Combatting coccidiosis with prompt corrective action

It is caused by the protozoan parasite Eimeria. There are many different species of Eimeria; some are more likely to cause severe disease (more pathogenic) than others. Eimeria ovinoidalis and Eimeria crandallis are two pathogenic species of this parasite that are host-adapted to sheep, meaning that they cannot infect or come from other species of animals on farm, such as cattle or poultry.

The life cycle of Eimeria is complex and generally takes up to four weeks to complete. This is why coccidiosis is not usually seen in lambs younger than four weeks of age. In Eimeria infection following oocyst ingestion, the parasite invades the cells lining the intestines. The parasite replicates inside and bursts out of these cells, causing extensive, often long-term damage to the gut. Oocysts, or eggs, are produced in the gut and expelled in the infected animal’s faeces. Oocysts are then consumed by other animals in the flock through exposure to infective oocysts in faeces and so the cycle continues.

Clinical

Oocysts are shed in the faeces of both sick and healthy animals and can quickly build up high numbers both outdoors and indoors. Adult sheep may carry and shed low numbers of Eimeria oocysts. They do not show clinical signs of coccidiosis like lambs do, as they are usually immune to the effects of the parasite by adulthood. Ewes, however, may shed more oocysts in response to stress at lambing time. Newborn lambs can be infected when exposed to the faeces of adult animals or sick animals and, thereafter, show clinical signs when the life cycle has been completed approximately four weeks later.
In clinical cases of coccidiosis, lambs are off form, straining to defecate, dehydrated, off their feed, and scouring. Scour will sometimes contain blood. In severe cases, lambs may strain with such force that they prolapse their rectums. Lambs at this stage are difficult to treat and may subsequently die. Clinical cases such as this are often the tip of the iceberg.

Subclinical

Coccidiosis is well-known to be a group disease, with other lambs in the flock most likely harbouring rising levels of the parasite also. Subclinical coccidiosis is a widely recognised hindrance to lamb performance. In subclinical cases of coccidiosis, lambs do not show obvious signs of illness. Subclinical coccidiosis is associated with reduced daily weight gain and failure to thrive. Coccidiosis can be diagnosed by your vet using faecal sampling. Faecal oocyst identification is important in coccidiosis outbreaks, as confirmation of the species and level of burden can aid in decisions pertaining to disease control strategy. Prevention of coccidiosis is preferred over treatment. Oocysts are extremely resistant and can survive in the environment for at least one year. They can withstand both high and low temperatures leaving many farmers frustrated when disease on their farm becomes an annual problem.

Hygiene

Hygiene is of the utmost importance in coccidiosis control. Lambing pens are excellent sources of Eimeria oocysts, particularly when not cleaned out regularly and properly. As coccidiosis is spread faecal-orally, it is important to ensure that feeding troughs and water sources are clean and free of faeces. If troughs are used for feeding outdoors these should be moved regularly to avoid build-up of oocysts around feeding spots. Good drainage and a dry environment are essential for coccidiosis control indoors, as coccidiosis thrives in damp conditions. When choosing a disinfectant, ensure that the product is effective against coccidian oocysts and that the correct contact time is adhered to. Many disinfectants do not work in the presence of organic matter (faeces) so surfaces must be thoroughly cleaned prior to application.

Immunity

Lambs may initially be protected against coccidiosis by antibodies consumed in colostrum, but levels of these antibodies soon begin to wane. At this point, lambs need to mount their own immune response to the parasite through environmental exposure. Coccidian immunity is very much a balancing act: avoiding exposure to high numbers of oocysts to prevent clinical outbreaks, while allowing exposure to low levels for immunity development. Understandably, it can be difficult to predict how many oocysts a lamb will be exposed to. Some farmers may recognise a pattern in coccidiosis outbreaks on farm, while others remain at a complete loss. Many choose to administer antiprotozoal treatments in advance of risk periods.

Treatment

Diclazuril and toltrazuril are two antiprotozoal drugs commonly found in oral drenches used to control coccidiosis in lambs and calves. The choice between these two drugs has long been a topic of debate. In one study, calves treated with diclazuril demonstrated better average daily weight gains compared to calves treated with toltrazuril. In addition, calves treated with diclazuril seemed to have had better exposure to Eimeria, leading to the development of protective immunity. Diclazuril has a short duration of action, allowing animals to be exposed to the parasite while building a natural immunity, decreasing the chances of reinfection later. In another study, calves treated with diclazuril had lower numbers of oocysts in their faeces after 42 days, while calves treated with toltrazuril shed higher numbers

of oocysts in their faeces after this time.

Coccidiosis is a well-recognised cause of disease and underperformance in Irish flocks, affecting lambs all over the country. When coccidiosis is diagnosed on farm, prompt corrective actions are crucial. There is no one-size-fits-all approach in coccidiosis control. It is important to always treat all the lambs in a group, as coccidiosis is a group problem, not an individual problem. A combination of improved husbandry practices and careful anticoccidial product use can aid in management. Your vet can recommend the product most suited to allowing safe immunity development in your lambs and advise on administration timings for your flock.