Mycotoxins' impact on swine fertility
The pig industries main aim is to maximize the quantity of quality meat produced per sow per year while maintaining sow condition and health. In the breeding herd, the animal performance is directly related to the reproductive performance of the sows latter to be measured by the number of weaned piglets per sow per year. The objective of pig producers in breeding herds is to increase this number while providing finishing herds piglets with good growth rates and carcass traits.
If it is true that genes are crucial in determining fertility, performance and carcass traits - thus corroborating the importance of genetic breeding programs - one should never forget that environmental factors will influence the way genes are expressed. Environmental factors manipulating gene's expression include diet, physical activity, infectious agents, chemicals, ultraviolet radiation and even emotions. A palatable diet guaranteeing the animal's nutrient requirements in its different stages which does not pose threats to the animals ingesting it is crucial for the animal production's success.
Mycotoxins are included in the toxic substances that often occur in animal feeds, posing a serious menace to animals ingesting them and acting directly and indirectly on pig fertility.
Reproductive failure, abortions, poor rearing ability and litter size are the cause for 45 % and 59 % of female pigs culled, in all parities and in gilts and second parities respectively. A high culling rate related to breeding problems has a big impact on the profitability of pig producers. A direct and important correlation can be made between mycotoxin-contamination and fertility problems; data collected in five Swedish pig farms showed that 85 % of all sows presented zearalenone in the bile liquid. Furthermore, the level of this mycotoxin in the bile liquid was significantly higher in farms having fertility problems in comparison with control farms.
Because of its multiple origins and high economic impact, reflected by decreased animal performance and increased culling rates, reduced fertility is one of the most complex and puzzling problems dealt by swine producers.
Mycotoxins and direct consequences on swine fertility
Zearalenone and T-2 toxin were shown to have direct impacts on animal fertility.
- 1) Zearalenone
Zearalenone is produced by fungi of the Fusarium sp., especially Fusarium graminearum and Fusarium culmorum. Although zearalenone (ZON) represents a relatively low toxicity to animals, this mycotoxin is well known due to its interference with the endocrine system. Zearalenone is the number one regarding its negative effects in fertility and swine are the animals that are most affected by it. The resemblance between zearalenone and the primary female hormone, estrogen, misleads the cells' estrogen-receptors causing hyperestrogenism and impaired fertility. Concentrations of zearalenone such as 1 to 30 ppm are related with infertility and other problems such as anoestrous, pseudo pregnancy, swollen and reddened vulva, mammary gland enlargement and vaginal and rectal prolapse. Moreover, other problems may also occur, such as disrupted placental and piglet development, resulting in decreased litter size and diminished viability of neonates. It is important to bear in mind that not only female animals are negatively affected by this mycotoxin, but also boars. A depression of serum testosterone, testicles' weight and spermatogenesis, along with feminization and suppressed libido can be observed in boars fed ZON-contaminated diets. Clinical signs in females involve reddened teats, swollen and reddened vulva and splay legs can be observed in newborn piglets, thus suggesting placenta and/or milk transfer from the female pigs.
- 2) Trichothecenes - T-2 toxin
T-2 toxin (T-2) is a part of the type A-trichothecenes, a family of mycotoxins produced by Fusarium sp. fungi, especially F. graminearum, F. culmorum and F. sporotrichoides. This trichothecene is known to inhibit protein synthesis. Its biological mode of action may be the explanation why this fusariotoxin is responsible for fertility problems in swine. T-2 has caused drastically decreased conception rates, infertility (repeated return to estrus), decreased litter size and reduced weight of piglets.
Mycotoxins and indirect consequences on swine fertility
Other mycotoxins, although not having direct impacts on swine fertility, are responsible for immune suppression and further health problems that will clearly affect the reproductive performance of animals.
- 1) Ochratoxin A (OTA)
This mycotoxin is produced by Aspergillus ochraceus and Penicillum viridicatum fungi. Tubular necrosis of the kidneys, porcine nephropathy, bladder and kidney inflammation, enteritis as well as birth-defects anvd carcinogenic effects (kidney and urinary tract tumors) are some of the pathological consequences observed in animals fed OTA contaminated diets. Cystitis and nephritis, inflammation of the bladder and kidney, respectively, are important causes of mortality in all ages of dry sows. The high mortality associated with these conditions affects the herd mortality rate and therefore pregnancy survival, ultimately affecting the herd fertility.
- 2) Trichothecenes – Deoxynivalenol
Deoxynivalenol, also known as vomitoxin, is part of the type B-trichothecenes, a family of mycotoxins produced by Fusarium sp. fungi, especially F. graminearum, F. culmorum and F. sporotrichoides. Feeding animals with DON-contaminated feeds may lead to digestive disorders such as emesis, diarrhoea and feed refusal. The feed refusal is particularly hazardous for female pigs, once the balancing and satisfaction of nutrient requirements, vital for a regular reproductive cycle, will be compromised. Once again, the immunosuppression caused by this mycotoxin can result in an increased susceptibility to other pathogens, namely Candida, Listeria, Salmonella and Mycobacterium, which predispose animals to abortions.
Economic Impact of Decreased Fertility
As mentioned before, breeding problems that can be increased by the ingestion of mycotoxin-contaminated feed include reproductive failure (increase of return to estrus), higher abortion rate, poor rearing ability and decreased litter size. The economic impact calculations of a lost cycle must take in account at least the extra semen and artificial insemination costs and the additional feeding expenditures, which represent anywhere between 7 and 11 €, or more, per animal, depending on the country. Frequently, veterinary costs and the culling costs will also be increased by the occurrence of these problems and obviously the reduction of the litter size and of the number of weaned piglets will be reflected in the pig producer's profits calculation.
Infertility in sows greatly compromises the breeding herd production and should not be considered in isolation. The existence of toxic agents such as mycotoxins in animal feeds should be monitored and counteracted by professionals in the pig industry as their occurrence may cancel the effects of work done both by the genetic programs and by the carefully stage-adapted feeding programs, thus impeding the evolution of a whole industry.
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