Parasites can rob heifer growth

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If the goal with a beef or dairy heifer is put a certain age and weight on them to prepare them for first breeding and conception, don’t let your clients throw a wrench in the whole works by ignoring the damage parasites can do to the process.

According to the USDA National Animal Health Monitoring Service (NAHMS) Beef 2007–2008 study, about 70% of operations dewormed beef replacement heifers one or more times per year. However, almost 25% of operations indicated they never dewormed weaned heifers.

On the dairy side, the NAHMS Dairy 2007 study indicated that nearly 70% of operations dewormed dairy heifers, however, only about 55% of heifers were actually dewormed.

Fortunately, calves aren’t born with parasites nor do they transmit through the milk, with the possible exception of Strongyloides which has been found in nursing beef calves as young as 2 weeks of age, though they seem to disappear from the calves fairly quickly after that.

Health impact on heifers

Pastured, Ostertagia is almost always a potential problem and the prevalence is pretty much throughout the country, according to Bert Stromberg, PhD, University of Minnesota. The NAHMS survey also found Haemonchus, Nematodirus and Cooperia. Each may have its own unique impact.

“We generally think of Haemonchus as not being too much of a problem in cattle compared with sheep,” he explains. “Nematodirus may have significant impact on growth and productivity. Cooperia, I believe, has impact on the small bowel, causing thickening and decreased absorption, causing reduced intake and reduced ADG.”

Beef heifers deal with the same parasite species as dairy heifers, however the difference is that beef are on pasture from the start and thus exposed to what is on the pasture.

As soon as we begin to impact the animal with parasites, stress then modifies the immune response, Stromberg continues. “We direct the immune response toward the parasite (helminths) and a Th2 response. This down regulates the Th1 response and the host’s response to viral vaccines. All of these slow growth down. We need to grow optimally for that first calf.”

When to deworm heifers

Timing means a lot in a young, growing animal. Stromberg says when to deworm dairy heifer depends on when they will first be exposed to parasites. “Assume they are removed immediately to a hutch so the only parasite control at this point is probably an anti-coccidial,” Stromberg explains. “Even if they are moved to super-hutch housing there should be no access to parasite infection. However when they have access to pasture, they have access to worms, so the age is variable.” This is true for helminths, flukes and tapeworms (Moniezia).

How often dairy heifers should be wormed is based on access to pasture and time of the year or pasture status. “I like to deworm when they go out onto pasture — spring in the North or newly growing pasture in the South,” Stromberg suggests. “My druthers would be to deworm again in eight to 12 weeks to produce a well-conditioned calf.” Stromberg says every eight to 12 weeks for beef heifers is also optimal.

For beef heifer calves, Stromberg also deworms them based on access to pasture. “We found that calves performed as well if we dewormed them eight weeks after turnout as compared to when dewormed at turn out and eight weeks later. It was also important that the dams were dewormed, this helps keep a clean pasture.”

Stromberg uses beef cattle in Minnesota as an example. On pasture at turnout there is little parasite problem, but there are some that survived on the pasture or in the cattle, so the numbers start to build. “This is the reason that it is important to deworm the adult cows to reduce parasite contamination for the young calves as they begin to sample the grass,” Stromberg recommends. “This delay in becoming infected is why I suggest that we can wait to deworm until eight weeks on pasture. Another deworming may be beneficial as we approach the end of the grazing season and again at turn out next spring. Keep the heifers parasite free as we approach breeding.”

Some who are raising stockers/replacements deworm too many times (3–5) in order to sell a heavier calf, Stromberg notes. Deworming too frequently raises the spectre of inducing resistance.  “While it may produce a heavier calf it may also select a worm population that is no longer susceptible to the dewormer,” he says.

“There are still some producers who put their replacements on the back pasture and forget about them until they need replacements, and are often surprised that none are of breeding size” Stromberg summates. “Replacements should be treated as an investment and vaccinated and dewormed accordingly.” 



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