Quality of Andropogon gayanus and animal productivity | [Calidad de Andropogon gayanus y productividad animal]

Based on the results reviewed, it can be inferred that the nutritional quality of A. gayanus is within the range of other tropical grasses. The relatively low digestibility of the grass (50 percent -55 percent) is perhaps the most limiting quality factor. As with other tropical grasses, increased maturity results in a decline of crude protein (-0.9 percent/week) and digestibility (-1.5 percent/week), as well as in reduction of intake. The P levels (0.08 percent, 0.14 percent) in A. gayanus are low even during the rainy season and with application of P fertilizer, indicating the need to supplement grazing animals with high nutrient requirements (e.g., growth, lactation). The quality of A. gayanus can be significantly improved with legumes, which contribute directly and indirectly to increased protein (6 percent to 11 percent) and P (0.11 percent to 0.16 percent) levels in the grass on offer and in the selected diet. However, even with legumes, the digestibility of A. gayanus can limit animal production. The improvement of quality in A. gayanus through the selection of leafy genotypes has not been demonstrated under grazing conditions. However, it is postulated that A. gayanus genotypes with a high proportion of leaves could facilitate management of the grass under grazing. Animal productivity of A. gayanus pastures in savanna ecosystems is low, ranging from 90 to 120 kg/animal/year, depending on stocking rate. This results from high weight losses during the dry season and moderate gains during the rainy season. Annual weight gains of about 150 kg/animal can be achieved by introducing legumes, using moderate stocking rates (e.g., 1.5 to 2.0 animals/ha) under savanna conditions and higher stocking rates in humid forest ecosystems. Long-term productivity studies of A. gayanus pastures are scarce. However, based on the experiences in the Colombian Llanos, it is apparent that the use of some form of rotational grazing system may be required for persistence, particularly with stocking rates of two or more animals per hectare