Abstract

The first two years of a breeding trial have shown that sires with slow clearance of glucose after a glucose tolerance test will produce progeny with similar slow clearance and leaner carcasses (Line 1), than progeny from sires with fast glucose clearance (Line 2). Six extreme animals from each Line were selected to study the biochemical mechanisms controlling the effects seen in the breeding trial. An euglycaemic clamp experiment involved infusing insulin at three levels, 0.63, 3.46 and 6.29 mU/kg liveweight 0.75/min, each for four hours. At the same time glucose was infused with adjustments to maintain plasma glucose at basal levels. The amount of glucose infused is a measure of the sensitivity of the peripheral tissues to insulin. Line 1 animals required significantly (P<0.05) more glucose to maintain euglycaemia during all three levels of insulin infusion. Because there were differences in basal plasma glucose (Line 1:71, Line 2:61 mg/100ml, P<0.05), glucose utilisation was corrected for basal glucose. Line 1 animals still had greater glucose utilization. Another measure of insulin sensitivity is the change in glucose utilization relative to the change in plasma insulin as insulin infusion increases. Line 1 animals had a significantly greater insulin sensitivity index than Line 2 animals (0.505 versus 0.193, P<0.01) for the change from level 1 to level 2. When corrected for differences in basal glucose, Line 1 animals were still significantly more sensitive to the increase in insulin (0.680 versus 0.346, P<0.01). Selecting animals for breeding by glucose tolerance produces sheep with differences in glucose utilization by peripheral tissues. These biochemical differences are important in partitioning nutrients for deposition of lean or fat tissue.

DL, Fraser, BK Hamilton, and DP Poppi

Proceedings of the New Zealand Society of Animal Production, Volume 50, , 43-47, 1990