Aspects of litter size (birth type) in goats and sheep production

Increasing kid/lamb production is of paramount importance to goat and sheep producers. As a matter of one choice enhancing litter size becomes inevitable, because apart from litter size impacting on flock productivity, it is also implored as a major determinant of profitability due to its influence on kid/lamb survivability. There is a positive correlation between litter size and lifelong dam contribution and overall flock productivity. Increasing litter size to an optimal level might be crucial especially for the intensive goat and sheep production systems. A number of studies have proved that litter size is under the influence of both genetic and non-genetic factors. Currently, genome wide selection targeting established genetic markers is being employed to increase the efficiency of goat and sheep selection for reproductive traits, such as prolificity. This is on the background that litter size is lowly heritable, but on the other hand, immense genetic variability between and within breeds exist that could be exploited in breeding schemes by collaborating additive polygenic differences, breed complementarities, heterosis effects and major gene inheritance. Among the non-genetic factors that influence litter size in goats and sheep, parity order, age of dam and seasonal variation have been rated highly. Litter size tend to improve with age and parity order as a result it is highly likely that dams with large previous litter size may have high chances of producing multiple births in consecutive kidding/lambing. Environmental conditions are also an important source of variation on litter size, with chances of large litter size within natural reproductive seasons. Seasonal influence might be confounded by other factors such as flock nutritional management and genetic improvement strategies. The adverse effect of increase in litter size has been associated with an increase in number of underweight kids/lambs which in turn lower their survival rates. Underweight at birth is the probable explanation for reduced kid/lamb viability in goats and sheep. This entails a balance should be strike on optimal litter size, where too large and/or too small litter size may be impracticable desired and/or uneconomical, respectively. Proffered suggestion is that litter size of two is economically feasible for an intensive goat and sheep enterprise. The present review gives an insight on the influence of litter on flock performance and discuss the factors that are the major determinants of litter size in goat and sheep meat production.

کلیدواژه ها:

Litter size ، Non-genetic factors ، Goats ، Sheep