Influence of Corymbia citriodora leaf extract on growth performance, ruminal fermentation, nutrient digestibility, plasma antioxidant activity and faecal bacteria in young calves

The effect of Corymbia citriodora leaf extract on growth performance, nutrient digestibilities, rumen fermentation, and health status of male crossbred Holstein calves was evaluated in the present study. Three treatments were evaluated by mixing C. citriodora leaf extract (CC) at 0 (CC0), 10 (CC10) or 20 (CC20) ml in the milk of the Holstein calves for 15 weeks. By GC/MS analysis, the main compounds identified in C. citriodora leaf aqueous extract were methyl(Z)-9-oleate (12.69 %), oleic acid (12.13 %), 2-methylene-5α-cholestan-3β-ol (11.18 %), and methyl 12,15-octadecadiynoate (7.73 %). A significant decrease was noticed in intakes of milk, calf starter, hay, and total dry matter (DM) in the calves supplemented with leaf extract at 20 ml. The supplementation of leaf extract at 10 ml/calf did not affect the final body weights, average daily gain, and feed conversion ratio, whereas the extract showed a quadratic decrease (P < 0.001) in the body weight gains and feed conversion ratio at 20 ml/calf. Digestibility of DM, crude protein, neutral detergent fiber, and acid detergent fiber decreased quadratically (P < 0.001) with supplementation of C. citriodora leaf extract in milk. The rumen pH and total volatile fatty acid concentration were similar among the treatments, while the molar proportions of volatile fatty acids differed with a decrease in acetate and butyrate and an increase in propionate concentrations in leaf extract supplemented diets. Further, ruminal NH3-N concentration showed a quadratic decrease with increasing levels of leaf extract supplementation. Feeding C. citriodora leaf extract resulted in lower dry matter and neutral detergent fiber degradation, acetate to propionate ratio, protozoan population, and methane production compared to control. Apart from increasing the plasma antioxidant enzymatic activities, the leaf extract supplementation, irrespective of the dosage, showed a marked reduction in faecal pathogenic bacterial counts, indicating an improved health status. The C. citriodora leaf extract could be supplemented at 10 ml/calf/day to improve the health status and manipulate rumen fermentation in mitigating methane production without any negative effects on the growth performance of calves