Buntha et al., 2006. Livest. Res. Rural Dev., 18 (3)

Fresh foliages of guinea grass (Panicum maximum), cassava (Manihot esculenta), stylo (Stylosanthesis guiensis, CIAT 183) and water spinach (Ipomoea aquatica) were fed to growing goats in a  Completely Randomized Block arrangement with 3 goats and 4 periods, each of 8 days. The aim was to compare the water-extractable DM of these feeds with NDF values as predictors of whole tract DM digestibility.

The proportion of leaf  in the foliages offered was highest in cassava with relatively lower values for stylo and water spinach which were similar to each other (only leaves were fed in the case of guinea grass) . Some degree of selection occurred during eating as there were indications that on the cassava the goats selected the same proportion of leaf as in the foliage offered, but ate more of the petioles than the stems. For stylo, leaves were preferred slightly more than stems while the opposite was the case with the water spinach. There was a close relationship between water-extractable DM and NDF in DM (R2= 0.77; n = 35) in the different botanical components of the four foliages. DM intakes were highest on guinea grass and lowest on cassava with intermediate values for stylo and water spinach. Highest DM digestibility was recorded on the water spinach diet with lowest values for cassava. N digestibility was also high for water spinach with the lowest value for guinea grass. Among the guinea grass, stylo and water spinach foliages, there was a close relationships between DM digestibility and the two chosen indicators:- NDF and water extractable DM , with the closest fit being observed for the  latter (R2 = 0.85 and 0.98, respectively; n=3). The data for cassava did not fit in either of these relationships.

It is concluded that the water-extractable DM technique is a simple, low cost, and effective method that is equal to, or superior than,  NDF  as a predictor of the the DM digestibility of most forages. Forages for which the method is inappropriate (eg: cassava) are likely to be those which contain anti-nutritional substances known to affect negatively feed intake and digestibility. Urine excretion was 6 times higher, relative to live weight,  and 2 times higher, relative to water consumed from the forages, in goats fed water spinach compared with the other foliages.