Chemical compounds and gas production kinetics of annual ryegrass hay in distinct nitrogen levels and cutting heights

Authors: JULIANA REOLON PEREIRA, MARCELA ABBADO NERES, ITACIR ELOI SANDINI, ANA CAROLINA FLUCK, OLMAR ANTÔNIO DENARDIN COSTA, LAÉRCIO RICARDO SARTOR

Abstract: The aim of our work was to evaluate the chemical composition and cumulative gas production profiles of annual ryegrass hay through in vitro incubations for two cutting heights and different nitrogen fertilization doses. The experimental design was randomized blocks with split-plots. The nitrogen doses (0, 75, 150, and 225 kg N ha$^{-1}$) were distributed in the main plot and the subplots. To make the hay, the annual ryegrass was cut at heights of 5 and 10 cm from the ground, with three replications each. In the experimental area, corn was cropped in the summer and annual ryegrass pasture in the winter. We evaluated the nutritional compounds, with fractionation of protein and carbohydrate content as the kinetics of ruminal degradation in the gas production technique in vitro. The carbohydrates decreased linearly with the increasing levels in N, as well as the kinetic parameters. Protein fractions increased with the increase in N. A higher nonfibrous content was obtained at a cutting height of 10 cm. Regardless of the cutting height, nitrogen fertilization increased the crude protein content and decreased the total carbohydrates content, especially the nonstructural carbohydrates. The increase of N in the plant decreased the specific rate of gas production due to the degradation of the soluble fraction of rapid digestion and caused a decrease in gas production of the slow digestion fraction.

Keywords: Haymaking, kinetics parameters, Lolium multiflorum Lam., winter grasses

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