overview of Major Genes Affecting Prolificacy in Sheep and Related Mechanisms

The objective of this review is to explore the current developments on major genes working on prolific sheep breeds and the mechanism behind it, while identifying the future working points. Productivity is the ultimate goal of farm animal production and prolificacy is a key feature in determining productivity in farm animals. Ovulation rate in mammals is an intricate process involving genetics and endocrine pathways. Exceptional reproductive capabilities along with higher ovulation rates were observed in many breeds of sheep from different parts of the world since the discovery of Booroola Merino sheep. These naturally occurring mutations acting on prolificacy are found in chromosomes 5, 6, 11 and X but speculations are around about the presence of more mutations on these genes or different genes on multi ovulating sheep breeds. The exact control mechanism of multiple ovulations and multiple births in prolific sheep breeds is poorly understood. Over the years it has been repeatedly shown that gonadotropins and intra ovarian factors play vital and variety of roles. More specifically, follicular stimulating hormone regulation during folliculogenesis could be a promise for the future studies. Among those intra ovarian factors, bone morphogenic protein system is one of the indispensable components, which exerts enormous enthusiasm among the scientific community towards manipulating ovarian folliculogenesis. Rather surprisingly, biological and physiological roles of bone morphogenic protein subfamily are not thoroughly elucidated and contradictory findings among the mammals make further twists, which will be the gaps to be filled in the near future. Presence of a regulatory control loop between oocyte, granulosa and theca cells throughtransforming growth factor B(TGFB) superfamily is proposed here.