Ochratoxin A in food and feed: occurrence, legislation and mode of action

Ochratoxins, of which ochratoxin A (OA) is the most prevalent, are secondary fungal metabolites of some toxigenic species of Aspergillus and Penicillium. OA has been shown to be nephrotoxic, hepatotoxic, teratogenic, carcinogenic and immunosuppressive. The natural occurrence of OA in food and feed stuffs is widespread, especially in temperate areas such as Canada, Denmark, Germany, Sweden and the United Kingdom, and detectable amounts were even found in randomly collected human milk samples in Germany, Sweden and Italy. Of greatest concern in humans is its implicated role in an irreversible and fatal kidney disease referred to as Balkan Endemic Nephropathy. The mean dietary intake for humans in the European Union was found to be in the range of 1 to 2 ng/kg bw/day. Compared with the Provisional Tolerable Daily Intake (PTDI) proposed by the WHO of 16 ng OA/kg bw/day for humans, the average OA intake in Europe seems to be rather low. The main contributor to the OA intake in humans are cereals and cereal products, other possible contributors are coffee, beer, pork, products containing pig blood/plasma, pulses and spices. Only very few countries have regulations for OA in food and feed products. Based on the current literature, the mechanisms involved in the toxicity of OA indicate three major effects: (1) inhibition of mitochondrial respiration correlated with a depletion of ATP; (2) inhibition of tRNA-synthetase accompanied by a reduced protein synthesis; and (3) enhanced lipid peroxidation. Generation of free radicals and lipid peroxidation as an important mode of action of OA in vitro and in vivo is discussed in detail, as well as counteracting effects of dietary antioxidants.

Dietary effect of phytogenic phytase and an addition of microbial phytase to a diet based on field beans, wheat, peas and barley on the utilization of phosphorus, calcium, magnesium, zinc and protein in piglets

The effect of the addition of microbial phytase to a diet based on field beans (30%), wheat (28%), peas (25%), and barley (14%) was studied in a 2-week experiment with 3 x 8 castrated male, individually housed, hybrid piglets (live weight range 12-16 kg). All diets contained about 4.7 g Ca, 4.2 g P (77% present as phytate phosphorus), 1.0 g Mg, 60 mg Zn per kg diet, and 17% crude protein. Group I was fed the basal diet with a native phytase-activity of about 260 U per kg diet. In group II, 350 U, in group III, 700 U of microbial phytase per kg diet were added. The addition of microbial phytase improved the apparent P absorption (% of intake) from 48% (group I) to 66% (group II) and 71% (group III). Comparable positive effects from the phytase treatment were obtained for the calcium utilization. The phytase supplementation also enhanced plasma zinc concentration significantly. The concentration of inorganic phosphorus in plasma, the zinc digestibility, and the magnesium balance were improved in tendency. The utilization of nitrogen remained unchanged.

Metabolism and excretion of ochratoxin A fed to sheep

Hydrolysis of the mycotoxin ochratoxin A (OA) to ochratoxin alpha (Oalpha) by microorganisms within the gastrointestinal tract leads to the excretion of OA as the nontoxic alpha form. The Oalpha form is the principal means for the detoxification of OA. In the current experiment, three groups of four sheep were fed diets consisting of 70% concentrates and 30% hay (dry matter basis, energy to supply 1.1 times the requirement for maintenance) for 4 wk with three dietary concentrations of OA (0, 2, or 5 mg/kg of concentrate feed). The OA content did not affect feed intake or nutrient digestibility. In a preliminary experiment, an OA dose of 20 mg/kg of concentrate feed greatly reduced feed intake. After 1, 2, 3, and 4 wk of the trial, significant concentrations of OA were detected in the serum of the animals fed 2 or 5 mg of OA/kg feed. This suggested that even at a dosage of 2 mg of OA/kg of concentrate feed, considerable amounts of OA were not degraded by ruminal and intestinal microorganisms. The analysis of the feces and urine samples reflected these findings; OA and Oalpha were found in significant concentrations, escaping fermentation in the rumen and in the hindgut. The current experiment demonstrates that OA hydrolysis in the gastrointestinal tract of sheep is substantially less than previously described, especially if OA is ingested in combination with concentrate-rich diets.

Methods to assess free radicals and oxidative stress in biological systems

Oxidative stress results from a disruption of the prooxidant/antioxidant cellular balance and monitoring free radical status becomes an interesting challenge in animal and human nutrition. In the present work, merits and limitations of different analytical techniques (HPLC, GC-MS, fluorometric and colourometric assays, ELISA, gel electrophoresis) for the measurement of radical mediated alterations in the cellular integrity of lipids (malondialdehyde, hydrocarbon gases, F2-isoprostanes) proteins (protein carbonyls, 3-nitrotyrosine) and DNA (8-hydroxy-2'-deoxyguanosine) are discussed. Besides these indirect methods, owing to the fact that free radicals are paramagnetic, electron paramagnetic resonance spectroscopy combined with spin trapping has become a valuable tool to directly assess and to better understand the mechanisms of free radical reactions. With this approach a radical that is too short-lived to be detected, adds to a spin-trapping agent to form a relatively long-lived radical adduct. Information obtained from the hyperfine splitting of the spin-trapped adduct can provide identification and quantification of the originally generated free radicals.

The effect of energy intake, genotype, and body weight on protein retention in pigs when dietary lysine is the first-limiting factor

This study tested the hypothesis that the effect of lysine intake, if first-limiting, on protein retention in growing pigs is completely independent of the effects of energy intake, differences in the protein retention capacity among genotypes and gender, and body weight. Protein retention, using the nitrogen balance technique, was measured in 12 castrated male German Landrace and Pietrain pigs at 44 and 77 kg of BW and at two energy intake levels (1.1 and 1.3 MJ ME/kg BW.75). All animals received a constant amount of a basal diet that provided a protein intake of 220 g/d and a total lysine intake of 13 g/d. Appropriate amounts of cornstarch were offered additionally to reach the intended energy intake levels. The results show that neither energy intake nor breed had any effect on the level of protein retention, whereas, at 77 kg BW, protein retention was significantly lower than at 44 kg (117.8 and 123.5 g/d, respectively), which can be attributed to the higher requirement for maintenance. The results of this experiment and the linearity of the relationship between protein retention and lysine intake as shown by several authors simplify both the prediction of protein retention from lysine intake and the calculation of the lysine requirement for a particular protein retention. However, to ensure accuracy of these predictions, it is essential to know when ratios of lysine to other amino acids and to energy and capacity for protein retention in the animal become first-limiting.