Ostertagiasis survey: summary and discussion

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Abstract
Opinions offered by 127 veterinary practitioners indicated that cattle ostertagiasis occurred throughout New Zealand; it was seen in all age-groups regularly in some regions; poorly fed animals were more susceptible to outbreaks accompanied by a gradual decline in health; both poor and well-fed cattle were subject to sudden outbreaks which were almost entirely associated with nutritional changes. Most cases were diagnosed by clinical signs. The prescription of multiple anthelmintic doses was the most common treatment. According to research data, winter and summer conditions reduced O. ostertagi numbers on pasture. Survival depended on a gradual accumulation of inhibited larvae before winter and a reduction after summer. Although clinical type II cases usually occurred in the winter and spring, it was theorised that subclinical production losses were more likely to occur in the autumn. Management was solely responsible for the level of pasture contamination and animal health. Similar O. ostertagi burdens were recorded in heavy and light cattle, although the latter were more likely to succumb to disease. Changes in worm populations were demonstrated on a farm during a 3-year period. Changes in diagnostic and treatment procedures using plasma-pepsinogen estimations and longeracting anthelmintics were discussed.