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Dairy Today Healthline

Don’t Open a Can of Worms

Jun 24, 2013

Producers seeking to reduce heifer-rearing costs with pasture should be mindful of the negative effects of parasitism.

Van Dyke 20small[1]By Tom Van Dyke, DVM, Manager of Veterinary Services, Merial

Dairy producers need the improved genetics and production of replacement heifers in the milking herd as quickly and efficiently as possible. Increased age and reduced weight at first calving carry the dual penalties of higher production costs and lower lifetime milk production.1 Producers seeking to reduce heifer-rearing costs with pasture should be mindful not to open up a "can of worms."

Younger animals, such as calves and replacement heifers, are most susceptible to negative effects of parasitism. 2 Heavier heifers at calving will produce more milk during first lactation than their lighter cohorts, so heifers are generally bred by weight rather than age. 3

On the other hand, delayed calving can dramatically increase rearing costs – as much as $50 per heifer for each month beyond 24 months.1,3 Accelerated growth rates needed to meet age and weight targets can be attained on pasture, but pastures must be managed intensively to achieve maximum forage quality and minimum parasite exposure.2,3 Gastrointestinal worm infections, even at a subclinical level, can delay time to first breeding and impair first lactation milk production. 4 Producers must think strategically to reduce the parasite population and prevent losses.2

Unfortunately, producers don’t always include parasite control into their grazing management plan, even though the two should be closely tied.2 The ultimate goal of a deworming program is to reduce the parasite burden on the pasture for as much of the grazing season as possible. 2 To break the recycling of pasture worm infestations, and significantly improve Average Daily Gain, multiple dewormings with conventional products have been needed.2,4 Producers using long-acting products could also benefit from reduced labor costs and animal handling. 2,5

Average Daily Gain and Age at First Calving are crucial measures of a successful heifer replacement program. Producers developing heifers on grass must take the steps necessary to ensure the pasture provides abundant high-quality forage with minimal parasite exposure all season long. Only with attention to both will cost savings and production improvement approach full potential.

About Merial
Merial is a world-leading, innovation-driven animal health company, providing a comprehensive range of products to enhance the health, well-being and performance of a wide range of animals. Merial employs approximately 6000 people and operates in more than 150 countries worldwide. Its 2012 sales were $2.8 billion. Merial is a Sanofi company. For more information, please see

©2013 Merial Limited, Duluth, GA. All rights reserved. RUMILGN1310 (5/13)

1 Van Amburgh M. Tikofsy J., The Advantages of "Accelerated Growth" in Heifer Rearing, Advances in Dairy Technology. 2001;13:79-97.

2 Williams JC, Loyacano AF. Internal parasites of Louisiana and other southern states. LSU Ag Center Research and Extension Research Information Sheet #104, 2001.

3 Looper M. Bethard G. Management Considerations in Holstein Heifer Development, College of Agricultural, Consumer and Environmental Sciences New Mexico State University, Guide B-118.

4 Elsener J. Villeneuve A. , DesCôteaux L., Evaluation of a strategic deworming program in dairy heifers in Quebec based on the use of moxidectin, an endectocide with a long persistency, Can Vet J. 2001;42:39-44.

5 Shultz T, E. Huffman EM, Baker N.F., Sustained-release bolus for deworming dairy heifers. California Agriculture.1988.

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