Acute mycotoxicosis in pigs is a relatively rare phenomenon these days, as awareness and technology have increased in recent years. Yet mycotoxins may also be present in low dosages, which can lead to subclinical health problems.

Mycotoxin effects on the immune system

While impeded growth and reduced productivity are economically significant, the intrinsic activity of many mycotoxins in an animal’s immune system is of even more concern. The presence of moderate to low amounts of mycotoxins in daily feed rations increases the susceptibility of animals to viral, bacterial and parasitic diseases. That elevated susceptibility to disease necessitates an increase in therapeutic interventions with antibiotics and anti-parasitic drugs. That, in turn, increases the cost of animal health care and the use of anti-infective agents – particularly antibiotics – with a consequent increase in the risk of induction and the spread of antimicrobial resistance. The immunosuppressive effects of mycotoxins may also result in the incomplete protection of farm animals against viral diseases following vaccination, as their antibody formation is impaired.

Mycotoxin effects on antioxidant status

Increased cellular oxidative stress is a common result of exposure to many mycotoxins, due to the associated increase in the production of oxygen and hydrogen radicals and the depletion of cellular defence mechanisms, such as glutathione. Cellular oxidative stress and enhanced radical production lead to lipid peroxidation and cellular necrosis. Many mycotoxins also affect the transport of vitamins and provitamins, which encourages lipid peroxidation, impairs vital cellular function and induces programmed cell death (i.e. apoptosis), followed by cell necrosis.

The incorporation of mycotoxins into membrane structures causes various detrimental changes that are associated with the peroxidation of long-chain polyunsaturated fatty acids (PUFAs), or lipid peroxidation. That, in turn, alters membrane permeability, flexibility and other important characteristics that can affect membrane function.

Moreover, it is not currently clear if mycotoxins stimulate lipid peroxidation directly by enhancing the production of free radicals or if the increased tissue susceptibility to lipid peroxidation is the result of a compromised antioxidant system (see Figure 1).

Managing the mycotoxin challenge

Although lower level mycotoxin contamination may not always be of great concern to every pig producer, it is clear that, by not paying closer attention to it, the industry may be unnecessarily incurring what are often avoidable economic losses. Underestimating those long-term subclinical effects can notably hamper both the pig’s immunity and its antioxidant status, with subsequent negative impacts on areas like productivity, reproduction and disease status.

While there has been significant progress in the area of controlling mycotoxins, it is still generally impossible to eliminate them entirely from the animal feed supply chain. Fortunately for pig producers, there are steps that can be taken – from crop planting to the delivery of the feed to animals – that can help mitigate the mycotoxin challenge.

One of the key tools within this cycle is mycotoxin detection. Until the actual risk is identified and quantified, it can be very difficult to establish effective mycotoxin control programmes or make successful use of in-feed ingredients, such as mycotoxin binders, that are designed to remove mycotoxins from the pig’s digestive tract before they have a chance to cause serious harm.

Signs that pigs may be ingesting low levels of mycotoxins

• Compromised pig performance, increased feed conversion ratio and reduced feed intake;
• Reduced reproductive performance and increased amount of abortions;
• The immune system being the only thing apparently affected;
• Poor response to vaccination, low titres of antibodies;
• Live vaccines having harmful effects on the animal (vaccines do have the potential to become active and cause disease, especially in animals with weakened immune systems);
• Antibiotics used as therapeutics are not performing, even when used at higher dosages or for longer periods;
• An impaired transference of antibodies from breeding animals to their offspring;
• Respiratory diseases of unknown origin or that are difficult to diagnose.

PigProgress | Radka Borutova | December 08, 

Tail biting continues to be a major health and welfare challenge in commercial pig production with diet being a major risk factor. Researchers from Denmark have studied the link between a pig’s diet, gut health and mood, and have uncovered some interesting results.

The feeding factor

This study looked closely at the diet and suggests that diet-related risk factors for tail biting are under- and oversupply of protein (including tryptophan), lack of satiation, fine feed particle size, low dietary fibre content and a limited number of feeder spaces.

These factors can cause social stress, gastric ulcers, dysbiosis of the gut microbiota, disruption of the intestinal epithelium, and affect the animal’s stress sensitivity via the microbiota-gut-brain axis, which can cumulatively lead to tail biting.

Protein and amino acid imbalances

The Danish researchers note that feeding diets with too low dietary protein levels, an imbalance in essential amino acid composition and/or mineral deficiency may increase the occurrence of damaging behaviours such as ear biting and tail biting.

Being protein deficient impairs the pig’s resilience to cope with stressors and predisposes behavioural depression signs and aggression and increase foraging motivation, which increases the risk of tail biting via increased exploratory motivation and tail-mouth behaviour. Meanwhile, an oversupply may increase anxiety behaviour.

Furthermore, mineral deficiency may increase attraction to blood (due to blood’s content of protein and several minerals), accelerating a tail-biting outbreak when skin has been broken.

The research team believes that adequate amino acid levels including tryptophan, and the inclusion of certain dietary fibres in the diet exceeding levels in standard diets, may stimulate the establishment of beneficial gut microbiota (e.g., microbial diversity and short-chain fatty acid-producing bacteria) that protect against inflammation and increase stress resilience.

Optimal levels of tryptophan

Tryptophan is a precursor of serotonin, which is an important neurotransmitter involved in many processes including mood, stress sensitivity, regulation of gut motility, appetite, immune function, sleep and memory. Tryptophan metabolism is modulated by gut microbiota, and an excess of tryptophan can also be metabolised into potentially harmful substances. So, the researchers note that careful consideration is needed in future studies investigating whether the optimal tryptophan level for gut and mental health differ from levels for optimal growth.

The role of antibiotics

Antibiotics are a useful and necessary tool to combat specific bacteria that pose a risk of tail biting, but antibiotics can also disturb the gut microbial balance, which in turn increases the risk of tail biting.

Conclusion and considerations

In conclusion, while tail biting is multifactorial, the researchers suggest that an imbalance in the microbiota-gut-brain axis, modulated via the diet, should be considered as a pathway for the development of tail biting, but needs more research. The team, led by Cecilie Kobek-Kjeldager, suggests a whole-animal approach, including considerations on gut health, satiety, a beneficial gut microbiota and an adequate feed supply avoiding social stress to mitigate tail biting.

PigProgress | Natalie Berkhout | December 13, 

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