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Small and undergrown heifers with loose stool and a rough, dry hair coat are unsightly to many dairy producers.  These clinical signs, though not specific to, are indicators of possible coccidiosis infection (invasion of coccidia in the gastrointestinal (GI) tract) within a group of young heifers.

Coccidia, a type of protozoan parasite that lives inside its host cells, is passed between animals via fecal-oral contamination. Infected cattle shed coccidia oocysts (eggs), which then sporulate (become activated) in the environment and infect other cattle when ingested.  Oocysts can be found in the pen environment, contaminated feedstuffs, water and hair coats.

When a calf is exposed to and ingests coccidia oocysts, the oocysts invade cells that line the lower small intestine, reproduce, and then infect cells farther along in the lining of the GI tract.  In a complex cycle of reproduction, coccidia possess the ability to invade and re-invade host cells until another generation of oocysts mature and exit their host cells, causing cells to rupture and die.   

Because this parasite causes host cells to rupture and die, it’s easy to understand how a coccidia infection can impair intestinal integrity to a degree that decreases the GI tract’s ability not only to absorb nutrients, but also to protect the calf against other environmental pathogens.

One study (Walker et al. 2015) showed coccidia’s ability to reduce gene expression that regulates tight junction proteins in the cecum of calves 28 days post-infection.  These tight junctions are responsible for selective uptake of beneficial molecules and ions along the GI tract.  They also prevent entry of opportunistic bacteria, such as Salmonella.  Leaky tight junctions along the GI tract further contribute to dehydration, malabsorption of nutrients, and other pathogens’ abilities to invade the gut.

Calves are at an elevated risk for developing severe coccidiosis infections during the winter months or this year’s unusually cold spring.  Moisture and cool weather are conducive to sporulation.  The combination of cold weather, which increases stress, plus high loads of coccidia can manifest as severe diarrhea and dehydration or nervous coccidiosis, both of which can increase mortality rates in calves and heifers.

Be sure to include your nutritionist and veterinarian in any conversations regarding prevention, control, and treatment of coccidiosis.  If you are suspicious of coccidiosis, have your veterinarian collect a few fecal samples to confirm a diagnosis.  Even if their diets already contain an ionophore, such as monensin or lasalocid, it is possible for calves to develop coccidiosis infections, especially if exposed to large numbers of oocysts in the environment.  Your nutritionist will help make sure the ionophore levels in the diet are safe for the size of group and age of cattle being fed, while a veterinarian can give guidance as to what additional medications and supportive treatments, such as fluid therapy, are appropriate for severely affected calves.

With coccidia’s ability to invade the host, especially during times of stress, prevention is often the best and most cost-effective medicine.  Management practices, including cleanliness and high-quality feed, are considered as important as preventative use of ionophores to control coccidiosis in calves.

The value of providing adequate fresh and clean bedding to calves in a facility with good air quality that prevents cold drafts cannot be overstated.  Avoid allowing manure build-up, feeding on the ground, feed and water contamination by manure, and overcrowding, all of which can increase the amount of coccidia oocysts to which the calf is exposed.  These practices, when combined with a solid nutrition program to fuel the calf’s immune system, are often the best strategy for preventing coccidiosis and other diarrhea-causing diseases.

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