In early April, we ran an article titled “Detecting and preventing drug-resistant parasites,” based on an FDA publication outlining possible causes for the development of resistant parasites and potential management solutions.
Knowing drug resistance in parasites is a complex issue with no clear consensus among the experts, we asked for responses from veterinarians and parasitologists to the FDA’s conclusions and recommendations.
Veterinary parasitologist Lou Gasbarre offered the following comments:
I have read with interest your article dated 4/10/2013 in Bovine Veterinarian concerning detecting and preventing drug-resistant parasites. I feel this is a very important topic and applaud you’re efforts in bringing this topic to the attention of the cattle industry. At the same time I feel it is very important to provide the industry with the best information we can.
I feel that there are a number of misconceptions in the FDA report that if these recommendations were followed by the cattle industry, they could pose very serious problems for the individual producers. I would like to briefly outline several of these misconceptions/over-simplifications and would be more than happy to discuss them in detail with you if you so desire.
First, the information sheet developed by FDA is a very good set of recommendations for the sheep and goat industry, but has serious flaws when applied to the cattle industry. As you are well aware, the cattle industry is not one management system but is stratified into several steps, i.e. cow/calf, backgrounder/stocker, feedlot and dairy. The recommendations in this article refer to only the cow/calf sector, and even here have some very severe errors. It is completely wrong to assume that the basic biology of the cattle-nematode system is the same as that of the sheep/goat- nematode system. The parasites are in some cases closely related but they may not have the same behaviors.
For instance the dominant parasites in cattle are cool weather parasites unlike the dominant H. contortus of small ruminants, as such treatment based on “high temperature, high humidity’ in cattle versus sheep can have very different results. Similarly, dragging the pasture at the wrong time would only spread the parasites over the pastures and alleviate the advantage of keeping stocking rates low to avoid having the cattle graze near fecal pats. There are similar errors in thinking, but I hope these two examples outline the danger in assuming the systems are identical.