The objective of this work was to evaluate the variations in root dry matter mass (RDM) and the percentage distribution (PD) of the root density of Florico grass (Cynodon nlemfuensis) in the 0-40-cm soil layer, when managed under different grazing strategies. Two defoliation frequencies (90 and 95% light interception, as the criterion for allowing animals in the paddock) and two defoliation severities (post-grazing heights of 20 or 30 cm) were assessed. Four seasonal evaluations of the root system were performed between the winter of 2012 and the autumn of 2013, using the monolith and trench excavation technique, collecting 1-dm3 samples from soil surface down to a depth of 40 cm, in four sequential extracts of 10 cm each. Lower RDM values (0.69 g dm-3) were obtained in winter, with the four grazing strategies, whereas higher values were observed in spring (1.64 g dm-3), for the 30-cm post-grazing residue, and in autumn (1.63 g dm-3) for the 20 cm post-grazing residue, regardless of the light interception value. Between 52 and 66% of the RDM density was observed in the 10-cm layer, for all four grazing strategies, in all seasons.
ABSTRACT. The ingestive behavior of crossbred heifers grazing on stargrass pasture was managed at two levels of light interception and two levels of post-grazing residual height. The experiment was conducted at Pesagro (Seropédica, Rio de Janeiro State) between April 2012 and January 2013. The grazing (GT), rumination (RT) and idling (IT) times were evaluated every 10 minutes throughout a 24-hour period. Forage samples were collected for the analysis of chemical composition and for leaf:stem ratio determination. Dry bulb, wet bulb and black globe temperatures were evaluated every hour along with the relative humidity, during grazing to characterize the environment and calculate the Black Globe Humidity Index (BGHI). The mean grazing time (6 hours) was inversely related to sward height. The rumination time was associated with lignin content, in autumn and spring. The mean idle time (9 hours) was related to the grazing time. Animals became tolerant to climatic variations, as GT, RT and IT showed no temporal variations. On the other hand, the sward structure and its chemical characteristics showed greater influence on the ingestive activities of cattle grazing on pasture.Keywords: BGHI, Cynodon nlemfuensis, grazing, idling, morphological composition, rumination.Comportamento ingestivo de novilhas mestiças nas quatro estações do ano e sua relação com a estrutura da pastagem de capim-estrela RESUMO. Avaliou-se o comportamento ingestivo de novilhas mestiças em pastagem de capim-estrela manejada sob dois níveis de interceptação luminosa e duas alturas de resíduo pós-pastejo. O experimento foi conduzido na Pesagro (Seropédica, Rio de Janeiro State) entre abril/2012 a janeiro/2013. Os tempos de pastejo (P), ruminação (R) e ócio (O) foram avaliados a cada 10 min. durante um período de 24h. Amostras da forragem foram colhidas para análise da composição químico-bromatológica, e para determinação da relação folha:colmo. Temperaturas de bulbo seco, bulbo úmido, globo negro e a umidade relativa do ar foram medidas a cada hora durante o pastejo para caracterização do ambiente e cálculo do ITGU. O tempo médio de pastejo (6h) apresentou inversamente relacionado à altura do dossel. O tempo de ruminação esteve associado ao teor de lignina, no outono e na primavera. O tempo médio de ócio (9h) apresentou relação com o tempo de pastejo. Os animais mostraram-se tolerantes às variações climáticas, uma vez que os tempos de P, R e O não variaram com as estações do ano. Por outro lado, a estrutura da pastagem e suas características bromatológicas exerceram maior influência sobre as atividades ingestivas dos bovinos em pastejo.
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