Chewing behaviour and voluntary grass silage intake by cattle

Abstract

Six Friesian heifers (Experiment 1) and four lactating dairy cows (83% Holstein; Experiment 2) were fed ad libitum with direct-cut or wilted grass silage. All animals were fitted with ruminal and duodenal cannulae. Extent and rate of ruminal forage digestibility were measured and chewing behaviour of the animals was recorded. Mean faecal particle size was also determined. Neither the concentration of fermentation products in the silages, i.e. their palatability, nor the rate and extent of ruminal digestion or the extent of particle-size reduction in the digestive tract could explain the increased dry-matter intake of wilted versus direct-cut silage (17.7% in heifers and 28.4% in lactating cows). The time spent eating per kilogram dry-matter intake was substantially reduced after wilting of the grass prior to ensiling (28% in heifers and 37% in lactating cows), but the time spent ruminating was not significantly different between the two types of silages. It was inferred that ruminating is firmly involved in augmenting functional density of feed particles in the reticulorumen by expelling pockets of air or fermentation gases. This permits sedimentation of the particles and their passage through the reticulo-omasal orifice. As daily chewing capacity of the animals is limited to around 950 min, the farmer can help more efficient eaters by facilitating dry-matter ingestion (wilting, chopping, etc.) and in this way, liberating more time and more jaw movements for ruminating. More direct evidence is needed to ascertain the exact mechanism and the importance of favouring ruminating at the expense of eating activity in relation to rumen fill.