EFFECTS OF DESIGN OF INDIVIDUAL CAGE-STALLS ON THE BEHAVIORAL AND PHYSIOLOGICAL-RESPONSES RELATED TO THE WELFARE OF PREGNANT PIGS

This experiment describes the effects of two designs of individual cage-stalls on the behavioural and physiological responses of pregnant pigs. There was a total of 32 experimental pigs housed in two designs of cage-stalls, vertical or horizontal bars, and two control treatments, tether-stalls (vertical bars) and group housing. Video recordings taken of individually housed pigs (over 3 consecutive days) for 60 min day-1 (commencing 10 min after the start of feeding) after 14 and 49 days in treatments were used to determine the time pigs spent in three areas of the stalls (0-31, 32-63 and more than 63 cm from the front of the stall), number of movements between these areas. the duration that four neighbouring (within a treatment) pigs were concurrently in the front area of the stall and the number and duration of aggressive interactions. The duration of head-to-head contact of four focal pigs per individual housing treatment was also determined. Plasma-free cortisol concentrations were determined after 30 and 5 7 days in the treatments. The design of the stall division in the individual cage-stalls affected both the spatial use of the stall, aggressive behaviour and cortisol concentrations. Pigs in the horizontal stall treatment spent more time in the back area of the stall (618 s vs. 388 s; P < 0.01) and spent less time concurrently (four neighbouring pigs) in the front area of the stall (55 s vs. 193 s; P < 0.05) than animals in the vertical stall treatment. Duration of aggressive interactions was less in the horizontal stall treatment (11.1 s v. 20.3 s; P < 0.05) and there were fewer pigs (2 vs. 8; P < 0.05) involved in aggressive interactions than in the vertical stall treatment. Head-to-head contact (of focal pigs) while standing was also less in the horizontal stall treatment (171 s vs. 374 s; P < 0.05). There was evidence of a chronic stress response in the horizontal stall treatment (mean free cortisol concentrations in the horizontal and vertical stall treatments were 6.6 nmol l-1 and 4.4 nmol l-1, respectively; P < 0.05). The behavioural data suggest that pigs in the horizontal stall treatment were actively avoiding their neighbours. In conclusion, this experiment has shown that the design of cage-stalls can affect the welfare of pigs. Pigs housed in stalls comprised of horizontal bars showed evidence of a chronic stress response of a magnitude sufficient to adversely affect welfare, and active avoidance by neighbouring pigs. Pigs housed in stalls comprised of vertical bars showed cortisol concentrations similar to group-housed pigs (and lower than pigs in tether-stalls) and they also showed the highest levels of aggression of all treatments. Across the individual housing treatments, the hormone data were not correlated with measures of aggressive behaviour and thus the relationship(s), if any, between aggressive behaviour and physiological responses are unclear and remain a subject for further research.