Follow five principles to control parasites in heifers

If you plan to turn your replacement heifers out on pasture this summer, don’t overlook the importance of deworming. Most dairy farms have room for improvement when it comes to parasite control programs in heifers.

Monitoring for internal parasites and removing them when present helps heifers get the nutrients they need to grow and develop at the proper rate. Treating heifers with an effective dewormer reduces parasite load when they enter the milking string or move back into confinement in the fall.

When parasites are controlled, heifers convert feed more efficiently, have fewer disease problems, and have more efficient reproduction.¹

Follow these five key principles for an effective parasite management program in dairy heifers:

1. Test feces for internal parasites.

Don’t guess whether internal parasites are present or not. Instead, use a fecal egg count (FEC) to determine if deworming is needed. FECs are both inexpensive and easy to perform.

Female worms inside the digestive tract of the animal lay eggs, which are passed in the feces. A FEC examines a fecal sample under a microscope to determine the number of eggs present.

For dairy heifers entering their first lactation, and particularly for those that are entering confinement (that is, no longer grazing pasture), any FEC result above zero means that adult worms are present. Deworming at this time is almost always recommended.

Ideally, the deworming treatment should be followed up with a Fecal Egg Count Reduction Test (FECRT). See details under “Measure deworming success” below.

2. Find the best times to deworm.

When heifers come off grazing to enter confinement, it’s a great opportunity to deworm because they won’t be on pasture again and re-exposed to parasites. Both grazed and non-grazed heifers should be dewormed just prior to entering the milking string.

Keep in mind that any time adult cows are exposed to pasture, they likely should be dewormed when they re-enter confinement. Pasture-based grazing dairies should work with their veterinarian to develop a parasite control strategy.

3. Choose effective dewormers.

Dewormers in the benzimidazole and macrocyclic lactone classes are the most widely utilized for cattle. Macrocyclic lactones are available as pour-on or injectable forms, while benzimidazoles are typically administered orally.

To keep existing dewormers effective and keep resistance to a minimum, dairy producers using a dewormer that ends in “-ectin” should consider adding another product where the active ingredient ends in “-zole,” such as fenbendazole.

No matter what product is chosen, accurate dosing is critical – not only to give the anthelmintic the best chance of working effectively, but also to help reduce development of resistance. When animals are dosed based on the average weight of the group, approximately 50% of the animals will always be underdosed. Ideally, animals should be weighed. When this is not possible, the weight of each animal should be estimated individually and the correct dose of dewormer administered.

In an operation where heifers are grazing throughout the summer, feed formulations of dewormers – including pellets, cubes, or free-choice mineral – are easy and highly effective ways to deworm.

4. Measure deworming success.

The only way to determine the effectiveness of your deworming program is through a Fecal Egg Count Reduction Test (FECRT). The FECRT protocol consists of taking samples from the group of interest on the day of treatment and then sampling from the same group again 14 days after treatment.

Pretreatment and posttreatment samples are sent to the same lab and tested to determine fecal egg count reduction. Ideally, 20 pre- and post- samples are taken. It is not necessary that the samples come from the same animals. An absolute minimum of eight samples is necessary to ensure that the conclusions drawn from the results are likely to be correct.²

Successful deworming should result in a 95% or greater reduction in parasite eggs in feces.  At minimum, a 90% or greater reduction should occur if the dewormer is effective.³ If the result is below 90%, the reason why should be investigated with the help of your veterinarian.

If improper dosing is ruled out, resistance could be at play – which means it’s time to change your protocol. You can request a free FECRT kit from your Merck Animal Health representative or by clicking here.

5. Monitor for parasites regularly.

Work with your veterinarian to set up an internal parasite control program that works best for your operation. You may decide that FEC testing every six months is necessary, but it should certainly be no less than once a year.

If your veterinarian recommends strategic deworming based on your heifers’ exposure to pasture, be sure to incorporate FECRT testing annually to measure the effectiveness of your program. Learn more at SafeGuardWorks.com.

 

References:

1. Mejía M, Perri A, Miglierina M, Formía N, et. al. Effect of anthelmintics on reproductive performance and first-lactation culling rate in Holstein heifers. The Veterinary record, 165(25), 743–746 (2009).
2. Kaplan R, Denwood M, Nielsen M, Thamsborg S, et al. World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) guideline for diagnosing anthelmintic resistance using the faecal egg count reduction test in ruminants, horses and swine. Veterinary parasitology, 318, 109936 (2023). Advance online publication. https://doi.org/10.1016/j.vetpar.2023.109936.
3. Dobson R, Jackson R, Levecke B, Besier B, et al. Guidelines for fecal egg count reduction tests (FECRT). Proceedings: 23^rd International Conference of the World Association for the Advancement of Veterinary Parasitology (WAAVP) (2001).

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