A study of factors affecting survival from birth to weaning and total weaning weight of the litter in swine.

University of Minnesota p RODUCTIVITY in brood sows during the pre-weaning period is measured by fertility, survival of the pigs born, and milk production. All three of these factors contribute to a large extent to the total weaning weight of the respective litters and are of individual economic importance to the hog producer. Therefore, from the breeder's standpoint, it is important to know to what extent these factors are related to one another or in. fluenced by other factors in order to select effectively for greater productivity in the breeding herds already established or in the development of improved lines. High survival of the pigs born is an important goal of all swine raisers. Even though improved methods in management and certain methods of breeding have helped to lower the death loss of little pigs the problem is still of major importance. From a study of several herds under varying conditions Kernkamp (i943, i946 ) found that the average loss of little pigs during the suckling period was about 2~ percent and that the losses were due to more than 35 different diseases, disorders, or conditions. The death rate was highest in pigs up to one to two weeks of age and was reduced as they grew older. The early experiments in guinea pigs by Wright (i9:~) and in swine by McPhee et al. (I93 I) and others have shown that a rapid increase in inbreeding had a deleterious effect upon the vitality of the newborn and thus reduced survival considerably in most instances. They also found that there was a decided decrease in weaning weights of the young as the inbreeding increased. This was reflected in a lower total weaning weight of the litter as inbreeding had decreased the size of the litters. Winters et al. (I943), by the use of a flexible program of inbreeding and rigid selection for all traits connected with vigor, reported an ability to maintain survival and weaning weight at a relatively high level as the inbreeding increased. It is generally