Introduction

Reproductive management of naturally breeding sheep varies considerably throughout the world, largely due to the significant number of genetically distinct breeds and the diverse ecosystems that they inhabit. Sheep reproduction is influenced by traditional, cultural, social, and economic conditions. Once-per-year lambing is traditionally practiced in most countries, although some developed countries have resorted to accelerated lambing management strategies, i.e., three lamb crops in two years, or twice-a-year lambing.

Like all farm animals, reproductive management of sheep falls under two major constraints: genetic inheritance from its ancestors, and environmental influences, i.e., nutrition, disease, parasites, animal facilities, location and climate, human management, and perhaps most important, the season of the year. Sheep are seasonal breeders, and most breeds are short-day breeders. The photoperiod (ratio of daylight to darkness hours) is a crucial consideration in reproductive management. Animal physiologists refer to sheep as being seasonally polyestrous in their breeding patterns. The genetic evolution of the breed and the latitude of their geographic area of origin have the most influence on seasonality of breeding activity.

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