Effect of nematode infections on productivity of young and adult cattle on commercial dairy farms.

In this study relationships between levels of exposure to gastrointestinal and lung nematode infections and production were investigated on commercial dairy farms in the Netherlands. Little was known about these relationships, particularly with respect to second-year cattle and adult cows. Knowledge about the effects of different levels of exposure to nematode infection on growth performance and milk production on commercial farms, may lead to estimations of the economic impact of nematode infections. This, in turn, may contribute to a better understanding of methods to control nematode parasitism. The present work comprised 8 studies, involving a total of 100 farms and conducted in 2 subsequent years. Where possible, first- season grazing calves, second-season grazing yearlings, heifers and adult cows were investigated on each farm. The design of the present studies resembled a cross-sectional type of survey and included some longitudinal investigations. Parameters used to estimate nematode infection were: faecal egg output combined with larval identifications, faecal lungworm larval counts, antibody titres against the gastrointestinal nematodes Ostertagia spp. and Cooperia spp. , antibody titre against the lung nematode Dictyocaulus viviparus , and serum pepsinogens. Parameters used to estimate production were: body weight and heart girth of calves and yearlings, and milk production in heifers and adult cows. Additionally, questionnaires were used to collect data about farm, herd and general management. The herd was the experimental unit in the statistical analyses. From faecal examinations in late summer and in the housing period, it was concluded that gastrointestinal nematode infections occurred in each herd, irrespective of age. In faecal samples from calf-herds the most frequent larval types found were of the genera Ostertagia and Cooperia . In faecal samples from yearling-herds the most frequent larval types found were of the genera Ostertagia , Cooperia and Trichostrongylus . In faecal samples from adult cows the most frequent larval types found were of the genera Ostertagia and Trichostrongylus . Faecal samples of approximately 20% of the calf-herds and 6% of the yearling-herds contained lungworm larvae. From the serological examinations it was concluded that all parameters demonstrated significant between-herd-variation in level of exposure to nematode infection compared to the within-herd-variat ion. This was most pronounced for calf-herds and least pronounced, but still strongly significant, for cow-herds. The between-herd-variation was highest during the grazing period for all age-groups. Antibody titres showed, generally, higher between-herd-variations than pepsinogen values. Significant differences in production parameters were demonstrated between herds, irrespective of age. Age-adjusted body weights of calves varied between herds from -68.1 to +84.1 kg. /calf and from -59.8 to +52.2 kg. /calf from the population mean after the first grazing seasons in 1985 and 1986, respectively. Growth rates of calves during winter housing varied per herd from 0.25 to 0.94 kg. /day and from 0.11 to 0.87 kg. /day in the respective years. Age-adjusted body weights of yearlings after the second grazing season varied per herd from -64.7 to +94.4 kg. /yearling from the population mean. Growth rates of yearlings during winter housing were strongly influenced by calving and lactation. Significant relationships were found between infection parameters and growth performance of calves and yearlings. Growth performance of calves during the first grazing season was negatively related to antibody titre against Cooperia spp. , faecal gastrointestinal nematode egg output and faecal lungworm larval count. This was demonstrated in 1985 as well as in 1986. Growth performance of calves during winter housing was negatively related to antibody titres against Ostertagia spp. and Cooperia spp. , and to pepsinogen values. Growth performance of yearlings during the second grazing season was negatively related to antibody titre against Ostertagia spp. Anthelmintic treatment of calves and yearlings after housing, significantly increased weight gains during the housing period. Anthelmintic treatment after stabling and during the housing period resulted in significantly increased milk production in cows and heifers. For adult cows a significant positive correlation was found between antibody titre against Ostertagia spp. and the milk yield response to anthelmintic treatment per herd. Concerning the longitudinal aspects of the present study, it was concluded that: 1) level of exposure to nematode infection during the first grazing season, as measured by antibody titres against Ostertagia spp. , positively affects growth performance during the second grazing season, due to acquired immunity; 2) milk yield in the first lactation is positively related to body weight achieved by the end of the second grazing season. Consequently, nematode infections in the first years of life negatively affect this milk yield by reduced weight gains; 3) levels of pasture contamination may continue over subsequent years, as suggested by significant positive correlations of single infection parameters between years for calf-herds and for yearling-herds on the same farms. Management practices on the farms influenced both level of exposure to nematode infection and growth performance of calves during the first grazing season. Supplementary feeding, vaccination against lungworm, treatments with anthelmintics at pasture or at housing, and date of housing were the most significant factors contributing to the explained part of the between-herd-variation in growth performance of calves. Finally, it was concluded that cross-sectional type of surveys are extremely useful in collecting data to investigate relationships between levels of nematode infections in calves, yearlings and cows. Antibody titres are the most valuable infection parameters estimating level of exposure to infection in all age-groups, to be considered for use in such surveys. Faecal examinations reflect the level of exposure to nematode infection in calves, but are for that purpose less useful in yearlings and in cows. Economical evaluations estimating the impact of nematode parasitism on production indicated that most of the economic losses occur in older cattle in the Netherlands. The value of such economic estimations based on results of the present study and some implications of these results for the use and value of control strategies were discussed.