Coccidiostats and coccidiosis

If a coccidiostat can be fed incorrectly, it will be fed incorrectly. How can calves and heifers still have coccidiosis when you are feeding them a coccidiostat?! Pointers for avoiding costly coccidiosis situations.


Coccidiosis is the name we give to the disease caused by coccidia. Coccidia are microscopic parasites. There are at least thirteen different species that infect cattle. The two most common ones that cause coccidiosis in heifers are Eimeria bovis and Eimeria zuernii.

Coccidia eggs called oocysts are present on nearly every dairy farm. They are very hardy. Extremes of hot and cold don’t kill them. Many of them survive when disinfectants are sprayed on calf hutches and in barns. It is extremely difficult to prevent exposure to any coccidia. Good sanitation procedures can substantially reduce the numbers of coccidia to which heifers are exposed.

By one way or another heifers get the coccidia eggs or oocysts in their mouths. The oocysts open inside the intestines and multiply. This growth damages the lining of the intestine. The immune system’s ability to fight off other diseases is depressed. Efficiency of feed conversion is lowered.

Coccidiostats *

Coccidiostats are chemicals commonly added to calf feeds. They control the growth of coccidia inside the heifer.

In order to be effective the heifer must consume them. In addition, the coccidiostats must be consumed at a rate related to the body weight of the heifer. As the heifer grows the amount eaten must increase in order to effectively control coccidial growth. Also, they must be fed daily. They do not have a residual effect that carries over from day to day.

Enter Murphy’s Law

Murphy’s law states that if anything can go wrong, it will. Examples are (1) if a gate can be left open, it will be left open; (2) if a milk transfer pump motor can burn out, it will burn out (at 5 AM on a Sunday morning); (3) if a coccidiostat can be fed incorrectly, it will be fed incorrectly.

How does Murphy’s law apply to coccidiostat use? First, the heifers must consume the coccidiostat for it to control coccidial growth.

Young calves commonly have a consumption problem. They are not yet eating very much medicated calf starter. Frequently the feed medication level requires starter consumption well in excess of a pound or quart per day for minimal control. These young calves need another source of coccidiostat to prevent coccidiosis. The most common solution is to medicate the milk or milk replacer.

Post-weaning calves are another group with consumption problems. Often as they move into group housing the feed is changed, too. It’s common for these heifers to have depressed feed intakes for three to seven days. Even if the medication is in the ration at the proper level, uneaten feed can’t provide coccidial control. Avoid changing housing and feed at the same time.

Second, the heifers must consume the coccidiostat every day for continuous control of coccidial growth. Breaks in medication allow newly ingested oocysts to establish themselves in the gut and allow maturing coccidia to multiply.

The most important rule in using coccidiostats is to always keep extra on hand. Also, if using a milk replacer medicated with a coccidiostat, always check when a new supply is delivered. Be sure that the “medicated” product actually contains the coccidiostat rather than an antibiotic additive. If a TMR is being fed, talk with the person running the feeding equipment. He or she needs to know how important it is that the coccidiostat is added every day. And, that includes his or her day off when a substitute is doing the feeding.

Third, the heifers must consume an adequate amount of coccidiostat in relation to their weight for effective control of coccidial growth.

Among preweaned calves the medication rate for liquid feed is often set for the youngest and smallest calves. If the same quantity of milk or milk replacer is fed to all calves regardless of size, then, as calves grow, the chance of under-medicating increases. The same risk is present among older heifers, too. The medication rate in a grower pellet is often set for the amount fed to two or three hundred pound heifers. If the same quantity of medicated grower pellets continues to be fed regardless of size then as heifers grow the chance of under-medicating increases.

* Coccidiostat is used here to refer to products that either kill or slow the growth of coccidia.

Stress & Coccidiosis

We have all heard the same story. These heifers (one to six months old) have coccidiosis. How can this be? I am feeding a coccidiostat. Look, right here (milk replacer tag, calf starter grain bag, TMR ration mixing sheet). See. I am doing things right. They can’t have coccidiosis.

The Impossible Can Happen

It’s always a good thing to just check on coccidiostat feeding rates before deciding that the impossible has happened. These are weight:dose additives. Bigger heifers need more coccidiostat. Often the “impossible” is traced back to underfeeding the control drug.

It’s always a good thing to just check that all the heifers are consuming the coccidiostat. If it’s in milk replacer, a calf that has not been drinking may be at risk because of this. If it’s in the calf starter, a calf that’s off feed may be consuming too little drug to do the job. If it’s in a TMR fed at a bunk some heifers may not be eating enough TMR. This is especially common when pens are overstocked even if the pen is never out of feed.

Well, I checked all of that stuff and they still have coccidiosis. And, it’s bad. Look at all that loose manure. Look at them, they have rough hair coats. Look at those dirty, smelly rear ends. The impossible has happened.

The Impossible Has Happened

The impossible did happen because we overstressed these calves or heifers. Preweaned calves may have been overstressed because we failed to feed enough to meet their needs for maintenance and growth. Or, we fed a poor quality milk replacer. Or, we tried to wean them without be sure they were rumen competent. Or, (fill in the blank).

Transition heifers may have been over stressed because we changed too many things at once. Stacking stresses is a common cause of coccidiosis outbreaks in heifers being fed normally adequate amounts of coccidiostat. Changes in feed and housing too often are piled on top of vaccinations and/or overly rough handling.

Overstocking of transition pens may result in uneven consumption of both the TMR and the control drug. When there is too little space for all the animals to eat at one time uneven consumption among transition age heifers is almost certain. This is especially common where calves are weaned in a lock-step manner by age. Often there is a big size difference among calves in a single pen. The bigger pushy ones bully weaker, shy heifers. Even when there is adequate feed available in at a too-small feed bunk these shy heifers have been dominated so much they hesitate to spend an adequate amount of time eating. These smaller heifers get stressed because they are barely meeting their maintenance needs. They often have subclinical pneumonia as well leading to even more stress.

Prevent the Impossible

Check out the sources of stress for your heifers. A stressed out heifer is a prime candidate for coccidiosis regardless of your coccidia control program.

Calf Feeder’s Tip

Not all of us are inside during windy winter storms. Many of us have outdoor hutch housing. Most of us experience strong winter winds. And, it’s not nice to discover hutches in the neighbor’s hedgerow or dooryard when we arrive in the morning. At least two nearby farms have taken to parking large equipment on the windward side of their hutches in the winter. Big ten-wheeler trucks are a great windbreak. Other pieces of infrequently used large equipment that can stand exposure to the weather work well also. One heifer grower stores the winter supply of wrapped bales of straw on the windward side. Windbreaks don’t have to be trees.


Offhaus Farms

Offhaus Farms

Batavia, NY

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