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15.6% and 30.6% when C. citriodora was supplemented at 10ml and 20ml, respectively. Since ruminal protozoa provide the perfect habitat for methanogenic bacteria, their reduction indirectly reduced the production of methane.


Antioxidant potency These researchers also associated the health status of calves with the antioxidant capacity of the leaf extract. They found that the plasma malondialdehyde (MDA) concentration de- creased with leaf extract supplementation, while the levels of glutathione peroxidase (GPx), superoxide dismutase (SOD) and catalase (CAT) enzymes increased. The reduced MDA con- centration is an indicator of reduced oxidative degradation of lipids, while the increased level of plasma antioxidant en- zymes indicates improved antioxidant capacity. Compounds of the leaf extract effectively impair the radical chain reactions by competing with the reactive host components, thus stopping the propagation of the oxidation chain.


Table 2 – Effect on calves fed C. citriodora leaf extract.


Parameter 0


Faecal pathogenic bacteria E. coli x 105


Enterococcus x 106 Clostridia x 106


Plasma antioxidant activity MDA (µmol/l) GPx (µkat/g Hb) SOD (µkat/g Hb) CAT (µkat/g Hb)


Protozoan count (x105 26 /ml)


ml CC/calf/day 10


20


18.67 11.33 8.67 17.67 12.67 7.67 8.33 5.67 2.67


35.85 30.88 26.93 3.62 5.28 6.44 11.96 13.43 14.63 2.57 3.65 4.37 6.01 5.07 4.17


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Nutrient digestibility and growth The researchers found lower nutrient digestibility, growth and weight gain from the 20ml leaf extract diet, but the 10ml diet was not different from the unsupplemented (0ml) diet. They attributed these results to the possible negative effects of some of the extract’s plant secondary metabolites (e.g. condensed tannins, saponins, alkaloids) on nutrient digesti- bility, which in turn affects nutrient absorption. They also cited a low feed intake that they observed as a con- tributing factor to low growth rates. They mentioned that the reduced intakes could be related to reduced palatability; encapsulation of these extracts would help overcome this.


In conclusion The leaf extract when supplemented at 10ml/calf/day manipulates rumen fermentation in mitigating methane production without any negative effects on the growth performance of calves. A reduction in methane production spares the energy for calf production and helps curb the negative effects of global warming due to this greenhouse gas emission. Apart from increasing the plasma antioxidant enzymatic activities, the leaf extract supplementation, irrespective of the dosage, shows a marked reduction in faecal pathogenic bacterial counts and increased antioxidant capacity, indicating improved health status.


This article is based on the original article by A. Hassan, S.H. Abu Hafsa, M.M.Y. Elghandour, et al. 2020. Influence of Corymbia cit- riodora leaf extract on growth performance, ruminal fermenta- tion, nutrient digestibility, plasma antioxidant activity and fae- cal bacteria in young calves, Animal Feed Science and Technology, Vol 261, 2020, 114394. 10.1016/j.anifeedsci.2020.114394.


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