Kinetics of milk production as a function of energy and protein supplementation

Abstract

Three 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^-1.day^-1), 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 r² = 0.91; Exp. 2: 1/Milk = 0.0181*(1/SM) + 0.196 r² = 0.99; Exp. 3: 1/Milk = 0.0140*(1/SG) + 0.116 r² = 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.