The transportation of chickens from the poultry farm to the slaughterhouse causes stress conditions that influence the oxidative status of the whole organism and subsequently change the organoleptic properties of the meat delivered to the consumer. The aim of this work was to investigate how administering 0.6% humic acids to broiler chickens for a period of 42 days affects the level of selected enzymes directly involved in oxidative stress elimination. For the most objective estimation of the oxidative state, parameters were determined in liver and kidney mitochondria, and in the blood plasma. With regards to the chelating properties of humic acids, our interest was in monitoring the effects on the distribution of the transition metals Fe, Zn, Cu, Mn, which serve as cofactors of antioxidant enzymes. We have found that, under normal conditions, 42 days of humic acid administration do not cause significant metal redistribution. It has a significant effect on Se excretion, according to the pronounced deposition of Se in kidney tissue, without significantly increased activity of the corresponding enzyme. This led to compensation by changes in other antioxidant enzyme activities. This is a noteworthy finding, especially after administration of longer than 42 days. In conditions caused by sudden stress, according to the detected element levels, it is possible to expect a better response in the case of humic acid administration. The effect of humic acid supplementation appeared to be organ-specific and may ultimately be beneficial for the chickens' health, stress elimination and, finally, the quality of the meat.

The possibility of administering lower amounts, and the corresponding decrease in side effects, would be important for clinical practice. Both prospective studies and our initial studies on humic acids have highlighted positive effects based on their antioxidant and chelating properties.

Chronic exposure to lead causes disruption to energy production mechanisms and tissue damage, in particular through its binding to thiol groups and competition for zinc binding sites. We investigated the possibility of preventing the consequences of chronic lead poisoning by administration of three different doses of humic acids (HAs) into feed with the aim of establishing an effective HA dose. During the 10-week experiment, a sub-lethal dose of lead acetate was given to rats during the first 5 weeks, with continuous administration of HA over 10 weeks. Measurements were taken to determine the content of the metals Pb, Mn, Cu, Fe and Zn; the metalloid Se; and selected antioxidant markers in the heart, liver, kidney and plasma after the first, fifth and tenth weeks of experiment. The administration of lead and HAs clearly affects the redistribution of the elements and the activity of the antioxidant enzymes. This fact was particularly highlighted in the lead-only group as, within the experiment, significantly higher Pb concentrations were found only in the plasma of this group. However, in the group with 1% HA administered with lead, we observed a rise in Zn concentrations in the organs and the deposition of Fe into the liver. Decreased glutathione reductase activity in the plasma and balanced reduced glutathione concentrations indicated sufficient efficiency of redox reactions. SOD activities were among those affected most strongly, with only the 1% HA group showing no effect on heavy metal redistribution as a result of HA administration.

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