Abstract

LACERDA, Paulo Drude de et al. Variation on the annual nutritive value of two grasses cropped in the litoral lowlands of the State of Rio de Janeiro, Brazil. Cienc. Rural [online]. 2004, vol.34, n.2, pp. 523-529. ISSN 0103-8478.  http://dx.doi.org/10.1590/S0103-84782004000200029.

Chemical analyses of grasses from three farms located in the coastal lowland region of Rio de Janeiro were made. Elephant-grass (Pennisetum purpureum) used as chopped fresh forage and in rotational grazing, and the limpo-grass (Hemarthria altissima), were sampled monthly. The values of dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), lignin (LIG) and the carbohydrate and nitrogen fractions were compared throughout the year. There were effects of the season on the grass and between grasses in a season of the year. Crude protein ranged from 37,2g kg^-1 of DM in the elephant-grass from the daily cut forage system to 131,5g kg^-1 of DM in the rotational grazing system. The limpo-grass showed values that ranged from 69,8g kg^-1 of DM to 99,7g kg^-1 of DM. The values of NDF varied between 702,9 and 811,6g kg^-1 of DM through the year, and the lowest means were obtained from the rotational grazing system of the elephant-grass. The daily chopped elephant-grass gave the highest values of lignin (55,3 to 81,3g kg^-1 of DM ). The non fibrous carbohydrate fraction (A+B1) ranged from 20,9 to 85,5g kg^-1 of DM. The fibrous fraction, containing fractions B2 and C, presented means between 673,6 and 794,5g kg^-1 of DM. The limpo-grass showed the highest values of the B2 fraction, and the lowest values of fraction C, during the year. The values of fraction C of elephant-grass from the two systems of exploration ranged between 126,1 and 135,3g kg^-1 of DM, and 149,2 and 177,7g kg^-1 of DM, while the limpo-grass ranged from 84,0 to 107,8g kg^-1 of DM. The nitrogen fractions varied between seasons and between species and types of exploration. Fractions ranged from 9,8 to 36,4g kg^-1 DM (A), 0,73 to 12,6g kg^-1 of DM (B1), 11,1 to 44,1g kg^-1 of DM (B2), 2,2 to 34,5g kg^-1 of DM (B3) and from 6,7 to 12,8g kg^-1 of DM (C).

Keywords : elephant-grass; limpo-grass; nitrogen and carbohydrate fractions.