This article appears in the September issue of Pig International. View all of the articles in the digital edition of this magazine.

Pig producers around the world are aware of the problems of piglet diarrhea, including mortality, poor performance and susceptibility to other diseases. Prevention strategies like hygiene and biosecurity will help to reduce the incidence of many types of diarrhea. However, it is important to know the cause in order to treat effectively and implement a specific control plan. In this article, the topic of coccidiosis in piglets is discussed.

Awareness of coccidiosis as a problem in piglets varies, but the disease is present worldwide. Studies conducted in most countries have shown a high prevalence on farms (45 to 85 percent) as well as a high incidence of litters infected (>30 percent). However, many believe the true prevalence isn’t known as it often goes unreported.

global prevalence of Isospora suis
Reports on the presence, prevalence and epidemiology of Isospora suis have come from virtually every country in the world. 

Parasite overview

The primary cause of coccidiosis in piglets is the parasite Isospora suis, which is a pig-specific coccidia. There are other coccidial species that can infect pigs, but they don’t commonly cause disease. Coccidial oocysts are shed from infected animals and can survive on the farm for months or even years. By ingesting oocysts still present in the environment, usually from previous litters, piglets become infected. Once inside the small intestine, the protozoa go through a number of developmental stages, which takes five to seven days before new oocysts are formed. Each stage invades and multiplies within cells then bursts out. This destroys the infected cells, which in turn damages the gut, leading to diarrhea. Once the new oocysts are shed in the feces, they go through a short maturation process in the environment before being ready to infect a new host.

Diagnosis and clinical signs

Clinical signs of coccidiosis can be seen in pigs from as early as six days of age up to about three weeks old. This is consistent with them becoming infected soon after birth, which is when they are most susceptible. As coccidiosis is the most frequent cause of diarrhea in piglets between six and 15 days of age, one of the main ways the disease is suspected is the very young age that the piglets scour. They will have poor body condition, be dehydrated and a rough coat may be observed. The diarrhea is pale yellow or grey and pasty.

coccidiosis piglet diarrhea
Diarrhea caused by coccidiosis is yellow or grey and pasty in consistency. | Bayer

It is possible to test for oocysts in feces in order to confirm a diagnosis. Veterinarians may also want to perform a post-mortem examination in order to observe the characteristic lesions and other gut pathologies. However, as the effect of leaving an infection untreated may be severe, response to drug therapy is a common method of confirming a diagnosis.

Health and production effects

The mortality rate of piglets infected with Isospora suis is usually low but can be variable, depending greatly on health status. It has been shown that if concurrent with rotavirus, for example, mortality can be as high as 30 percent.

There can be variation in the severity of the disease within a litter. Similarly, a few animals may present diarrhea at seven days, but the rest don’t show clinical signs until a week later, as the infection pressure increases. In most cases, pigs do become age-resistant to coccidia, so coccidiosis is rarely seen after three to four weeks of age.

The effects of both clinical and sub-clinical coccidiosis have short- and long-term effects. Coccidiosis is characterized by uneven batches of piglets. These animals are also extremely prone to secondary infections; for example, E. coli intestinal infections. The parasites cause considerable damage to the gut wall, which is why bacteria are able to more readily colonize. Poor gut integrity also leads to reduced nutrient absorption, lower growth rates and a poor feed conversion ratio (FCR). Weaning weight is therefore affected, and in the longer term, this is correlated with a greater age at slaughter weight. This in turn increases finishing costs, in particular increased feed consumption.

Poor weaning weights can be a sign of sub-clinical coccidiosis.

Sub-clinical infections of coccidiosis are common; even if the piglets aren’t scouring, there will still be significant damage to the gut. Poor and variable weaning weights can be a sign of subclinical infection. These animals may not show clinical signs but will shed a large number of oocysts. This then causes a problem for future litters.


electron micrograph of villi
Intestinal villi five days after infection with Isospora suis, showing epithelial loss. | Bayer 

electron micrograph of villi close up
Close up of the intestinal surface, showing secondary bacterial colonization of damaged villi. | Bayer


Antibiotic treatment with sulphonamides has been used historically and is still used in some countries. Oral dosing with toltrazuril is also practiced. The possibility of a vaccine for pigs is being investigated but, at present, none is available. Treating animals straight away if you see clinical signs is strongly advised. If the diagnosis is uncertain fecal samples can be taken for oocyst identification and count at the same time. In this way you prevent losses as well as reducing ongoing damage to the gut. In order to prevent clinical signs of coccidiosis, many pig producers use timed metaphylactic treatment. This involves treating all piglets on a farm at three to five days of age.


Coccidiosis is a disease of massive multiplication. Piglets may consume only a few oocysts but will then shed millions. For this reason, control of coccidiosis is not only important for the individual piglet but for its littermates and subsequent litters born. The aim of any prevention plan is therefore to reduce the infection pressure on the farm overall.

General hygiene and biosecurity are as important in controlling coccidiosis as for any other infectious disease, particularly before a sow or litter is moved in. The oocysts are resistant to many disinfectants, so cleaning and removal through pressure washing are important. However, there are coccidia specific disinfectant products available in some markets.

Farrowing hygiene is especially important, as piglets are infected so young. Infected animals will be shedding a large number of oocysts, so areas around feeders and drinkers should be kept clean and dry, with bedding replaced frequently. It is also prudent to clean piglet feeders and drinkers on a regular basis. Ensuring healthy litters also reduces the effects of coccidiosis. Maximizing colostrum intake, preventing dehydration and providing warm, dry creep areas are always important.


If pigs are being reared in brand new accommodation, coccidiosis may not be an immediate concern. However, it will be important to look out for signs and consider testing for the parasite. Preventative measures can be effective to a degree, but it is likely that at some time coccidiosis will be a problem.

In many countries, coccidiosis is high on the watch list when rearing piglets, but in other areas awareness is limited. It is important to educate producers and farm workers about the disease. It should also be discussed with the veterinarian responsible and included in every farm’s veterinary health plan.

Managing coccidiosis in the right way has been shown to significantly reduce antibiotic usage. This is another positive both in terms of costs and targets for judicial use of antibiotics. To summarize, if coccidiosis is not being controlled on farm, it will be adversely affecting performance and hence a producer’s bottom-line.


Read more: Piglet diarrheas: A common problem explained