Genetic improvement of meat sheep. 4. Effect of age of dam on productivity of Dorset and Border Leicester sheep

Abstract

The effect of age of the dam on the number of lambs born (LBL) and weaned (LwL) and the weight of lambs weaned (WLWL) per ewe lambing and on the number of lambs weaned per lamb born (LwB) and lamb weaning weight (WWT) has been estimated for Dorset and Border Leicester sheep. In both breeds, LBL, LWL and WLWL showed a clear association with age of the dam, rising to a peak at a dam age of five years in the Dorsets and at between four and six years in the Border Leicester. The association between age of dam and WWT and LWB was less marked. WWT rose to a peak in both breeds at a dam age of five years and LWB rose to a peak at four and three years in the Dorsets and Border Leicester respectively. The estimates of ewe productivity were used to calculate the productivity of Dorset flocks of differing age structures. It was found that maximum productivity would be achieved with a flock aged from two to six years.