MAINTENANCE OF ACQUIRED-IMMUNITY TO TRICHOSTRONGYLUS-COLUBRIFORMIS INMERINO SHEEP THAT ARE LOSING WEIGHT

The effect of loss of weight on maintenance of acquired immunity to Tr ichostrongylus colubriformis in Merino sheep was assessed in 2 experim ents, Adult Merino sheep with previously acquired immunity to T colubr iformis were housed in individual pens, Sheep were infected 3 times we ekly with 2000 T colubriformis larvae, A diet based on chopped oaten a nd lucerne hay (experiment 1) or a pelleted diet based on lucerne hay and grain products (experiment 2), was offered in amounts to sustain a moderate gain in body weight, or was reduced step-wise to cause a los s in body weight. Worm egg counts were determined weekly, The reductio n in feed on offer resulted in a mean weight loss of 4.0 kg over 9 wee ks (experiment 1) or 4.8 kg over 7 weeks (experiment 2). Based on worm egg counts, there was no indication of a change in immunity to T colu briformis in either of the experiments. These results suggest that acq uired immunity to T colubriformis in adult sheep that are exposed to i nfection is maintained during periods of moderate loss of weight assoc iated with inadequate nutrition.