Patterns of parasitic nematode infection and immunity in dairy heifers treated with ivermectin in a sustained‐release bolus formulation either at turnout or in the middle of the grazing season

Abstract

Twenty-eight Holstein-Friesian heifers, born the previous year and weighing between 130 and 310 kg, were allocated to one of two treatment groups by restricted randomisation, based on their initial weight. The heifers in group 1 were each treated with ivermectin in a sustained-release bolus formulation at turnout in April, and those in group 2 were each given an ivermectin bolus on July 10, 84 days after turnout. On that day the mean geometric worm egg counts of groups 1 and 2 were 0.4/g and 38.8/g, respectively, and they both had a mean plasma pepsinogen concentration of 0.59 iu/litre; in group 1, two of 14 faecal samples were positive for Dictyocaulus viviparus larvae, and in group 2 all 13 samples were positive; in group 1 eight calves were positive and three inconclusive for the presence of antibodies to D viviparus, and in group 2 the corresponding figures were 10 positive and two inconclusive; the mean liveweights of groups 1 and 2 were 274.4 kg and 262.8 kg, respectively. By December 4,231 days after turnout, the corresponding results were: mean geometric worm egg counts of 2.2/g and 0.5/g; one of 13 and none of 14 faecal samples positive for D viviparus larvae; 12 positive and two inconclusive and none positive and 10 inconclusive for the presence of antibodies to D viviparus; 214 days after turnout their mean liveweights were 361.1 kg and 358.3 kg. Although the patterns of parasitic nematode infection were different in the two groups during the grazing season, by the time they were housed both groups had achieved similar liveweights and showed evidence of an immune response to both D viviparus and gastrointestinal nematodes.

LongRange™ (eprinomectin 5%) extended-release injection parasiticide and the utility of extended-activity antiparasitics in cattle

“…Anthelmintics given during this period can help avoid disease and mitigate the impact of PGE on livestock performance (Satrija et al, 1996). Regardless of whether a strategic or a tactical approach to the use of anthelmintics in calves is used, there are advantages in terms of convenience and compliance in using long-acting products (Forbes and Rice, 2000).…”

Lungworm in cattle: epidemiology, pathology and immunobiology

“…In some studies there was an inverse relationship between the effectiveness of the anthelmintic regime in controlling lungworm infection and the level of protective immunity (Borgsteede et al, 1998). Also of interest is the observation that cattle exposed to natural lungworm challenge (Forbes and Rice, 2000) or induced infections (Taylor et al, 2000) can seroconvert to D. viviparus in the presence of effective concentrations of anthelmintic.…”