Abstract
The objective of this work was to determine macromineral requirements by Zebu steers grazing Brachiaria decumbens supplemented with concentrate. It was used 24 non-castrated steers, at an average age of 7 months and at initial average weight 180 kg. Eight control animals were slaughtered for determining initial body composition. The 16 remaining animals were divided in four four-animal plots, in a complete random design. Each plot received mineral mixture or supplements at the levels 0.75; 1.50 or 2.25 kg/animal/day. The right half-carcass of eight animals, two per group, was dissected in muscle, fat and bones and all body constituents were weighted for determination of empty body weight and body composition. Net requirements of calcium and phosphorus for an animal at 400 kg body weight were 11.13 g and 5.40 g, respectively. To estimate dietary requirements of maintenance and after, sum them to dietary requirements for gain in order to obtain total dietary requirements, it was adopted endogenous losses and bioavailability present in literature for each mineral macroelement. Total dietary requirement for calcium, phosphorus, magnesium, sodium and potassium for a 400-kg BW animal with 1.0-kg daily weight gain were 34.59; 17.36; 7.82; 5.19 and 41.11 g/day, respectively. Macromineral requirements by beef cattle under pasture supplementation are similar to those recommended by BR-Corte for beef cattle in feedlots.
Highlights
IntroductionBesides appropriate supplement of minerals, AFRC (1991) stresses that proper levels of protein and energy are needed for a normal development of the bones
Determination of mineral dietary requirements for bovines being raised on pasture conditions is extremely complex due to the several factors that directly or indirectly (ARC, 1980; Conrad et al, 1985; AFRC, 1991; Coelho da Silva, 1995; NRC, 2000).Besides appropriate supplement of minerals, AFRC (1991) stresses that proper levels of protein and energy are needed for a normal development of the bones
It is listed in NRC (2000) requirements of calcium and phosphorus for protein daily gain and Conrad et al (1985) stated that appropriate nutrition of these minerals depends on D vitamin level in the diet
Summary
Besides appropriate supplement of minerals, AFRC (1991) stresses that proper levels of protein and energy are needed for a normal development of the bones. It is listed in NRC (2000) requirements of calcium and phosphorus for protein daily gain and Conrad et al (1985) stated that appropriate nutrition of these minerals depends on D vitamin level in the diet. Greater fat depositions reduce mineral depositions and, their requirements by the animals inasmuch as concentration of these inorganic elements in the adipose tissue are lower than in the muscles and in the bones, which contain approximately 99% and 80% of body calcium and phosphorus, respectively (NRC, 2000)
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