Do sows need straw for nest-building ?

Abstract

The motivation of sows to obtain straw was measured in 4 experiments using operant conditioning apparatus. In the first experiment there was no significant difference in the operant level of response when lifts on a lever produced access to an empty box or a box containing straw. None of the 6 sows, 4 about 10 weeks pregnant and 2 non-pregnant, showed any interest in the straw. In the second experiment variation in motivation to obtain straw was measured by testing pigs for 7 consecutive days every 2 weeks from mating to weaning. All pigs showed little change in lever lifting behaviour, although 2 gilts showed increased responsiveness to straw at farrowing time. In the third experiment 4 sows were allowed to farrow in the test pen with access to the lever and straw box. The sows showed an increase in activity prior to farrowing which coincided with increased manipulation of the lever. The response to straw was variable, although all pigs showed an increase in pawing behaviour. However, in a fourth experiment, 4 control pigs showed similar increases prior to farrowing in activity, lever manipulation, and pawing behaviour when the straw box was empty. The apparent low motivation of sows towards utilisation of straw is discussed in relation to its importance as a key stimulus for nesting behaviour and its role in thermal protection of the piglets, and also in relation to possible absence of appropriate nest-building stimuli, previous experience, genetic adaptation and animal welfare.