Serum protein changes in ponies on different parasite control programmes

Serum protein responses were examined in 52 ponies divided into five groups and subjected to various control strategies that resulted in pasture infectivity ranging from 706 to 18,486 infective third stage, cyathostome and Trichostrongylus axei larvae per kilogram of herbage (L3/kg) by 17 September 1984. Major protein changes occurred only in young ponies (Groups 4 and 5) and were observed before exposure to maximum numbers of pasture larvae (Group 4; 10,210 L3/kg, Group 5: 10,042 L3/kg) on 17 September. It appeared that a primary infection of T axei was a greater stimulus to serum beta-globulin and immunoglobulin (Ig)G(T) responses that provided by continued infection with cyathostome (small strongyle) worms. The large strongyles (Strongylus vulgaris, S edentatus and S equinus) were not detected in any larval cultures or on pastures grazed by the young ponies. A fall in beta-globulin and IgG(T) concentrations of Group 5 ponies one month after treatment with ivermectin indicated a larvicidal action against T axei and/or the cyathostomes. A subsequent rise in serum albumin concentrations of Group 5 ponies suggested that a protein-losing gastroenteropathy had been alleviated by the larvicidal action of ivermectin. Mature control ponies (Group 1) showed little beta-globulin response and only a modest IgG(T) response in six of the 10 ponies after exposure to heavily infected lawns (18,486 L3/kg) in September 1984. It was concluded that serum protein and IgG(T) responses were of limited value as an aid to diagnosis of parasitism because of numerous difficulties of interpretation.