Constraints to improving reproductive efficiency of ruminant livestock in developing countries

Reproductive performance in ruminants is closely linked to efficiency of production measured either directly as the number of surplus animals available for sale, or indirectly as amount of produce harvested per animal. In developing countries, the major limiting factors to reproductive rate are biological, of which the most important is nutrition. Undernutrition has detrimental effects on age at first calving owing to delay in attaining the target weight at puberty. Reconception is also adversely affected in animals that suffer high loss of weight after parturition owing to undernutrition in early lactation. Genetic variation in mature body weight among breeds is important. Under conditions of feed stress in cattle, there is a negative relationship between mature weight and fertility owing to the high maintenance requirements of larger animals. The most important socioeconomic factor contributing to reproductive inefficiency is the fostering of large herds containing disproportionate sex groups, thus reducing feed availability. In small ruminants, although multiple births increase reproductive rate, the high mortality associated with twinning makes it undesirable in some situations. Opportunities for increasing reproductive rate in these species seem to be greater through decreasing parturition interval than through increasing litter size. (author). 28 refs, 1 fig., 5 tabs