Types of mycotoxins

Swine are particularly susceptible to mycotoxicosis. Mycotoxicosis is the intoxication that results from the consumption of grains or feeds contaminated with mycotoxins. The degree of mycotoxicosis depends on mycotoxin type and concentration present in the feed and the category of swine consuming the diet. Table 1 presents the effects of mycotoxicosis in each category of swine according to mycotoxin concentration in the feed. In addition, the Food and Drug Administration determines regulatory limits of aflatoxins to commercialize feed ingredients and feeds for swine to 20 ppb for grower pigs, 200 ppb for finisher pigs over 100 lb BW, and 100 ppb for breeders.

Mycotoxicosis affects many body systems with a wide variety of signs, lesions, and impaired performance. Typically, young pigs and sows are more susceptible and the effects of mycotoxicosis are more evident (Osweiler and Ensley, 2012). Moreover, contamination with more than one mycotoxin is frequent and the combination of mycotoxins often have additive effects (Vila-Donat et al., 2018). However, while there is data available on the effects of a single mycotoxin contamination on swine performance, little is known about the effects of multiple mycotoxin contamination.

Aflatoxin

Aflatoxins are produced by molds of Aspergillus species before harvest and in storage. Aflatoxin B₁is the most abundant and toxic aflatoxin and is often produced by Aspergillus flavus. Aflatoxins affect liver function and cause immunosuppression (Osweiler and Ensley, 2012). Acute aflatoxicosis is uncommon in swine but causes severe liver lesions and signs are a consequence of liver disfunction, such as hemorrhages, jaundice, and sudden death (Osweiler and Ensley, 2012). Aflatoxin at lower doses is cumulative. Thus, chronic aflatoxicosis is more common in swine, as a result of ingestion of lower amounts of aflatoxin for a prolonged period of time and is expressed as lower feed intake and growth rate (Devreese et al., 2013). Also, the occurrence of secondary diseases can increase as well as response to vaccination can decrease because of immunosuppression (Pierron et al., 2016). Nursery pigs are more susceptible to aflatoxicosis than grower-finisher pigs or sows. However, suckling piglets are also considered susceptible to aflatoxicosis because aflatoxin passes through milk when sows in lactation consume contaminated feed.

Vomitoxin

Vomitoxin is the term for deoxynivalenol (DON), a mycotoxin produced by Fusarium graminearum before harvest. Vomitoxin is the most common contaminant of corn, wheat, and DDGS in North America and Europe (Rodrigues and Naehrer, 2012; Hendel et al., 2017) and swine is the most sensitive species. Vomitoxin interferes with protein synthesis, modulation of immunity, and activity of neurotransmitters in the brain (Osweiler and Ensley, 2012). Despite what the name suggests, vomitoxin rarely induces vomiting in swine. Acute toxicity is uncommon, but in that case vomit, diarrhea, severe digestive lesions, and sudden death occur (Young et al., 1983). Chronic vomitoxin toxicity is more common and of practical importance. In most cases, a sharp decrease in feed intake is evident and, consequently, a reduction in growth rate upon first exposure (Frobose et al., 2015). The impact on feed intake is dose-dependent, with an estimation of 4% decrease in feed intake for every additional ppm of vomitoxin above the dietary concentration of 1.5 ppm (Frobose et al., 2015).

Zearalenone

Zearalenone is produced by Fusarium graminearum generally before harvest. Zearalenone is similar in structure and mimics the effects of the hormone estrogen (Zinedine et al., 2007). Thus, the primary effects of zearalenone are in the reproductive tract of swine (Osweiler and Ensley, 2012). In gilts, a characteristic of zearalenone is swelling and redness of the vulva. Rectal and vaginal prolapses often occur. In sows, zearalenone induces modification in heat behavior with either prolongation of standing heat or no manifestation of standing heat. In bred sows, false pregnancy and early embryo loss also occur. During lactation, zearalenone passes through milk and induces vulvar swelling and redness in newborn suckling gilts (Hennig-Pauka et al., 2018). In boars, zearalenone suppresses testosterone levels, sperm production, and libido, particularly in young boars (Benzoni et al., 2008). The normal reproductive performance of swine typically resumes after the removal of zearalenone contamination from the diet.

Fumonisin

Fumonisins are produced by Fusarium species before harvest. Fumonisin B₁is the most abundant fumonisin and is more likely produced by Fusarium verticillioides. Fumonisins interfere with cell function and signaling in many tissues, but mainly the lungs, heart, and liver (Haschek et al., 2001). Fumonisins also cause immunosuppression (Pierron et al., 2016). Acute toxicity causes a condition called porcine pulmonary edema, which is characteristic of fumonisin intoxication and causes heart failure and fluid accumulation in the lungs (Haschek et al., 2001; Osweiler and Ensley, 2012). Pigs with acute toxicity have severe respiratory signs, with labored and openmouthed breathing, cyanosis, and death. Chronic toxicity develops as a result of ingestion of smaller amounts of fumonisins for a prolonged period of time. Pigs with chronic toxicity have lower feed intake and lower growth rate, but may also have greater susceptibility to secondary diseases and lower response to vaccination because of suppression of the immune system (Pierron et al., 2016). Fumonisins toxicity to the liver is common and is both time- and dose-dependent (Haschek et al., 2001).

Ochratoxin

Ochratoxin is mainly produced by Aspergillus ochraceus, Penicillium verrucosum, and Penicillium viridicatum during storage. Ochratoxin A is toxic for kidneys and liver (Osweiler and Ensley, 2012). In most of the cases of ochratoxin A toxicity, pigs have low growth rate and poor feed efficiency due to impaired kidney and liver functions. But feed intake is often unaffected (Malagutti et al., 2005). In some cases, the only effect of ochratoxin A toxicity is found at slaughter by the appearance of pale, firm, enlarged kidneys (Stoev et al., 2002). Ochratoxin A contamination is also a concern for human health because pork and pork-derived products may contain ochratoxin residues with carcinogenic potential (Malagutti et al., 2005).