ENDOCRINE AND METABOLIC CHANGES IN SHEEP ASSOCIATED WITH ACCLIMATION TO CONSTANT INTERMITTENT COLD EXPOSURE

Abstract

Plasma noradrenaline (NA), adrenaline (A), and dopamine (DA) concentrations and cortisol metabolism were studied in three groups of three sheared year-old wethers exposed for 50 days to either 22–26 °C, 8–9 °C or to 19–24 °C from 0900 to 2100 h and −2–4 °C from 2200 to 0800 h. Plasma samples for catecholamine and cortisol determination were taken weekly, 3 h following the daily 0800 h and 1700 h feeding periods. Midway and near the end of the 50-day exposure period, cortisol entry rate and metabolic clearance rate (cMCR) were estimated using a ³H-cortisol continuous infusion technique. Respired gas analysis was used to estimate the heat production (HP) of all sheep 51 h after feeding at a thermoneutral temperature. An increase in thermoneutral HP following 27–30 days of cold exposure indicated that sheep of both cold treatment groups had developed some form of cold acclimation. Exposure of sheep to 8–9 °C resulted in a three- and twofold increase in plasma NA and A levels, respectively, which remained elevated throughout the experiment. Initially, nightly cold exposure of the intermittent-cold-exposed sheep increased daytime plasma NA levels but this effect declined with time. Intermittent cold exposure did not significantly affect plasma A level and neither of the two cold treatments significantly affected plasma DA level. Chronic exposure to 8–9 °C but not intermittent cold exposure caused an increase in cMCR and plasma cortisol level. Cortisol entry rate did not differ significantly between treatment groups. It is concluded that intermittent as well as constant chronic cold results in a metabolic acclimation of sheep.