The effect of residual grain on the utilization of sweet lupin stubbles and concurrent changes associated with lupinosis, in particular changes in liver copper and zinc in weaner sheep

Abstract

An experiment was conducted with Merino wether weaners to examine the influence of lupin grain on the utilization of stubbles from crops of sweet, narrow-leafed lupins (Lupinus angustifolius cv. Unicrop). Sheep grazed at 25 ha^-1 without additional grain or with grain (350 kg ha^-1) added to the stubble gained weight over 65 days, but those with the additional grain grew faster (av. 126 v. 77 g d^-1). At 50 ha^-1, sheep grazed on normal stubble gained weight for only 44 days at a mean rate of 82 g d^-1, while those with the additional grain (350 kg ha^-1) reached a peak weight after 65 days of little growth (31 g d^-1).

The sheep developed lupinosis. Those grazed at 50 ha^-1 suffered more liver damage than those at 25 ha^-1, and liver copper levels increased while zinc levels decreased as the severity of liver damage increased. Plasma ornithine carbamyl transferase (OCT) was of minimal value in the diagnosis of lupinosis.

The levels of plasma glucose were generally higher in the sheep grazed at the low stocking rate.