Energy partition, nutritional energy requirements and methane production in F1 Holstein × Gyr bulls, using the respirometric technique.

The nutritional energy requirements of animals for maintenance and weight gain, such as the energy partition of the diet, were determined in different feeding plans. Fifteen F₁ Holstein × Gyr, non-castrated male bovines with a mean initial liveweight of 302 kg were used. The diets were corn silage and concentrate, formulated to enable gains of 100, 500 and 900 g/day, called low, medium and high weight gains, respectively. Tests of digestibility and metabolism were conducted to determine energy losses through faeces, urine and methane emissions. Heat production was determined using respirometry chamber. Net energy for maintenance was calculated as the antilogarithm of the intercept of the regression of the logarithm of the heat production, as a function of the metabolisable energy intake. Retained energy was obtained by subtracting the heat production from the metabolisable energy intake. With the increased consumption of dry matter, there was an increase in faecal and urinary energy loss. Retained energy increased linearly with the metabolisable energy intake. The net energy for gain in the diet did not differ among the treatments, such as the efficiency of use of metabolisable energy for weight gain k_g (0.34). The net energy for maintenance was 312 kJ/kg LW^0.75, and the metabolisable energy for maintenance was 523 kJ/kg LW^0.75. The daily methane production (g/day) increased with the dry matter level and the daily loss represented 5.31% of the gross energy consumption. The determination of the nutritional energy requirements for bovines of different genetic groups and under different feeding conditions allows the appropriate adjustment of feed formulation for each animal category. Knowledge of the energy partition of the diet and methane production allows the development of appropriate nutritional strategies respecting the environment. [ABSTRACT FROM AUTHOR]