The effects of stocking density on behavior and biological functioning of penned sheep under continuous heat load conditions
Stocking density may impact sheep welfare during live export voyages that occur under hot and humid conditions. The aim of this study was to assess the welfare implications for sheep housed at three allometric stocking densities (k = 0.030, 0.033, 0.042), while exposed to hot and humid climatic conditions. For 21 d, Merino wethers (n = 216) were housed in 12 pens of 18 wethers, in two climate-controlled rooms where wet-bulb temperature (TWB) mimicked the conditions of a live export voyage with high heat and humidity, and limited diurnal variation. Scan sampling of standing and lying behaviors was conducted on days 2, 5, 8, 11, 15, 18, and 20, at hourly intervals. Agonistic interactions were scored continuously on the same days between 1750 and 1800 h. Liveweights were recorded at the start and end of the study. For a subset of focal wethers (3 per pen), whole blood variables were assessed at the start and end of the experiment, along with fecal glucocorticoid metabolites (FGCM), which were also assessed on days 7 and 14. Rumen temperatures (TRUM) of focal wethers were recorded at 10-min intervals, and their respiration rates (RR) were measured every 2 h on days 1, 3, and from days 7 to 21. Focal wethers were slaughtered for necropsy after the study, and both adrenal glands were excised and weighed. The expression of some lying positions was impaired at high stocking densities, and lying with outstretched legs increased at high TWB. For respiration rates, there was an interaction between stocking density and TWB, such that RR was reduced by the provision of additional space at high TWB. TRUM was relatively unaffected by stocking density but increased at higher TWB, and any effects of stocking density on FGCM concentrations, liveweights (LW), adrenal gland weights or blood variables were minimal. Necropsy examination showed no indication that the wethers had experienced ongoing respiratory distress. These results suggest that the wethers were able to cope with these increases in stocking density under the conditions imposed. However, based on this evidence, the provision of additional space under hot conditions may be beneficial to facilitating the expression of some lying positions. Whilst the experiment was designed to emulate certain conditions relevant during live export voyages, other factors that may induce stress during this mode of transport were not present, and so the conclusions must be interpreted in the context of the experimental conditions.
Stocking density, restricted trough space, and implications for sheep behaviour and biological functioning
Stocking density and trough space allowance can potentially impact sheep welfare during live export voyages. The aim of this study was to assess the welfare implications for sheep housed at five allometric stocking densities, with either unrestricted or restricted trough space allowance. Merino wethers (n = 720) were housed in 40 pens of 18 heads for 18 days. Two 5-min continuous focal animal observations (n = 3/pen) were conducted on days 3, 5, 11, and 17. Scan sampling of standing and lying behaviours were conducted on the same days at hourly intervals. Live weights and immune cell counts were quantified at the start and end of the experiment, as well as faecal glucocorticoid metabolites (FGCMs), which were also assessed on days 6 and 12. Focal animals housed at higher stocking densities spent less time lying during one of the continuous observation periods, but no important effects on the overall number of animals lying or on the synchronicity of lying were evident. The scan sampling results indicated that the expression of some preferred lying positions was impaired at high stocking densities, and that high stocking densities also resulted in increased agonistic social interactions and displacement events at the start of the trial. There was a slight reduction in day 18 live weights for animals housed at higher stocking densities, but FGCM concentrations and immune cell counts were essentially unaffected. Trough space had no important effects on day 18 live weight, FGCM concentrations, or immune cell counts, and had limited effects on sheep behaviour. The lack of important impacts on biological fitness traits suggests that the behavioural responses observed were sufficient in allowing sheep to cope with their environment. However, we provide evidence that the provision of additional space is beneficial in reducing the time it takes for animals to adapt to their environment and to facilitate the expression of some preferred lying positions. While designed to emulate certain conditions relevant during live export voyages, some factors that may induce stress during this mode of transport were not present such as heat and ocean swell, so the conclusions must be interpreted in the context of the experimental conditions.
The welfare implications of stocking density, feed trough space allowance, and warm climatic conditions for Australian sheep exported to the Middle East - Dataset
Physiological and behavioural data collected from sheep in two experiments related to the thesis.
The Influence of Pen Space Quantity and Quality on Sheep Welfare in the Context of Australia's Live Export Industry
Australia is a major exporter of live animals, and around half a million sheep were exported in both 2021 and 2022. Countries of the Middle East represent the largest market demand for live Australian sheep, and most sheep exported to these destinations depart from Fremantle, WA, for a sea voyage that generally lasts between 14 to 21 days. In recent years, there has been extensive public concern regarding the welfare of animals, including sheep, on live export ships. The live export process is complex and involves various stages, including sourcing, handling, loading and the sea transport phase, which was the focus of the work described in this research. Specifically, this research investigated how sheep welfare is impacted by the quantity and quality of pen space during periods of intensive housing, such as what is experienced during live export voyages. An accumulated stressors approach was implemented to first investigate the impacts of stocking density severally, and then also in combination with restricted feed trough space, and then in combination with hot and humid conditions.
Chapter 3 of this thesis examined how the quantity of pen space (i.e., stocking density) and the quality of pen space with regards to feed trough space restriction, impact the welfare of intensively housed sheep in a land-based experiment conducted in thermoneutral conditions. The provision of additional pen space was beneficial in reducing the time taken for sheep to behaviourally adapt to their environment, and in facilitating the expression of some preferred lying positions. Despite this, a lack of important impacts on the stress physiology and biological fitness characteristics of the sheep was observed. Unlike pen space, the trough space allowances investigated here had no important effects on the behaviour, stress physiology or biological fitness characteristics.
Chapter 4 of this thesis built upon the findings from Chapter 3, to investigate the potential impacts of stocking density on the biological functioning and thermoregulation of sheep housed intensively on land, under continuously hot and humid conditions. The climatic conditions imposed were similar to what would be experienced by sheep travelling from Australia to the Middle East at certain times of the year that have been identified as problematic by the industry and the public, with regards to heat stress risk. Similar to the work described in Chapter 3, additional pen space facilitated the ability of sheep to lie in preferred positions, such as with legs outstretched from their body or in physical isolation from conspecifics in their pen, but the effects on stress physiology and biological fitness characteristics were limited. Stocking density did not have an effect on the thermoregulatory ability of the sheep, although results did indicate that the reliance on evaporative cooling through the respiratory tract may be reduced by providing more space at high temperatures. Importantly, individual variation and maximum rumen temperature and respiration rate values suggested that not all wethers were able to effectively regulate their core temperature under these conditions.
In chapter 5, the presence and consistency of individual differences in aggressive behaviours expressed by wethers in a competitive feeding environment was investigated. Sheep were provided with restricted feed trough space and fed a maintenance quantity of pelleted feed, and the results indicated that sheep that displayed more aggression were at an advantage for accessing feed faster and more frequently within each feeding period. As such, the attempts of individuals to cope with the competitive feeding environment were not equal.
This research provides evidence that while the provision of additional pen space may allow sheep to adapt to an intensive housing environment faster, and facilitates the expression of some lying positions, implications for stress physiology and the biological fitness of sheep are limited, at least under highly controlled experimental conditions. In addition, sheep do not have an equal ability to access feed in competitive feeding environments, so the provision of feed trough space which permits synchronous feeding, or an ad libitum quantity of feed are important for industries, such as during livestock export voyages, which feed sheep from troughs. This thesis also identified 5 clear recommendations for future research which continue to accumulate relevant stressors and build on the theories about stocking density reported here, so that potential interactions between stocking density and other relevant factors present during voyages can be explored.