Treatment of sweet narrow-leafed lupin crops to reduce phomopsin-induced liver damage (lupinosis) in Merino wether weaners

Abstract

An experiment was carried out with 4 methods of utilising sweet narrow-leafed lupin crops (unharvested, stubble, cut before leaf drop, cut and conserved as rolls), to compare the development of lupinosis in wether weaners at 2 stocking rates while they were growing during the summer period. Growth of weaners grazed on the cut lupin treatments was greater than on lupin stubbles at both 25 and 50 weaners/ha (grazing period 98 and 63 days, respectively). Weaners grazed on unharvested lupin crops gained the most liveweight at the lower stocking rate; at 50/ha, weaners on unharvested lupin grazed for longer than those in the other 3 treatments (98 v. 63 days). After 63 days of grazing over all lupin treatments, weaners at 50ka had more (P<0.05) liver damage than did those at 25ka. Amongst lupin treatments, weaners given fodder rolls had the least liver damage, whereas those on the stubbles had the most (P<0.05). After 98 days, the weaners grazed at 50ka on the unharvested crop and 25ka on stubble had the most liver damage. Those grazed at 25ka on the unharvested crop or on lupin fodder rolls had very little liver damage. Although fodder rolling of lupins did offer some protection against development of liver damage associated with the intake of phomopsins in lupins, larger liveweight gains were obtained on unharvested lupin crops. Therefore, greater flexibility would be available to farmers by leaving lupin crops to mature before deciding how to use them. This would avoid the cost of preparing fodder rolls, which provided no marked advantage in this experiment.