Comportamento ingestivo de novilhas mestiças Holandês-Gir em pastagem de capim-estrela (Cynodon nlemfuensis) em quatro estações do ano na Baixada Fluminense-RJ

Abstract

The objective was to evaluate the ingestive behavior of Holstein-Gir crossbred heifers grazing stargrass (Cynodon nlemfuensis) managed under two levels of light interception (LI - 90 and 95%) and two post-grazing residual heights (20 and 30 cm). This study was divided into two chapters; in the first one, the contents of dry mater (DM), mineral matter (MM), crude protein (CP), insoluble neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin, cellulose and leaf to stem ratio of plucked samples were quantified, as well as their relationship with the feeding behavior (bite rate, food stations and bolus chewing) of crossbred heifers on stargrass (Cynodon nlemfuensis) pasture managed under two levels of LI and two post-grazing residual heights in four seasons at Baixada Fluminense, Rio de Janeiro. In the second chapter, environmental characteristics (dry bulb temperature, skin surface temperature and Wet Bulb Globe Temperature) and pasture structure (height, leaf to stem ratio and nutritive value) were related to the grazing time, rumination and leisure of crossbred heifers grazing on stargrass (Cynodon nlemfuensis) managed under two levels of light interception (LI) and two of post-grazing residual heights in four seasons at Baixada Fluminense – RJ. The experiment was conducted at PESAGRO-RIO, in the city of Seropédica - Rio de Janeiro, between the months of April 2012 to January 2013, comprising the four seasons. During this period, 16 evaluations, each lasting 24 hours, were held considering two grazing periods (input and output). The nutritive value of the pasture varied across the length of the seasons with one treatment combination (LI with residual height) standing out each season in relation to the nutritional value of forage. Lower levels of NDF, higher levels of CP, as well as greater leaf to stem ratio and higher bite rate were however found at the time of grazing commencement, regardless of the treatment evaluated. The bite rate showed association with the leaf to stem ratio. 24 hour grazing in stargrass managed under the aforementioned conditions did not result in any change in food station searching behavior. The grazing time showed an inverse relationship with the canopy height. The rumination time varied between treatments in the autumn and spring, being related to the lignin content of forage. Leisure time was related to grazing time. The temperatures varied during the seasons, however the grazing, ruminating and leisure times did not change between these, demonstrating that under the evaluated conditions, the structure and chemical characteristics of pasture, more so than the environmental characteristics, exert influence over the ingestive behavioral activities of grazing cattle.