Abomasal mast cell counts from naïve and previously infected yearling sheep. Previously infected sheep were orally infected with 2,000 L3 larvae three times per week for eight weeks. All sheep were treated with Levamisole (7.5 mg/kg) then challenged one week later with 50,000 L3 larvae and killed on day 0, 2, 5 or 10 following challenge. An additional group of naïve sheep were killed on day 21 following challenge. Data analysed using Mann–Whitney U-test for non-parametric data with a 95% confidence interval, n = 6 sheep per group for each time point. Significant difference between naïve and previously infected groups, **P < 0.01. Significant difference between day 0 and corresponding day 2, #P < 0.05.