Between 1998 and 2004 a sire progeny test was run at the Poukawa Research Farm in Hawke’s Bay. Four ewe genotypes were used (Romney, East Friesian x Romney, Finn x Romney and Poll Dorset x Romney) with up to 900 ewes mated each year. Data was collected on 4614 lambs born to 74 rams (an average of 62 progeny per ram). Rams used represented 13 different terminal sire and dual purpose breeds. Ewes were mated using AI or single-sire mated in the paddock for one cycle. Lambs were tagged and weighed within 24 hours of birth. At 12 weeks of age, lambs were weighed and scanned for eye muscle dimensions from which eye muscle area was estimated. Data were analysed using a REML animal model taking account of repeat matings among parents, genetic relationships among animals and incorporating adjustments for fixed effects associated with year, ewe genotype and litter size. At a mean lambing percentage of 165%, the mean birth weight across all sires was 4.91 kg and ranged between 4.21 and 5.46 kg for individual sires. The mean 12 week liveweight was 29.8 kg and ranged from 26.5 to 33.1 kg for progeny from individual rams. There was a wide range in GR fat depth (mean 8.9 mm, sire range 6.9 to 12.3 mm) when corrected to a constant carcass weight of 18.3 kg. The top rams for liveweight were not necessarily top for other characteristics. Significant numbers of lambs are sold store at weaning on a liveweight basis and this makes it possible to place a value on pre-weaning growth. At $2/kg liveweight, the average lamb sired by the top ram for growth would be worth $66.20 and the progeny from the bottom ranked sire would be worth $53 - a difference of $13.20 per lamb. Assuming these rams had an active lifespan of 4 years and mated 80 ewes rearing 125% per year, each ram would leave 400 progeny. At $13.20 per lamb the difference in value between the top and bottom ranked rams would be $5280. These results show the differences between rams and highlight the importance of using breeding values in the ram selection process.
Proceedings of the New Zealand Society of Animal Production, Volume 66, Napier, 373-376, 2006
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