Effect of exposure on the chemical composition and in vitro dry matter digestibility of untreated and formalin treated green chop

Abstract

Green chop, made from babala ( Pennisetum typhoides) and forage sorghum ( Sorghum bicolor sudanense) which were each harvested from six different rows at the pre-bloom and bloom stages of maturity, were exposed to the environment with and without formalin treatment (4.9 ± 0.8 g formaldehyde per 100 g crude protein) for a period of 21 ± 3 h. This was done at laboratory scale in a room at 27°C. These treatments were compared in a complete randomized design with each other and with a corresponding non-exposed fresh green chop treatment. Exposure without formalin treatment caused a significant increase ( P < 0.05) in the acid detergent fibre (ADF) content (41.0 vs. 38.3%) and a concomitant decrease ( P < 0.05) in the in vitro dry matter digestibility (IVDMD) (63.1 vs. 66.6%) when compared with the non-exposed fresh material. This was accompanied by an increase ( P < 0.05) in the non-protein nitrogen (NPN) fraction (41.6 vs. 32.4%). Exposed material treated with formalin had a higher ( P < 0.05) total dry mass (58.6 vs. 51.6 g) and a lower ( P < 0.05) ADF content (39.2 vs. 41.0%) than exposed untreated material. The decrease in IVDMD caused by exposure was totally prevented by formalin treatment. The IVDMD of exposed formalin-treated material was 67.8% in comparison with 63.1% ( P < 0.05) and 66.6%, respectively, for the exposed untreated and the non-exposed fresh material. The NPN contents for exposed material being treated and untreated were the same (40.5 vs. 41.6%) while the nitrogen fraction appearing in ADF was higher ( P < 0.05) for formalin-treated material (22.1 vs. 12.8%). It is concluded that the exposure of green chop led to some deterioration of forage quality, which was largely prevented by formalin treatment.