C.G. Winfield

The effect of individual and group housing on behavioural and physiological responses related to the welfare of pregnant pigs

Abstract The effects of four housing treatments (neck-tethers, stalls, a group indoors and a group in a paddock), imposed at 3–5 weeks after mating, were determined on the behaviour and physiology of 24 pigs. Behaviour observations were made 2–3 days after the treatments began and 4 and 9 weeks later, and physiological measurements were made 18 and 46 days after the treatments began. Pigs in tethers spent less time in active behaviours than all other treatments, and the pigs housed in stalls showed increased amounts of oral—Nasal behaviours such as manipulation of drinkers and licking/biting pen components (7% of observations) compared to all other treatments (3.1–4.8% of observations). The pigs in tethers had highest free corticosteroid levels “at rest” (2.2 ng ml −1 compared to an average of 1.4 ng ml −1 for the other treatments), a disrupted rhythm of corticosteroid levels and, at the second sampling period (9–12 weeks of pregnancy), a lower response to transport; these responses in the tethered pigs were associated with an increase in plasma glucose and a decrease in plasma urea levels. These physiological data indicate a chronic stress response and a significant metabolic cost resulting from housing pigs in tethers. The implications of the results to the welfare of pregnant pigs are discussed.

The effects of individual and group penning of pigs on total and free plasma corticosteroids and the maximum corticosteroid binding capacity.

Abstract Total and free plasma corticosteroid concentrations and the maximum corticosteroid binding capacity (MCBC) were measured twice a day in pigs penned individually or in groups following a period of individual penning. Moving animals into groups after 5 weeks in individual pens resulted in a short-term stress response as evidenced by an increased corticosteroid concentration measured 5 1 2 hr later, but within 24 hr the hormonal pattern established was of higher levels in the morning than in the afternoon. In group-penned pigs the total corticosteroid concentration was generally well below that of the MCBC. In contrast, in individually penned pigs the MCBC was lower and the afternoon corticosteroid concentration was elevated to levels similar to the morning values. Both morning and after-noon mean corticosteroid values approached the mean MCBC. It was concluded that individual penning resulted in a chronic stress response.

Effects of social environment on welfare status and sexual behaviour of female pigs. II. Effects of space allowance

Abstract This study examined the effects of housing groups of adult female pigs (6 pigs per group) with a space allowance of 1, 2 or 3 m2 per pig on sexual behaviour and welface status, determined by plasma free-corticosteroid concentrations. A lower percentage of gilts was detected in oestrus and a lower percentage of gilts was mated when housed with a space allowance of 1 m2 per gilt than with a space allowance of either 2 or 3 m2 per gilt (oestrus detection rate of 79, 88 and 100%, respectively, and a mating rate of 77, 85 and 97%, respectively). There was a significant increase in plasma free-corticosteroid concentrations when gilts were housed with a space allowance of 1 m2 per gilt. The elevated free corticosteroid levels of gilts in the 1 m2 per gilt treatment suggests that a chronic stress response due to crowding may have been responsible for the apparent impairment in the sexual behaviour of these animals.

The welfare of adult pigs: the effects of five housing treatments on behaviour, plasma corticosteroids and injuries

Abstract The effects of 5 housing treatments (tethers, pairs, or a group indoors, in a yard or in a paddock) on the behaviour, physiology (stress physiology and blood metabolites), health (injury status) and production (food eaten and oestrous expression) of 30 non-pregnant adult female pigs were determined at regular intervals over 12 months. Pigs housed in pairs exhibited a chronic stress response; they had the highest free corticosteroid levels “at rest”, a disrupted diurnal rhythm of plasma corticosteroids and a slower corticosteroid response to, and recovery from, transport. Behaviourally, these pigs spent more time lying alone than pigs in other treatments, and there was a significant regression between lying alone behaviour and free corticosteroid levels, suggesting this behaviour may be a useful indicator of welfare status. The group of 6 pigs housed indoors consistently showed the lowest total and free corticosteroid levels during the entire experiment, and also the least lying alone behaviour; however, these responses may have been influenced by their similar rearing and experimental environment. While the occurrence of inappropriate behaviours such as champing, biting and excessive drinking was generally low, it was higher in pigs housed indoors, particularly the tether and pair treatments, suggesting mild frustation in these latter 2 treatments. A comparison of the two most contrasting environments (tethers and paddock treatments) showed no clear welfare advantage in housing non-pregnant adult pigs in a more extensive environment.

