Thein vitrodigested cell wall and fermentation characteristics of grasses as affected by temperature and humidity during their growth

Abstract

SUMMARYTotal cell wall,in vitrodigested cell wall and fermentation-gas production were determined in the separated tops and stubble of five tropical and two temperate grass species grown under controlled temperatures and humidities. As the day/night temperatures increased from 18/10 to 25/17 °C the total cell wall andin vitrodigested cell wall increased. With a further increase to 32/24 °C the total cell wall increased, but not thein vitrodigested cell wall.In vitrodigested cell-wall values were also calculated from a previously derived relationship betweenin vitrodigested cell wall and total cell wall. The differences between observed and calculated values increased (negatively) with increasing growth temperature suggesting that thein vitrodigested cell wall was depressed with increasing growth temperatures, but the extent of this depression was small.In vitrogas production from the fermentation of plant tops or stubble in buffered rumen fluid for 24 h was significantly affected by growth temperature and humidity, apparently because of changes in chemical composition induced by the treatments. The volume of gas produced between 24 and 48 h fermentation times was appreciably lower from stubble than from plant tops and this was thought to be due to a higher resistance of part of the cell wall of stubble to digestion by rumen bacteria. Gas production in this period was slightly lower in the tops of grasses grown at the lower temperatures, but this could have been an indirect effect from an associated decrease in the total cell wall.