Factors and their effects on birth weight, average daily gain, and 120-day weight of purebred Hampshire lambs

Sheep production in Tennessee is comprised predominantly of the commercial production of milk fat spring lambs with some purebred production and a very limited amount of lamb feeding. The production of spring lambs is a special type of enterprise in Tennessee. These spring lambs are produced primarily by mating either native, western crossbred or grade fine wool ewes to rams of the Hampshire, Suffolk or Southdown breeds. The success of spring lamb production demands breeding for the desired type and weight of lamb and providing succulent, highly nutritious, cheap feed. The object is to produce fast-growing lambs that are properly finished at market time in May and June. Since the purebred breeder is the source of supply of rams for the commercial sheepman, it is the purebred breeder's responsibility to provide the kind of rams for market lamb production which will sire fast-gaining, good-type lambs of desirable market quality. Therefore, the purebred breeder must continually strive to improve performance if he is to meet this responsibility. Research results indicate that improvement can be made in the productivity of sheep through selection. Performance records and their use in a selection program provides an effective tool which can be used by breeders to improve productivity. However, before performance records can be used effectively as a basis for selection, the records of individual animals must be placed on a comparable basis. Many environmental and other factors operate to conceal true genetic merit, thereby confusing the breeder and obstructing his efforts to select those animals having the greatest breeding value. In many cases, variation due to environmental factors can be eliminated or controlled but in others adjustment or correction for major environmental effects is necessary to place animals on a comparable basis. Information is needed on the extent and magnitude of these effects in sheep in order to adjust performance records before selections are made. The purposes of this study were (1) to evaluate the effects of various factors including age of dam, season of birth, sex, type of birth, type of birth and rearing and year of birth on birth weight, average daily gain from birth to weaning and 120-day weight in pure-bred Hampshire sheep and (2) to determine correction factors to be used to adjust performance records of lambs for these effects.