Effect of cold exposure on profiles of metabolic and endocrine responses and on responses to feeding and arginine injection in sheep1

Abstract

The effect of cold exposure (0 degrees C) on profiles of total heat production (HP), energy metabolism, and blood metabolite and hormone concentrations were measured in nine shorn Suffolk rams. Blood metabolite and hormone responses to feeding and to i.v. arginine injection (.625 mmol/kg BW) and postprandial changes in HP were also measured. Heat production was greater (P < .05) during cold exposure than in the thermoneutral environment due to enhanced (P < .05) nonprotein oxidation. Protein oxidation and nitrogen balance remained unchanged during cold exposure. Plasma glucagon concentrations increased (P < .05) during the initial period of cold exposure. Heat production increased (P < .01) after the initiation of feeding in both environments. Heat production returned gradually to prefeeding values in the thermoneutral environment, but it remained close to the higher levels during cold exposure. Plasma insulin and glucagon concentrations increased (P < .05), and plasma growth hormone concentrations decreased (P < .10) after the initiation of feeding in both environments. Plasma glucagon responses to feeding (P < .05) and plasma insulin responses to arginine injection (P < .01) were reduced by cold exposure. We suggest that 1) enhanced HP in sheep exposed to cold is maintained by enhanced nonprotein oxidation and 2) endocrine responses to stimulants are influenced by cold exposure, even though profiles after cold exposure change little.

Tissue responsiveness and sensitivity to insulin in sheep fed plantain and orchardgrass and exposed to cold

“…Therefore, it may moderate a variety of stresses for ruminants and may improve their performance. Cold exposure is one of the stresses which reduce productivity, and influence digestive and metabolic responses, intermediary metabolism, and the actions of hormones in ruminants (Weekes et al 1983;Tsuda et al 1984;Young et al 1989;Sano et al 1995). We found that in sheep fed the PL diet and the orchardgrass (OR, Dactylis glomerata L.) diet, net blood glucose turnover rate was similar between the diets in both thermoneutral and cold environments (Sano et al 2002).…”

Metabolic response of early-lactating cows exposed to transport and high altitude grazing conditions

“…The pastured cows in experiment 2 were estimated to require twice as much energy to cover maintenance requirements than is necessary under lowland conditions (Christen et al, 1996). Cold stress may contribute to the increased energy demand, further increasing plasma NEFA levels (Sano et al, 1995). Cows are able to produce milk partly from body reserves.…”

“…This explains reduced thyroid hormone levels during energy deficiency (Kunz et al, 1985;Ronge et al, 1988) but also increased levels at low ambient temperatures, as was found in the case of T 3 by Aceves et al (1987). Considering that ambient temperature was considerably lower at high altitude than at lowland (Christen et al, 1996), the effect of cold exposure on heat production (Sano et al, 1995) obviously exceeded the decrease in heat production expected in the state of deficient energy supply (Ortigues and Vermorel, 1996). According to the present data, it required about 1 week until other adaptive mechanisms replaced the T 3 and T 4 effects to sustain body temperature at low ambient temperatures.…”

Metabolic and endocrine responses to cold and feed restriction in ruminants

“…Thyroid status is known to increase respiration via increased 87 Abbreviations: A, ad libitum; ADG, Average daily gain; C, cold; R, restricted; T3, triiodothyronine; T4, thyroxine; W, warm activity of the sodium pump in the plasma membrane of liver cells (Gregg and Milligan 1987). Cold exposure elevates plasma concentrations of T4, T3 and cortisol (Kennedy et al 1977;Fregly et al 1979;Sasaki and Weekes 1984), and reduced plasma insulin concentration (Christopherson and Thompson 1983;Sano et al 1995). Feed restriction is also associated with reduced plasma insulin concentrations (Lobley 1992) and decreased, unaltered or increased T4 and T3 concentrations (Beaver et al 1989;Ellenberger et al 1989;.…”