ANIMAL GROWTH AND MILK PRODUCTION AS A FUNCTION OF NUTRIENTS SUPPLY FOLLOW THE SATURATION KINETICS MODEL OF MICHAELIS-MENTEN

Abstract

The objective of this study was to evaluate the responses in weight gain and milk production through concentrate supplementation in cattle (growing and lactating) kept on pasture or in feedlot. The data were collected from 25 experiments with bovines at the growing phase supplemented with different levels of concentrate on pastures and seven experiments conducted in feedlot, which did not include control treatments, and one experiment with animals at the growing phase and three experiments with cows at lactation that, except for one experiment with cows, included control treatment (forage + mineral salt). The results from the two databases presented linear response of 0.12 kg gain/kg of concentrate in natural matter, which provides an 8.3:1 conversion of concentrate, for both pastures from the dry season and feedlot. The linear effect was due to the variation from experiment to experiment and the lack of a control treatment. In the experiment with animals at the growing phase on pasture, in the dry season, daily weight gain was curvilinear, where the marginal increase in daily gain reduced with the increase in concentrate level. In the three experiments with lactating cows, milk production and variations in body weight (assessed only in one experiment) were curvilinear, presenting a hyperbolic function in which the response is more marked in low levels of concentrate and low nutritional values of the tropical pastures during the dry season. The model of Michaelis-Menten explained the curvilinear response of animal growth and milk production as a function of nutrient supply, and can be utilized to estimate the responses to the nutrients and to make recommendations of nutrients in diets for cattle.