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

Abstract

Gastrointestinal nematodes, such as Ostertagia ostertagi and several species of Cooperia, are ubiquitous in temperate climates and have been shown to have detrimental effects on production in adult dairy cattle. A published meta-analysis demonstrated that overall, producers lose approximately 0.35 kg of milk per parasitized cow per day. Enzyme-linked immunosorbent assays (ELISAs) have the ability to quantify nematode infections in cattle, and thus, could be used to estimate the amount of milk production loss due to differing levels of parasitism at the individual cow level. 2ELISA results from individual cow milk samples were used to predict milk production response following a randomized anthelmintic treatment in a large field trial. To increase statistical power, the data collected from this field trial was pooled with data from two other published field trials to form an individual patient data meta-analysis (IPDMA).The ability to predict the effect of anthelmintic treatment on milk production depends on the level of parasitism quantified by an ELISA measuring milk antibodies against Ostertagia ostertagi, and reported as optical density ratios (ODRs). Therefore, the estimates from the interaction between ODR and treatment on milk production were used to determine how well the ODR predicted the response of the treatment. It was anticipated that the relationship between milk production and ODR was unlikely to be linear, so fractional polynomials were applied to the continuous ODR values.The interaction in the field trial showed a trend (p=0.138) towards a beneficial treatment effect when the individual ODR values, measured in late lactation and using Svanovir®, were greater than 0.12. When individual data from two other similar studies were included in an IPDMA, the interaction terms became statistically significant (p=0.009) indicating that there is a beneficial treatment effect when ODR values are slightly elevated. A graph was used to demonstrate the treatment effect (the estimated difference of kg/cow/day of milk yield between the treated and placebo cows), with 95% confidence intervals, as the ODR values increase. It is important to note that the methods of quantifying the ODR values differed between the three studies in the IPDMA, therefore some caution should be used when using these final estimated values. However, the shape and magnitude of the treatment 3 effects, as well as the other fixed model estimates, were very similar between the field trial and the IPDMA suggesting that any bias would likely be minimal.

Non-invasive indicators associated with the milk yield response after anthelmintic treatment at calving in dairy cows

“…Previously the anti-O. ostertagi antibody level in individual milk samples has been proposed as a useful indicator of which animals would benefit most from treatment [3,11,12,16]. Here, we confirm that the highest treatment responses were observed in the cows with the highest anti-O.…”

“…A recent study on anthelmintic treatment at calving in Canada found a maximal treatment effect of 0.67 kg milk/day per cow, which is considerably lower than some of the observations reported here [12]. A study performed in New Zealand, found a positive effect after treatment in only one of the three participating herds of 0.78 kg energy corrected milk/day per cow [24].…”

“…Previously some indicators have been associated with the milk yield response after anthelmintic treatment. The parameter yielding most consistent results is the anti-Ostertagia ostertagi antibody level in individual milk samples, with studies showing higher treatment responses in cows with a high antibody level [3,11,12,16]. As for the age of the cow, some studies found no relationship with treatment effect [10,14,17], whereas others reported a higher milk yield gain in older cows [3,13] or conversely, in younger cows [5].…”

“…However, a cost-benefit analysis suggested that the economic benefit of anthelmintic treatment of dairy cows is considerably larger when cows are treated around calving compared to treatment at housing [9]. Studies assessing the effect of anthelmintic treatment around calving have been carried out in Canada [10][11][12] and New Zealand [13], but significant differences in climate and farm management practices may result in different parasite epidemiology and different production effects when compared to European circumstances.…”

Enjeux et outils du traitement raisonné contre les strongles gastro-intestinaux chez les bovins et les petits ruminants

“…Plus rarement, une chute significative de production laitière post-traitement est rapportée (Tharaldsen et Helle 1989, Ravinet al 2016. De plus, l'effet du traitement sur la PL est très variable entre troupeaux et entre individus (Ploeger et al 1989, Sanchez et al 2004, Vanderstichel et al 2013, Ravinet et al 2014, Verschave et al 2014.…”