Applied Animal Behaviour Science, 26 (1990) 143-155 143 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands Behaviour and Weight Changes at Weaning and Regrouping of Pigs in Relation to Teat Quality B. ALGERS, P. JENSEN and L. STEINWALL Swedish University of Agricultural Sciences, Department of Animal Hygiene, P.O.B. 345, S-532 24 Skara (Sweden) (Accepted for publication 16 November 1989) ABSTRACT Algers, B., Jensen, P. and Steinwall, L., 1990. Behaviour and weight changes at weaning and regrouping of pigs in relation to teat quality. Appl. Anim. Behav. Sci., 26: 143-155. One hundred and one individually marked healthy piglets in 10 litters were followed from birth to 9 weeks of age in order to elucidate the relationships between weight changes and behaviour at weaning and regrouping. The piglets were weighed once a week and additionally at extra instances just before and after weaning and regrouping. The pigs were weaned by removal of the mother 6 weeks post-partum and the litters were mixed two by two, 7 days later, so that the pigs with weight rank 1, 3, 5 etc. in one litter were mixed with the corresponding pigs of the other litter. The behaviour of the pigs was recorded on video during 24 h before and after weaning and regrouping, and at 9 weeks of age (before moving to the fattening unit) by obtaining 20 s of continuous recording every fifth minute. Both weaning and regrouping markedly increased the frequencies of eating, drinking, aggression and submission, although the latter was only substantially increased by regrouping. Piglets having had the largest weight gain between 3 and 4 weeks post-partum (indicating good teat quality) ate less solids on all observations, except just before moving to the fattening unit, and drank less water before weaning. The same piglets had a lower relative weight gain at regrouping than their litter mates. During weaning, those pigs gaining more weight than their litter mates were more submissive, but there was no effect on aggression. When the pigs were regrouped, the pigs gaining more weight than their pen mates were more aggressive and those gaining less weight were more submissive. Aggression and submission were not observed in all pigs. During regrouping, those pigs showing submission were those that had used more productive teats than those that performed both aggressive and submissive behaviour. Pigs that showed aggression at regrouping were heavier than their pen mates and had a higher weight gain. In general, we conclude that the teat quality determines the nutritional change of the piglet at wean- ing, and also the degree of agonistic interactions at weaning and subsequent regrouping. INTRODUCTION Artificial weaning is a potential source of behaviour and health problems in pigs. In semi-natural environments, piglets are weaned at ~ 17 weeks of age, and the weaning process is gradual and prolonged (Jensen, 1986, 1988a, b; 0168-1591/90/$03.50 © 1990 Elsevier Science Publishers B.V.