The Effects of Design of Individual Stalls on the Social Behaviour and Physiological Responses Related to the Welfare of Pregnant Pigs

Abstract Plasma free-corticosteroid concentrations, aggressive behaviour and levels of motivation to socially interact and explore a novel environment were observed in an experiment to test the hypothesis that the chronic stress response previously observed in tether housed pigs may have been due to unresolved aggression between adjacent pigs, and was attributable to the design of the stall. Twenty-five pregnant gilts were housed in 4 treatments: unmodified tether stalls; modified tether stalls (designed to reduce aggressive interactions between adjacent pigs by the addition of steel mesh to part of the stall division); cage stalls (also with mesh divisions); and a group. Gilts in the unmodified tether stalls showed a sustained elevation of free-corticosteroid concentrations, indicative of a chronic stress response, changes in their level of motivation to interact with stimulus pigs in a standard test, and a higher proportion of aggressive interactions between neighbouring pigs resulting in withdrawal rather than retaliation. These data suggest reduced welfare in the unmodified tether stalls. The addition of mesh to the sides of the tether stalls reduced the number of interactions between neighbouring pigs compared to the unmodified tether stalls treatment and virtually eliminated aggressive interactions. Concomitant to the reduction in aggressive interactions was a reduction in free-corticosteroid concentrations, suggesting that the welfare of pigs in the modified tether stalls, cage stalls and group treatments was similar. It was concluded that modifying the design of the tether stall to minimize aggressive interactions between adjacent pigs improves welfare by avoiding a chronic increase in free-corticosteroid concentrations.

The effects of pregnancy and parity number on behavioural and physiological responses related to the welfare status of individual and group-housed pigs

Abstract Plasma free-corticosteroid concentrations, aggressive behaviour and motivation to socially interact and explore a novel environment were observed in 39 female pigs housed in either groups of 4–7 animals or tether stalls over 2 parities. Gilts in tethers in their first pregnancy had significantly higher free-corticosteroid concentrations compared to non-pregnant gilts housed in tethers and gilts housed in a group of 7 (4.1, 2.9 and 3.0, ng ml −1 , respectively). A significant difference was also found between free-corticosteroid concentrations of group- and tether-housed animals at the second pregnancy (2.6 and 4.7, ng ml −1 , respectively), but there were no effects of previous experience of tethers or parity number. The chronically elevated free-corticosteroid concentrations were associated with reduced immunological reactivity (72 and 48% reductions in IgM and IgG response at 8 days after challenge, respectively) in tether- compared to group-housed pigs. In standardized motivation tests, social interaction, but not exploration, was higher in tether-compared to group-housed sows in both first and second pregnancies. In tethers, a higher proportion of social interactions between adjacent animals were aggressive and a higher proportion of these involved retaliation (25 vs. 0%) compared to the social behaviour of group-housed animals. It was concluded that unresolved aggression in tether-housed pigs may result in a chromic stress response with adverse effects on their welfare status. The effect of the design of stall divisions on the nature and level of aggressive behaviour warrants investigation.

EFFECTS OF SOCIAL ENVIRONMENT ON WELFARE STATUS AND SEXUAL BEHAVIOUR OF FEMALE PIGS. I. EFFECTS OF GROUP SIZE

Abstract This study examined the effects of housing 24 adult female pigs in groups of 2, 4 or 8 with a space allowance of 1.4 m 2 per pig on welfare status, as indicated by plasma free-corticosteroid concentrations and behaviour patterns, and sexual behaviour. Housing gilts in pairs resulted in an increase in free corticosteroid concentrations(measured 11 and 84 days after the start of the treatments) and an increase in the number of observations of lying behaviour without physical contact with another pig (recorded 21 days after entering the treatment) compared to housing in groups of 4 or 8. Overall mean free corticosteroid concentrations (±S.E.) were 3.1 ± 0.29, 2.3 ± 0.26 and 1.9 ± 0.12 ng ml −1 , and the mean numbers of observations of lying-alone behaviour (out of a total of 88 observations) were 6.4, 3.6 and 1.9 for gilts housed in groups of 2, 4 or 8, respectively. Although there were no differences between treatments in agonistic behaviour around the time of feeding, these data suggest there are undefined social stressors in pigs housed in pairs. Housing treatment had no significant effects on sexual behaviour. However, the mating rate was low in all treatments, possibly due to a sub-optimal space allowance.

