Genetic improvement of reproductive efficiency of sheep and goats

Sheep and goats are produced in a wide range of production systems and climatic conditions and possess great genetic diversity in reproductive potentials. Mean litter sizes range from near 1 to 3 or more, and patterns of seasonal reproduction are often strongly synchronised to local conditions. Thus, optimisation, rather than maximisation, of reproductive potentials is required, and optimum reproductive rates are often well below those which could be achieved. However, changing employment patterns, increasing urbanisation, and emergence of new markets provide corresponding opportunities for sustainable intensification of small ruminant production, potentially requiring enhancements in reproductive potentials. Heritabilities for most reproductive traits are less than those for many other traits, usually ranging from 0.05 to 0.15, and opportunities for within-breed selection are therefore limited. Substantial changes in litter size or major changes in seasonal breeding patterns are thus best achieved by crossing of divergent breeds to rapidly reset genetic potentials for these traits, followed by within-breed selection to optimise reproductive potentials. Various mutations influencing ovulation rate and litter size in sheep provide additional opportunities to rapidly adjust genetic potentials, but require careful breeding management. Comparable major genes have not yet been found in goats or for traits associated with breeding season.