Do sows respond to sibling competition at the udder Day 1 post-partum?

The aim of the present follow-up study was to assess sibling competition during nursing on Day 1 post-partum (i.e., 24 h after the end of parturition), as well as whether sows respond to increased sibling competition. A total of 19 healthy sows and their piglets were directly observed and video recorded for 6 h on Day 1 post-partum. Piglet behaviours (presence at the udder, fighting and screaming) were scored at 15 s intervals, commencing 5 intervals (i.e., 75 s) prior to milk ejection, and continuing for 9 intervals (i.e., 135 s) after milk ejection. The proportion of piglets which missed the milk ejection, postural changes by the sow, and whether the nursing was without milk ejection (non-nutritive nursing) were also noted. The mean number of piglets per sibling exhibiting fights (FIGHTS), and exhibiting fights with screams (FIGHT-SCRES) was calculated for both before (pre-massage) and after milk ejection (post-massage). There was a significant correlation between the number of piglets exhibiting FIGHTS and the number of piglets exhibiting FIGHT-SCRES during pre-massage (ρ = 0.92), as well for post-massage (ρ = 0.93). Based on this high correlation, only the results for the number of piglets exhibiting FIGHTS were included in the paper. A higher number of piglets exhibiting FIGHTS (P < 0.001) was associated with a higher proportion of piglets missing a milk ejection. There were no significant effects of the number of piglets exhibiting FIGHTS during pre-massage detected on the probability of non-nutritive nursings. A higher number of piglets exhibiting FIGHT (P < 0.05) increased the probability of a sow terminating post-massage (P < 0.05). In conclusion, even when higher sibling competition indicates more piglets missed milk ejection, sows only responded to higher sibling competition during post-massage when the milk was already released.