9 February 1996

Improving carcasses in hill sheep without tears

A third of genes of all sheep slaughtered in the UK derive from hill breeds. Scottish research is under way to discover how to improve the carcass composition of these sheep without compromising hardiness and maternal traits. Rebecca Austin reports in the first of a focus on Scottish research

BREEDING leaner hill ewes improves returns by 57p a lamb at the sametime as increasing ewe prolificacy and retaining mothering ability.

These are the latest results from the on-going Hill Sheep project carried out by Dr Geoff Simm and Joanne Conington, animal breeding specialists, at the Scottish Agricultural College, Edinburgh.

The main objectives of the project are detailed in the panel.

Scottish Blackface rams, selected at the Roslin Institute for differing fatness but not liveweight or muscle depth, were mated to 600 ewes at SACs Castledaw Farm, Midlothian and to another 600 ewes at SAC Kirkton/Auchtertyre in Perthshire. While Castledaw rises to 500m (1640ft) above sea level and experiences 800mm (32in) of rainfall a year, Kirkton is harder on ewes as its highest point is 1000m (3281ft) above sea level and it has 3000mm (118in) of rain a year. There is a 7kg to 10kg difference in adult ewe liveweight due to environmental differences.

Ewe lambs born in 1991 and 1992, described as being either from the lean or fat line were retained in the flocks and mated at 18-months old. These have been recorded for maternal performance, survivability and lamb performance over the years.

Ram lambs are finished each year at the Bush Estate, Penicuik, on silage aftermaths, swedes and concentrates from September to March.

They are drawn fortnightly to condition score 3. Results are outlined in the table. Lean lambs showed a 14% improvement in ultrasound backfat measurements. Their carcasses also weighed 340g more than fat lambs and were therefore worth an extra 57p each.

Lean lambs were also heavier at weaning which showed lean ewes were milking better than their fat peers. They were also more prolific at scanning and were able to rear more lambs. Castledaw lean ewes born in 1991 pregnancy scanned at 150.5% last year, whereas their fat peers achieved 136.4%. At Kirkton lean ewes recorded 129%, while fat ewes scanned at 121.5%. Lean ewes were also recorded as carrying heavier, but poorer quality, fleeces.

"As lean lambs grow to heavier weights without becoming too fat, these lambs will be more attractive to store lamb buyers as the window of marketing opportunity is extended. And with lean ewes retaining their maternal traits, but showing improved prolificacy, which must be a bonus," says Ms. Conington.

Usually ewes breed four crops of lambs on the hill before moving further down to produce Mules by matings to Longwool breeds. As this project is emphasising the leaner ewes hardiness, they will stay on the hill for five years.

So far the project has been funded to the tune of £100,000 a year by the Scottish Office of Agriculture, Environment and Fisheries (SOAEFD), the Meat and Livestock Commission and the British Wool Marketing Board. Once the relationships between all traits are understood, Dr Simm and Ms Conington will develop an index for hill sheep. Ewes will be selected on that index in an attempt to further improve lamb performance and maximise economic returns without compromising ewe hardiness.

"With a large proportion of hill income coming from subsidies there is enormous potential for increasing performance by improving technical performance," says Dr Simm.

&#8226 Does selection for improved carcass and growth characteristics affect maternal performance and survivability?

&#8226 What are the links between growth, carcass, reproduction, wool and survival traits?

&#8226 Which of the above would be useful in an index of overall merit?

&#8226 Does selection for differing fat levels under intensive concentrate feeding have any effect on progeny reared extensively?

Researchers will soon develop an index to help hill and upland producers select rams and ewes whose progeny will maximise economic returns.

Joanne Conington:"Lean ewes retain their maternal traits but show improved prolificacy."