Plasma glucose and insulin responses to propionate in preruminating calves

Eighteen preruminating calves obtained at approximately 38 d of age were used to determine whether the ruminant insulin response to propionate is an inherent response or one that is acquired because of ruminal propionate production. A liquid milk replacer diet was fed alone or with isocaloric additions of propionate [50 mmol . (kg BW . 75-1 . d-1] or glucose. Both additions caused a strong insulin response, but the response by propionate-fed calves appeared to be independent of plasma glucose concentrations during the early post-feeding hours. After receiving the experimental diets for 18 d, all calves were given an iv infusion or propionate [.035 mmol propionate . (kg BW . 75-1 . min-1 for 20 min]. All calves demonstrated a plasma insulin rise and glucose decline due to the infusions, but glucose-fed and propionate-fed calves appeared less sensitive to the iv propionate than the calves fed only milk replacer.