Got Worms?

By Robyn Hall

Dairy producers make their entire living based on the amount of milk they produce.  Their financial well-being lies within the dairy cows and their milk production.  To maximize production, it is in the dairy farmers best interest to take part in animal health practices.  As grazers, it is not uncommon for dairy cows to contract a large variety of helminths.  Of course, the effect of internal parasites will vary with the severity of infection.  Younger cows and immunocompromised animals are more likely to show higher levels of parasitism while mature cows acquire a certain level of immunity to a low-level infection.  However, cows in early stages of lactation have a suppressed immunity based on the stress of lactation.  These cattle are affected more than cows later in lactation, due to the smaller levels of milk being produced.  This clearly creates a huge concern for dairy farmers when their greatest interest is to get as much milk as possible from healthy cows because the effects of parasitism effect animal productivity (milk production, weight gain) and clinical issues (symptoms that need to be addressed by a veterinarian for the animal’s well-being).  Dairy cows can be affected by nematodes, cestodes, and flukes which are in the helminth category.

Traditional treatments for dairy cows include regular de-worming after the end of lactation to avoid discarding milk.  The use of any drug, including anthelmintics, requires a milk discarding window where the milk is not usable for human consumption.  A typical protocol would be where heifers are wormed as newborns, yearlings, and again before entering the milking herd.  There are many anthelmintic drugs that are not allowed to be used on dairy cattle due to the lasting effects and chemicals that are passed on to human consumable products.  Something as common as ivermectin, as seen in the horse and beef industry, is not approved for lactating dairy heifers or cows.  The amount of ivermectin that can be detected in milk is considered illegal and is not allowed in the dairy world.  Milk, by the truck loads, are tested for these particular drugs.  Anthelmintic resistance is a growing issue in today’s world.  It creates health related issues and economic problems throughout the world.  The dairy industry, in particular, is being heavily affected.  

This past summer, I was able to work for a dairy vet.  We primarily preg checked cows and came up with antibiotic and de-worming protocols for the dairy workers to follow.  I was able to see a side of the dairy industry and veterinary work that most people don’t see.  A dairy veterinarian’s job is to be able to look at a facility and come up with programs and plans for these farms to treat their animals so that they can be at their highest level of health for the highest-level quality products.  During my time there, one of the trucks loads of milk had tested positive for a certain chemical deemed illegal for use of dairy cows.  It was found that one of the head cattlemen had been bringing drugs from Mexico and using it for treating cows in the herd and milking those particular cows.  A “hot” milk truck can be detrimental to a dairy and causes federal employees to come take a look at the facility.  The after effects of misused drugs was even seen in the calves.  There was an extremely high mortality rate in the calves at this particular dairy farm.  They were dying from helminth infections that were not responding to the legal, small group of anthelmintic drugs suggesting that there was some level of resistant parasites in these calves. 


Helminth infections in livestock are one of the most important productivity limiting problems found in our world today.  The switch from determining whether herds have the presence of infection to detecting its impact on productivity will help farmers make important decisions on when to treat creating less issues with resistance, and create more effective control strategies