Response in maternal traits to selection for growth and feed efficiency in swine
The objective of this study was to determine the relationship between the traits of average daily gain, backfat, loin muscle depth, feed intake and feed conversion measured in growing gilts and their subsequent feed intake (as estimated by feed delivery) in lactation, and to estimate the effects of lactation feed intake on subsequent maternal productivity and sow longevity. Phenotypic performance measurements and estimated breeding values (EBV) were compared with first and second parity lactation feed delivery in a group of selected nucleus gilts of 3 genetic lines. The effects of lactation feed delivery on weaning to conception interval, total piglets born in the subsequent litter and lifetime productivity measures were investigated. Genetic parameters for the growing period traits of average daily gain, backfat, loin muscle depth, daily feed intake and feed conversion, as well as maternal productivity traits of litter size (number alive at day 2), weaning to conception interval and litter weaning weight were estimated and EBV were computed. Phenotypes of growth rate, feed intake, backfat and loin muscle depth recorded in the growing period were not good predictors of lactation feed delivery. However, one genetic line (YO-A) showed significant correlations between second parity lactation feed delivery and growth rate and loin muscle depth measured in the growing period. EBV calculated for the growing period traits of growth rate, feed intake and feed conversion showed much stronger relationships with lactation feed delivery than the growing period phenotypes, particularly for parity 2. Parity 2 lactation feed delivery showed favorable correlations with EBV for growth rate and feed conversion and an unfavorable correlation with the growing period daily feed intake EBV. Lactation feed delivery in the first and second parity had significant effects on the odds of occurrence of the next litter, next litter total born, stayability to parity 3 or parity 4 and sow longevity. Since lactation feed intake is very important to subsequent productivity and longevity of sows and has a positive (unfavorable) genetic correlation with growth period feed intake, it is recommended that lactation feed intake be measured directly and included in the selection goal. The correlation between lactation feed delivery in parity 1 and parity 2 was low at 0.28 across genetic lines, leading to the conclusion that lactation feed delivery in the first and second parities appear to be different traits under different control mechanisms. It is concluded that a balanced selection program for maternal lines that includes selection for reduced feed intake, feed conversion or residual feed intake measured in the growing period, should also include selection for increased lactation feed intake (probably in combination with changes in sow body weight or backfat during lactation in order to prevent negative consequences for sow longevity or productivity). It is also recommended that lactation feed intake in the first and later parities be evaluated as separate traits.
selection, swine, feed efficiency, maternal traits
Master of Science (M.Sc.)
Animal and Poultry Science