Heterosis analysis of Haemonchus contortus resistance and production traits in Rhoen sheep, Merino Land sheep and crossbred lambs.

A crossbreeding program was conducted to evaluate the resistance status to Haemonchus contortus in reciprocal crossbred (F(1)) lambs and their Merino Land sheep (Ml) and Rhoen sheep (Rh) purebred counterparts. A total of 406 lambs were included in the study. Faecal egg counts (FEC) and haematocrit values (Hc) of all the lambs were collected 4 and 8 weeks after an artificial infection with H. contortus. FAMACHA scores were given at the same time. Worm counts of all lambs were obtained after slaughtering at 21 weeks of age. The Ml group consistently showed the highest body weights, daily weight gains and best carcass performances, whereas the Rh group showed the lowest results. Most of the body weight parameters in the F(1) group fell intermediately between the Ml and Rh groups, though the heterosis analysis of body weight and carcass parameters showed a tendency to favour the crossbreeding group Rh x Ml. The Rh group showed, on average, the highest FEC and the lowest Hc values compared to the Ml. However, the nematode counts were not significantly different between the pure breeds. In comparison, the worm counts of the Rh x Ml crosses were significantly different from those in the Ml x Rh crosses. A heterosis analysis showed that FEC, Hc and the worm count in the F(1) group favoured the crossbreeding group Rh x Ml. These results suggested that crossbreeding Rh to Ml sheep may be a suitable way of producing lambs with improved resistance to H. contortus infection without any negative effects on production traits.