The net energy value of three subtropical forages

Abstract

Energy and nitrogen balance experiments with three subtropical forages, a legume and two grasses, are reported. Each forage was given to four sheep at several levels of feeding.

One of the forages had a low nitrogen content (4% crude protein) and was supplemented with urea and molasses containing 7 g nitrogen and 56 kcal/day. This caused voluntary consumption to increase by 50% and digestibility of all chemical constituents to increase by 6–12 units. Utilization of metabolizable energy for maintenance also improved by approximately 10%.

Digestible energy (42–62%) was predicted quite accurately from chemical composition by means of published equations which refer to forages grown in temperate climates. Metabolizable energy was close to 82% of digestible energy, as found with non-tropical forages. Net availability of metabolizable energy for maintenance ranged from a very low 60% to 80%. It was predicted more accurately from percentage metabolizable energy than from digestible crude fibre: the reverse applied to net availability for production (40–50%).