Raising dairy heifers on pasture can offer significant feed cost savings, but these animals may have a heightened risk of internal parasites. Parasite infections can manifest as poor productivity, including reduced feed intakes, slower growth rates, delayed breeding, decreased milk production and depressed immune responses, according to Boehringer Ingelheim.

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, Boehringer Ingelheim said. As producers transition their herds off pastures this fall in preparation for winter, there are many reasons to consider a fall deworming program.

Pastures are a primary cause of exposure to internal parasites, which 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 with Boehringer Ingelheim. “The eggs hatch and develop into larvae. When the heifer grazes and swallows the 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,” Foulke said. “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.”

Heifer health

Internal parasites can affect the animal’s digestion ability, which can reduce feed efficiency and how the animals 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, Boehringer Ingelheim said.

Approaching 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,” Foulke said. “We’ll deworm them in the fall because we don’t want any lingering worms causing damage.”

Properly dosing a dewormer requires the right timing and knowing the animal’s weight, he added. Although convenient, dosing to the average weight of the herd will underdose or overdose many animals. With underdosing, the potential for resistance to the dewormer can come from the parasites being exposed to non-therapeutic levels. Underdosing will diminish effectiveness of the dewormer, while overdosing 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.

Regional plans

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

“There’s not going to be one best program for everyone, because parasite challenges will vary by region,” Foulke stressed. “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.”