Deficiências minerais em bovinos de Roraima, Brasil. IV. Magnésio, sódio e potássio

An experiment was conducted to verify the mineral levels in beef cattle from six regions of northeast Roraima Federal Territory, Brazil. The soil, forage, and bovine tissue (blood, bone) were collected during the wet and dry seasons of the year. Only the soil from Surrão region showed medium level of Mg (0.500 meq/100g) all the others presented low levels. Soil K was at medium level in Caumé region (65 ppm), and low in all the other five regions. Soil Na levels were in a range from 47 ppm to 102 ppm. Forage Mg was sufficient to meet the requirements of growing and finishing steers, but was apparently deficient for lactating cows in five of six regions studied. Forage Na and K levels were low in all six regions. The levels of Mg, Na and K in the forages were significantly (P<0.05) lower during the dry season than during the wet season. In cultivated forage Mg levels, were sufficient to meet the requirements of beef cattle and in the native species were adequate only for growing and finishing steers. Magnesium plasma levels in cattle were normal in both seasons. Rib bone ash Mg means were low and ranged from 0.32% to 0.44% in the lactating cows and form 0.28% to 0.47% in the other animals.Foi realizado um estudo das deficiências minerais de bovinos em seis regiões localizadas ao nordeste do Território Federal de Roraima, onde foram amostrados solo, forrageiras e tecido animal (sangue e osso) durante as épocas seca e chuvosa. Teor médio de Mg no solo foi encontrado apenas na região do Surrão (0,500 meq/100 g). Todas as outras regiões apresentaram níveis baixos. Nível médio de K também foi observado em apenas uma região, a de Caumé, com 65 ppm. Nas demais regiões os níveis de K no solo foram baixos. Os níveis de Na no solo variaram de 47 ppm a 102 ppm entre regiões. As forrageiras apresentaram teores de Mg adequados para bovinos de corte em crescimento e terminação, porém aparentemente inadequados para vacas em lactação, em cinco das seis regiões estudadas. Os níveis de Na e K nas forrageiras foram deficientes em todas as regiões. Os níveis de Mg, Na e K nas forrageiras foram significativamente menores (P