Osteopenia and reduced serum alkaline phosphatase activity in grazing lambs naturally infected with gastrointestinal nematodes

The effect of gastrointestinal nematode infections on bone development was investigated in growing sheep on pasture. Forty-five weaned lambs from six groups in a two-factorial design incorporating stocking rate (SR; low, medi um and high) and presence or absence of infection on pasture were sampled i n the late grazing season. Worm counts were performed at slaughter, and the left metacarpal bones were excised for bone assessment. Faecal egg counts and worm burdens, primarily of Ostertagia circumcincta and Trichostrongylus vitrinus, were considerably higher in the high SR infected group ("I-High" ) than in comparable animals at low or medium SRs, whereas uninfected group s showed negligible egg excretion. Clinical biochemistry revealed significa ntly reduced serum concentrations of albumin, calcium and alkaline phosphat ase in infected lambs. Nematode infections were associated with significant reductions in bone mineral density (30% at high SR), measured by dual ener gy X-ray absorptiometry, and in bone size (9%). Histomorphometry indicated thinning of the trabecular structure and reduced bone formation in the infe cted groups, particularly the I-High group. Bone mineral density, bone tiss ue volume and structural changes were strongly associated with log-transfor med worm counts. The study showed that lambs suffering from moderate to hea vy degrees of naturally acquired gastrointestinal nematode infection develo ped marked osteopenia after weaning, i.e., during the later part of the gra zing season. (C) 2001 Harcourt Publishers Ltd.