Liver damage and the liveweight changes in Merino wether weaners grazing mixed crops of oats and sweet narrow-leafed lupins

Abstract

Merino wether weaners were grazed on mixed crops of oats and sweet lupins at 3 stocking rates (15, 30 and 60 sheep/ha), pure lupins (60 sheep/ha) or pastures (7.5 sheep/ha) with and without an ad libitum ration of an oat-lupin grain mix in 2 experiments. Changes in liveweights and liver damage due to lupinosis were measured. In experiment 1, when grazing commenced in late January 1982, the weaners grazed on the mixed crops at 15, 30 and 60 sheep/ha gained 4.8 kg over 91 days, 2.9 kg over 43 days and 1.2 kg over 43 days, respectively, while those on the pure lupins gained 0.7 kg over 14 days. These liveweight gains were all less (P<0.05) than the 10 kg increase over 70 days by the weaners on pasture which received the ad libitum supplement of oat-lupin grain (about 2.2% N). Liver damage developed at a slower rate in the sheep on the mixed crops. In experiment 2, when grazing commenced in late November 1983, the weaners grazed on the mixed crops at 15,30 and 60 sheep/ha gained 1 1.3 kg over 70 days, 6.2 kg over 42 days and 3.5 kg over 28 days, respectively, while those on the pure lupins gained 3.4 kg over 28 days. These liveweight gains compared with a 12.5 kg gain over 84 days by the weaners on pasture which received the ad libitum supplement of oat-lupin grain (about 2.60%N). There was less Phomopsis leptostromiformis on the lupin stems in this experiment and the sheep livers were not as badly damaged as in the previous experiment. The development of liver damage was again delayed in the weaners grazed on the mixed crops. It was concluded that Merino wether weaners can increase liveweights when grazed on mixed crops of oats and sweet lupins. The amount of increase depends on the grain available to the sheep and the degree of lupinosis-associated liver damage suffered by the sheep. Grazing mixed crops reduces the development of lupinosis.