Studies on the epidemiology of bovine parasitic bronchitis

Abstract

In the West of Scotland the epidemiology of parasitic bronchitis in grazing calves was studied over a two year period with the aid of tracer calves and herbage examinations for Dictyocaulus viviparus larvae. The observations of both years emphasised the importance of overwintered lungworm larvae as a source of disease. In the first year it was shown that the ingestion and development of these overwintered larvae were, by themselves, directly responsible for severe morbidity, high faecal larval counts and deaths. In the second year it was shown that pasture ungrazed during the winter and spring and from which a hay crop was removed in mid-summer was still capable of producing clinical parasitic bronchitis in susceptible calves within three to four weeks of their introduction in later summer. In both years there was some evidence that the outbreaks appeared to be associated with the sudden availability of infective larvae on the herbage. The possibility that such larvae may have survived for many months in the soil is discussed. Despite the heavy challenge with lungworm larvae experienced by the grazing calves in the first year those vaccinated with lungworm vaccine survived, their clinical signs were mild and of short duration and their faecal larval output was greatly reduced.

Lungworm in cattle: epidemiology, pathology and immunobiology

“…The freeliving larval stages of D. viviparus do not feed and develop into infective (L3) rapidly: in less than a week under optimal conditions (Rose, 1956). Absence of feeding may explain why they appear to be relatively inactive as presumably they have to conserve their limited energy resources; nonetheless, although infective larvae may only survive for a few weeks on pasture under warm, dry conditions, somewhat paradoxically, they can survive for over a year, even when the fields have been used to make hay in the interim (Duncan et al, 1979;Nelson, 1977;Oakley, 1977).…”

Grassland management and helminth control on cattle farms

“…Several of the grazing management practices for the control of PGE in cattle are based on the predictable annual pattern of pasture infectivity in untreated, weaned, grazing cattle, however, the epidemiology of lungworm does not follow the same patterns and is unpredictable (Jacobs and Fox, 1985, Duncan et al, 1979, Eysker and van Miltenburg, 1988. Furthermore, older cattle can play an important role as carriers of infection, including over-winter (Eysker et al, 1994, Saatkamp et al, 1994, and hence any mixed age systems in cattle may expose youngstock to the risk of husk/hoose.…”