Figure 1. Higher demands placed on a sow‘s liver functions.
With the higher demand for energy around farrowing and milk production increases, the liver plays a crucial role (Figure 1). This greater need for energy causes an increase in body fat and protein mobilization that can result in metabolic disorders. The liver is often under stress due to problems such as fatty liver syndrome and poor nutrient utilization. This is often shown in weak born piglets, lower birth weights, more splayed legs and a lack of milk production. It is important to keep the liver as healthy as possible and to avoid additional stress from toxins, e.g. mycotoxins, endotoxins, antibiotics, diseases such as Porcine Circovirus 2 (PCV2) infection and feed with high concentrations of fat or protein.
Recent data from the BIOMIN Mycotoxin Survey shows that 80% of all tested samples were found to contain at least one mycotoxin.
Mycotoxicoses are caused by oral uptake of mycotoxin-contaminated foods and feeds by animals. Specific mycotoxins affect various organs and tissues like the liver, kidneys, brain as well as mucous membranes of the gastrointestinal, respiratory and genital systems. The course of mycotoxicoses can be acute, subacute or chronic, depending on several factors like the presence of other toxic substances and farm management practices.
Acute outbreaks of mycotoxicoses are infrequent in modern animal production. Animals are often exposed to other interacting factors in the field. The impact of mycotoxins are therefore often subclinical and affect, for instance, the immune system (antibody titre after vaccination, phagocytic activity, immunoglobulins, lymphocytes), antioxidant systems (uric acid, antioxidant enzymes, vitamins) and blood chemistry (liver enzymes, total proteins, albumin/globulin ratio).
Mycotoxins affect the liver
Major mycotoxins such as aflatoxins, ochratoxin A and fumonisins and lesser known ones such as sporidesmin, rubratoxins and phomopsins are known to cause significant liver damage in swine. Table 1 provides an overview of the negative impacts of the major (more well-known) mycotoxins in swine. Among them, aflatoxins are the most potent liver toxins and animals exposed to these toxins show signs of liver disease ranging from acute to chronic. Acute aflatoxin toxicity causes significant biochemical alterations in the liver resulting in hemorrhage or parenchymal cell necrosis. Aflatoxins are rapidly transformed in the liver into various metabolites. The metabolism of AfB1 has been extensively reviewed (IARC, 1993; IARC, 2002 and Eaton et al., 2010). AfB1 in liver and other tissues is metabolized by P450 cytochromes enzymes to aflatoxin P1, aflatoxin M1, or aflatoxin Q1 and AfB1-8,9-epoxide (Riley and Voss, 2011).
Table 1. Selected mycotoxins primarily affecting the liver and their basic symptoms.
Mode of action
Aflatoxins enter the cell and are either metabolized via monooxygenases in the endoplasmic reticulum to hydroxylated metabolites. They are then metabolized to glucuronide and sulfate conjugates or oxidized to the reactive epoxide which go through hydrolysis to the AFB1-8,9-dihydrodiol and bind to proteins resulting in cytotoxicity. The epoxide can react with DNA or protein, or be detoxified by an inducible glutathione S-transferase to the glutathione-conjugate.
Mycotoxin residues in liver
Several cases of aflatoxin carry-over in swine have been reported with residues found in porcine liver and muscle tissues. OTA tends to accumulate in the kidneys, liver and muscle tissue, but also in blood serum and, therefore, represents a potential hazard in the human food chain (Battacone et al., 2010). Similar results were also reported for fumonisins. Fumonisin carry-over in sow milk and pork meat may only occur after a high level of exposure over a longer period, accumulating in the liver and kidneys (Völkel et al., 2011; Meyer et al., 2003).
In many cases it is seen that sows in an overly fat condition have more problems coping with even low levels of toxins.
Sows with already fatty livers have less capacity to detoxify and transport the different toxins out of the body. It is therefore crucial to keep sows in the right condition and avoid the compound stress of liver problems and toxins.
Prevention and mitigation strategies
Some nutrients and feed additives can support the liver supporting the citric acid cycle with some B-vitamins, choline chloride, L-carnitin and plant extracts. Depending on the situation, these can be added in the lactation, transition or even in the gestation diets. Proper mycotoxin risk management combining multiple strategies that offer proven protection against the major agriculturally-relevant mycotoxins (aflatoxins, trichothecenes, zearalenone, fumonisins, ochratoxin A and ergot alkaloids) is essential. Moreover, it should include a blend of scientifically studied and carefully selected plant and algae extracts that counteract the negative effects caused by mycotoxins by supporting the immune system, reducing the risk of inflammation and protecting against liver damage.