Plasma insulin and glucagon responses to glucose, arginine and propionate injections were measured to establish indicators of the endocrine status in lactating cows and growing calves. The metabolites were intravenously injected at a dose of 0.625 mmol kg-1 and the time courses of changes in plasma insulin and glucagon concentrations were determined. Basal plasma glucagon concentrations were higher (P < 0.05) for lactating cows than for growing calves, while basal plasma insulin concentrations did not differ between animal groups. Concentrations of plasma insulin increased (P < 0.01) after glucose injection, whereas plasma glucagon concentrations decreased in both lactating cows (P < 0.05) and growing calves (P < 0.01). Plasma insulin and glucagon concentrations increased in response to arginine (P < 0.01) and propionate (P < 0.01 except insulin for lactating cows at P < 0.05) injections. Plasma insulin and glucagon responses were greater (P < 0.05) to arginine than to glucose or propionate. Plasma glucagon responses to arginine were greater (P < 0.05) for lactating cows than for growing calves. The insulin:glucagon molar ratio increased in response to the metabolite injections except following injections of arginine and propionate into lactating cows, when the ratio did not increase significantly. It is possible that in cows the enhanced responsiveness of glucagon secretion plays a role in the maintenance of lactation.
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