Anthelmintic treatment of dairy cows and its effect on milk production

Abstract

The results of more than 80 experiments on gastrointestinal parasitism and the impact of anthelmintic treatment on milk production in dairy cattle were reviewed. Abattoir surveys of culled dairy cows, faecal egg counts in milking cows, and serological tests and worm counts in cull cows in milk production studies were collated to assess the level of parasitism in dairy herds. The studies were divided into four general categories: induced infections in previously uninfected cattle; naturally infected cattle treated in mid-lactation; naturally infected cattle treated one to three times during the dry period and/or just before or just after parturition; and naturally infected cattle treated repeatedly from early lactation or given strategic treatments throughout the year. In most studies, the milk production of anthelmintic-treated cattle was compared with that of untreated controls. The anthelmintics investigated included members of the organophosphate, benzimidazole, imidazothiazole and macrocyclic lactone groups. The number of experiments in which the medicated (or uninfected) group had a higher milk yield was compared with the number of experiments in which the control (or infected) group had a higher yield. Overall, the studies demonstrated that grazing dairy cattle are likely to be infected with gastrointestinal nematode parasites, usually Ostertagia ostertagi and Cooperia species. These infections may be present as inhibited larvae, and a periparturient or spring rise is associated with their emergence. There is, at present, no reliable means of determining whether a cow or a herd may be parasitised subclinically at a level sufficient to interfere with milk production. In 70 of 87 experiments (80 per cent) there was an increase in milk production (P < 0.001) after anthelmintic treatment, with a median increase of 0.63 kg/day. In each of the four trial categories, a majority of the studies showed that anthelmintic treatment increased milk production. The yield of milk fat by the medicated cows was greater than by the controls in 26 of the 35 experiments in which that variable was studied (P < 0.01).

Epidemiology and effects of gastrointestinal nematode infection on milk productions of dairy ewes

“…In dairy cows many studies with controversial results have been carried out to assess whether anthelmintic treatment have a beneficial effect. The review of Gross et al (1999) showed that in general there was an economical profit from treatments, with a median increase of 0.63 kg of milk per cow per day over that of untreated cows. On the other hand, there are few corresponding references on dairy sheep, as the sheep industry was primarily focused on wool or meat, in which milk production is only considered a maternal aptitude or capacity to rear their lambs.…”

Predicting the effect of anthelmintic treatment on milk production of dairy cattle in Canada using an Ostertagia ostertagi ELISA from individual milk samples

“…Fecal egg counts have traditionally been utilized to identify and quantify infections, however, this test is plagued with false negatives, high variability between consecutive tests (low repeatability), and overall underestimation of the level of infection (Gross et al, 1999;Agneessens et al, 2000;Borgsteede et al, 2000;Eysker and Ploeger, 2000). Serum pepsinogen tests have had some success with quantifying levels of parasitism in first-season grazers, but were less reliable when used to quantify infections in adult cattle (Gross et al, 1999;Agneessens et al, 2000;Borgsteede et al, 2000). Unfortunately, the accuracy of the pepsinogen test depends on the current life cycle stages of the nematodes in the host (Berghen et al, 1993).…”

Control of gastrointestinal parasitism with nematodes in dairy goats by treating the host category at risk

“…It has been suggested from both experimental studies and epidemiological surveys in dairy cattle that animals from high producing herds are more infected than others [44] and that, both on a herd and on an individual basis, high producing cows benefit more from anthelmintic treatments than low producing ones [3,25,55].…”