2 April 1999

Sires at 70kg is an accurate guide

SELECTING terminal sires at 70kg provides an accurate reflection of the quality of their lambs, proving that lean growth index helps improve lean carcass composition, according to Ron Lewis of SAC Edinburgh.

Reporting on a study of Suffolk sheep, Dr Lewis said there were concerns that selecting sires at 70kg when lambs were sold at 40kg wouldnt result in the expected lean composition of carcasses.

A nine-year study of selected lines – the best performing animals on index, improving each year – and control lines, which were kept at a constant index value, shows selected animals produced an extra 6kg (10%) liveweight, 13% more muscle depth and 13% (1mm) less fat.

But Dr Lewis wanted to know whether lean growth index was important when lambs were marketed at 40kg, and trials found that it was.

"Benefits are seen with animals at market weight even when animals for breeding are selected at heavier weights."

Selected group animals grew more quickly, with 10-15% higher growth rates, but didnt eat more feed so were 5-10% more efficient, he said.