Breed and Age Effects on Lamb Production of Ewes

Abstract

Breed and age effects on fertility for 8,129 ewe matings and on spring lamb crop for 6,726 lambings were examined in seven domestic breeds and two strains of crossbred origin during 4 years. Fertility changed curvilinearly with age at lambing from 45 to 75% at 1 year to 85 to 95% at 4 to 6 years and to 60 to 80% at 9 years, with large breed and year differences in the fertility-age curve. Breed differences in age-adjusted fertility were large within years but rather inconsistent among years. Lambs born per ewe lambing increased curvilinearly with age of ewe, from 100+% at 1 year to 160% at 6 years and back to 135% at 9 years. The influence of age differed importantly among breeds for total and live lambs born but not for live lambs at 4 or 10 weeks of age. Most prolific breeds were Suffolk at 1 to 5 years, Dorset at 6 to 9 years and Targhee; breed differences were highly significant for total born (161 to 140%), barely significant for live lambs born (150 to 135%), but not for lambs weaned (108 to 94%). Based on live lambs born, size and wool production of ewes and boneless cuts from ram lambs, expected relative ewe-efficiency in producing crossbred lambs ranked Dorset (103), Suffolk (100) and Coarse Wool (97), Targhee (95), Corriedale (94), Hampshire (93) and Rambouillet (89). Using lambs weaned, efficiency ranked Coarse Wool (108), Targhee and Dorset (104), Suffolk and Rambouillet (100), Hampshire (98) and Corriedale (96).