La necesidad de atender la demanda de nutrientes en el ganado lechero, de forma constante a través del año, se inicia con un balance forrajero, fundamentado en las metas de productividad animal de la finca, el crecimiento y la disponibilidad estacional de los forrajes y el almacenamiento de una reserva forrajera para disponer oportunamente. El forraje de maíz ha sido empleado con mucha frecuencia en los países subtropicales como parte del balance forrajero anual (Bruno et al. 1995, Cuomo et al. 1998), formando la reserva generalmente ensilada (Aldrich y Leng 1974). En Costa Rica, la práctica de ensilaje ha tomado auge en los último seis años (Boschini 2002), obteniendo experiencia los productores en los aspectos metodológicos del proceso. El cultivo de maíz ha sido tradicional para la producción de grano en Costa Rica, especialmente en las zonas bajas. No se cuenta con la misma experiencia en las zonas lecheras de altura, en cuanto a variedades e híbridos, densidades de siembra y edades de cosecha óptima para la producción de forraje. Materiales genéticos criollos de la parte alta de Cartago han dado rendimientos de 11,2 a 15,1 t/ha de materia seca (107 días) con relaciones:

The experiment was condunted at the Alfredo Volio Mata Experimental Station of the University of Costa Rica, located at 1542 meters above sea level. The purpose was to determine the effect of plant density on total forage mass and the nutritive value of corn. Three diferent plant distances were used: 30 x 70 cm, 50 x 70 cm and 70 x 70 cm resulting in 47619, 28600 and 20449 plants per hectare, respectively. The first sampling was taken out 42 days after establishment and every two weeks thereafter, until 126 days. Dry matter, crude protein, ashes, neutral detergent fiber (NDF), acid detergent fiber (ADF) and lignin were analyzed for different parts of the plant. The values for celulose and hemicelulose were calculated. Total forage mass (kg/ha) was greater at higher plant densities. Dry matter content of leaves was higher than in stems, all of the plant densities. No significant difference (P<0,05) was found for crude protein content in the different parts of the plant. ADF was always higher in stems than in leaves. Stage of growth considerably affects biomass yield and nutritional quality of fodder. Before 70 days the dry matter content in leaves was higher than in stems. Latter accumulation of dry matter in stems was greater than in leaves. Crude protein content in leaves was over 18% during the first 70 days, then decreases a level of 13% at the end of the period. The lowest value of ADF was found before 84 days in leaves and stems. Under the enviromental conditions of this experiment, it appears that plant densities of about 48000 plants per hectare are optimal.

The purpose of this study was to determine the ruminal degradability of dry matter, crude protein, neutral detergent fiber and their fractions, contained in regrowth of mulberry at 56, 84 and 112 days. The degradation of leaves, stems and the whole plant was calculated. The potential degradability of these three components diminished as the regrowth aged. The soluble fraction of the dry matter was reduced from 29% to 25% in the leaves and from 27% to 19% in the stems between the 56th and the112th day. The degradable fraction in the stem remained constant (61-63%) on the three measuring days, with ruminal degradation levels of 14%, 10% and 9%/h respectively. In the stem the degradable fraction diminished from 42% to 30% between the 56th and 112th day, with degradation speeds of 8.4%, 6.7 % and 5.3%/h. The soluble crude protein diminished with age from 41% to 33% in the entire plant and the degradable fraction remained constant between 49% and 51%. The degradation rate was higher than 9.4%/h. The neutral detergent fiber had a degradable fraction of 71%, 62% y 43% on the 56th, 84th and 112th day, with degradation rates of 13%, 10% y 9%/h respectively. The degradation of the neutral detergent fiber began in the rumen with a lag time of 1.5 to 3.2 hours.

The purpose of this study was to determine the phenological development and the nutritional quality of Sorghum almun during different growth stages. The seed was cultivated in the Alfredo Volio Mata Experimental Station of the University of Costa Rica. Eighteen kg of 88% germinal seed per hectare were planted. The first sample was taken 24 days after sprouting and every 14 days thereafter, up to 150 days. The production of biomass of the stems, leaves and ears of grain were measured and the amounts (content) of dry mater matter, crude protein, total ashes, neutral fiber and detergent acid, hemicellulosa, cellulose and lignin were determined. During the first 52 days of growth, the output of leaves was higher than that of stems. On the 57th day, a yield of 1395 kg of dry matter per hectare, 50% leaves and 50% stems, was estimated. The ears of grain appeared after 94 days, contributing 50kg per hectare of dry matter. The concentration of dry matter in the leaves was highest from the moment of sprouting to the 136th day. The content of crude protein in the leaves was always superior to that in the stems. In the leaves the crude protein diminished 16%-28% between the 38th and 150th day of growth. In the same period, the crude protein in the stem diminished 5%-18%, and in the whole plant 8%-26%. The neutral fiber and detergent acid in the leaves and the stems were less than 60% during the first two months of growth and more than 70% in the latter period.

No abstract