Nutritionist > Pig
Mycotoxins in pig production
Mycotoxins are compounds produced in grain by specific moulds or fungi as secondary metabolites that may or may not be toxic to man or animal. Fungal infestation and subsequent mycotoxin production can occur during plant growth, maturity, harvesting, storage, and processing of grains, and is influenced primarily by moisture level, temperature, and availability of oxygen. In addition, grain that is damaged, immature, drought stricken or otherwise stressed is more susceptible to mould growth.
Moulds may reduce the nutrient content and quality of the grain, but the toxic effects of metabolites are generally of primary concern. Scientists have identified 300 to 400 mycotoxins to date, but only a few have been shown to cause significant, detrimental health and performance problems in pigs fed mycotoxin-contaminated plant based feedstuffs. These include aflatoxin, deoxynivalenol, zearalenone, fumonisin, ochratoxin, ergot, and T-2 toxin.
It is important to remember that the presence of moulds in grains does not automatically indicate mycotoxin presence. Aspergillus, Penicillium, Claviceps, and Fusarium fungi have been identified as producing the mycotoxins most detrimental to pigs.
The symptoms exhibited and the degree with which pigs are affected by mycotoxin toxicity is largely affected by the kind of mycotoxin involved and its concentration in feed, but also by the age and phase of production of the pig. Young pigs and breeding pigs are generally the most susceptible to mycotoxins.
In addition, combinations of certain mycotoxins may produce elevated negative effects on performance above that normally expected for each of the mycotoxin levels evaluated individually, and therefore must be considered. (Table 1)
Table 1. Maximum Tolerable Level of Mycotoxins Commonly Found in Pig Feeds
Adapted by "Feedstuffs Reference Issue" (1997)
Mycotoxin
Maximum tolerable level
Comments
Aflatoxins (B1, B2, G1, G2)
< 20 ppb for human use, dairy feed, feed for immature animals
< 100 ppb for breeding swine
< 200 ppb for finishing swine (>120 lbs body weight) Carcinogenic. Immunosuppressant.
Acute signs: anorexia, depression, ataxia, epistaxis.
Chronic signs: reduced feed efficiency, reduced milk production, icterus, decreased appetite.
Zearalenone
< 1 ppm for young growing pigs
< 2 ppm for breeding herd
< 3 ppm for finishing pigs and young and old boars. Oestrogenic effects. Swollen vulvas, vaginal or rectal prolapses in pre-pubertal gilts. Enlarged uterus, swollen or twisted uterus, shrunken ovaries. In boars, testes atrophy, enlarged mammary glands, decreased fertility.
Deoxynivalenol (vomitoxin)
< 5 ppm on grain and grain by-products. DON contaminated feedstuffs should not exceed 20% of the diet. (< 1 ppm in complete feeds)
Reduction in feed consumption and weight gain are inversely proportional to concentration of DON. High concentrations cause feed refusal and vomiting.
T-2 toxin
< 1 ppm
Potent immunosuppressive agent that directly affects immune cells and modifies immune response as a consequence of other tissue damage. Frequent defecation, vomiting, weight loss and feed refusal.
Fumonisin
Not established
< 5 ppm (extrapolated from horse data) Carcinogenic in laboratory tests using rats. Associated with pulmonary oedema in pigs.
Ochratoxin
< 200 ppb has been associated with kidney damage in swine
Ochratoxin A is most common and potent.
Reduction in growth, feed efficiency, increased mortality, liver and kidney damage.
Ergot
< 200 ppb
Vertigo, staggers, convulsions, temporary posterior paralysis, eventual death. Decreased peripheral blood supply. Reduced growth, tail loss, reduced reproductive efficiency of sows.
The development of novel feeding and housing systems has added a new dimension to mycotoxin control in pigs. Mycotoxin exposure can occur in both dry and wet feeding systems, especially the latter, with long distribution lines that are hard to clear. High welfare systems using straw bedding pose an additional risk and this is especially pertinent to the group-housing of sows. Mycotoxins suppress immune function in pigs and this may eventually decrease resistance to infectious diseases, re-activate chronic infections and/or reduce vaccine and therapeutic efficiency.
Common symptoms associated with mycotoxicosis include:
A summary of different fungi, the mycotoxins they produce and the effect of these in pigs, is summarised in Table 2.
Table 2. Common mycotoxins and their effects on pigs
(Smith et al., 2005)
Fungi
Mycotoxin
System affected
Aspergillus flavus
Aflatoxin B1, B2, G1, G2
Liver necrosis, fatty infiltration of the liver, immune-suppression
Aspergillus ochraceus catum
Ochratoxin A
Renal nephropathy, immune-suppression
Fusarium moniliforme
Fumonisin
Fusaric acidPulmonary oedema, Immune-suppression
Vomiting, lethargy, loss of muscle condition
Fusarium graminearum
Deoxynivalenol (DON, Vomitoxin etc.)
Vomiting, intestinal lesions, immune-suppression
Fusarium roseum
Zearalenone
Hyperestrogenism, abortion, infertility, prolapses, ulceration
Claviceps purpurea
Ergotoxin
Reduced appetite, gangrene, agalactica, mammary gland failure
Liquid Feeding
Liquid or wet feeding systems can present a significant challenge to the pig industry with respect to mycotoxins. It is important to employ strict hygiene procedures to minimise the presence of mycotoxins within the mixer tanks, feed lines and troughs. Although regular cleaning should be performed, it should be noted that mycotoxins are extremely resilient and can survive in the biofilms of feed lines and equipment for significant periods. It is also important not to recycle the waste water after the system is cleaned as this serves to re-introduce mycotoxins into the system.
