Once cattle are turned out on spring pasture the parasite clock starts ticking. Left unchecked, it's just a matter of time before your cattle are loaded with profit robbing parasites. The only way to stop it is with a strategic deworming program that cleans your pastures and your cattle of parasites.

Clean pastures are key to stopping parasites from robbing production efficiency and profits from your herd. Deworming will clean out the parasites in your cattle, but without parasite safe pastures they will continue to reinfect themselves over and over.

"The pasture is absolutely crucial in a parasites' life cycle," says Don Bliss, consultant at the Mid America Ag Research Center in Verona, Wis. "A cow may only pick up one larva, but if that one larva doesn't get killed, it will start laying thousands of eggs. If you can keep that multiplication from happening on the pasture, then the animal can stay fairly parasite free."

Safe pastures

Because a pasture never can be truly free of all parasites, the term parasite safe pastures is used. This means that you have minimized the parasites on grass that are available for your cattle to pick up. Often, in a parasite safe pasture the second year of treatment has greater benefits than the first. After the first year, parasite levels are so low that they are easy to control. But if you stop deworming they will reappear the next year.

"Say you run a few stockers and you've got plenty of grass, so you decide to bring some more cattle in," explains Dr. Bliss. "What I'd do is deworm those new cattle and kick them out on the pasture with the rest of the herd. I don't have to worry about deworming them again because I've already cleaned the pasture with my dewormings of previous cattle. To me, that's a parasite safe pasture. I can let dewormed cattle eat the grass, and they are not contributing or picking up parasites from the pasture."

Life cycle

In order to keep your cattle and the grass parasite free, use a strategic deworming program. This will break the vital life cycle that allows parasites to multiply and infect your cattle.

Strategic deworming is nothing more than using the parasites' life cycle to time dewormings to keep pastures parasite safe. "Parasites really have a tremendous ability to survive on pasture," says Gerald Stokka, extension veterinarian at Kansas State University. "You can't rely on the cold of winter to kill off the parasites for spring grazing. With strategic deworming you estimate the time from when the cows are picking up larvae, the larvae develops into an adult and the cow's shedding eggs. By hitting them at the right time with a dewormer, there won't be as many eggs shed-and ultimately larvae-to pick up on the pasture."

It's important to remember that a parasite lives two lives - one inside your cattle and one outside. The outside life begins as a first stage larva (L1) develops within the egg, then hatches. The developing larva passes through two growth and molt cycles (L1 to L2 to L3). The L3 stage is the infective stage for cattle. Cattle become parasitic when the L3 larva is ingested, molts to an L4 (fourth stage) then to an immature adult (L5), which then matures into an adult. The adult then sheds its eggs, which cattle redeposit onto pastures in their manure pats. This restarts the life cycle. But infection does not occur by the ingestion of fresh feces from an infected host. The eggs are not infectious at that point, rather most must develop to the infectious L3 stages outside the host and be picked up on blades of grass.

Strategic timing

"It breaks down to the simple fact that parasites survive on pasture year to year," says Dr. Bliss. "The key is that you don't want cattle shedding eggs at the beginning of the season. When grass starts to grow you want clean cattle. Infected cattle will only keep reinfecting pastures."

Cows will usually start to shed eggs about 40 days after they're out on those spring pastures. That's when you want to treat again. For younger stock it's a little quicker. "If you don't do this part right, you'll contaminate your pastures," Dr. Bliss says. "And then you'll always have those problems."

If you miss the timing by 4 or 5 days you can put millions of eggs on a pasture. Dr. Bliss suggests writing on a calendar the exact day you want to deworm so you don't spoil the pasture. If you turnout May 1, write down that you'll treat cattle on June 15, then try to get within only one or two days of that.

The best strategic deworming program involves two dewormings a year-one in November and another six weeks after spring grazing turnout. The deworming in November will keep cattle clean until March and April. If you start grazing April 1 and you treat again six weeks into the grazing season (May 15), you can stop that cycle and the earliest cows can be shedding eggs again is the first of July. By then, any eggs that go down on the pasture in July and August won't fully develop because it's too hot. Their development will be delayed until September or October, and since you're going to deworm again in November, you've stopped the parasites for the year.

"You let the cow work like a vacuum cleaner," says Dr. Bliss. "As the grass starts to grow in spring, she's going to pick up all the parasites that survived the winter. Just as those worms are maturing and starting to lay eggs and repopulate the pasture, we terminate that infection. That means that the cow has to go out and eat more larvae to start the cycle over again. By never allowing her to shed eggs, we minimize the parasites she can pick up on the pasture."

The hard part is to not be tricked by the grass. You may receive a little grass growth, then nothing will happen for weeks. You want to start timing when the grass starts its steady growth pattern, then deworm six weeks later.

Cost effectiveness

Young cattle will shed eggs much faster than old cows. For this reason you need to deworm them an extra time. So rather than a single mid-spring deworming, you need to deworm three to four weeks after turnout and again three to four weeks after that treatment.

The reason young animals shed eggs faster is because old cows build up immunity to internal parasites. These antibodies work much like a vaccine does. For this same reason, some producers do not deworm their older cows.
"There has to be a cost benefit to deworming adult beef cows," says Dr. Stokka. "And there has been some debate on whether deworming adult beef cows pays. In areas with more acres per cow-calf unit that don't get much rain, you may want to weigh out the cost."

Dr. Bliss agrees. "Because adult cows are immune to parasites you can do therapeutic treating where you let the animal build up a load and then treat if they need it," he says. "But when you're trying to clean up a pasture, that cow becomes very important because she becomes a source of infection for that calf."

Because parasites depend on a host for survival, the cow adds to how many larvae are allowed to complete their life cycle and multiply. That means that more are available for the calf to pick up. Using a strategic deworming program creates a parasite safe pasture for all ages of cattle and will pay off in production efficiency and profits for your whole operation.