Effects of diet on short-term regulation of feed intake by lactating dairycattle

Physical and chemical characteristics of dietary ingredients and their inte ractions can have a large effect on dry matter intake (DMI) of lactating co ws. Physical limitations caused by distension of the reticulo-rumen or othe r compartments of the gastrointestinal tract of ten limit DMI of high produ cing cows or cows fed high forage diets. Fermentation acids also limit DMI from a combination of increased osmolality in the reticulorumen and specifi c effects of propionate, although the mechanisms are not clear. The specifi c physical and chemical characteristics of diets that can affect DMI includ e fiber content, ease of hydrolysis of starch and fiber, particle size, par ticle fragility, silage fermentation products, concentration and characteri stics of fat, and the amount and ruminal degradation of protein. Site of st arch digestion affects the form of metabolic fuel absorbed, which can affec t DMI because absorbed propionate appears to be more hypophagic than lactat e or absorbed glucose. Dry matter intake is likely determined by integratio n of signals in brain satiety centers. Difficulty in measurement and extens ive interactions among the variables make it challenging to account for die tary effects when predicting DMI. However, a greater understanding of the m echanisms along with evaluation of animal responses to diet changes allows diet adjustments to be made to optimize DMI as well as to optimize allocati on of diet ingredients to animals. This paper discusses some of the charact eristics of dietary ingredients that should be considered when formulating diets for lactating dairy cows and when allocating feeds to different group s of animals on the farm.