Stocking density, restricted trough space, and implications for sheep behaviour and biological functioning

Stocking density in intensive housing and the implications for beef cattle behavior, stress physiology, and liveweight

Stocking density can potentially impact cattle welfare during livestock export voyages. The aim of this study was to assess selected measures that reflect the welfare of cattle housed at 3 allometric stocking densities (k = 0.027, 0.030, 0.047). Bos indicus cross Bos taurus steers were housed in 12 pens, each with 5 steers, for 10 d. Scan sampling of standing and lying behaviors were conducted on days 2, 5, 7, and 9, at hourly intervals. Continuous observations were conducted on the same days between 1030 and 1130 h, to count aggressive interactions. Liveweights were recorded at the start of the study, and on days 6 and 10. For a subset of focal steers (3 per pen), white blood cell counts, and fecal glucocorticoid metabolite (FGCM) concentrations were assessed on days 0, 6, and 10. More pen space led to a small increase in the number of steers lying, as well as a small increase in lying synchronicity. Results also indicated that the number of cattle lying in isolation from conspecifics is higher when more space is available. More pen space also resulted in more steers lying with outstretched legs on days 2 and 5, but there was no evidence of this after day 5. Stocking density had no important effect on day 6 or 10 liveweights or FGCM concentrations. Only small decreases in total white blood cell and lymphocyte counts between days 6 and 10 were observed, as well as small increases in neutrophil counts and the neutrophil-to-lymphocyte ratio, but all mean counts still fell within reference intervals for healthy cattle. The lack of important effects on stress physiology and liveweight suggests that the cost of attempting to adapt to pen space restriction was relatively low, leading to behavioral responses only. Results for lying behaviors also suggest that additional pen space may facilitate adaptation upon introduction to a new housing environment and is beneficial in facilitating the expression of some lying behaviors. While designed to emulate stocking densities applicable to Australian cattle export voyages, other environmental factors that may induce stress during these voyages were not present, and so the conclusions must be interpreted in the context of the controlled experimental conditions.

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.

Effects of α-lipoic acid on growth performance, antioxidant capacity, and immune function in sheep

α-Lipoic acid (α-LA) was usually applied to improve the ability of removing the reactive oxygen species of host. The affection of α-LA on ruminants was mainly focused on the variation of serum antioxidant and immune indexes, but the research on tissues or organs remained limited. The aim of this study was to explore the effects of dietary supplementation with different levels of α-LA on growth performance, antioxidant status, and immune indexes of serum and tissues in sheep. One hundred Duhu F1 hybrid (Dupo♀ × Hu sheep♂) sheep aged 2 to 3 mo with similar body weight (27.49 ± 2.10 kg) were randomly allocated into five groups. Five diets supplemented with 0 (CTL), 300 (LA300), 450 (LA450), 600 (LA600), and 750 (LA750) mg/kg α-LA were fed to sheep for 60 d. The results showed that α-LA supplementation significantly increased the average daily feed intake (P < 0.05); however, no significant variation was found in the average daily gain, feed conversion rate, carcass weight, and slaughter rate among groups (P > 0.05). Compared with CTL group, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities in serum of LA600 and LA750 groups were increased (P < 0.05). At LA450-LA750 groups, SOD, CAT activities in liver and ileum tissues and GSH-Px activities in ileum tissues were increased than CTL group (P < 0.05), while malondialdehyde (MDA) contents in serum and muscle tissue were decreased than CTL group (P < 0.05). The total antioxidant capacity contents in liver, muscle, and ileum tissues of LA600 group were increased compared with CTL group (P < 0.05). Additionally, the interleukin-10 (IL-10) contents of serum in LA450-LA750 groups were increased than CTL group (P < 0.05); the contents of interleukin-1β (IL-1β) in serum, interleukin-2 (IL-2) in liver, and interleukin-6, IL-1β in muscle were decreased than CTL group (P < 0.05). The content of immunoglobulin A in serum of LA600 group, ileum, and muscle of LA750 group was increased than CTL group (P < 0.05). Based on the quadratic regression analysis of GSH-Px, MDA, IL-2, IL-10, and IL-1β, the optimal dietary α-LA levels were estimated to be 495.75, 571.43, 679.03, 749.75, and 678.25 mg/kg, respectively. This research will provide certain contribution for the effective utilization of α-LA in sheep production.