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 weaning, 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 gender and the development of this immunity. Ninety-six Merino lambs were allocated to one of four treatment 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 worm 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.(ABSTRACT TRUNCATED AT 250 WORDS)