Abstract:
The significant contribution of the livestock subsector to global warming and dietary energy loss as a result of enteric methane emission has drawn the attention of contemporary ruminant nutritionists to engage in more research to reduce methane production while ensuring viable livestock production. Tannins have been documented to suppress methanogenesis and facilitate dietary protein utilization, though depending on the source of tannin and level of its inclusion in the diet may adversely affect feed consumption and nutrient digestion. The objectives of this study are: to assess the effect of pentanol and ethyl acetate purified Acacia mearnsii tannins on methane, gas and in vitro organic matter digestibility of Eragrostis curvula hay; to evaluate the morphology, density, encapsulation efficiency and tannin release rate of A. mearnsii tannin encapsulated in sunflower and palm oils; to evaluate the capacity of palm and sunflower oils based encapsulated A. mearnsii tannins to bind and release protein in buffers simulating gastrointestinal tract; to determine the effect of various doses of A. mearnsii tannin encapsulated in sunflower oil on methane, gas, in vitro organic matter digestibility, ammonia nitrogen and volatile fatty acids concentrations of total mixed ration and Eragrostis curvula hay; and lastly to evaluate the influence of encapsulated A. mearnsii tannin in sunflower oil on methane, nutrient utilization, growth changes and rumen fermentation characteristics of South African mutton Merino ram lambs. A series of in vitro and/or in vivo experiments were carried out at the Department of Animal Science Nutrition Laboratory and University of Pretoria Experimental Farm, Hatfield, Pretoria, Republic of South Africa to examine the possibility of enhancing dietary tannin utilization as a feed additive in ruminant nutrition by adopting Sheep as a model experimental animal.
Tannin purification with pentanol and ethyl acetate improved the proportion of condensed tannin and decreased gas and methane production with slight reduction on digestibility at dose of 30 g/kg feed DM. Moreover, lesser dosage of purified tannin extracts showed similar impact on gas and methane comparable with higher inclusion level of non-purified tannin. Tannin encapsulation with sunflower oil and palm oil exhibited excellent encapsulation efficiencies, smaller particles sizes, lighter in density and delayed tannin release in the gastrointestinal tract simulated buffers compared to unprotected tannin. However, non-encapsulated tannin bound and released more protein in the buffers simulating rumen and abomasum. Whereas, the encapsulated tannin in sunflower and palm oils released more protein in small intestine simulated buffer. Among the two oils, sunflower oil microparticles bound and released more protein than palm oil microcapsules. Addition of encapsulated and non-encapsulated acacia tannin at dose of 20 g/kg feed DM decreased methane and total gas yield without affecting ammonia nitrogen, volatile fatty acids and in vitro organic matter digestibility. Moreover, encapsulated tannin reduced more methane yield compared to equivalent dosage of free tannin. Nevertheless, 30 g/kg feed DM inclusion of encapsulated tannin reduced feed digestibility. In vivo results showed that A. mearnsii tannin encapsulated in sunflower oil at a dose of 20 g/kg feed DM reduced methane emitted by sheep while increasing the intake of dry matter, organic matter and fibre without decreasing the digestibility of dry matter, organic matter and crude protein compared to the unencapsulated tannin and monensin treatments. Feed conversion ratio was unaffected by inclusion of tannins and was comparable to those animal on monensin additive. Thus, supplementation of encapsulated acacia tannin at the dose of 20 g/kg feed DM could be adopted as safer natural alternative and eco-friendly approach of ruminant animal production to replace the use of ionophore.
