Review article
A critical review and meta-analysis of the magnitude of the effect of anthelmintic use on stocker calf production parameters in Northern US States

https://doi.org/10.1016/j.vetpar.2015.09.019Get rights and content

Highlights

  • A critical review and meta-analysis.

  • Aimed at quantifying the effect of use of anthelmintic products on production metrics in stockers.

  • Compared average daily gain in stockers in northern US climates, treated compared with placebo.

  • Conclusion was made that anthelmintic use is associated with an increased weight gain.

  • However, reporting was poor throughout all studies included in the review.

Abstract

Parasitism of the gastrointestinal tract of cattle leads to diminished health and productivity of grazing livestock. Anthelmintics are used to decrease parasite loads in cattle for improved weight gain. This critical review and meta-analysis aims to quantify the magnitude of the effect of use of anthelmintic products on production metrics in beef stocker calves. Four databases were searched in March 2013. Eligible studies compared average daily gain (ADG), or weight gain in stocker calves in northern climates of the United States that received anthelmintic treatments compared with placebo or an alternative anthelmintic treatment. Study results were extracted, and where possible, summary effect measures were calculated. Of 512 citations identified by the search, 9 manuscripts with 23 relevant individual studies were selected. Risk of bias was assessed for all studies included in the review and assessed to be unclear for the majority of the studies. There were 23 studies that assessed the magnitude of effect of anthelmintic use on ADG (summary mean difference in ADG = 0.05 kg (50 g), 95% CI = 0.03–0.07 kg, p < 0.00001). The magnitude of weight gain associated with anthelmintic use could not be assessed, as measures of precision (standard errors or standard deviations) were not reported in these studies. Overall, the conclusion was made that anthelmintic use is associated with an increased weight gain. However, the approach to reporting employed by authors for this type of study means that many studies could not be included in the meta-analysis and the magnitude of effect not determined.

Introduction

Gastrointestinal parasitism is a leading cause of diminished health and productivity of grazing livestock in North America (Ballweber, 2006). Treatment with anthelmintics to control parasitism is currently recommended to reduce the impacts. However, the expected increase in performance from treatment, to control parasitism, is difficult to estimate. Although results from primary research are available, it is often difficult for veterinarians or producers to combine the results reported in multiple studies to help gauge the benefits and variation that could be expected. Without knowledge of magnitude of gain and variation, producers and veterinarians are given only partial information upon which to base product selection decisions.

The family Trichostrongylidae, including the genera Trichostrongylus, Haemonchus, Ostertagia, Cooperia, and Nematodirus, cause most subclinical and clinical infections in beef cattle production systems in the United States (Yazwinski and Tucker, 2006). It is known that anthelmintic effects are modified by climate; therefore, this review is limited to northern climates of the United States.

To reduce the impact of nematodes on cattle production, it is necessary to have control programs that aim to reduce worm burdens within cattle, and to prevent reinfection by reduction of parasites on pastures. Anthelmintic products are available to reduce burdens within cattle, and the timing of application impacts the burden of the pasture (Corwin, 1997). A chemical parasite control program is therefore composed of the product, the dose, and the timing of administration.

The purpose of this critical review was to evaluate the magnitude of change in production outcomes associated with the use of anthelmintics in stocker cattle in northern climates of the United States. Further, the aim was to assess if season of administration or product type modified those outcomes. The review question was defined by four question components: the population, the intervention, the comparison and the outcome (European Food Safety Authority, 2010, O’Connor et al., 2010a, O’Connor et al., 2010b). Populations of interest were stocker calves in the northern United States, where overwintering of parasite populations was likely. The intervention and comparator of interest were any anthelmintic that is approved for use in the United States used at the labeled dose approved by the United States Food and Drug Administration. The outcomes of interest were any production outcomes for stocker calves such as, but not limited to, average daily gain and weight gain.

Section snippets

Protocol and registration

A review protocol was generated before the start of the project. The protocol was not registered, as mechanisms for registrations did not exist at the time. No major modifications were made to the protocol other than those noted in the ancillary analysis. The protocol was established for all cattle in beef production systems. There were two classifications of cattle production systems that were studied separately. One group was stocker cattle and the second group was cow-calf pairs. This study

Study selection

The results of the search process are presented in Fig. 1. 512 Citations were reviewed for eligibility, this included both cow/calf and stocker manuscripts. 459 did not meet the predetermined eligibly criteria and 53 articles were retrieved for further assessment. After evaluation of the full text, only 9 manuscripts and 23 studies were relevant to the stocker review (Ballweber et al., 1997, Cleale et al., 2004, Epperson et al., 2001, Ferguson et al., 1971, Kunkle et al., 2013, Mertz et al.,

Discussion

One goal of this review was to summarize the magnitude of gain associated with use of anthelmintic productions and to determine if there was empirical evidence that treating beef cattle in northern climates of the United States, with different anthelmintic protocols (including season of administration) had an effect on production outcomes such as ADG or weight gain. Our rationale for assessing these outcomes was that improved weight gain or ADG is often reported as an outcome in anthelmintic

Conflicts of interest

Dr. Baltzell has no direct research funding, private consulting contracts (permanent or intermittent), or institutional indirect support. Additionally, Dr. Baltzell has not accepted any private gifts or travel from companies that manufacture or market anthelminthic products.

Dr. Engelken has received direct research funding from the state of Iowa to support research directly related to the assessment of anthelmintics. This was through the Iowa Livestock Health Advisory Committee grant program in

Acknowledgements

The authors would like to thank Stacie Gould, Andrea Dinkelman, and Rungano Stan Dzikamunhenga for their help with this project.

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