Evaluation of leonardite as a feed additive on lipid metabolism and growth of weaned piglets

We evaluated the effects of leonardite supplementation, mainly composed of humic acids (HAs), as a functional feed additive in weaned piglets. One hundred and twenty piglets (Large Withe × Landrace) were weaned at 28 ± 2 days, and randomly divided into two groups (6 pens per group, 10 piglets per pen). After one week of adaptation, for 40 days groups were fed a control diet (CTRL) and an HA enriched diet (0.25% of leonardite; HAG). Body weight (BW), average daily feed intake (ADFI), average daily gain (ADG), feed conversion ratio (FCR) were measured throughout the experimental period. On the last day of the trial four piglets per pen were randomly selected and the blood was collected to evaluate the serum metabolic profile and diamine oxidase content. Chemical analyses showed that leonardite was characterized by a high content of ash 23.27% (as-fed basis), polyphenolic content of 35.18 ± 3.91 mg TAEq/g, and an antioxidant capacity of 73.31 ± 8.22 μmol TroloxEq/g. The HAG group showed an increase in BW, ADG and ADFI (P < 0.01) compared to the CTRL group during the experimental period. In terms of the serum metabolic profile, the HAG group showed a significant increase in total protein content (P < 0.001), albumin (P < 0.001), albumin/globulin ratio (P < 0.01), phosphatase alkaline (P < 0.01), calcium, phosphorus and magnesium (P < 0.05) compared to the CTRL group. A modulation in the serum lipid profile was recorded. The HAG group showed a decrease in total triglycerides (P < 0.05) with higher total cholesterol (P < 0.05), however only high-density lipoprotein showed a significant increase (P < 0.001) compared to the CTRL group. No significant differences in the amount of diamine oxidase were found between groups. In conclusion, leonardite inclusion in the diet at 0.25% was shown to have a positive effect on the serum lipid profile and animal growth. This thus suggests that leonardite can be considered as a new feed additive, which improves the health and performance of weaned piglets.