Intake rate, sward structure and nutritive value of elephant grass cv. Napier subjected to strategies of rotational stocking management

Abstract

Sward structure is influenced by grazing management and interferes with herbage accumulation, morphological composition, nutritive value and intake rate of the produced herbage, important factors determining animal performance and productivity. However, these relationships are static and do not take into account variations in herbage chemical composition due to variations in the balance between photosynthesis and respiration throughout the day, which may alter soluble carbohydrate concentration and, in turn, the contents of dry matter (DM), crude protein (CP), neutral (NDF) and acid detergent (ADF) fibre and dry matter digestibility (IVDMD) for a given management target (sward condition), with potential implications to the intake of nutrients and animal performance. This kind of study and information allows better integration of plant and animal responses to variations in sward structure, favouring intensification and rational exploitation of pastures using sward targets, as sward height for example, for defining grazing management practices. The objective of this experiment is to evaluate that kind of plant-animal interaction on elephant grass cv. Napier subjected to strategies of rotational stocking management defined in terms of pre and post-grazing targets of sward structure. Treatments corresponded to combinations between two post (sward heights of 35 and 45 cm) and two pre-grazing (95% and maximum canopy light interception during regrowth - LI) targets, and were allocated to experimental units (850 m2 paddocks) according to a 2x2 factorial arrangement and a complete randomised block design, with four replications. Measurements comprised the following response-variables: sward structure (vertical distribution of morphological components in sward herbage mass), herbage mass (HM) and bulk density (BD) above targets of post-grazing height, morphological and chemical composition of extrusa and simulated grazing samples, and the content of soluble carbohydrates in herbage mass pre-grazing early in the morning and late in the afternoon. Measurements were performed during seasons of the year considered references for transition in sward structure (autumn/winter, spring and summer) as part of a series of experiments carried out concomitantly in the same experimental area aiming at evaluating aspects of plant growth and development and herbage accumulation. The results are expected to generate important information for improving comprehension and planning of adequate and efficient use and management of this important forage tropical grass under rotational stocking management. (AU)