J.A.M. Groten

Effects of forage maize type and maturity stage on in vitro rumen fermentation characteristics

An experiment with forage maize plants representing early and late-ripening types of Dry Down and Stay Green cultivar types was conducted to study the effects of cultivar and maturity stage on in vitro rumen fermentation characteristics and to investigate the validity of the generally supposed qualities of these cultivars. Plants were harvested at an estimated whole plant dry matter (DM) content of 250, 320 or 390 g kg‾1, on 20 August, 16 September and 3 October 2003, respectively. Chemical composition and in vitro rumen fermentation characteristics, using the gas production technique, were determined of samples from entire not ensiled plants, ears and stover and from entire plants after ensiling. The increase in whole plant DM content from 250 to 320 g kg%sup-1; (20 August - 16 September) caused starch content of the whole plants to increase and neutral detergent fibre (NDF) digestibility to decrease, both more than prolonged ripening (to 390 g DM kg-1). DM content at harvest had a statistically significant influence on degree and rate of in vitro rumen fermentation. Calculated in vitro starch degradation after 10 h of incubation in rumen fluid suggested an increased content of rumen escape starch in the older samples. Maize type had only minor effects on fermentation characteristics, which were most pronounced for the ears and the remaining stover. Although the observed differences caused by the Dry Down or Stay Green characteristics were statistically significant in some cases, they were not systematic not for the early nor for the late-ripening types.

Effects of chop length and ensiling period of forage maize on in vitro rumen fermentation characteristics

The effect of chop length and ensiling period on in vitro rumen fermentation characteristics of forage maize was studied in two experiments. In the first experiment, maize plants of eight cultivars representing different combinations of Dry Down, Stay Green, early ripening, late ripening, starch and cell wall types were chopped at harvest into pieces of 6 or 15 mm and ensiled in small laboratory silos. After 8 weeks, silage samples were taken and freeze-dried (not ground) before in vitro rumen fermentation characteristics were determined using the gas production technique. Chop length appeared not to affect the in vitro fermentation characteristics. In the second experiment, plants of two of these maize cultivars were chopped into 6-mm pieces and ensiled for different periods in small laboratory silos and in large bunker silos as used in practice. After 0, 14, 42 and 180 days of ensiling, chemical composition and in vitro rumen fermentation characteristics were determined using the gas production technique. The in vitro fermentation characteristics were not influenced by the ensiling period up to 180 days. During the first two weeks of the ensiling period sugar content decreased and so did the gas production caused by fermentation of the soluble components.