Experimental Diabetes in Lactating Sheep: Effects of Alloxan on Plasma Insulin, Glucose, Glucose Kinetics and Milk Characteristics

Abstract

After intravenous administration of alloxan (50 mg kg-1 liveweight) to lactating ewes, there were triphasic changes in plasma glucose and insulin. Almost immediately, plasma insulin decreased and hyperglycaemia occurred, then, between c. 5-12 h, insulin increased and ewes became hypoglycaemic. Thereafter, insulin decreased and glucose increased from c. 20 h after alloxan and the diabetic state was established. Changes in glucose production and utilization correlated with changes in plasma glucose.Exogenous insulin was administered from 30 h after alloxan, and it took some 2 weeks to stabilize ewes. During this period, when mild hyperglycaemia persisted, milk yields and feed intakes were decreased but milk fat content was elevated. Once ewes were stabilized, plasma glucose, milk yield, feed intake and milk fat content returned to levels prior to alloxan. These observations are consistent with insulin playing a role in the aetiology of the 'low milk fat syndrome' in the ruminant.It appears that the alloxan-treated, insulin-stabilized ewe would be a useful model for studying the role of insulin during lactation, but it is necessary to allow time for animals to overcome effects of administration of alloxan.Extra keywords: glucose production and utilization, milk yield and fat content, feed intake.

Control of Glucose Homeostasis in Lactating Ewes: Use of the Alloxandiabetic/ Insulin-stabilized Ewe to Study Effects of Insulin and Growth Hormone

“…Despite the mild hyperglycaemia that prevailed after ewes had been stabilized with exogenous insulin, the concentration of fat in milk tended to be higher between days 11 and 14 after alloxan than before alloxan (see Table 1). This observation is consistent with insulin playing a key role in the aetiology of the 'low-milk-fat syndrome' as discussed previously by Leenanuruksa and McDowell (1988).…”

“…The observations made in Experiment 1 that feed intake, milk yield and milk composition were maintained after induction of the diabetic state are similar to results of our recent studies in which injections of long-acting insulin were used to replace endogenous insulin (Leenanuruksa and McDowell 1988). It is interesting to note that the infusion rates of insulin required once the ewes had been stabilized on exogenous insulin (viz.…”

“…Five ewes were rendered diabetic with intravenous alloxan (Leenanuruksa and McDowell 1988) then maintained on intravenous infusions of variable amounts of insulin (regular insulin; Commonwealth Serum Laboratories, Melbourne). Blood glUcose was monitored frequently every day with a glucometer (Miles Laboratories, Elkhart, U.S.A.) and the insulin infusion rate was adjusted to maintain euglycaemia.…”

“…Recently, we described procedures for induction of diabetes in lactating ewes with alloxan and subsequent stabilization of the diabetic state with exogenous insulin (Leenanuruksa and McDowell 1988). In the studies reported here, alloxan-treated, lactating ewes stabilized with intravenous insulin were used with the view to gaining insights into the roles of insulin and GH in controlling glucose homeostasis.…”