In the tropics it is very common to find diets for animal production based primarily on forage crops, and these diets are limited by their low quality. This investigation was conducted to determine the digestibility and fiber content in two varieties of king grass (Pennisetum purpureum), green and purple, with different frequencies of pruning and application of fertilizers. The study used a completely randomized block design sub-divided into plots. An analysis of variance indicated no differences between varieties or effect of fertilization on in vitro digestibility, neutral detergent fiber (NDF), acid detergent fiber (ADF) and total N. The average digestibility for the green variety was 29.6 %, while the purple variety was 28.6 %. In the case of NDF the averages were 75.3 % and 75.8 %, respectively for the same varieties, with a reverse effect of age of regrowth in the cell wall content.