Genetic resistance to Heterakis gallinarum in two chicken layer lines following a single dose infection.

Groups of White Leghorn and New Hampshire male and female chicks were reared under helminth-free conditions and divided into two groups at an age of 8 weeks. One group was artificially infected with 100 embryonated Heterakis gallinarum eggs, while the other group was kept as uninfected control. After 8 weeks all animals were harvested and worm burden was established. Maximum of 60 worms per bird randomly selected were measured for length. Body weights were recorded at 8 and 16 weeks of age. Total worm burden was significantly (P<0.0001) higher in infected males than in infected females. Furthermore, White Leghorns showed a significantly (P=0.011) higher number of worms when compared with New Hampshire animals. Average worm lengths were not significantly different between the breeds (P=0.155) and sexes (P=0.062). Correlations between worm burden and worm length was 0.08 (P=0.140). The daily weight gains between 8 and 16 weeks of age of the infected animals were significantly (P=0.038) lower when compared with the control group. There was no significant correlation between daily weight gain and worm burden. The estimated heritabilities for logarithm (ln) worm burden were 0.41 (S.E.+/-0.086) in White Leghorn and 0.31 (S.E.+/-0.126) in New Hampshire, respectively. Based on the estimated heritabilities it is possible to select for H. gallinarum resistance in both genetically distinct chicken breeds. This approach may be of importance for chickens kept in floor husbandry systems.