Foraging behavior and ruminal fermentation of dairy cows grazing ryegrass pasture alone or with white clover

Resumo

The objective of this work was to evaluate the influence of pasture composition and regrowth age on the relationship between feeding behavior and ruminal fermentation in dairy cows grazing perennial ryegrass with or without white clover. The experiment was carried out in a 2x2 factorial arrangement, with two sward types and two ages of regrowth. Swards of perennial ryegrass sown alone (PRG) and of perennial ryegrass mixed with white clover (GC) were evaluated. Twelve late‑lactation Holstein cows, fistulated at the rumen, were distributed in a 4x4 latin square experimental design with four 12‑day periods. Daily distribution of grazing was similar in the PRG and the GC swards, but the concentration of rumen volatile fatty acids (VFA) was higher and the proportion of propionate was lower on mixed swards during the day. Daily distribution of grazing was similar in pastures of different ages. However, in the oldest swards, rumen fluid pH increased and VFA concentration decreased after evening milking. Time spent grazing does not influence ruminal fermentation, which depends on the changes that occur as different sward layers are grazed. azevém perene consorciado com trevo branco (TB) – e duas  idades de rebrota. A distribuição diária do pastejo foi semelhante nos pastos AZ e TB, mas a concentração ruminal de ácidos graxos voláteis (AGV) foi maior e a proporção de propionato foi menor nos pastos em associação, ao longo do dia. A distribuição das atividades de pastejo foi semelhante nos pastos com idades diferentes. Entretanto, nos pastos mais velhos, o pH ruminal aumentou e a concentração de AGV diminuiu após a ordenha da tarde. O tempo de pastejo tem pouca influência sobre a fermentação ruminal, a qual depende de alterações que ocorrem à medida que os diferentes estratos são pastejados.