Mycotoxins Impact on Swine Immunity

DI InÃªs Rodrigues, Product Manager Mycofix^Â® Product Line BIOMIN Holding GmbH, Herzogenburg, Austria.

Ing. (BSc) Fergus Neher

Mycotoxins' impact on swine immunity

In the modern animal production, the animal's performance boundaries are continuously being challenged in order to provide the farmer highest profitability. Disease outbreaks in farms are known to have economically devastating effects as the whole herd can be affected. The word "health" means not only free of disease but it represents a whole new concept of welfare in which the animals are able to fully express their genetic potential, maximizing performance and as a consequence the farmers' profit.

Mycotoxins are toxic substances that disrupt the normal function of the animals' immune system, leading to significant negative economic impacts.

The profit of farmers

The economic viability of modern pig production farms is affected by numerous factors. Amongst them, some exist that cannot be controlled by the farmers, namely the agricultural products and the meat's market price fluctuations and the stricter policies imposed by the agriculture regulatory organisms. Nevertheless there are many of them which can be improved as a result of the farmers' management strategy.

The occurrence of diseases has a direct negative impact on the economic viability of pig farms as outbreaks represent major cost increases and loss of profit. Disease control and treatment is therefore crucial for the economic viability of pig farms.

Promoting positive health status

Pigs' immunity dictates the health status of a herd playing a crucial role as animals are constantly being threatened by different external factors. The balance between a farm challenged by disease and a farm with good health status is easily disrupted, thus it is vital to avoid the hazardous agents, promoting the beneficial ones.

Assuring animal health involves in a great extent the control of animal feeds as these should not only be efficient in satisfying the animals' nutrient requirements but also, and very importantly, they should always be considered harmless for the animals ingesting them.

It was already described how mycotoxins, the secondary toxic metabolites produced by fungi, negatively impact the swine performance and fertility. Nevertheless, their hazardous effects are even broader involving also the immune system of contaminated animals.

The immune system of pigs

As in the case of all mammals, the pig's immune system is the major defensive system which should be able to counteract any agents trying to disrupt the organism integrity. It involves:

1) Innate and non-specific resistance, which develops as animals grow independently of exposure to pathogens. This is the first and quicker barrier potential harmful external agents come across when trying to damage the body. This involves:
- Physical barriers â€“ external and internal body surfaces (ex.: skin, hair, mucous membranes);
- Chemical barriers â€“ body fluids that naturally contain antibacterial and anti-viral substances (ex.: saliva);
- Complement system â€“ a complex system of proteins existing in the blood that activate each other in a cascading manner, attacking cells which are not recognized by the organism (but not virus, bacteria or parasites);
- Phagocytosis â€“ phagocytes (macrophages and neutrophils) are the defense cells responsible for swallowing foreign material and for its expulsion of the body.
- Probiotic flora â€“ are mostly bacteria organisms that exist in the skin, mouth, intestines, vagina and prepuce which inhibiting the growth of pathogenic bacteria.

2) Acquired specific immunity, which will develop as the animal is exposed to pathogens (antigen), either actively (by direct stimulation of the immune system) or passively (by transfer of antibodies from milk, colostrum or antiserum, without a stimulation of the immune system). When a pathogen invades the organism, a defense mechanism is triggered - the active immune system. This involves:
- Humoral immunity â€“ the antigen stimulates the production of antibodies by specific cells called B-lymphocytes. The humoral immunity can either be developed by a natural exposure to the antigen or by vaccine administration (where an antigen without toxicity will still be able to stimulate antibodies' production).
- Cell-mediated immunity â€“ this immune process is complex involving T-lymphocytes which are responsible in the production of other cells such as macrophages and natural killer cells.

Mycotoxins' influence on the immune function

When an animal is exposed to a hazardous agent its immune system will make all the efforts to eliminate the foreign organism and to counteract its negative effects. Animals which are fed mycotoxin-contaminated diets will have a reduced response as these toxic substances disrupt body's normal immune mechanism. Mycotoxins such as aflatoxins, ochratoxin A, fumonisins and trichothecenes pose negative effects at different levels of the immune response.

Several scientific research papers have found that mycotoxins negatively alter the innate and non-specific resistance of pigs, by reducing the phagocytic activity of both macrophages and neutrophils and the humoral and cell-mediated response to antigens. A practical consequence of the occurrence of these facts in a pig farm is the higher susceptibility to infectious diseases and the failure of the vaccination programs.

Economic impact of mycotoxins in the immune system

Pigs with a deficient immune system caused by mycotoxins' exposure will be a preferred target to the infectious diseases caused by different agents such as Viruses, Bacteria (namely Chlamydia, Anaplasma and Mycoplasma) Fungi and Parasites. Resistance to the most economically hazardous diseases and syndromes such as PPRSV, PMWS, Mycoplasma pneumonia, Colibacillosis (E. coli) and dysintery will be therefore reduced with consequent serious impacts on the viability of farms.

Vaccination program schemes are well established in the pig industry in most countries. The knowledge behind vaccination is that the animal is exposed to an antigen which toxicity has been removed but that is still able to stimulate the production of antibodies. Therefore, if the pathogen is later presented to the animal, its immune system will be prepared to counteract it efficiently. This ideal scenario is easily destroyed by mycotoxins contamination, since it is known that they will disturb the normal macrophage activity and the antibody titers, meaning that the animal's organism is not responding to the vaccination as it should. This fact results in two hazardous effects for the farm:

1) The money invested by the farmer in the vaccination program will be considered as lost as the disease has occurred. Vaccine costs correspond to approximately 2/3 of all medicine costs.
2) The costs due to the occurrence of the disease will be reflected in many factors representing an enormous burden for the farmer.

Calculating the costs of disease is not an easy task as its occurrence affects many factors:

1) Increased mortality â€“ pig mortality can go up to 30% in the case of piglets infected with PPRSV. Mortality cost can represent from â‚¬0.68 per pig when the mortality rate is 0.5% up to â‚¬7.48 per pig, with a 10.0% mortality rate (finishing).
2) Increased veterinary costs and medicines â€“ In a normal situation, these costs represent 5% of the variable costs (cost of running a 350 sow unit).
3) Decreased animal performance and increased feed costs â€“ the decrease of daily weight gain will reflect on the number of days animals remain in a set stage, with obvious increase of feed costs. A Salmonella outbreak on a sow farm, for example, represented extra 8.5 days in the flat decks in which 4.5 tons of extra feed were used (2300 pigs x 8.5 days x 0.23 kg feed/pig/day). In the next department, animals had to remain 12 extra days after this outbreak, which represented extra 31.7 tons of grower feed.
4) Increased labor costs â€“ labor costs represent already a big portion in the pig production industry. At least extra 15 hours of labor are required in emergencies such as disease problems. These include activities such as moving the animals, cleaning and disinfecting the areas, caring and giving extra attention to animals, amongst others.
5) Increased stocking density â€“ in order to provide animal's replacement in case of culling. The stocking density increase per se, is also a factor disrupting the air quality and increasing disease's risk.

As disease occurrence negatively impacts many factors, calculating its costs in pig farms is almost as complex as explaining the function of the immune system in a simple way.

Avoiding disease on pig farms is almost impossible but prevention is possible and should be paramount in daily management protocols. It is up to the producer to effectively control the disease potential entry ports, such as feed, in order to minimize its occurrence. Mycotoxins usually found in feeds depress the immune function of the animals, making them an easy target for the pathogenic agents. Preventing these negative substances such as mycotoxins will undoubtedly be more cost effective than treating the diseases triggered by such agents.