Chemical composition, digestibility and feeding value of maize cobs

Abstract

The digestibility of treated maize cobs was studied using Romney Marsh wether sheep in a 2 × 3 factorial design; maize cobs were ground through a 10- or 6-mm screen and three chemical treatments were applied to each grinding: distilled water (control); sodium hydroxide (4.5 g per 100 g cob dry matter); and Magadi soda (9.0 g per 100 g cob dry matter). Cobs were treated for 24 h using one litre of solution per kg of maize cobs. The digestion coefficient of crude protein was lowered ( P< 0.01) by finer grinding of the maize cobs. Dry matter digestibility coefficients were 44.7, 54.2 and 61.6% for maize cobs treated with water, NaOH and Magadi soda, respectively. Digestibility of energy, cell walls and cellulose was increased more by Magadi soda than by NaOH. Digestibility of acid detergent fibre (ADF) was depressed ( P< 0.05) by NaOH but improved ( P< 0.05) by Magadi soda. Chemical treatment lowered ( P< 0.01) the digestibility of crude protein from 28.0 to 17.0% (NaOH) or to 18.7% (Magadi soda). Grinding and chemical treatment of maize cobs interacted ( P< 0.01) in their effects on digestibility of crude protein. Friesian cattle, grazed on a predominantly Nandi Setaria ( Setaria sphacelata) and Silver Leaf Desmodium ( Desmodium uncinatum) pasture, and supplemented with water-, NaOH- and Magadi soda-treated maize cobs, gained 0.41, 0.55 and 0.51 kg per day, respectively. Daily maize cob intake was higher on NaOH-treated than on water- and Magadi soda-treated cobs. Cattle on NaOH- and Magadi soda-treated cobs required more than 1 month to adapt to the cobs and show superior gain.