The chemical composition and in vitro dry matter digestibility of untreated and ammoniated crop residues

Abstract

The chemical composition and in vitro dry matter digestibility (IVDMD) of untreated and ammoniated crop residues, sampled at various sites in the North West Province of South Africa, were investigated. The mean IVDMD of maize residues obtained by means of a whole plant maize harvester was found to be relatively high (IVDMD = 55.6±7.0%) while the crude protein (CP) (46±10 g/kg dry matter (DM)) and phosphorus (P) (1.2±0.5 g/kg DM) concentrations were below the maintenance requirement for dry gestating beef cows. The neutral detergent fibre (NDF) concentration was 837±39 g/kg DM. Maize residues obtained by means of a cob harvester tended to be of a somewhat higher nutritional quality (IVDMD = 58.3±7.7%; CP = 64±19 g/kg DM; NDF = 817±42 g/kg DM; P = 1.2±0.6 g/kg DM). Grain-sorghum residues, like maize residues, were low in CP (61±11 g/kg DM) and P (1.9±0.5 g/kg DM) concentration, but also had a low IVDMD (37.7±9.3%). Ammoniation (35 g ammonia/kg DM, 320 g moisture/kg DM) increased the IVDMD (17.6 and 18.1 percentage units) and CP concentration (89 and 93 g/kg DM) and decreased the NDF concentration (207 and 148 g/kg DM) of maize- and grain- sorghum residues, respectively. The IVDMD (71.5±6.2%) and NDF concentration (380±73 g/kg DM) of sunflower-cob residues reflected a high-energy value while the CP (93±26 g/kg DM) and P (2.2±0.7 g/kg DM) concentration met the needs for dry gestating beef cows. Ammoniation increased the CP concentration (186±21 g/kg DM), but had no effect on the IVDMD and NDF concentration of sunflower-cob residues.


South African Journal of Animal Science Vol.32(2) 2002: 83-88