Does an increase in lamb birth weight though mid-pregnancy shearing necessarily mean an increase in lamb survival rates to weaning?

摘要

Lambing percentages in New Zealand have risen over the past decade and will most likely continue to rise, while the price for lamb remains high in relation to wool. Any technique that can increase the birth weights of multiple-born lambs may increase survival rates to weaning. Mid-pregnancy shearing as a possible technique to increase lamb survival under commercial conditions was examined in the present study. Mid-pregnancy shearing was found to significantly (4.7 vs. 5.1 kg, P < 0.05) increase thebirth weights of twin-born lambs but had no effect on birth weight of singletons or triplet-born lambs. Both the magnitude of the response, and the fact that it did not occur in all birth ranks, are consistent with previous mid-pregnancy shearing studies. Mid-pregnancy shearing had no significant effect on lamb survival rates to weaning. To achieve an increase in survival rate to weaning through an increase in lamb birth weight alone, the lamb must be born within a birth weight survival range below optimum and the increase in birth weight must be large enough to move a significant proportion of these lightweight lambs into a higher survival rate range.