Energy intake is a primary limitation on milk yield for high producing dairy cows and is determined by net energy content of the diet and DMI. The maximal productive capacity of an animal will depend on its genetic potential and will vary over the animal’s life time according to its age, physiological status (e.g. lactating, pregnant), and climate (133). Each animal has a maximal rate at which it can utilize nutrients and metabolic fuels and unless DMI is limited by physical capacity, mechanisms must exist that balance supply with demand for nutrients.
Dry matter intake is a function of meal size and meal frequency that are determined by animal and dietary factors affecting hunger and satiety. Most research on feeding behavior of ruminants has focused on dietary characteristics affecting satiety, which determines meal length and size. Distension and hypertonicity in the reticulo-rumen (RR), and effects of metabolic fuels oxidized in the liver, among other factors, have been proposed as satiety factors of ruminants. Much less is known about the control of the interval between meals determined by hunger. In addition, the effects of site and temporal pattern of digestion on feeding behavior have been largely unexplored. Stimulation of receptors that transmit signals to brain satiety centers is deter mined by changes in concentration or flux of the stimulatory nutrient or metabolic fuel. Thus, degree of stimulation of ruminal epithelial receptors by VFA and possibly electrolytes, and hepatic receptors by propionate is determined by the rate and extent of fermentation of feeds in the RR. Feeds with a rapid rate of fermentation are expected to result in shorter meal length and size when these mechanisms are effectual.
Short-term controls that affect meal size and intermeal interval within a day can have sustained effects over weeks or months. However, home orhetic controls probably alter thresholds of stimulation required for hunger and satiety over a lactation cycle. This review focuses on the effects of diet on short-term regulation of DMI of lactating cows and includes dietary factors that affect distension in the RR and site of starch digestion, as well as protein, fat, and conservation method of forage.
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