An epidemiological study of helminthiasis in cattle in subtropical Argentina.

Nine farms were each visited regularly for a year in 1979 and 1980 in Salta Province in the subtropics of Argentina. A necropsy was done at each visit and faecal and blood samples were taken from other animals mostly aged between 6 and 18 months. Ninety necropsies were done and nearly 1,500 faecal samples collected. Gastro-intestinal helminthiasis was most general and severe in autumn when calves were about 9 months old and this was followed by a dramatic fall in numbers of worms by the end of winter. Helminths were found in other organs but were not considered important. At peak periods 20% of the animals had worm egg counts of more than 750 epg and contained more than 1,000 Haemonchus worms. This species was considered to be the most important but other frequently encountered species were Oesophagostomum, Cooperia and Trichostrongylus spp. A list is given of all species found. Tracer calves were used to determine the periods of infestation. No hypobiosis was encountered. It was concluded that the sharp fall in numbers of worms after the autumn peak was due to the development of immunity by the majority of the young animals.