Parasites have long proven their ability to overwinter in pastures - especially mild winters, such as this year's. Young stock - dairy and beef calves, yearlings, and first-calf heifers - don't have the tolerance of older animals to internal parasites, warns Dr. Donald Bliss, president of MidAmerica Agricultural Research, Verona, Wis.
"The key is to deworm when we get the greatest benefit," says Bliss. "In the late fall, we deworm to 'clean up' before winter. In the spring, we deworm to reduce environmental contamination."
Dairy calves, heifers and beef stocker/feeders require a more aggressive strategy because worms shed eggs earlier when their host is a younger animal. "Dairy replacement heifers, for example, can lose 50 to 60 pounds of potential gain over a summer when they are infected by parasites," observes the veterinary parasitologist.
Cows infected by parasites lose an average of nearly 6.5 pounds of milk/cow/day. He calculates that it amounts to $3,000 per month in lost income for a 150-cow herd at $12 milk.
Here's the strategy Bliss recommends:
- If cattle were dewormed in the fall, then spring deworming should occur as follows:
- Mature cows - five to six weeks after grazing start;
- Calves, heifers and stockers - three to four weeks into grazing, plus a second deworming three to four weeks later.
- If cattle were not dewormed in the fall, treat at the start of grazing, and follow-up using the previous recommendations.
- To avoid developing resistance, continue using pour-on avermectin products. Injectables and pour-ons work through the bloodstream.
"We're seeing resistance occur when pour-ons fail to deliver consistently high enough blood levels to the gastrointestinal tract," Bliss explains. The result is inconsistent and incomplete kill and build up of resistance within surviving worm populations.
Contact your animal health or nutrition representative to learn more.