Cerebral ventricular injections of pentobarbital, glucose, and sodium chloride into sheep and calves, and feeding

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

Physical and chemical characteristics of dietary ingredients and their interactions can have a large effect on dry matter intake (DMI) of lactating cows. Physical limitations caused by distension of the reticulo-rumen or other compartments of the gastrointestinal tract often limit DMI of high producing cows or cows fed high forage diets. Fermentation acids also limit DMI from a combination of increased osmolality in the reticulo-rumen and specific effects of propionate, although the mechanisms are not clear. The specific physical and chemical characteristics of diets that can affect DMI include fiber content, ease of hydrolysis of starch and fiber, particle size, particle fragility, silage fermentation products, concentration and characteristics of fat, and the amount and ruminal degradation of protein. Site of starch digestion affects the form of metabolic fuel absorbed, which can affect DMI because absorbed propionate appears to be more hypophagic than lactate or absorbed glucose. Dry matter intake is likely determined by integration of signals in brain satiety centers. Difficulty in measurement and extensive interactions among the variables make it challenging to account for dietary effects when predicting DMI. However, a greater understanding of the mechanisms along with evaluation of animal responses to diet changes allows diet adjustments to be made to optimize DMI as well as to optimize allocation of diet ingredients to animals. This paper discusses some of the characteristics of dietary ingredients that should be considered when formulating diets for lactating dairy cows and when allocating feeds to different groups of animals on the farm.

Feeding following intraventricular injection of CA++, MG++ or pentobarbital in pigs

The effects on food intake, of injections into the lateral ventricle of Ca++, Mg++ or equimolar mixtures of the 2 ions have been studied in pigs. The chloride salts were made up in normal saline which together with 1.35 percent NaC1 was used as a control injection. Dosages of 12.5 mumoles, 25 mumoles, or 50 mumoles either Ca++ or Mg++ elicited increased food intake in the 30 min following the injection and there was a predominantly linear feeding response to increasing concentration of the two ions. Ca++ was more effective in eliciting increased food intake than Mg++. Equimolar mixtures of Ca++ and Mg++ of 6.5 + 6.5 mumoles, 12.5 + 12.5 mumoles or 25 + 25 mumoles also increased food intake linearly and the mixture of ions was more effective than equivalent concentrations of Ca++ or Mg++ alone. No antagonism between Ca++ and Mg++ was seen with respect to food intake. Intraventricular injections of 16 mumoles of sodium pentobarbital also elicited increased food intake in the 30 min following injection. It is suggested that the ions and the barbiturate probably act by deression of periventricular neurons, particularly in the medial hypothalamus which is adjacent to the third ventricle.