Intake and digestibility of diets derived from stovers and straws compared with lucerne hay and sweet potato haulm

Abstract

In order to learn more about the feeding value of stovers and straws, seven diets were compared in one experiment and nine in another. The diets in the first experiment were: the upper and lower parts of lucerne (Medicago sativa) hay, the leaves, upper stem and lower stem of maize (Zea mays) stover and the leaves and stem of sorghum (Sorghum vulgare) stover. The diets in the second experiment were: the upper and lower parts of lucerne hay, the leaves, stem and whole stover of millet (Setaria italica), the straw and chaff of wheat (Triticum aestivum), rice (Oryza sativa) straw and sweet potato (Ipomoea batatas) haulm. The diets were fed to sheep to record rate of intake, voluntary intake and in vivo digestibility. The diets were analysed for cell wall (as neutral detergent fibre), crude protein and lignin. Organic matter degradation and cell wall degradation were recorded in nylon bags in the rumen of cattle.

The highest rates of intake (6·8–9·6 g dry matter/min) and voluntary intake (75–103 g dry matter/kg W^0·75/day) were with sweet potato haulm and the upper, leafy part of lucerne hay. The voluntary intake of millet leaves, wheat chaff and the lower, stemmy part of lucerne hay was moderately high (46–70 g dry matter/kg W^0·75/day). Voluntary intake of leaves was higher than that of stems in the case of millet, sorghum and to a lesser extent maize. The lowest rates of intake were with millet stem, sorghum stem and rice straw (1·8–2·4 g dry matter/min). In vivo digestibility of organic matter was highest (59–67%) for the upper part of lucerne hay, sweet potato haulm, the lower part of maize stem and millet leaves. The leaves of maize were less digestible than the stem, while the reverse was the case with millet. Cell wall content was particularly high (74–78% of dry matter) in millet stem, wheat straw and chaff, rice straw and sorghum stem. Lignin content was low (3·6–4·2% of dry matter) in millet leaves, maize leaves and the upper part of maize stem. Organic matter degradation after 24 h incubation in the rumen was highest (80%) in sweet potato haulm and lowest (39–44%) in millet stem, wheat straw and chaff and rice straw. Cell wall degradation after 96 h in the rumen was highest (76–81%) with the leaves of maize, sorghum and millet and lowest (40–59%) with lucerne hay, millet stem and stover, wheat straw and chaff and rice straw.