Extracted and Characterized Humic Substances as Feed Supplement in Rabbit Feeding: Effects on Performance, Blood Metabolites and Caecal Fermentation Activity

This study aimed to evaluate the effect of dietary humic acid (HA) supplementation on the growth performance, nutrient digestibility, carcass characteristics, blood metabolites, and caecal fermentation activity in growing rabbits. Six-week-old New Zealand White (NZW) rabbits (n = 63) with an initial body weight of 726.32 +/- 42.85 g, were randomly allocated to three groups of 21 rabbits each. Rabbits were fed on the basal diet with 0 (HA0, control), 5 (HA5) and 10 (HA10) gram/kilogram diet for 70 days in a completely randomised experimental design. A significant heavier (P < 0.001) final body weight and a higher average daily gain, with lower feed intake, and a better feed conversion ratio were in HA5 and HA10 rabbits. The digestibility of HA-supplemented diets was greater than that of HA0. Heaviest carcass weights (P < 0.05) were observed in the HA5 rabbits, followed by the HA10 rabbits vs. HA0. Protein and ash content of meat increased (P < 0.001) in all HA rabbits, while the ether extract decreased (P < 0. 01) in HA5 and HA10 rabbits. The HA-treated rabbits were distinguished by increased (P < 0.001) total protein, albumin, and globulin levels. However, the total cholesterol, triglycerides, and urea levels decreased (P < 0.001), and the blood glucose and creatinine levels remained unaffected with HA supplementation. Addition of HA reduced the pH of caecum and sharply decreased (P < 0.001) NH3-N content but it had no significant effect on the levels of total volatile fatty acids and acetic acid. Levels of propionic and butyric acid increased (P < 0.001) in response to HA supplementation. In conclusion, supplementation of HA of up to 10 g/kg can be used in diets of growing rabbits, with significant effects on the digestion, growth performance, blood cholesterol concentration, and caecal fermentation activity. Graphic

Automated summary

This study found that dietary supplementation of humic acid (HA) in growing rabbits significantly improved growth performance, promoted protein and ash metabolism, reduced blood lipid levels, and improved caecal fermentation activity.