Estimates are given for various traits associated with reproduction rate at each age from 3 to 9, 2 to 7, and 3 to 6 years for Merino, Corriedale, and Polwarth ewes respectively. The number of lambs born per ewe joined for Merino ewes decreased steadily with age, while the number of lambs weaned per ewe joined and the survival rate of both single and twin lambs rose to a peak at 4–5 years, with a subsequent fall; the reproduction rate for Corriedale and Polwarth ewes increased with age to the oldest age of 6 years. The estimates are used to predict the reproduction rate of flocks with different age structures, the conclusion being that the average number of lambs born per ewe joined would decrease progressively with increase in flock age, and the average number of lambs weaned per ewe joined would increase with the age of the oldest group of ewes up to 6 years for Merino flocks, and with the oldest group to at least 6 years for Corriedale and Polwarth flocks.
Predator-Prey Interactions, Age Structures and Delay Equations
