Abstract

Feed intake is regulated and limited by the physical and metabolic requirements of animals. Physical control of voluntary dry matter intake (DMI) in high productivity dairy cows is, to a large extent, dependent on the reticulo-rumen capacity/volume. Physical fill is thought to be mainly determined by the rate of digestion of feed, the passage rate and the fill effect of the diet. The neutral detergent fibre (NDF) and water contents of feed, reticulo-rumen motility, reticulo-rumen volume, and neutral detergent fibre digestibility (NDFD) in the rumen are the main factors controlling physical regulation. When the energy or protein requirements of dairy cows are met by the feed, then further intake is stopped/depressed as a result of feedback via a message from the satiety centre within the central nervous system. Volatile fatty acids (VFA) are produced as a result of microbial degradation of feed in the rumen. The amount of each acid produced and absorbed has both an individual and a combined effect (as a part of the mixture of acids) on the regulation of the voluntary intake of feed. Propionate is the most important of all VFA since it enhances the release of insulin into the blood which, stops further intake of energy from feed. Glucose on the other hand, has little or no role in the control of feed intake in ruminants. Diets that are highly fermentable in the rumen produce instant VFA and the titratable acidity of these has very strong inhibitory effects on reticulo-rumen motility, causing rumen stasis and cessation of further intake. Starch from cereal grains is normally added to the diets of high productivity dairy cows to meet the energy requirements for milk yield. Rapid degradation of starch has a negative impact on the rumen and total tract digestibility of fibre. Starch rumen digestibility and availability depends on the type of cereals and the type and intensity of any processing that they have undergone. Grass and legume silage cut and ensilaged at early maturity is associated with increased intake and digestibility of NDF and organic matter (OM) although it is reported that such silages regulate feed intake metabolically rather than physically. However, the chemical composition and physical characteristics change as the plant matures. A number of models have been proposed for predicting intake; their accuracies vary. Possible strategies for improving energy utilization from starch and increasing voluntary feed intake include: shifting the site of starch digestion from the rumen to the small intestine through the use of processed cereals (e. g. physical processing); selecting correct cereal type; and determining the optimum level of maturity of forages (grasses and legumes).

Keywords

physical regulation; metabolic regulation; starch sources; stages of maturity; grass silage

Published in

Röbäcksdalen meddelar
2008,
Publisher: Institution för norrländsk jordbruksvetenskap, Sveriges lantbruksuniversitet

Permanent link to this page (URI)

https://res.slu.se/id/publ/125979