The reaction of calves to helminth infection under natural grazing conditions. II. Pathology of terminal disease

Abstract

Calves raised worm-free were exposed to natural infection on unimproved pasture infected with Trichostrongylus axei, Haemonchus placei, Ostertagia ostertagia, Cooperia punctata and C. pectinata, and Oesophagostomum radiatum. Some calves received, in addition, experimental infections of O. radiatum and H. placei. All calves showed depressed body weight gains. Haematocrit, haemoglobin, and serum protein levels were reduced, returned to normal after 15–18 weeks' grazing in calves that survived, but continued to fall and reached lower levels in those that died. Calves killed in extremis showed emaciation, oedema, degenerated fat tissue, inflammatory and degenerative changes in the gastrointestinal tract, and atrophy of the lymphatic tissues and thymus. These symptoms are reminiscent of a "wasting syndrome".