Reproductive Efficiency in Sheep: Estimates and Relationships with Fertility, Fecundity and Lamb Survival.

Addressing increased demand for sheep meat globally is dependent on reproductive efficiency (lambs weaned per 100 breeding ewes). Efficiency is determined by ewe fertility (pregnancy rate) and fecundity (litter size), as well as lamb survival. This paper provides estimates of these components from the world literature and examines their relationships with breed class (wool, dual-purpose, meat, milk, prolific) and within breed class, country and global region. Reproductive efficiency was estimated at 97.7 ± 2.68, while values for fertility, fecundity and lamb survival were 83.9 ± 0.95, 144.6 ± 3.48 and 80.8 ± 0.93%, respectively. Efficiency increased for each component, with the response being greatest for fecundity (R2 = 0.4896, p < 0.001). Within breed classes, medium- and strong-wool Merinos were more (p < 0.05) efficient than fine-wools, while narrow-tailed meat breeds were more fecund (p < 0.05) than fat-tail, wool-shedders and hair types. Efficiencies in the single- versus multiple-gene prolific groups were 124.6 ± 32.52% and 152.9 ± 10.1%, respectively. In conclusion, these findings provide an overview for the reproductive efficiency of the world's sheep population (though based on <5% of breeds), quantify how the parameters controlling efficiency interact, and estimate contributions made by breed, country and world region toward reproductive output.