Using crossbred hill ewes can improve finishing lamb performance
There is significant potential to improve the carcass quality of lamb sourced from the hill sheep sector by crossing a proportion of Blackface ewes with upland or terminal sires to produce crossbred replacement females. This was the key finding of a study to investigate the effects of switching to crossbred hill ewes, on lamb performance during finishing, which was outlined to delegates at this year’s British Society of Animal Science’s annual conference.
Hill sheep flocks in the UK are dominated by purebred ewe genotypes, with the Scottish Blackface, Welsh Mountain and Swaledale being the most common. However recent changes to the Common Agricultural Policy have lead many hill producers to consider keeping crossbred ewes on the hill, with the aim of introducing complementary traits to increase lamb output and improve carcass quality.
“And it could well be a good move,” Ronald Annett from Hillsborough’s Agri-Food and Biosciences Institute. “Our work demonstrated that retaining crossbred ewes with Cheviot and Texel genes improved lamb carcass conformation and reduced the level of carcass fat cover relative to pure Scottish Blackface lambs.
“Introducing Swaledale genes into the maternal line, however, had no effect on lamb performance or carcass quality relative to Blackface ewes,” he added.
During November 2001 and 2002, 200 purebred Blackface ewes on each of the six Northern Ireland-based hill farms that took part in the trial were tupped with Blackface, Cheviot, Lleyn, Swaledale, and Texel rams. The female progeny from these crosses were retained for breeding, which began when ewes were approximately 18 months old.
The crossbred ewes were mated to Texel, Lleyn and Dorset rams in single sire mating groups, balanced for ewe genotype, liveweight, body condition and age. And during a two-year period, 588 male and female lambs were moved after weaning to a central location for finishing. Lambs were permanently housed in groups of six and finished on one of four ad-lib concentrate diets comprising grass nuts, standard barley/soya based-concentrate, standard concentrate plus rapeseed meal and standard concentrate plus fish oil.
Lambs were weighed at weekly intervals until they reached their allocated slaughter weight of 42 or 50 kg for male lambs and 38 or 46 kg for female lambs.
“Higher concentrate intakes were recorded for lambs born from Texel cross ewes relative to those from Swaledale cross ewes, although there were no significant differences in feed conversion ratio between any of the ewe genotypes studied,” said Dr Annett.
“Lambs from Texel cross and Cheviot cross ewes tended to have higher daily live weight gains compared with those from Swaledale cross ewes, but there were no significant effects on daily carcass weight gain or killing-out percentage between any of the ewe genotypes.
“And carcasses of lambs from Blackface and Swaledale cross dams had poorer conformation compared with the other ewe genotypes. Higher carcass fat scores were observed in lambs from Blackface and Swaledale cross ewes relative to those from Texel cross and Cheviot cross ewes,” he added.
Presented to the British Society of Animal Science Annual Meeting, March 31 to April 2, 2008, Scarborough, UK.
Full details: Annett R, Carson A, Dawson L and Irwin D: “Crossbred versus purebred ewe genotypes for the hill sheep sector: effects on finishing lamb performance.”
summary (pdf) Presentation_022annett (pdf)
For further information visit http://www.bsas.org.uk/Publications/Annual_Conference_Proceedings/ or contact BSAS on 0131 445 4508 bsas@sac.ac.uk
