The voluntary intake and apparent digestibility of kleingrass (Panicum coloratum cv. Verde) were measured in seven periods, comprising one full year. The forage was offered twice a day ad libitum to seven rams, fitted with faeces collection bags; each experimental period was composed of 8 days for adaptation and 8 days for collection of data. The dry-matter (DM) intake (DMI) varied from 36·1 to 64·9 glkg M075, the digestible dry-matter intake (DDMI), from 17·4 to 41·9 glkg M0·75 and the in vivo dry matter apparent digestibility (DMD), from 0·471 to 0·667.
Daily samples of offered forage were taken and pooled subsamples from each of the seven periods were incubated in nylon bags in the rumen of three Hereford steers. The data were fitted to the exponential equation: p = a + b (1-e-ct) to estimate p (the proportionate loss of DM at time t of incubation); effective degradability (ED) and lag time (L) were also estimated.
The parameters obtained in situ were related to the in vivo results by simple and multiple regression. The correlation coefficients of the rate of degradation (c) and ED with DMI, DDMI and DMD were, respectively, 096 and 0·97; 0·97 and 0·96; 0·86 and 0·88. By including a, b, c and L into a multiple regression analysis, the coefficients of determination (R2) were: DMI: 0·99; DDMI: 0·99 and DMD: 0·91. Within the conditions of this study, the parameters obtained in situ were reasonable estimators of voluntary intake and apparent digestibility.