Effects of level of larval intake on the productivity and physiological and metabolic responses of lambs infected with Ostertagia circumcincta

Abstract

The interrelationships between level of exposure to Ostevtagia circumcincta infection, production loss and physiological and metabolic effects were examined over 24 weeks in groups of weaner lambs on larval dosing regimes (LDR) of either 0, 1200, 3750, 12000, 37500 or 120000 infective larvae per week. During the first 12 weeks, liveweight gain and wool growth were significantly depressed in lambs on both LDR 37 500 and 120000, but food consumption was significantly reduced only on the latter. Faecal nitrogen excretion was increased by both of these LDR but the efficiency of retention of apparently digested nitrogen was generally unchanged. Enteric plasma loss and albumin turnover rate were significantly increased by LL)R 120000 during the 4th week, at which time albumin concentration was most severely depressed. After the 12th week there were generally no significant effects of infection, and total liveweight gain over 24 weeks was similar for all lambs. Recovery coincided with a decline in faecal egg counts, abomasal worm counts and plasma pepsinogen concentrations. It was concluded that, under the conditions of this experiment, an intake of more than 12000 O. civcumcinctu larvae per week is necessary to have significant effects on the physiological and metabolic functions of weaner lambs with consequent losses in productivity.