Abstract
Group size (GS) and space allowance have major implications for the welfare of production species, however their effects are often confounded. In a previous study we investigated the impact of varying space allowance at constant GS. In the present work we report the consequences of varying GS on pregnant ewes while controlling space allowance. We housed ewes at 6 (GS6) or 12 ewes/enclosure (GS12), while controlling space allowance to 1.5 m2/ewe (3 enclosures/treatment), and necessarily varying enclosure size. Therefore, when indicating GS effects we implicitly reflect a confounding effect with that of enclosure size. Movement, use of space, behaviour, serum cortisol concentration and body condition score (BCS) were collected during the last 12 gestation weeks. Movement, use of space, and behaviour were collected every other week, during 2 days/week, using 10 minute continuous scan samplings. Blood was collected during weeks 10, 13, 17, and 21 of gestation, and BCS during weeks 15 and 21. Data were analysed using repeated measures, generalized linear mixed models, with GS, week, and their interaction as fixed effects, and enclosure as random effect. GS mainly affected movement and use of space. GS12 ewes walked longer distances using longer steps (P<0.001). An interaction GS by week was observed for angular dispersion (P<0.0001), which was smaller for GS12 from week 10 onwards. Initial restlessness levels were lower for GS12, as shown by the reduced frequency of location changes (P<0.0001). Furthest and mean neighbour distances increased with GS (P<0.0001). The effect of GS on behaviour was only evident for eating behaviour as an interaction with gestation week (P<0.05). Changes in behaviour, movement and use of space along the study indicated an activity peak during weeks 3 to 5. Cortisol changes during gestation (P<0.01) also reflected this activity peak, while BCS (P<0.001) reflected normal physical condition changes during pregnancy. Although the separate effects of GS and enclosure size cannot be disentangled, we conclude that if enough space/ewe is given during gestation, larger GS will result in larger effective space, and no major implications for the welfare of ewes should be expected as GS increases. Ewes will adapt their movement patterns and use of space to enclosure size, and no further behavioural, physiological and physical consequences should be expected.
Highlights
Most animal species form social groups, which represents a trade-off between the costs and opportunities of belonging to a community [1]
Total and net distances walked by GS6 ewes were significantly shorter than those of GS12 ewes, while the net to total distance ratio remained unaffected by group size (GS)
Higher movement activity was detected for GS6 ewes as compared to GS12 at the onset of the study, while angular dispersion was initially higher for GS12, for weeks 14 and 16 was higher for GS6
Summary
Most animal species form social groups, which represents a trade-off between the costs and opportunities of belonging to a community [1]. Continuous re-adjustments are required to maintain a reasonable social stability, and wild animals can join or leave a community if necessary This is not an option for farm animals, which are usually reared within static groups in which any conflict cannot be solved by GS readjustments. Large GS may be advantageous for farm animals, since increased social tolerance will lead to a reduction of aggressions [4], but they may become inadequate if resources are limited, such as the case of high stocking densities or limited access to feed [4]. In such cases larger GS may be stressful and, in severe cases, lead to reduced welfare and performance
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