Effect of sodium hydroxide treatment and/or extrusion cooking on the nutritive value of peanut hulls

Abstract

Sodium hydroxide treatment and/or extrusion cooking of peanut hulls was evaluated in vitro and in vivo. The hulls were treated with 0, 30, 40, 50 or 60 g of NaOH kg −1. As the level of NaOH increased a linear reduction in neutral detergent fibre ( P<0.01) and increase in dry matter digestibility in vitro ( P<0.01) was observed. Digestibility in vitro was doubled by treatment with 50 or 60 g NaOH kg −1. Attempts to extrude the alkali treated hulls alone were unsuccessful because of high fibre and low density. Two complete diets were formulated with 40% peanut hulls untreated or treated with 50 g alkali kg −1. Half of each of these diets was extruded in a S-40 L cooker extruder. The four complete diets were evaluated in a 4 × 4 latin square experiment using Nellore ram lambs. Alkali treatment significantly increased ( P<0.01) hemicellulose digestibility and reduced ( P<0.05) ether extract (EE) digestibility. Extrusion cooking lowered hemicellulose ( P<0.01), crude protein (CP) ( P<0.05) and EE ( P<0.01) digestibility. Alkali treatment or extrusion cooking did not affect digestibility of dry matter, organic matter, crude fibre, neutral detergent fibre, acid detergent fibre and cellulose. Alkali treatment increased ( P<0.01) water consumption, urine output and urine pH. Extrusion cooking decreased ( P<0.01) water consumption as well as urine output. Although there was a substantial increase in the in vitro dry matter digestibility of peanut hulls with 50 g NaOH kg −1, alkali treatment or extrusion cooking did not improve nutrient digestibility in lambs given complete diets containing 40% of peanut hulls.