Terminal crossbreeding of Dorper ewes to Ile de France, Merino Landsheep and SA Mutton Merino sires: Ewe production and lamb performance

The effect of crossing Dorper ewes with Ile de France (IdF), Merino Landsheep (ML) and SA Mutton Merino (SAMM) rams in a terminal crossbreeding program was investigated during 2000 and 2001. Expressed as percentage of purebred Dorper lambs, the average birth weights of IdF cross and ML cross lambs were increased by 12 and 7%, respectively. Crossbred progeny of IdF sires were 10% heavier than purebred Dorpers at weaning. A corresponding difference in favour of ML sires amounted to 5%. IdF crossbred lambs reached slaughter weight earlier than the other cross lambs and purebred Dorper lambs. Lamb mortality prior to weaning was unaffected by the breed of the service sire, and ranged between 0.13 for lambs sired by IdF rams to 0.22 for purebred Dorper lambs. Ewe joining weight, as well as number of lambs born and weaned per ewe lambed was independent of the breed of the service sire. When weight of lamb weaned per ewe lambed was considered, there was a tendency towards higher lamb outputs in ewes that were joined to IdF and SAMM sires. Estimated repeatability derived for joining weight and the various measures of reproduction generally accorded with literature estimates. Backfat depth (taken at the 13th rib, 25 mm from the midline) indicated that purebred Dorper lambs had a thicker fat cover compared to all combinations of crossbred lambs. Corresponding sire breed differences were found between the 3rd and 4th lumbar vertebra, 25 mm from the midline. Terminal crossbreeding of Dorper ewes with IdF, ML and SAMM sires did not deleteriously affect lamb growth and survival or ewe reproduction. Terminal crossbreeding could thus be implemented in commercial Dorper flocks, without compromising productivity and/or product quality.