Ask a farmer what coccidiosis is, and he or she will inherently mention ‘blood scour’. Are they right? Yes and no.
Coccidia is species-specific, the single-celled organism of the protozoan family. An infected host (e.g. lamb/calf) will shed billions of coccidia oocysts in their environment. These oocysts are extremely resilient and can persist across seasons. As a result, it is almost inevitable that commercially farmed animals will be exposed to coccidia.
As farmers, we want our animals to be exposed to coccidia. Coccidia and coccidiosis are not the same things. Coccidiosis is what occurs when immuno-naive animals (young or stressed) are exposed to a significant burden of pathogenic coccidia. The term ‘pathogenic’ is important here; in calves and lambs, there are two dangerous species of the parasite and 8-10 other harmless species. A basic fecal sample will not differentiate and so shouldn’t be the sole determinant of a coccidiosis diagnosis.
Coccidiosis can be either clinical (usually 4% prevalence in an infected group), where the animal exhibits scouring, straining, and in some cases death, or subclinical. The subclinical form of coccidiosis, on average, causes a reduction in the thriving of ~19% across full groups of infected animals.
The number one weapon a farmer has against coccidiosis is not a drench, a medicated bucket, or a medicated ration. It is in fact the animal’s own immunity. When an animal is challenged with pathogenic coccidia, its immune system springs into action. A naïve animal‘s (one that hasn’t had previous exposure) immune response to the parasite will require the diversion of significant ingested energy to ‘fuel’ the immune system, reducing available energy for growth. This leads to the group-wide 19% reduction in thrive. The 4% of animals who display clinical symptoms are generally the ‘most stressed’ in a group – stressors for example being a lack of colostrum at birth, a dam with poor milk ability, them being twin, being over-handled etc.
In some cases, the stressor is obvious. In cases where the environmental burden of coccidia is extremely high, stressors are less obvious, and this 4% figure can climb higher. This 4% figure will also climb after extremes in weather or handling events such as a long period of transport.
Generally, after a period of consistent exposure, an animal will be fully immune to both sub-clinical and clinical coccidiosis. This is what we aim for as farmers – natural immunity against the parasite because it is inevitable that they will continue to be exposed to burdens throughout their lives. In fact, older immune animals often carry the parasite in their intestines and act as a source of pathogenic coccidia oocysts for young animals. These older animals will be perfectly healthy, as their immune system is suppressing the parasite, but still shedding small amounts of coccidia oocysts into the environment that can affect our young animals. This is why the eradication of the parasite from a farm is unrealistic.
The problem is that the best way to achieve immunity is via sustained exposure to small burdens of the parasite, but on a commercial farm a naïve animal can very quickly be exposed to huge burdens which overwhelm their immune systems. Add in the typical stressor events found on a UK farm in the springtime (weighing, vaccinating, transport, tagging, weaning, turnout etc.) it’s easy to see why coccidiosis is becoming more and more common.
To help the animals’ immune systems we first optimise the environment. Keeping it as clean as possible, means using lots of clean dry bedding, using the approved disinfectants, keeping feed and water troughs clean, and keeping yourself clean (boots dipped, etc.)
In general, the above steps will act to postpone coccidiosis outbreaks on a farm. When it then occurs, we have a number 3 licensed medications we can use as a helping hand to the animals’ immune systems.
