RESUMOTrês experimentos foram conduzidos com o objetivo de avaliar os efeitos da suplementação energética e proteica sobre a produção e composição do leite de vacas mestiças. Doze vacas foram distribuídas em três experimentos, em quadrados latinos 4 x 4, em quatro períodos de quatorze dias. Os tratamentos consistiram de níveis crescentes de fubá de milho -M (0,0; 0,85; 1,70; e 3,40 kg vaca -1 dia -1 ), farelo de soja -FS (0,0; 0,65; 1,30; e 2,60 kg vaca -1 dia A produção máxima teórica de leite (1/a) foi de 5,9; 5,1 e 8,6 kg animal -1 dia -1 e a quantidade de concentrado para atingir a relação custo-benefício zero foi de 0,95; 0,60 e 0,90 kg para M, FS e GS. Os modelos de saturação cinética são apropriados para explicar esses efeitos e prescrever recomendação de nutrientes na alimentação animal.Palavras-chave: desempenho, gado de leite, Lineweaver-Burk, Michaelis-Menten, nutrição
Kinetics of milk production as a function of energy and protein supplementation
ABSTRACTThree studies were conducted to evaluate the effects of energy and protein supplementation on milk production by crossbred cows in pasture and feedlot. Twelve cows were allotted in three-4 x 4 Latin squares, in four periods of fourteen days. The treatments consisted of increased levels of corn meal-CM (0.0, 0.85, 1.7 and 3.4 kg.cow ), soybean meal-SM (0.0, 0.65, 1.3 and 2.6 kg) and grinded soybean grain-SG (0.32, 0.65, 1.3 and 2.6 kg). There were no treatment effects, although the mean data of milk production presented a curvilinear response to concentrate levels, following a Michaelis-Menten relationship, according to the next equations of Lineweaver-Burk: Exp. 1: 1/Milk = 0.0384*(1/CM) + 0.168 r 2 = 0.91; Exp. 2: 1/Milk = 0.0181*(1/SM) + 0.196 r 2 = 0.99; Exp. 3: 1/Milk = 0.0140*(1/SG) + 0.116 r 2 = 0.98. The theoretical maximum milk production (1/a) were 5.9, 5.1 and 8.6 kg.animal -1 .day -1 and the calculated amounts of supplements to reach marginal cost-benefit zero were 0.95, 0.6 and 0.9 kg for CM, SM and SG. The models of saturation kinetics are appropriate to explain these effects and to make nutrient recommendations.