Changes in faecal trichostrongyle egg count and haematocrit in naturally infected Rhon sheep over two grazing periods and associations with biochemical polymorphisms
2002
Gauly, M. | Erhardt, G.
The changes in trichostrongyle faecal egg counts (FEC) and haematocrits were determined in naturally infected Rhon sheep during two grazing periods and their relationships to biochemical polymorphism were estimated as possible parameters of resistance to gastrointestinal nematodes. Animals were characterized for a total of four polymorphic loci: haemoglobin beta (HBB), carbonic anhydrase 2 (CA2), albumin (ALB) and group-specific component (GC). Mean FEC were lower (p < 0.05) and also highly variable in the second grazing period (March-July) when the two grazing periods were compared. Mean log10 FEC were also higher. Animals with lower FEC in the first grazing period (May-November) had lower mean FEC in the second grazing period and higher haematocrit values. Therefore lambs with relatively low FEC in the first grazing period are likely to retain their advantage in the following year. FEC of animals with HBB BB were significantly higher (p < 0.01) and haematocrit significantly lower (p < 0.05) compared to HBB AA and AB genotypes. Furthermore, ALB SS was associated with significantly lower (p < 0.01) FEC compared to genotypes ALB DD and ALB DS. No statistical differences were found for mean FEC and haematocrit among the genotypes of CA2 and GC (p > 0.05). From these observations, the polymorphic systems of HBB and ALB open a way of selection in Rhon sheep for genetically based trichostrongyle resistance in an environment where Haemonchus contortus, Trichostrongylus spp., Teladorsagia spp. and Cooperia spp. are the predominant species.
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