Genetic progress speeds with index
USING genetics to improve carcass quality is one way of improving hill sheep flock margins, but progress is often slow.
Since 1999, ADAS Redesdale, Northumberland, has used a revised selection index incorporating liveweight, CT-scan measurements and body conformation scores to select replacements for a nucleus flock of 60 superior Scottish Blackface ewes.
The nucleus flock and a control group of 40 ewes are managed on a typical Northumberland system for all except two weeks a year. For those two weeks, at mating time, ewes graze in-bye fields to facilitate multiple ovulation and embryo transfer procedures.
Earlier studies indicated that the heritability of traits – such as liveweight, ultrasonic muscle depth and width, and fat depth – are higher in extensively managed flocks than previously reported. But the new index had significantly improved carcass conformation in only two years, with no adverse effects on other important traits, such as lamb survival. *