Changes in faecal trichostrongyle egg count and haematocrit in naturally infected Rho Èn sheep over two grazing periods and associations with biochemical polymorphisms M. Gauly * , G. Erhardt Department of Animal Breeding and Genetics, Oberer Hardthof 18, Justus Liebig University Giessen, D-35398 Giessen, Germany Accepted 10 February 2002 Abstract ThechangesintrichostrongylefaecaleggcountsFEC)andhaematocritsweredeterminedinnaturallyinfectedRho Ènsheep 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-speci®c component GC). MeanFECwerelower p < 0:05 andalsohighlyvariableinthesecondgrazingperiodMarch±July)whenthetwograzing periodswerecompared.Meanlog 10 FECwerealsohigher.AnimalswithlowerFECinthe®rstgrazingperiodMay±November) hadlowermeanFECinthesecondgrazingperiodandhigherhaematocritvalues.ThereforelambswithrelativelylowFECinthe ®rst grazing period are likely to retain their advantage in the following year. FECofanimalswithHBBBBweresigni®cantlyhigher p < 0:01 andhaematocritsigni®cantlylower p < 0:05 compared to HBB AA and AB genotypes. Furthermore, ALB SS was associated with signi®cantly lower p < 0:01 FEC compared to genotypesALBDDandALBDS.NostatisticaldifferenceswerefoundformeanFECandhaematocritamongthegenotypesof CA2 and GC p > 0:05. Fromtheseobservations,thepolymorphicsystemsofHBBandALBopenawayofselectioninRho Ènsheepforgenetically basedtrichostrongyleresistanceinanenvironmentwhere Haemonchus contortus, Trichostrongylus spp., Teladorsagia spp.and Cooperia spp. are the predominant species. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Gastrointestinal parasites; Sheep; Haematocrit; Blood polymorphism 1. Introduction Theincreasingresistanceofovineinternalparasites to anthelminthic treatments Hertzberg and Bauer, 2000) and concerns over possible chemical residues, environmentalimpactandcostoftreatmentshaveled to an increasing interest in genetic selection for resis- tancetoparasitesasanalternativeorsupplementtothe use of anthelminthics Madsen et al., 1990; Lumaret et al., 1993). Evaluation of sheep breeds in different breeding situations and environments have demonstrated the possibility of breeding for nematode resistance Gray, 1997; Kominakis and Theodoropoulos, 1999; Mugambi et al., 1997). Small Ruminant Research 44 2002) 103±108 * Corresponding author. Tel.: 49-641-9661320; fax: 49-641-68122. E-mail address: mgauly@aol.com M. Gauly). 0921-4488/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0921-448802)00042-1