Spring parasite control — while ultimately helping to protect herd health and performance — is more about reducing levels of pasture contamination than curing sick animals.
“Only 5 percent to 10 percent of parasites in the total system are actually in cattle at any given time,”1 explains Dr. Frank Hurtig, director, Merial Veterinary Services. “A single cow can pass millions of parasite eggs during the grazing season,1 which is how the remaining 90 percent to 95 percent of parasites end up on pastures — set to infect grazing cattle.”
Targeting parasites in the spring hits parasites at a key stage in their life cycle and helps keep cattle from becoming parasite factories,2 he explains. This reduces the number of parasites on pastures and helps producers proactively avoid losses or reduced productivity.
“Many cattle producers only control parasites at the end of the grazing season. But at that point we’ve already lost growth and productivity, and contaminated the pasture with even more parasites,” says Dr. Bert Stromberg, parasitologist and professor, University of Minnesota. “If producers are only going to treat once, it should be at spring turnout.”
Northern producers may skip a spring treatment because they mistakenly believe a cold winter has taken care of parasites for them, or that one fall treatment is enough to protect cattle all year, Dr. Hurtig says.
“Parasites can and do survive the winter on pastures,”1,2 Dr. Stromberg says. “If producers are under the impression that they solved their parasite problem with one treatment in the fall, they will miss the parasites that are present on pasture as cattle enter the grazing season.”
Research in Oregon found that parasites were transmitted even during freezing temperatures.3 And those not picked up during the winter can survive to spring. A blanket of snow helps survival,4 Dr. Stromberg notes. It insulates parasites and is like putting them in the refrigerator — which is exactly where he keeps his live specimens for research.
“Parasites such as Ostertagia, also known as the brown stomach worm, effectively survive the winter in an inhibited juvenile state in the lining of a cow’s stomach,5 but they also can burrow into the soil where they are protected from severe temperatures,”2 Dr. Hurtig explains. “When warm weather arrives, infective juveniles migrate onto the grass where they are picked up during grazing.”