Effects of ewe breed and management system on efficiency of lamb production: II. Lamb growth, survival and carcass characteristics.

Lamb growth, survival and carcass characteristics were compared for progeny of either 1/2-Suffolk, 1/2-Rambouillet (Western) ewes or 1/2-Suffolk, 1/4-Rambouillet, 1/4-Finnsheep (1/4-Finn) ewes produced over 3 yr in three different management systems. System 1 lambs were born in late fall and fed to slaughter on a concentrate diet. System 2 lambs were born in January and February and grazed pure stands of alfalfa or ladino clover after weaning. System 3 lambs were born in March and April and remained with their dams on native bluegrass-white clover pasture throughout the grazing season. Lambs were slaughtered as males reached 55 kg and as females reached 50 kg. One-half of the males in System 1 were left intact; all males in Systems 2 and 3 were castrated. Lamb survival did not differ among systems. Lambs from yearling 1/4-Finn ewes had higher survival rates than lambs from yearling Western ewes, but at older ewe ages, progeny of the ewe groups did not differ in survival. Lambs in System 1 grew fastest (mean lifetime gains of 310 +/- 4 g/d) and were youngest at slaughter (156 +/- 3 d), and lambs in System 3 were oldest at slaughter (234 +/- 2 d). System 2 lambs differed considerably among years in growth rate and slaughter age (mean slaughter ages of 191, 230 and 193 d across years), primarily in response to differences in rainfall. Lifetime gains and slaughter ages of lambs did not differ between ewe breeds. Ram lambs grew 15% faster than wethers and were leaner. Differences among systems in carcass traits were small. System 1 lambs tended to be fattest and System 2 lambs leanest. Progeny of 1/4-Finn ewes had higher subjective scores for carcass fatness (e.g., feathering, flank fatness) and conformation but did not differ from progeny of Western ewes in objective measures of fatness (e.g., backfat, yield grade).