Parasites threaten dairy heifer health and productivity

Pasture-raising heifers can offer significant feed cost savings, but these animals may have a new friend from the wrong side of the tracks … or grass, in this case. Millions of parasite eggs are deposited on grazing pastures every year. The moment dairy heifers hit even a well-managed pasture, parasites pose a significant health threat.

Parasite infections can manifest as poor productivity, including reduced feed intakes, slower growth rates, delayed breeding, decreased milk production and depressed immune responses.

A fall deworming program can be an option for producers looking to manage the health of the animals exposed to internal parasites, as well as eliminate any external parasites as they overwinter. As producers transition their herds off pastures this fall in preparation for winter, there are many reasons to consider a fall deworming program.

Pastures increase risk of exposure to parasites

Pastures are a primary cause of exposure to internal parasites, as they are transmitted through grazing practices. When an entire herd is put on pasture, that exposure builds up fast.

“When the worm larvae are already in the stomach of the heifer, they will mature and start laying eggs through the feces that end up in the pasture,” explained Dr. Stephen Foulke, DVM, DABVP, Boehringer Ingelheim. “The eggs hatch and develop into larvae. When the heifer grazes and swallows that larvae, they are back in the stomach. The larvae matures, becomes an adult and starts the whole cycle all over again.”

According to Foulke, nearly 90% of the parasite eggs are actually in the pastures. Through the animal’s feces, millions of eggs are left on the ground during each life cycle.

“When animals are confined to the same pasture, the parasites’ eggs are continually dumped on the ground, and then they’ll start building up,” said Foulke. “If pastures aren’t properly managed, or if animals are confined to a smaller space on the land, the heifers are going to start eating the grass down, and will start eating closer to the fecal pats. This increases the chance they have to get exposed to more worms.”

How parasites impact heifer health

Internal parasites can affect the animal’s ability to digest, which can reduce feed efficiencies and how they utilize their nutrients. This can result in repercussions that diminish their overall health, such as decreased average daily gains, decreased milk production and decreased immune function. External parasites can cause irritation, pain and itching with the potential to cause loss of fluids and blood.

Consider fall deworming practices

As we approach winter after the first hard frost, internal parasites go into hibernation in the ground and in the animal. This is an opportune time to manage the heifers exposed to parasites in pastures before they overwinter.

“The heifers will not have any more exposure to the parasites, so it’s a great time to clean them out internally for the winter,” said Foulke. “We’ll deworm them in the fall because we don’t want any lingering worms causing damage. We also want to watch for lice once the animals start coming indoors. I often recommend a product that manages both internal and external parasites.”

Administering the correct dose

Properly dosing a dewormer requires the right timing and knowing the animal’s weight. Although convenient, dosing to the average weight of the herd will under- or over-dose many animals. With under-dosing, the potential for resistance to the dewormer can come from the parasites being exposed to non-therapeutic levels. Under-dosing will diminish effectiveness of the dewormer, while over-dosing wastes product and money. Using a scale, weight tape or a cull-weight slip to determine a heifer’s weight will increase dosing accuracy, along with product efficacy.

Managing parasites in your region

Another thing to keep in mind to help your deworming practices succeed is to realize these parasites aren’t going to play the same game on every operation.

“There’s not going to be one best program for everyone, because parasite challenges will vary by region,” stressed Foulke. “Your veterinarian is going to know your local situation and what the major parasites are in your area. They can help direct and steer your program to be more specific to your operation.”

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