Nutritional elucidation of rice- and maize gluten meal-based diets: in vitro gas production, digestibility, methane and rumen fermentation
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Evaluating rice- and maize gluten meal-based diets in vitro
Quest for cleaner and planet-friendly livestock-derived food systems, in the recent times, has entailed a closer integration of ruminant production, nutrition and associated carbon emission thereof with the sustainable dairying. This experiment intends to elucidate the nutritional potential of alternative ingredient – rice gluten meal (RGM) with groundnut cake (GNC) and maize gluten meal (MGM) at incremental levels in the complete diets under in vitro system. Nine complete diets were formulated using concentrate mixture, green maize and wheat straw in the ratio of 40:40:20 on a dry basis. The dietary treatments differed in the source of major protein sources used in three concentrate mixtures, i.e., GNC in control, while incremental levels of RGM and MGM – both at 25, 50, 75 and 100% substituted GNC on an isonitrogenous basis. These diets were characterised for comparative evaluation using chemical composition, protein fractions, in vitro gas production parameters as well as rumen fermentation attributes. The chemical composition of diets showed a mean crude protein (CP) and total digestible nutrient values of 12.9 and 63.6%, respectively. The range of values obtained for various CNCPS protein fractions (% CP) was 11.3-12.4, 9.42-14.0, 40.9-44.4, 19.1-20.1 and 13.6-14.9 for PA, PB1, PB2, PB3 and PC, respectively across diets. Furthermore, rumen undegradable protein was maximum at 100% MGM inclusion and least for the control. However, intestinal protein digestibility did not differ due to treatments. While the GV24 was maximum (P<0.01) in the control, it was lowest at 100% MGM. Additionally, in vitro dry matter and organic matter digestibilities were higher (P<0.01) for 100% MGM diet and lowest (P<0.01) at 100% RGM level. Moreover, the control diet generated maximum (P<0.01) CH4 but was minimum (P<0.01) for 100% MGM diet. In addition, values of PF, MBP and MBP:GV24 were highest (P<0.01) for 100% MGM and lowest (P<0.01) for control diet. The pH of rumen fluid did not differ; however, concentrations of ammonia nitrogen and total volatile fatty acids were recorded to be maximum (P<0.01) in control and minimum (P<0.01) at 100% MGM. Further, the molar concentration of acetic acid was higher (P<0.01) with MGM-based diets than that of control and RGM diets. Lastly, the proportion of both propionic and butyric acids was minimum with MGM-based diets than with either control or RGM-based diets. Therefore, it could be recommended that RGM could substitute 50-75% of GNC, corresponding to 5-8% inclusion in the complete diet of ruminants. In addition, MGM-based diets excelled in terms of greater digestibility, reduced CH4 emission as well as beneficially influenced rumen fermentation.