Effect of digestible energy intake on glucose synthesis in reindeer and caribou

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Abstract
Glucose parameters were estimated by multicompartmental analysis after the single injection of [U-14C] glucose in pen-fed reindeer and caribou. During the rut, the plasma concentration, pool size, space, total entry rate, irreversible loss, and glucose turnover time of male reindeer and caribou declined; all parameters increased significantly after the rut ended and feeding had begun again. In female reindeer and caribou the lowest estimates of glucose pool, space, total entry rate, and irreversible loss were noted during midpregnancy (February–April). During early lactation (May–June) significant increases were noted in total entry rate, irreversible loss, and the plasma concentration of glucose.For non-lactating reindeer and caribou, inflections in relationships between glucose total entry rate and irreversible loss with digestible energy intake were noted at a daily digestible intake of about 195 kcal/W0.75 (where W0.75 = metabolic body weight); three times more glucose was synthesized per unit digestible energy intake above the point of inflection than was synthesized below it. Per unit of protein intake, total entry rate and irreversible loss of glucose for males exceeded that of the females by 4 to 5 mg/W0.75 per minute. In female reindeer and caribou a close correlation was noted between the glucose irreversible loss and total entry rate. Glucose resynthesis was constant at 1.5 mg/W0.75 per minute.