Genetic parameters and predicted selection results for maternal traits related to lactation efficiency in sows

¹ IPG, Institute for Pig Genetics, P.O. Box 43, 6640 AA Beuningen, The Netherlands; Animal Breeding and Genomics Centre, Wageningen University, P.O. Box 338, 6700 AH Wageningen, The Netherlands
² Animal Breeding and Genomics Centre, Wageningen University, P.O. Box 338, 6700 AH Wageningen, The Netherlands
³ Animal Nutrition Group, Wageningen University, P.O. Box 338, 6700 AH Wageningen, The Netherlands
⁴ IPG, Institute for Pig Genetics, P.O. Box 43, 6640 AA Beuningen, The Netherlands

^* To whom correspondence should be addressed. E-mail: Rob.Bergsma{at}IPG.nl.

	Abstract

Increased productivity of sows increases the risk of a more pronounced negative energy balance during lactation. One possibility to prevent this is to genetically increase lactation efficiency (LE) and thereby increase milk output for given feed intake and mobilization of body tissue. The benefits of selection for LE depend on its heritability and the relationships with other traits of interest. The objective of this study was to estimate genetic parameters for LE, its underlying traits, and to predict the consequences of current selection strategies in dam lines. Data from four farms were available to estimate genetic parameters. Heritabilities were estimated using a univariate repeatability model and genetic correlations were estimated bivariately. Selection index theory was used to predict the genetic progress by three alternative breeding programs: (1) a breeding program which aims at balanced progress in total number of piglets born, piglet mortality and % prolonged interval from weaning to estrus; (2) extension of this breeding goal with LE; (3) a breeding goal which included only one selection criterion, litter weight gain, to demonstrate the effect of indirect selection for milk production. The heritability for LE was low (0.12). Body fat mass (0.52) and body weight (0.45) of sows at start of lactation showed the highest heritability. Protein mass at start of lactation, protein loss, weight loss and ad libitum feed intake during lactation showed a moderate heritability (0.39, 0.21, 0.20 and 0.30, respectively). Low to moderate heritabilities were found for litter weight at birth, within-litter SD in birth weight of piglets, litter weight gain, fat loss and restricted feed intake during lactation (0.19, 0.09, 0.18, 0.05 and 0.14 respectively). Within-litter SD in weaning weight of piglets showed no genetic variability. It was predicted that a breeding goal for dam lines with emphasis on total number of piglets born, piglet mortality and % prolonged interval from weaning to estrus will not dramatically change body weight and body composition at start of lactation, nor mobilization of body tissue and feed intake during lactation. Inclusion of LE in the breeding goal will improve stayability as defined by 1^st litter survival of sows and LE itself without negative consequences for other economically important traits. Nevertheless, it might be worthwhile to design a breeding goal where LE increases and feed intake remains unchanged.

Key Words: energy balance, genetic parameters, lactating sows, maternal traits