Potential nutritional assessment of dwarf elephant grass (Pennisetum purpureum Schum. cv. Mott) by chemical composition, digestion and net portal flux of oxygen in cattle

This study was conducted to evaluate changes in chemical composition of dwarf elephant grass hay cut at 30, 40, 50 and 60 days of growth, and its effect on apparent digestibility and particle-phase passage through the gastrointestinal tract (Experiment 1) and on oxygen utilization by the portal-drained viscera of cattle (Experiment 2). The experiments were carried out using four Holstein steers in each experiment (mean live weight of 129±17 kg and 139±3 kg in the Experiments 1 and 2, respectively) in a 4×4 Latin square experimental design. The animals of Experiment 2 were implanted surgically with permanent indwelling catheters in portal and mesenteric veins. The experimental diets were chopped hay (10–15 cm length particles) fed two times a day in amounts restricted at 2% of the animal live weight. The content of neutral detergent fiber, acid detergent fiber, acid detergent lignin, titratable cross-ester links and acid detergent insoluble nitrogen increased, but the content of total, non-protein and soluble nitrogen decreased with plant growth. The apparent digestibility of different compounds of hay was not affected (P>0.05), but retention times in the reticulum-rumen (P<0.01) and in the caecum-proximal colon (P<0.05) decreased linearly and, the passage rate of particles through reticulo-rumen (P<0.01) and through caecum-proximal colon (P<0.05) increased linearly with plant growth. In addition, oxygen utilization and estimated heat production by the portal-drained viscera, as a proportion on digestible energy intake, increased linearly with dwarf elephant grass growth (P<0.01 and P<0.05, respectively). In conclusion, if the nutritional value of forage decrease with plant maturity, the results of present study suggest that, at restricted level of intake and within of vegetative stage of dwarf elephant grass this is so due, at least partially, an increase of metabolizable energy use by the gastrointestinal tract. Therefore, energy availability for productive purposes, such as live weight gain or milk synthesis decrease.