Metabolic and endocrine responses to cold and feed restriction in ruminants

Twenty-four wether lambs were assigned to different temperature and feeding levels to assess their metabolic and endocrine profiles and to test the hypothesis that energy conservation responses of sheep to feed restriction occur in warm but not cold environments. Lambs were kept in warm (W; 23 +/- 2 degrees C) or cold (C; 0 +/- 2 degrees C) environments and received either an ad libitum (A) or a restricted (1.35 x maintenance) (R) level of feed intake, thus creating four treatment groups (WA, WR, CA and CR). Average daily gain (ADG), feed intake, metabolic rates, rectal temperature, and plasma levels of insulin, thyroxine (T4), triiodothyronine (T3) and cortisol were recorded during three periods of 5 wk each. The ADG was lower (P < 0.001) in feed-restricted groups. Cold exposure reduced the ADG along with feed efficiency in the first period (P < 0.01). Metabolic rate was lowered by feed restriction (P < 0.01) in periods 1 and 3, but was increased by cold exposure in ad libitum-fed sheep during period 1 (P < 0.05). Both cold exposure and feed restriction lowered rectal temperature (P < 0.001). Plasma insulin concentration was lowered by feed restriction (P < 0.05) and was increased (P < 0.05) by cold exposure during periods 2 and 3. Plasma T3 concentration was reduced (P < 0.05) by feed restriction and was increased by cold exposure during periods 1 and 2. Plasma T4 level remained unaltered (P > 0.05) while plasma cortisol concentration was increased by both cold exposure and feed restriction (P < 0.01). The results indicate that lambs show metabolic and physiological responses to feed restriction, which conserve energy in a cold as well as a warm environment.