EFFECTS OF FOOD LEVEL ON PERFORMANCE AND BEHAVIOR OF SOWS IN A DYNAMIC GROUP-HOUSING SYSTEM WITH ELECTRONIC FEEDING

Evidence from studies of group-housed sows in unbedded systems indicat es that hunger may be a cause of increased aggression between animals. The present study aimed to investigate the effects of food level on p erformance, aggression and skin damage in a deep-straw system. Sixteen groups of five gilts were introduced over 8 months to one of two dyna mic groups in a deep-straw yard (2.35 m(2) per sow) receiving differen t food levels from an electronic sow-feeding system: high (H: 3.0 kg a nd 38 MJ/day) and low (L: 1.6 kg and 20 MJ/day). Seventy second-parity sows were returned to the same treatments in the same subgroups. The behaviour of the animals was recorded throughout both pregnancies usin g a time sampling technique. Severity of skin damage tons recorded as a number from 0 to 4 for each of nine areas, the average of which bein g the 'damage score'. The total number of animals in each dynamic grou p was maintained at around 30, through the use of additional saws. As expected, H sows were heavier than L sows but no effect of food treatm ent was found on litter size or performance. L sows were move active ( L v. H; standing: 41 v. 31% of total observation time respectively, F- 1,F-14 = 7.65, P < 0.05) and showed more straw manipulation than H sow s (L v. H: 17 v. 10% respectively, F-1,F-14 = 18.4, P < 0.001). No dif ferences between treatments were found either in number of aggressive interactions (L v. H: 3.6 v. 3.8 interactions per sow per observation day, F-1,F-14 = 0.82, P > 0.05), or in damage score (L v. H: 0.24 v. 0 .28; F-1,F-14 = 0.27; P > 0.05). However, introduction of Mew animals did influence aggression, with sows being move involved in aggressive interactions on the day they were introduced, than on other sow's intr oduction days and on no introduction days (Tukey, P < 0.05). Average s kin lesions pel experimental sow were also higher in the days immediat ely following introduction. It can be concluded that in it sequential feeding system with plentiful straw, aggression is not influenced by t he level of feeding. In these systems, the major factor giving vise to aggression is the introduction of new sows to the resident group.