In vitro Evaluation of Different Levels of Cashew (Anacardium occidentale) Nut Meal Supplementation on Rumen Fermentation Kinetics and Digestibility

A shortage of feed resources poses challenges for sustainable livestock production. Researchers are increasingly investigating alternative feeds to replace conventional ones. Cashew nut meal (CNM), a by-product of the cashew nut kernel industry, is a promising alternative feed for ruminants owing to its good nutritive value. Due to limited research on optimal inclusion levels in ruminant diet, this study aimed to evaluate the effect of incorporating varying levels of CNM as a supplement on in vitro rumen fermentation kinetics and digestibility.

Seven distinct compounded feed mixtures (CFM) were formulated, with CNM progressively replacing 0 (C0), 10 (C1), 20 (C2), 30 (C3), 40 (C4), 50 (C5) and 60 (C6) per cent of the soybean meal (SBM) protein present in the control CFM. Additionally, seven experimental complete diets (T0 to T6) were prepared by blending these CFM with Super Napier (Pennisetum purpureum × Pennisetum glaucum) hay in a 40:60 ratio. These CNM based complete diets were subjected to rumen in vitro gas production (IVGP) study with cumulative gas production (GP) measured at 0, 2, 4, 6, 8, 12, 16, 24, 36, 48, 60, 72 and 96 h post-incubation. Subsequently, in vitro true dry matter digestibility (IVTDMD) and neutral detergent fiber digestibility (NDFD) of the diets were determined using a modified in vitro two-stage technique. Later, total volatile fatty acids (TVFA) were estimated using gas chromatography.

Analysis of chemical composition revealed that CNM contains good protein of 256.5 g/kg. The potential gas production (D) and the rate and extent of gas production (c) for diets containing CNM ranged from 54.63 to 60.24 mL and 0.036 to 0.043 h^-1, respectively. IVTDMD and NDFD analysis of the seven complete diets fell within the range of 79.12 to 80.80% and 64.72 to 66.47%, respectively. The estimated TVFA for seven complete diets ranged from 17.87 to 23.65 mM. Further, the metabolisable energy (ME) of diets ranged from 7.89 to 8.08 MJ/kg DM. Importantly, no significant differences were observed in rumen fermentation kinetics parameters, IVTDMD, NDFD and TVFA among treatments (T0 to T6). CNM could be used as an alternative to SBM in compounded feed mixtures of ruminants up to 30% (w/w) without any adverse effect on rumen fermentation pattern and digestibility.