The relationship between serum anti-rSvSXP IgG(T) antibody levels (expressed as percentage of a positive control (PP)) and counts of migrating Strongylus vulgaris larvae categorised by their number of larvae. a) All 102 horses in the data set. b) The 86 horses in the data set aged 7 months and older. Group 0: No larvae, migratory tracts nor evidence of previous infection (Figure 6a: n=42; Figure 6b: n=28); group 1: Migratory tracts or evidence of previous infection (n=16); group 2: 1–5 larvae (n=16); group 3: 6–25 larvae (n=17); and group 4: >25 larvae (Figure 6a: n=11; Figure 6b: n=9). The middle black line of the boxes is the median and the range of the box is the inter quartile range (IQR) giving the first and third IQR. The lower and upper lines are up to 1.5 IQR away from the first and third quartile. Groups with different letters are significantly different (P-value < 0.05).