The effect of agonistic interactions on the heart rate of group-housed sows

Abstract

Inter-sow aggression can be a major welfare problem in group-housing systems and can also affect productivity. This experiment investigated the effect of different types of agonistic interaction using heart rate as an indicator of physiological response. The heart rates of nine Large White × Landrace sows housed in a large group with an electronic sow feeder system, were monitored during agonistic interactions. Interactions were categorised into: (1) interactions involving physical contact, (2) non-physical interactions involving threat only. Both were recorded as win or loss, giving a total of four encounter types. The data were analysed to give the peak heart rate value during the encounter and also the increase from the pre-encounter mean to the peak value. Although there were some statistical difficulties presented by small sample size, sows involved in physical encounters had a greater increase in heart rate and a higher peak value (+ 59.1 beats per min (bpm), 137.0 bpm) than sows involved in threat encounters (+ 31.6 bpm, 107.3 bpm). Sows which lost a physical encounter tended to have the highest heart rates (+ 85.7 bpm, 157.7 bpm). The results demonstrate that all sows involved in agonistic encounters show an acute and transient response indicated by a rise in heart rate; however, the rise is greatest for sows which lose a physical encounter.