The incidence of, and factors associated with, failure to mate by 245 days of age in the gilt

The incidence of, and factors associated with, gilts failing to mate between 29 and 35 weeks of age were studied over 12 months at a large intensive piggery in southern Australia. After excluding gilts culled as physically unsound, 10.5% of the remaining 2484 gilts failed to mate and were slaughtered. Seventy percent of unmated gilts had ovulated, and of these, 54% had shown negative or low responses to the back-pressure test (BPT) and 16% had shown moderate or high responses. Few prepubertal gilts (1%) had abnormal reproductive tracts. When group size was greater than 50 gilts (< 0.9 m2/gilt) immediately prior to mating (27–28 weeks of age), there was a higher incidence of unmated gilts and an increase in the proportion of unmated gilts which had shown negative or low BPT response than when groups were less than 50 gilts (12.9 vs. 8.6%, P < 0.001; and 8.0 vs. 3.6%, P < 0.001, respectively). The incidence of prepubertal gilts at 35 weeks was lower during spring than other seasons (1.48 and 3.36%, P < 0.05) and higher during summer than other seasons (4.61 and 2.37%, P < 0.01). Fewer Large White gilts remained unmated at 35 weeks of age than Landrace or Large White-Landrace synthetic breed gilts (7.7 and 14.1% of those selected, P < 0.001). More purebred gilts were prepubertal at 35 weeks of age than crossbred gilts (5.4 and 2.4%, P < 0.01).

The effect of design of tether and stall housing on some behavioural and physiological responses related to the welfare of pregnant pigs

Plasma-free corticosteroid concentrations, aggressive behaviour and levels of motivation to socially interact in a standard test were determined in two experiments. The two experiments used 32 and 40 pigs, respectively, and differences between experiments were to take into account the effects of neighbouring pigs between treatments (Experiment 1) and positional effects in the shed (Experiment 2). There were five treatments involving two types of housing (cage-stalls and tetherstalls), two designs of stall division (bars and mesh, that affected the level of aggressive behaviour between neighbouring pigs) and a control treatment of group-housed pigs. Pigs in tether-stalls separated by bars showed evidence of a chronic stress response; free corticosteroid concentrations were 1.28 and 1.21 ng ml−1 in Experiments 1 and 2 compared with 0.63 and 0.54 ng ml−1 for group-housed pigs, respectively (P < 0.01), and these changes were sufficient to affect plasma glucose concentrations (P < 0.01). Separating the tether-stalls with mesh obviated the increase in free corticosteroid concentrations (0.68 and 0.53 ng ml−1 in Experiments 1 and 2, respectively). Pigs housed in cage-stalls separated by bars or mesh showed only slight increases in free corticosteroid concentrations compared with group-housed pigs in Experiment 1 (0.87, 0.81 v. 0.63 ng ml−1, respectively, P 0.05). The increase in free corticosteroid concentrations in Experiment 1 was of insufficient magnitude to affect plasma glucose concentrations. Behaviourally, pigs in the cage-stalls with bars and tether-stalls with bars showed higher levels (P < 0.05) of aggression than pigs in their modified counterpart treatments using mesh divisions, and the proportions of retaliatory and withdrawal behaviours were similar in the two treatments. Pigs in cage-stalls with bars moved backwards and forwards more often (P < 0.05) than pigs in the tether-stalls with bars and this increased movement, possibly in response to aggression, may be a factor affecting the different physiological responses in cage-stall and tether-stall treatments; in cage-stalls aggressive behaviour sequences may be terminated in a manner that does not induce a physiological response. In conclusion, the two experiments confirm that pigs housed in tether-stalls can show evidence of reduced welfare as a consequence of the design of the tether-stall divisions, but show that the design of the cage-stall has no effect on physiological responses. Thus, in this context, cage-stall housing does not appear to pose a risk to welfare.

THE EFFECTS OF TWO OESTRUS DETECTION PROCEDURES AND INTENSE BOAR STIMULATION NEAR THE TIME OF OESTRUS ON MATING EFFICIENCY OF THE FEMALE PIG

Abstract In the first experiment, a higher oestrus detection rate (percentage of cycling gilts that were detected in oestrus) and a higher mating rate (percentage of cycling gilts that were mated) were achieved when cycling gilts were checked for oestrus in the corridor adjacent to the boar pens than when they were checked in their own pens, which were separated from the boar pens by a 1.0 m-wide corridor (90 v. 52% and 87 v. 52%, respectively). In the second experiment, several housing treatments were imposed over a 21-day period. A lower proportion of gilts were detected in the I stage of oestrus (positive response to the back-pressure test both in the presence and absence of a boar) and a lower mating rate was achieved when cycling gilts were separated from the boar by a wire-mesh pen division than when separated by a 1.0 m corridor (48 v. 81% and 47 v. 81%, respectively). It was concluded that cycling females should be housed near, but not adjacent to, boars and that at the time of oestrus detection using the back-pressure test, females should be very close to boars.