Genetic evaluation of crossbred lamb production. 3. Growth and carcass performance of second-cross lambs

This study evaluated the growth and carcass performance of second-cross lambs that were the progeny of common terminal sires and a range of first-cross ewes. The first-cross ewes were the progeny of 91 industry sires from several maternal breeds including the Border Leicester, East Friesian, Finnsheep, Coopworth, White Suffolk, Corriedale, and Booroola Leicester breeds. The first-cross ewes were generated at 3 sites over 3 years, and 3 common maternal sires were used at each site and each year to provide genetic links for combined analysis. The 2726 first-cross ewes were mated naturally to common terminal sires for 3 years at each site to quantify the variation in maternal genetics on the performance of 11 341 second-cross cross lambs. The birthweight, weaning weight (at an average age of 100 days) and post-weaning weight (at an average age of 200 days) of the second-cross lambs were analysed using mixed-model procedures. The lambs were slaughtered (n = 8878) at an average target carcass weight of 22 kg and dressing yield, carcass fat, muscle, meat colour, and meat pH were analysed. Crossbred ewe breed (the maternal grand sire breed) was significant for birthweight (range of 0.9 kg), weaning weight (range 4.4 kg) and post-weaning weight (range 4.6 kg). Type of birth and rearing, age of dam, and sex effects were significant for all liveweights. Ewe breed was significant for hot carcass weight, carcass fat levels, and muscle dimensions, but not for meat colour and ultimate meat pH. There was a significant difference between wether and ewe lamb carcasses for most traits, with other fixed effects generally being small when carcass weight was included as a covariate. Lamb carcasses from East Friesian-cross ewes were very lean compared with carcasses from all other ewe breeds (∼2 mm lower fat depth at the GR site at 22 kg carcass weight). This comprehensive study of maternal sire breeds provides an opportunity to exploit between-breed variation for some maternal growth and carcass traits. There was, however, considerable overlap among breeds and opportunities exist for additional improvement by exploiting between-maternal sire genetic variance. The role of improved growth and carcass performance in profitability of prime lamb enterprises is discussed.