Comparing the responses of grain fed feedlot cattle under moderate heat load and during subsequent recovery with those of feed restricted thermoneutral counterparts: metabolic hormones

Comparing the responses of grain-fed feedlot cattle under moderate heat load and during subsequent recovery with those of feed-restricted thermoneutral counterparts: blood cells and inflammatory markers

Given the climate projections for livestock rearing regions globally, understanding the inflammatory status of livestock under various heat loads will be informative to animal welfare and management. A survey of plasma inflammatory markers was conducted, and blood leucocyte counts followed to investigate the capacity of the ~ 500 kg grain fed Black Angus steer to respond to and recover from a moderate heat load challenge. Two sequential cohorts of 12 steers were housed in climate-controlled rooms (CCR) for 18 days. A thermally challenged (TC) group (n = 2 × 6) experienced five consecutive periods: PreChallenge, Challenge, and Recovery within the CCR, and 40 days in outdoor pens (PENS and Late PENS). PreChallenge (5 days) and Recovery (7 days) delivered thermoneutral conditions, whereas in Challenge the TC steers experienced a diurnal temperature range of 28-35 °C. A feed-restricted thermoneutral (FRTN) treatment (n = 2 × 6) was run concurrently to differentiate between responses to reduced feed intake alone and moderate heat stress. Blood neutrophil counts were particularly sensitive to moderate heat load with higher numbers during Challlenge and in PENs. The plasma concentrations of TNFα and IL-1β were depressed in the TC group compared to the FRTN counterparts and remained so for 40 days after Challenge. Linear relationships of the concentrations of IL-1β, IL-10, and haptoglobin with rumen temperature or dry matter intake detected in the FRTN group were altered or absent in the TC group. The findings suggest significant impacts of moderate heat load on the inflammatory status of feedlot cattle.

Using Recombinant Superoxide Dismutase to Control Oxidative Stress in the Gastrointestinal Tract of Cyclic Heat-Stressed Pigs

Climate change is associated with an increased frequency and intensity of heat waves, posing a threat of heat stress to pig production. Heat stress compromises the efficiency of pig production partly due to causing oxidative stress, intestinal dysfunction, and inflammatory responses. Superoxide dismutase is an antioxidant enzyme reported to reduce oxidative stress and inflammation. Therefore, this experiment aimed to investigate whether recombinant superoxide dismutase (rSOD) could ameliorate oxidative stress and inflammatory responses in heat-stressed grower pigs. Sixty-four female pigs (Large White × Landrace, 27.8 ± 1.65 kg, mean ± SD) were randomly allocated to a control diet (standard grower feed, CON) or the control diet supplemented with 50 IU recombinant superoxide dismutase (rSOD) for 14 days. After acclimation to the diet, pigs were then housed under thermoneutral (TN, 20 °C, 35-50% relative humidity) or cyclic heat stress conditions (CHS, at 35 °C: 9 a.m. to 5 p.m. and 28 °C: 5 p.m. to 9 a.m., 35-50% relative humidity) for 3 days. Heat stress increased respiration rate (RR), skin and rectal temperature (RR and RT) (p < 0.001 for all), and reduced plasma thyroid hormone concentration (p < 0.001). The amount of oxidized glutathione (GSH:GSSG) was increased in the jejunum and ileum of CHS pigs. In the jejunum, rSOD also increased the amount of oxidized glutathione in both TN and CHS pigs, without any change in endogenous SOD activity. In the ileum, rSOD prevented increases in oxidized glutathione formation in the CHS pigs only. Taken together, this may reflect increased oxidative stress in both the jejunum and ileum in CHS pigs. Alternatively, rSOD increased the conversion of reduced to oxidized glutathione independently of CHS, possibly reflecting an increased overall SOD activity due to the addition of exogenous SOD. In conclusion, the use of in-feed SOD enzymes at a dose of 50 IU/kg may be a useful strategy for preventing oxidative stress in pigs.