Effect of dietary inclusion of cashew nut shell liquid on in vitro and in vivo protein digestibility and utilization in West African dwarf goats

Abstract

Effect of cashew nut shell liquid (CNSL) in diets for West African dwarf (WAD) goats on protein digestibility and utilization was evaluated in vitro and in vivo. Four diets consisting of Panicum maximum supplemented with concentrate pellets containing 0, 5, 10 and 15 mL/kg of CNSL were used. Panicum and pellets were combined in ratio 70: 30 of required dry matter (DM). For in vitro experiment, 500 mg (n=8 per diet) of diet samples (DM basis) were incubated at 39°C for 48 h following the procedure of Menke and Steingass (1988). Dry matter and crude protein digestibility, ammonia nitrogen (NH₃-N) and bacteria count were determined after 24 and 48 h incubation by recovering feed residues and rumen liquor. For in vivo experiment, twenty-four WAD goats were divided into four groups of six animals each. Each group was fed one of the four diets at 5% body weight (DM basis). Dry matter and crude protein intake, weight gain, protein efficiency ratio, rumen NH -N, bacteria count and crude 3 protein digestibility were measured during 98 days of feeding and digestibility trial. Experiments were arranged in a completely randomized design and data analyzed using one way analysis of variance procedure of SAS (1999). Results showed that 5 – 15 mL/kg CNSL in supplemental pellets reduced (P < 0.05) protein digestibility in vitro but increased (P < 0.05) total-tract protein digestibility in vivo. In vitro rumen NH -N decreased (P < 0.05) with 5 – 15 3 ml CNSL inclusion after 24 and 48 h. At 30 and 60 days post-feeding, 10 – 15 mL CNSL reduced (P < 0.05) rumen NH -N in goats Protein efficiency ratio was higher (P < 0.05) with 3 CNSL and goats fed 15 mL CNSL had the highest (P < 0.05) protein efficiency ratio. Rumen bacteria population in vitro and in vivo decreased (P < 0.05) with 5 – 15 mL CNSL in supplemental pellets. In conclusion, the reduced in vitro protein digestibility with reduced NH -Nproduction and bacteria population in vitro and in vivo suggests an inhibitory effect of 3 CNSL on rumen proteolysis. Cashew nut shell liquid in supplemental pellet for WAD goats up to 15 mL/kg therefore inhibited dietary protein breakdown in the rumen with consequent improvement in protein digestibility and utilization at the lower tract.