EFFECTS OF WEANING, SUPPLEMENTATION AND GENDER ON ACQUIRED-IMMUNITY TO HAEMONCHUS-CONTORTUS IN LAMBS

This study was designed to investigate whether delaying the age of wea ning, or feeding a protein-rich supplement alters the rare at which la mbs develop immunity to Haemonchus contortus and whether there is any interaction between nutrition, stress of weaning, and gender and the d evelopment of this immunity. Ninety-six Merino lambs were allocated to one of four treatment groups: supplemented-unweaned; supplemented-wea ned; unsupplemented-unweaned; unsupplemented-weaned. There were approx imately similar numbers of male and female lambs in each group. Supple mented lambs received 80 g/head/day of a protein-rich pellet from 16 t o 23 weeks of age. Over the same period the lambs were drenched with 3 00 H. contortus larvae twice per week, Faecal worm egg counts were det ermined every week, and PCV and liveweight every 2 weeks for each lamb , Neither weaning nor sex had any effect on PCV (P > 0.05) but from da y 50 after the start of infection, the decline in PCV was more pronoun ced in unsupplemented than in supplemented lambs, Faecal worm egg coun ts were higher (P < 0.001) in unsupplemented-weaned than in supplement ed-weaned lambs and in females when compared with castrates (P < 0.03) . There was a weaning x supplementation x age interaction (P < 0.03) w ith unsupplemented-weaned lambs developing a higher faecal egg count t han supplemented-weaned lambs. There was also a significant (P < 0.02) sex x weaning x age interaction with weaned-female lambs having a hig her faecal egg count than weaned-castrate lambs; egg counts increased more rapidly in unweaned-female lambs than in weaned-female lambs. Tog ether, these data suggest that protein supplementation of lambs enhanc ed the development of immunity to haemonchosis, whereas weaning at 4 m onths of age bad no significant effect.