Voluntary intake: a limiting factor to production in high-yielding dairy cows?

Abstract

AbstractIn principle, food intake by lactating dairy cows might be limited by rate of eating, capacity to produce saliva, rumen or intestinal capacity, rates of digestion and passage of food residues, or by factors such as chemicals and osmolality in the rumen. It is likely that a combination of these is used by the central nervous system to control intake. In practice, the positive relationship between digestibility and intake of forages means that high-quality material must be offered to cows during lactation if a reduced level of concentrate supplementation is envisaged but undue mobilization of body reserves avoided. Better supplementation is possible, both in terms of more frequent, smaller allocations, and of more appropriate concentrate composition with regard to the composition of the basal forage. Intake of maize silage dry matter is usually greater than for grass silage and a mixture of the two, perhaps offered in free or restricted choice, is likely to become more widely practised. Changes in body reserves are difficult to monitor and this has made it difficult to resolve the question of the magnitude of diet/environment interactions, i.e. is the same breeding and selection programme appropriate for those animals which are intended to be pushed to high yields in intensive systems and those intended to be given principally forages in semi-extensive systems?