Consumo de nutrientes por novilhas de corte em pasto consorciado sob metas de manejo com base na interceptação luminosa

Abstract

In order to define the best grazing management strategy, it is important to assess animal response to variations in the structure and composition of tropical forages. The objective of this study was to evaluate nutritive value, forage intake and N metabolism of beef heifers grazing mixed canopies of Marandu palisadegrass {Brachiaria brizantha (Hochst. ex A. Rich.) R.D. Webster [syn. Urochloa brizantha Stapf cv. Marandu]} and Calopo (Calopogonium mucunoides Desv. cv. Comum) under intermittent stocking. The treatments consisted of three grazing management: defined by the rest period interrupted at 90 (90LI), 95 (95LI) and 100% (100LI) of light interception (LI). The evaluations were carried out for 2-yr, in a randomized complete block design with four replications, within the rainy seasons and transition (between rainy and dry seasons), with repeated measure over time. Post-grazing height target was 15 cm for all treatments. The 100LI had less crude protein (CP) and in vitro dry matter digestibility (IVDMD) than the other treatments, both for grass (P = <0.001 and P = <0.001, respectively) and in the legume (P = 0.003 and P = 0.067, respectively). The neutral detergent fiber (NDF) concentration was greater in 95LI and 100LI than in 90LI, in the grass (P = 0.002) during the transition (P = <0.001), and in the legume (P = 0.077). The Calopo had a greater CP and IVDMD, and less NDF than Marandu palisadegrass. The digestibility of organic matter in the diet was less in 100LI than in 90LI and 95LI (P = 0.005) and in the transition (P = 0.047). There was no difference between the treatments for forage, grass and legume intake (P = 0.351, P = 0.155 and P = 0.412, respectively). The treatment 100LI resulted in less N, total CP intake and from the grass (P = <0.001, P = 0.005 and P = <0.001, respectively). The greater production of microbial N (P = 0.093) was in 90LI, followed by 95LI and less in 100 LI. The ratio CP/OM digestible, urinary N excretion and retained N were lower in 100LI compared to the other treatments (P = <0.001, P = 0.007 and P = 0.014, respectively). The target of grazing management between 90 and 95% of LI is recommended because it provided greater intake of CP and use of N by the animals and improved the nutritive value of mixed pastures of Marandu palisadegrass and Calopo.