PSV-A-3 - Insulin in Sheep Under Different Patterns of Heat Stress

Abstract: Livestock welfare and production are readily affected by thermal environment. However, the coordinate physiological shifts associated with heat stress differ substantially when animals have the opportunity to acclimate to thermal environments, or when night cooling occurs. Although some of these responses to thermal environment change have been characterized within some species, physiological signals in sheep associated with gradual versus drastic changes in ambient temperature have not been well studied. The objective of this study was to investigate changes in insulin concentration in sheep exposed to\ thermal environments representing different patterns of temperature change. We hypothesized that insulin would increase in response to rapidly elevated temperature. Six sheep (Suffolk, Dorset, or Suffolk x Dorset, 74.3 ± 13.3 kg) were assigned to 1 of 2 groups exposed to a cross-over experiment. Groups were assigned to 1 of 2 rooms, where they were housed for 20 d, prior to switching rooms. The thermal environment changed five times per period (every 4 d), starting at thermoneutral (20°C, 27°C, 35°C, 27°C, 20°C) in one room and hot (35°C, 27°C, 20°C, 27°C, 35°C) in the other room. Blood samples were collected via jugular venipuncture on day four of each sampling period. Plasma samples were analyzed for concentrations of insulin and glucagon by using a commercial enzyme-linked immunosorbent assay (Ovine Insulin ELISA kit, Eagle Biosciences Inc, #INO91-K01) per manufacturer’s instructions. Relationships were analyzed as a generalized linear model with insulin concentration as the response variable and temperature, room, period, and animal as fixed effects; 2- and 3-way interactions among temperature, room, and period were also evaluated. Insulin concentration ranged from 0.02 to 0.61 ng/mL, and was significantly influenced by animal (P = 0.044) and the interaction (P =0.004) between room and period. The interaction supports the idea that the pattern of heat loading, so more than absolute heat load modulates physiological adaptation to environment in the short-term