Longevity unaffected and output increased by crossbreeding hill flocks
Take Home Message: Using crossbred ewes will increase lamb output by 20% and have no negative effects on ewe longevity.
Crossbreeding has a key role to play to help ensure that the UK hill sheep sector remains economically viable in the future. Just one of the findings of study, carried out by researchers at Hillsborough’s Agri-Food and Biosciences Institute in Northern Ireland, to investigate the lifetime performance of a range of crossbred genotypes under hill conditions.
We found that adopting a crossbreeding strategy on hill flocks to produce crossbred replacement ewes is unlikely to have any adverse effects for ewe longevity and flock replacement rate,” said AFBI’s Ronald Annett. “But lifetime lamb output of hill ewes could be increased by up to 20% by crossing Blackface ewes with Lleyn, Swaledale or Texel sires to produce flock replacements, rather than maintaining a purebred status.”
He explained, during a presentation at the 2009 British Society of Animal Science’s annual conference, that a long term decline in economic returns, combined with recent changes to the Common Agricultural Policy, has led many hill sheep producers to consider keeping crossbred ewes to exploit the benefits of hybrid vigour for lamb survival and to introduce beneficial traits for prolificacy, ease of lambing and carcass quality.
Provisional data has already identified that retaining Lleyn X Blackface and Texel X Blackface ewes can improve lamb output at weaning by up to 10% relative to purebred Blackface ewes. But ewe longevity is a major issue for hill flocks, where the annual replacement rate often exceeds 20%.
The Hillsborough study was carried out, between 2001 and 2003, on six hill farms, representative of the main hill farming regions of Northern Ireland. A total of 200 purebred Blackface ewes per farm were allocated to one of five mating groups, balanced for ewe live weight, body condition score and age. Each year ewes were mated with Blackface (B), Cheviot (CH), Lleyn (LL), Swaledale (SW) and Texel (T) rams.
In 2001, single sire mating groups were used on each farm while in 2002 and 2003, a team of rams was used across all farms using artificial insemination. A total of 15 rams from each of the five sire breeds were used to produce the crossbred progeny.
Where possible, rams were selected on the basis of their genetic indices to represent the top 10% of recorded animals for the breed. The female progeny from these crosses were retained for breeding, which began at 18 months old. During a four-year period (November 2003-2006), the crossbred ewes were mated in single sire mating groups to a range of sire breeds, which were balanced across all genotypes.
Total lifetime output per ewe was calculated for each breed as the product of the proportion of productive ewes and the mean productivity per ewe lambed.
“And we found that longevity of all crossbred ewe genotypes, in terms of the proportion of ewes remaining at the fourth parity, were similar to that of purebred Blackface ewes. However, during a four-year period, the total number of lambs born and the total weight of lambs born per ewe were significantly higher in SWXB, LLXB and TXB ewes than BXB and CHXB ewes,” said Dr Annett.
These genotype effects remained at weaning, with SWXB, LLXB and TXB ewes successfully rearing a greater total number and total weight of lambs. These genotypes were also superior in terms of output efficiency, achieving a higher total lamb output per kg of metabolic live weight than BXB and CHXB ewes due to their greater weaned lamb output.
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