AN APPRAISAL OF CERTAIN SOURCES OF ENVIRONMENTAL VARIATION IN THE PRODUCTIVITY OF YORKSHIRE SOWS

Abstract

Analysis of the records of 616 Yorkshire litters farrowed over a 20-year period in the University of Alberta swine herd indicated that litter performance was not associated with differences in weight changes of the sow during gestation or with gestation length. Gestation weight change was negatively correlated with breeding weight and lactation weight changes. Age of sow, breeding weight and litter order were highly correlated and were mutually dependent in their effect on litter performance. Least squares estimates of year, season, breeding weight of sow, and weight change during lactation effects were obtained for several performance traits of the litter. Year differences were large but erratic for all traits. Seasonal differences appeared to be important only for litter size with fall litters averaging 0.78 more pigs at weaning than spring litters. Weight of sow at breeding exerted an important influence on litter performance. Weight change during lactation appeared to be a function of litter size.Study of the relative influence of age and weight of gilts at breeding on first litter size at birth and weaning indicated that breeding weight exerted the greater influence.It is concluded that comparisons between litters in the same herd and born within the same year and season must provide for statistical control of variation in weight of dam at breeding. If inter-year comparisons are desired additional statistical control is essential.