Effects of Heat and Social Stressors and Within-Pen Weight Variation on Young Pig Performance and Agonistic Behavior

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Abstract
A total of 486 crossbred weanling pigs was used in a series of experiments to determine first the effects of heat and social stress and their interaction on pig performance and, second, to determine a possible cause for the observed effects. Pigs were held six/nursery pen and fed and watered ad libitum. In Exp. 1, pigs were held at either thermal neutral 26.6 C for the 21 d and 23.8 C for the final 7 d, or at the heat-stress temperature (32.2 C) for the entire 28-d period. Within each temperature treatment, one-half of the pigs were left as single-litter controls and one-half were randomly regrouped (social stress). Pig feed intake and weight gain were reduced (P<.05) among heat-stress pigs during the 7- to 28-d and 0- to 28-d periods. The interaction between social and thermal stress was significant for gain:feed ratio for the 7- to 28- and 0- to 28-d periods. Regrouping depressed gain:feed ratio only among heat-stressed pigs. In Exp. 2, a two-pig behavioral bioassay was used to determine if agonistic behaviors were influenced by heat stress. Pigs that were regrouped into 32.2 C rooms exhibited reduced mean level (P<.05) and variation (P<.001) of submissive behavior. Duration of aggressive behavior and latency to attack were unaffected by thermal treatments. Increased social stress at the time of regrouping could not account for poor performance of heat-stressed, regrouped pigs. The third experiment was conducted, at a thermal neutral temperature, to evaluate performance of pigs regrouped into pens containing low, medium and high within-pen body weight variations. During the 0- to 7-d period, pigs in the medium variation pens gained faster with improved gain:feed ratio (P<.05). Over the entire 28-d trial, pig productivity was unaffected by body weight variation treatments or their interaction with floor-type. In the fourth experiment, pigs were held in either high or low weight variation pens during heat stress (32.2 C). Treatments did not influence pig weight gain or feed efficiency. We conclude that regrouping does not impair weanling pig performance while pigs are held at thermal neutral temperatures. However, during heat stress, regrouping should be avoided. Copyright © 1987. American Society of Animal Science . Copyright 1987 by American Society of Animal Science