Managing Parasites In Cattle

It doesn’t matter whether you do management-intensive grazing or simply let your cows take advantage of the spring flush, one thing is for certain – parasites are enjoying the pastures also.

The parasites which do the most damage to your cows’ health are the common stomach worms. These worms have been hibernating in the stomach lining all winter long. They can sense it is now the right time to emerge and come back to life. Perhaps it is the green grass being re-introduced into the stomach, perhaps the different enzymes at work to digest fresh grasses, perhaps different internal ph or different microbial activity in the rumen. No one knows for sure actually. BUT, it is well known that youngstock are most susceptible to infestations and true health problems such as anemia due to the worms sucking blood from the animal, weight loss and decreased immune capabilities. It is basic biology.


1)     Worm your youngstock (and horses for that matter) so they don’t “seed” your pastures with their worm-infested manure. Note: At this time of writing, the new proposed Federal rule for the National Organic Program will permit therapeutic worming of young dairy animals if the need is proven by a simple fecal test. This is NOT yet in place and if you are certified, check with your certifier. (PCO does not currently allow worming of any animals, without taking the animal out of organic production.)

2)     Don’t follow cows with youngstock through your pastures. Adult cows can live “in balance” with worms in general, but they will still potentially shed eggs and larva which youngstock can easily pick up if grazing the paddocks cows just went through.

3)     Allow at least 21 days until you put animals back in the same paddock. Eggs and larva deposited with manure need to be re-ingested within 21 days or they will die in general.

4)     If you know that you cannot wait 21 days before re-grazing a paddock, clip your pastures. This will (a) splatter out manure paddies, allowing the drying action of sun and wind to kill worm larva, and, (b) help to have uniform re-growth of the paddock.

5)     In no obvious infestation or signs of worm burden in your animals (it’s always best to check the manure under the microscope!), then use approximately 10 pounds diatomaceous earth (DE) per ton of grain mix. Note: I have found DE to be totally ineffective for worm control in horses (by fecal samples run by the state and me).

Practical tips: Do not graze your paddocks to less than 3” high. This is your reserve for stress times and will respond if allowed. Also, consider planting Sudan grass in late May for July/Aug grazing. Not great nutrition but grows when other local grasses won’t.

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