Intake, nutrient digestibility, nitrogen balance, serum metabolites and growth performance of lambs supplemented with Acacia mearnsii condensed tannin extract

Abstract

The objective of this study was to determine the optimal amount of condensed tannins (CT) from Acacia mearnsii extract for inclusion in lamb diets. Forty noncastrated lambs with a mean age of four months and a mean body weight (BW) of 21.5 ± 1.9 kg were randomized into five treatment groups: 0, 20, 40, 60 and 80 g CT/kg dry matter (DM). Eight lambs were included in each treatment group to evaluate their intake, nutrient digestibility, nitrogen (N) balance, serum metabolites and growth performance. Intake of DM, crude protein (CP), ether extract (EE), neutral detergent fiber (NDFap), nonfibrous carbohydrates (NFC) and N, N retention, final BW, average daily gain (ADG), and ADG to DMI ratio quadratically (P < 0.05) increased with increasing CT inclusion in the lamb diets. In contrast, the total digestible nutrients (TDN) intake and digestibility of DM, CP, NDFap, TDN, urinary and fecal N excretion (g/day), and blood urea nitrogen (BUN) concentrations linearly (P < 0.05) decreased with CT addition. The NFC digestibility linearly (P = 0.043) increased, and serum cholesterol tended (P = 0.06) to increase in response to the inclusion of CT in the lamb diets. The CT inclusion promoted a quadratic (P < 0.01) decrease in urinary N excretion (g/100 g N intake) from the lambs. However, the inclusion of CT from Acacia mearnsii extract did not affect EE digestibility, serum concentrations of triglycerides, glucose, total protein, albumin, globulin, creatinine, aspartate aminotransferase enzymes, alanine aminotransferase enzymes, and γ-glutamyl transpeptidase enzymes. Inclusion of Acacia mearnsii extract up to level of 40 g/kg dietary DM improves the DM, CP, and NDFap intake (g/day and g/BW0.75) and leads to greater ADG, thus maintaining nutritional efficiency in lambs. Inclusion of Acacia mearnsii extract as a source of CT above 40 g/kg dietary DM should be avoided because they have deleterious effects on feed intake, nutrient digestibility and N balance, thereby reducing the growth performance of the lambs.