Effects of diurnal variation in pasture nutritive value and the defoliation start time on animal performance

Abstract

Diurnal variations in the concentration of nonstructural carbohydrates have been studied in several forage species. In all experiments were detected increased levels of nonstructural carbohydrates in the evening compared to morning. This is possibly in response to environmental factors. Thus, the magnitude of the responses vary according to grass species, time of year, growth cycle, location and vertical profile of the sward. Ruminants, feedlot or pasture, prefer forages with higher concentration of soluble carbohydrates and are able to detect appreciable differences from one food over another. Therefore, knowing the accumulation of nonstructural carbohydrates in forages can be useful to determine the best time to perform the harvest, whether for grazing, silage or hay. Through three experiments, the objective is (i) assessed the concentrations and the content of nonstructural carbohydrates and nitrogen in Palisadgrass (Brachiaria brizantha Hochst ex A. Rich. Stapf) over 24 hours in an experiment with pots in a greenhouse. The samples of leaf, stem and roots of plants will be collected for the analyses at 0, 3, 6, 9, 12, 15 and 24 hours after sunrise, (ii) determine the diurnal (6:00 AM vs 5:00 PM), temporal (four cycles) and vertical (30-20cm, 20-13cm) variation of nonstructural carbohydrate concentration, chemical composition and organic matter digestibility of Palisadgrass in an experiment in plots, (iii) to verify the hypothesis that the start time of defoliation in the morning or late afternoon has influences on the ingestive behavior, herbage intake and animal performance, a field experiment will be held with six groups of Nellore heifers grazing Palisadgrass pastures in rotational stocking methods in a frequency of one day of occupation and 25 days of rest. The treatment will be the time of paddock change, three groups at 6:00 PM versus the other three groups at 4:00 PM. (AU)