Factors Affecting Weaning Weights of Crossbred Spring Lambs

Abstract

Suffolk rams tended to sire lambs which were heavier at weaning than did Southdown rams, although the differences were not significant. Hampshire-cross ewes produced the fastest growing lambs of the breeds compared. Hampshire-cross lambs were significantly heavier than Cheviot and Romney-cross lambs. There were no significant differences in the weights of Cheviot and Romney-cross lambs. This study is concerned with weaning weights on a lamb rather than ewe basis.Lambing percentages were 134, 127, 124, and 115 for Hampshire, Cheviot, Border Leicester, and Romney-cross ewes, respectively, and lamb mortality was 6.4, 5.7, 4.8, and 14.8%, in the same order. Birth weight was one of the most influential of the variables which was studied. The differences among breeds are partly due to differences in birth weights. The regression of weaning weight on birth weight ranges from 2.5O±.65 to 5.96±.76 lb. increase in weaning weight for each pound increase in birth weight. In the production of heavy spring lambs, the ability of individuals within a breed to produce lambs which are large at birth should be considered as well as a choice of a breed. Birth type imparted the greatest effect on lamb growth of any of the environmental factors studied. Single lambs weighed, on the average, 17 lb. more at weaning than did twin lambs. A large portion of the difference in weights of singles and twins is established at birth; however, in years of good feed supply, the relative growth rates may be similar. Copyright © . .