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 weaming, or feeding a protein-rich supplement alters the rate at which lambs develop immunity to Haemonchus contortus and whether there is any interaction between nutrition, stress of weaning, and gander and the development of this immunity. Ninety-six Merino lambs were allocated to one of four treatmeat groups: supplemented-unweaned; supplemented-weaned; unsupplemented-unweaned; unsupplemented-weaned. There were approximately similar numbers of male and female lambs in each group. Supplemented lambs received 80 g/head/day of a protein-rich pellet from 16 to 23 weeks of age. Over the same period the lambs were drenched with 300 H. contortus larvae twice per week. Faecal worm egg counts were determined 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 day 50 after the start of infection, the decline in PCV was more pronounced in unsupplemented than in supplemented lambs. Faecal werm egg counts were higher (P < 0.001) in unsupplemented-weaned than in supplemented-weaned lambs and in females when compared with castrates (P < 0.03). There was a weaning X supplementation X age interaction (P < 0.03) with unsupplemented-weaned lambs developing a higher faecal egg count than supplemented-weaned lambs. There was also a significant (P < 0.02) sex X weaning X age interaction with weaned-female lambs having a higher faecal egg count than weaned-castrate lambs; egg counts increased more rapidly in unweaned-female lambs than in weaned-female lambs. Tegether, these data suggest that protein supplementation of lambs enhanced the development of immunity to haemonchosis, whereas weaning at 4 months of age had no significant effect.