Ostertagiasis in calves. I. The effect of control measures on infection levels and body weight gains during the grazing season in Denmark

Abstract

Abstract The investigation was designed to study the gastro-intestinal helminth infection established in yearling calves with reference to fluctuations in the larval contamination of the herbage during the grazing season. In a 2 × 3 factor experiment, comprising six groups, each of six calves, a comparison was made between infection levels, growth rates etc. in calves grazing the same paddock over an entire season and calves moved before the July rise in herbage contamination to paddocks not grazed earlier in the same season. A comparison was also made between animals receiving no anthelminthic treatment, animals treated 3 weeks after the start of the grazing season and again when moved, and animals treated every 3 weeks during the season. Before July there were no weight gain differences between the various groups of calves. During the rest of the season, the calves which were moved gained 647–869 g, while those that remained on the same paddock, and were exposed to a high level of larval contamination gained only 81–361 g per day. The effect of anthelmintic treatment was less pronounced, though significant. The weight gains were correlated to a high degree with the larval contamination levels of the respective paddocks ( r = − 0.79) as well as with the serum pepsinogen ( r = − 0.75) and albumin levels ( r = 0.75) of the calves and to a minor degree also with faecal egg counts ( r = − 0.45). The observed weight gain differences could not be accounted for by differences in grass quantity or quality.