Effects of Intravenous versus Intraruminal Injections of Acetate on Feed Intake of Goats

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Abstract
Sodium acetate injections into the rumen depressed feed intake while the same amounts injected intravenously had no such effect. Specifically, goats fed a grain ra- tion ad libitum were injected either intra- ruminally or intravenously with acetate solutions concomitantly with eating spon- taneous meals. Five-minute injections of acetate given intravenously caused blood levels to increase to 8 to 12 m~ while injections given intraruminally caused an increase of only 0.5 to 1.0 m~. These data suggest that receptors sensitive to acetate are more likely to be situated in the lumen side of the ruminoreticulum than in an area where they would respond to blood levels. Although it seems apparent that there are acetate receptors in ruminants, it cannot be concluded that the feed intake depression following an acetate injection is related to satiety. The volatile fatty acids, acetic acid in par- ticular, have been suggested as a possible feed- back component initiating satiety in ruminants. A severe depression of feed intake in ruminants in one study occurred during an eight-hour intravenous (jugular) injection of acetic and propionic acids and their sodium salts (11). The rate of injection was sufficient to provide in eight hours 12.5% of the estimated digestible energy maintenance requirement for 24 hours for the dairy cows. In another study with sheep trained to eat a single two-hour meal per day, jugular vein injections of sodium acetate at approximately 60% of the rate of the above study per unit metabolic mass failed to cause a feed intake depression (13). The injection was initiated about two hours before feeding. The rate was such that at the time of feeding the blood acetate concentration had been in- creased to a level comparable to maximum post- prandial values. Intraruminal injections of acetic acid and sodium acetate in cattle (18, 19), sheep (6, 20), and goats (4) cause depression of feed intake. It has been suggested that this depres-