Feeding dairy cows with soybean by-products : effects on metabolic profile

Abstract

Os subprodutos de soja vêm sendo utilizados como fonte protéica na alimentação de vacas leiteiras no Rio Grande do Sul. Entretanto, a elevada degradabilidade ruminal desta fonte causa perda da qualidade intrínseca da proteína e leva a aumento da uréia plasmática, com conseqüências deletérias no metabolismo animal. O tratamento térmico do grão de soja pode superar essa limitação. Este trabalho teve como objetivo avaliar o metabolismo de vacas leiteiras alimentadas com grão de soja cru e tratado termicamente, mediante o perfil metabólico no plasma e no leite. Foram utilizadas doze vacas da raça Holandesa no terço médio da lactação, nas quais foram aplicados quatro tratamentos: concentrado protéico comercial, farelo de soja, grão de soja cru e grão de soja tostado. No leite, foram dosados os teores de proteína e uréia. Não foram detectadas diferenças significativas entre os tratamentos na concentração de glicose, beta-hidroxibutirato, cálcio, fósforo e magnésio. Houve maiores níveis de colesterol plasmático nos animais consumindo grão de soja cru e tratado com calor. As vacas consumindo soja tostada tiveram menor teor de uréia no plasma e no leite da ordenha da manhã, sugerindo que o tratamento com calor no grão de soja foi efetivo para diminuir a degradação protéica no rúmen. Recomenda-se usar amostras de leite coletadas pela manhã para avaliar o perfil metabólico.

Soybean by-products are currently used in Rio Grande do Sul, Brazil, as a source of protein in dairy cows. However, the high protein breakdown of this feed source in the rumen causes loss of the intrinsic quality of the protein and increases plasma urea with deleterious consequences to animal metabolism. Thermal treatment of soybean can overcome this limitation. The aim of this study was to evaluate the metabolism of dairy cows fed with thermally treated soybean and raw soybean, through the analyses of the metabolic profile of plasma and milk. Twelve Holstein cows in mid-lactation period were studied using four treatments: commercial concentrated of protein, soybean meal, raw soybean and roasted soybean. Protein and urea levels in milk were measured in morning and afternoon samples. Data were arranged in a Latin square design (4 treatments and 3 animals in each square). There were no significant differences in glucose, beta-hydroxybutyrate, calcium, phosphorus and magnesium concentrations among treatments. Cows consuming raw and thermally treated soybean had higher levels of plasma cholesterol. Cows consuming roasted soybean had lower level of plasma and milk urea in the morning. Afternoon milk samples had higher levels of urea than morning samples. It is suggested that thermally treated soybean was effective in diminishing the breakdown of protein in the rumen. It is better to employ morning milk samples to evaluate metabolic profile than afternoon samples.