THE IDENTIFICATION OF BEHAVIORAL INDICATORS OF STRESS IN EARLY WEANED PIGLETS

An approach to identifying behavioural indicators of 'stress' is illustrated with early weaned piglets serving as an example. From a total of 39 behaviour patterns, ten were selected for further study because they were readily obvious, clearly defined, easily distinguished and relatively frequent. The ten patterns were tested using 256 piglets weaned at 4 weeks of age. The piglets were exposed to two different levels of environmental and social stressors: half of the piglets were placed in pens with eight littermates, had an area of 0.30 m2 per piglet, and were given straw each day. The other half of the piglets were mixed with non-littermates, had 16 piglets in each pen with an area of 0.15 m2 per piglet, and received no straw. Mixing, crowding and lack of straw have been shown by others to be related to physiological stress reactions. The occurence of belly-nosing, manipulating other piglets (whether directed at ears, tails or other parts), chewing the chain and sitting passive differed (P < 0.001) between the treatments in Weeks 2 and 4 after weaning. It was concluded that these behaviour patterns, as well as play, are effective behavioural indicators of 'stress', induced by mixing with non-littermates, crowding and lack of straw, in early weaned piglets.