Ostertagiasis survey: summary and discussion

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. ()stertagi 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 plasmapepsinogen estimations and longeracting anthelmintics were discussed.

Helminth parasites of economic importance in cattle in New Zealand

“…dairy, dairy-beef, traditional beef). This conclusion agrees with the findings of Chalmers (1980), who surveyed veterinary practitioner opinion on ostertagiosis in cattle in New Zealand.…”

“…Factors precipitating the acute form of the disease are not fully understood. Veterinary opinion is that precipitation of the disease is related to a variety of factors including nutrition, weather, and calving, which lead to "stress" (Chalmers 1980). This is consistent with the results of Bisset & Marshall (1987), who observed no clinical disease in field-grazed animals despite large pre-type II burdens.…”

“…However, the presence of large burdens of arrested Ostertagia spp. do not inevitably lead to the development of the acute form of the disease (Chalmers 1980;Bisset & Marshall 1987). Where the acute form of the disease is not precipitated, resumed development of arrested burdens appears to progress over an extended period, possibly reflecting the extended period of accumulation characteristically seen under New Zealand conditions (Bisset & Marshall 1987).…”

Nematodes and liver fluke in New Zealand

“…It is not increased by cold-conditioning (Bisset 1994) and the increase in numbers of inhibited larvae acquired by grazing stock results from their slow accumulation over time. This accumulation does not necessarily lead to clinical disease and, generally, it appears that the larvae resume their development and are lost progressively over the spring and summer (Chalmers 1980;Bisset and Marshall 1987). Occasional disease outbreaks caused by the sudden resumption of development of large numbers of previously arrested larvae do occur.…”

“…However, what precipitates these is not fully understood. Clinical observations indicate that a variety of stress factors which may adversely affect host immunity, perhaps impairing the host's ability to reject developing worms, can be involved (Chalmers 1980;Bisset and Marshall 1987;Bisset 1994).…”