Some observations on the worm burdens of calves infected daily with Ostertagia ostertagi

Abstract

Two experiments are described in each of which three groups of calves received infective larvae of Ostertagia ostertagi daily, each group at a different rate. Changes in worm burdens were followed by the periodic slaughter of calves.Numbers of adult worms quickly rose to and remained at levels which bore a positive relation to the infection rate. There was evidence that a turnover of worms was occurring and it appeared that burdens of adult worms were regulated by a loss of worms which depended on the number present. As the host's experience of infection increased, the adult worms present were smaller and an increasing proportion of females lacked a fully developed vulval flap. Evidence is presented which suggests that these were effects of resistance and that they depended on separate mechanisms.Faecal egg counts of groups carrying different numbers of worms rose to the same peak and then declined according to the same logarithmic curve. This finding, together with data concerning the number of eggs in the uteri of the worms, suggested that the egg output of the entire population was restricted by the host to a limit which depended on previous egg-laying.Infection did not have an adverse effect on the growth of the calves unless the infection rate exceeded a critical value. The resistance of calves to infection was impaired by clinical ostertagiasis.

Efficacy of ivermectin against gastrointestinal nematodes of cattle in Denmark evaluated by different methods for analysis of faecal egg count reduction

“…The inclusion of untreated animals in a FECRT has been recommended to detect changes in the FEC of a herd not related with the treatment, and for the correction of such fluctuations in the estimation of drug efficacy (Coles et al., 1992, Lyndal-Murphy et al., 2014). However, the inclusion of a control group is based on the assumption that treated and untreated animals with comparable FEC share similar worm burdens, which may not be always the case in cattle (Michel, 1967, Michel, 1969). Moreover, the density-dependent control of fecundity in some bovine nematodes, such as in O. ostertagi , may reduce the FEC in untreated animals due to newly acquired infections and could increase the egg excretion of female worms in treated groups due to lower worm burden and competition (Dobson et al., 2012).…”

Epidemiological observations on helminth infections of calves in southern Ghana

“…Worm egg counts were made using the modified McMaster technique (Michel, 1969). All other animals were sampled at weekly intervals.…”

Variation in size of Ostertagia circumcincta, a nematode parasite of sheep, induced experimentally and during preparation and preservation

“…The abomasum and its contents were processed in the manner described by Michel (1969) where the material was sieved through a tier of screens, a process involving prolonged washing with a jet of cold tap water. The residue containing the live worms was fixed by the addition of an approximately equal volume of 5% formol-saline and stored.…”