7th World Congress on Genetics Applied to Livestock Production, August 19-23, 2002, Montpellier, France GENETIC ANALYSIS OF SOWS’ REACTION TO A SCREAMING PIGLET, AND ITS RELATION TO PIGLET MORTALITY AND GROWTH K. Grandinson 1 , L. Rydhmer 1 , E. Strandberg 1 and K. Thodberg 2 1 Swedish University of Agricultural Sciences, Dept. of Animal Breeding and Genetics, Funbo-Lövsta, SE-755 97 Uppsala, Sweden 2 Danish Institute of Agricultural Sciences, Research Centre Foulum, Dept. of Animal Health and Welfare, P.O. Box 50, DK-8830 Tjele, Denmark INTRODUCTION The number of piglets weaned per sow is an economically important trait for pig producers. Most breeding programs include number of piglets born, or number born alive, to improve litter size at weaning. There are, however, unfavourable relationships between litter size at birth and survival during the pre-weaning period. To avoid an increasing problem with high pre-weaning mortality, we need to balance the selection for litter size at birth by also selecting for a trait that describes the sow’s ability to take care of her litter. Piglet survival rate in itself has a low heritability. Genetic studies on survival from birth to weaning show estimated heritabilities averaging 0.05 (Rothschild and Bidanel, 1998). It is desirable to find a trait that is related to piglet survival, but less influenced by environmental variation. The most common causes of post-natal death in piglets are crushing by the sow and starvation. Both these causes of death are highly related to the behaviour of the sow. Earlier reports indicate that sows showing a strong response to the sound of a piglet distress call display less risky behaviour around their piglets early postpartum (Wechsler and Hegglin, 1997; Thodberg et al., 2002), and have fewer crushed piglets (Wechsler and Hegglin, 1997). The aim of this study was to investigate the genetic background of how sows respond to the sound of a piglet screaming, and to estimate the phenotypic and genetic relationships between this behaviour trait and early piglet survival and growth. MATERIAL AND METHODS Data. The piglet scream test was used to test sows’ responsiveness towards a piglet distress call, as when it is being crushed under the sow (Thodberg et al., 1998). The test was recorded during 2.5 years, 1999 to 2001, in 6 Swedish breeding herds and at Lövsta research station, Swedish University of Agricultural Sciences. On the farrowing day or the day after, as the sow was lying on her side but not nursing, the farmer quietly reached a small tape recorder into the pen and played back the sound of a screaming piglet to the sow during approximately 20 seconds. The sow’s maximum response to the sound was recorded in four ordered categories as: no reaction, lying down and looking for the sound, sitting up, or standing up. Data on the scream test and on mortality was collected from 829 sows, with 1336 litters. These sows had 397 dams and 209 sires. All tested sows were pure-bred Swedish Yorkshire, housed in farrowing pens without crates during lactation. Cross-fostering was practised in the breeding herds, but not at the research station. Mortality was recorded as total mortality, including stillborn piglets, at day 4 (±1 S.D.), and as the number of piglets the farmers considered had Session 14. Behaviour and welfare Communication N° 14-11