The effect of essential fatty acid deficiency on metabolic rate in euthermic and hibernating marmots (Marmota flaviventris) [L'effet de la déficience en acide gras essentiel sur le taux métabolique des marmottes euthermiques et hibernantes].

Résumé

In order to survive the winter, many homeothermic mammals retreat to their burrows to hibernate. One such hibernator, the yellow-bellied marmot (Marmota flaviventris), meets virtually all endogenous energy needs by metabolizing stored white adipose tissue. We investigated the hypothesis that dietary composition can alter metabolic rate in the marmot. We provided marmots with two different diets; eight animals divided into two groups of four, one fed a control diet of Purina rodent chow (5001) and the other fed a diet deficient of essential fatty acids (EFA) (Purina chow 5803). Metabolic rate was determined by indirect calorimetry during the summer and winter season. The metabolic rates of animals on the different diets wa significantly different. The mean metabolic rate (Watts/kg) measured during the summer was 2.52 for the control group and 2.49 for the EFA deficient animals. Both animal groups gained weight during the summer with body weights peaking in September. Fatty acid analysis performed on white adipose tissue from each group revealed significant differences (P < 0.01) in percent composition of fatty acid species 16:1 , 18:1, 18:2, 1 8:3 and 20:0. Winter mean metabolic rate for the control group was significandly lower (P < 0.05) than EFA deficient animals for all stages of hibernation. During entrance, mean metabolic rates (Watts kg/hr) for control and EFA deficient animals were 2.21 and 3.25, respectively. Arousal mean metabolic rates were 5.17 and 8.28 respectively and deep hibernation mean metabolic rates (Watts kg/day) were 0.22 and 0.65, respectively. Average total hibernating bout length for the control group was 7.76 days, significantly higher (P < 0.05) than the average duration of 5.72 days found in the EFA deficient group. No significant difference in thermal conductance (Watts/kg/ C) was found between control and EFA animals during the summer and winter. These results support the hypothesis that EFA alter metabolic rate in marmots and are necessary for normal thermoregulation during hibernation. Thermal conductance studies reveal that the dermatologic effects of an essential fatty acid deficiency may not be responsible for the increase mean metabolic rate.