By Matt Akins, Ph.D., Extension Dairy Specialist and Associate Scientist, University of Wisconsin-Madison, Department of Animal and Dairy Sciences, and Division of Extension
Dairy calves and heifers are a critical piece of dairy herd productivity as they are the future lactating cows. Heifer health is generally less of an issue than with dairy calves, with typically less respiratory and digestive problems. However, calves and heifers can have significant incidence of disease especially during stressful events/changes such as adjusting to grouping or new diets, or after transportation to another location which causes stress and exposes heifers to new pathogens.
Coccidiosis is one digestive disease in dairy heifers that often occurs during these stressful events, especially if the heifer had not been previously exposed to the coccidia protozoa species of Eimeria bovis or Eimeria zurnii. It is most often found in calves and heifers from 1 month to 1 year of age. The protozoa can be prolific in facilities with poor cleanliness, use of bedded pack management, or inconsistent feeding additive (coccidiostat) usage across pens. Before getting into how operations can control the disease, you should understand how the protozoa’s lifecycle works. Figure 1 shows the Eimeria lifecycle in a simple diagram. The Eimeria lifecycle starts off similar to other digestive parasites with the animal consuming the protozoa egg or oocyst. This consumption is by various routes including eating contaminated feed, bedding or water; grooming themselves or other animals; or licking their contaminated surroundings (walls, gates, feeders, etc.). The oocyst has a very protective outer wall that resists breakdown from chemical and physical action, and can be viable in a moist, warm environment for several months to years. After consumption, the oocyst then releases the infective ‘sporozoites’ which enter the animal’s small intestinal cells to replicate and form ‘merozoites’. After a couple replication cycles in the small intestines, the ‘merozoites’ sexually reproduce in the large intestine to then form oocysts. Oocysts are then excreted in the feces and restarts the cycle. This cycle is continuously occurring as animals are ingesting oocysts daily. The typical complete lifecycle is 15-20 days so there is a delay of about 2-3 weeks from ingestion until you may see clinical symptoms.
Symptoms are dependent on the ingested parasite load with a small portion of cased typically being clinical. Sub-clinical infections are more prominent but can affect feed intake and growth, so minimizing parasite load is critical to reducing these impacts. When ingested parasite loads are high or heifers are under stress, clinical symptoms can become more common. Reduced feed intake, diarrhea and condition loss are the common symptoms commonly associated with coccidiosis. Growth is also severely depressed when clinical symptoms occur. The invasion of the small and large intestine cells causes direct damage to the intestinal lining and reduces the ability to absorb nutrients. This reduced ability to absorb nutrients (sugars, amino acids, minerals) then causes diarrhea as the intestine attempts to balance osmotic balance. In severe cases, bloody diarrhea and mucus secretions can occur if damage to the cell lining persists. By the time the animal is showing clinical symptoms, the protozoa has already completed their lifecycle and are excreting oocysts into the environment and perpetuating this problem. Prevention and treatment are thus important to control parasite loads, reproduction in the animal, and impacts on heifer growth.
Minimizing parasite load in the environment is key to preventing coccidiosis incidence and severity. Similar to other diseases, maintaining heifers in similar age groups, using all in/all out management, and cleaning of pens/feeders/waterers between moves can help reduce pathogen loads. In addition to maintaining a clean environment, most operations use a coccidiostat (lasolocid, monensin, decoquinate, amprolium) in their feed mix to control the protozoa in the heifer’s digestive tract. These coccidiostats control the parasite while in the digestive tract to minimize oocyst production and excretion into the environment. Use of a coccidiostat allows the heifer to develop immunity to the protozoa while controlling protozoal levels to minimize coccidiosis. Coccidiostats work very well in controlling incidence of clinical coccidiosis and maintaining heifer growth, however there can still be a subclinical infection occurring so producers need to be consistent with coccidiostat feeding to prevent clinical disease. Feed mixing and administration are critical to ensuring the proper dosage is provided for controlling the protozoa. Another advantage of using certain coccidiostats (lasolocid and monensin) are that these act as ionophores in the rumen to improve feed efficiency.
Recent research at the University of Wisconsin-Madison Marshfield Agricultural Research Station explored the use of alternative feed additives to control coccidiosis in heifers that were transported from the Arlington research location (about a 3-hour transport). We used a novel egg-based antibody to interleukin-10 (IL-10) which may help maintain the heifer’s normal immune system. In short, the Eimeria protozoa is capable of ‘fooling’ the animal’s immune system by causing the immune cells in the gut to produce IL-10, which is a communication signal to shutdown the immune system after an infection. The antibody we fed is supposed to bind IL-10 in the digestive tract and allow the immune system to act normally, with positive results previously in some chicken and beef cattle studies. However, we have not yet found positive results from feeding this antibody to heifers, but continue to evaluate this antibody as a possible coccidiosis prevention strategy. During this work, we also found other interesting results for the coccidiostat treatment group. Heifers fed a coccidiostat had lower fecal oocyst counts for the first 4 to 6 weeks of the trials, however after 6 weeks the heifer’s fecal counts were similar to the control and antibody treatments likely due to them being moved into a bedded-pack barn. The bedded-pack barn likely had a higher oocyst load as the pens were only divided by gates and the bedding is groomed/mixed daily thus spreading oocysts across pens. The coccidiostat groups did have fewer clinical symptoms and treatments as the heifer’s immune system was able to adapt to lower protozoa levels over the first 4 weeks of the study. This result shows the importance of facility cleanliness even if being fed a coccidiostat.
Treatment for coccidiosis symptoms (mainly diarrhea) should focus on controlling the protozoal infection and replacement of lost fluids and electrolytes. Before treatment, work with your veterinarian to determine if it is coccidiosis by doing a fecal float test, and to determine the appropriate treatment strategy. Amprolium is commonly used for treatment of heifers with clinical symptoms to quickly control the growth and reproduction of the protozoa in the animal’s digestive system. Amprolium mimics the B-vitamin thiamin when taken in by the protozoa, which causes a thiamin deficiency and energy deficit ultimately killing the protozoa. Treatment of a pen is generally advised because if a few animals are showing clinical symptoms, it is likely that the other animals are under stress from parasite loads. Treatments are done over 5 days either by a drench, in the water tank, or in the feed using a pellet. Use of fluid therapy (electrolytes) is also essential to reversing clinical symptoms as heifers will become severely dehydrated from coccidiosis.
Coccidiosis is a common dairy calf and heifer disease that can significantly reduce growth and lead to death. However, the disease is preventable with good management practices (cleanliness, pen management) and use of coccidiostats to allow heifers to adapt to the parasite over time with fewer symptoms. Make sure to work with your veterinarian and nutritionist to discuss prevention strategies and ensure you are using the correct levels of coccidiostats.
Figure 1. Coccidia Lifecycle
Source: Huvepharma Corid Website – https://www.corid.com/Coccidia.html
Matt Akins is an Associate Scientist and Extension Dairy Specialist at UW-Madison. He conducts research and extension programs on dairy heifer management to improve nutrition and dairy profitability. His extension work has focused on collaborating with county agents to conduct surveys to estimate the cost of raising dairy replacements and on-farm testing of alternative forages. Recent research at the Marshfield ARS includes evaluating coccidiosis prevention methods, alternative forages for feeding heifers, and using stockpiled forage for grazing heifers. Please contact Matt with any questions at firstname.lastname@example.org or 715-384-9459.
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