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Feed Intake of Goats and Sheep Following Acetate or Propionate Injections into Rumen, Ruminal Pouches, and Abomasum as Affected by local Anesthetics

Department of Nutrition, Harvard School of Public Health Boston, Massachusetts 02115

ABSTRACT

Previous experiments indicated that changes in rumen fluid concentration of volatile fatty acids especially in the dorsal rumen may play a role in the control of feed intake of ruminants. Experiments were designed to test for influence of possible ruminal nerve receptors in this feeding response. In Experiment 1, water (control), M acetate, M propionate (pH 6.5), or M acetate or propionate plus 400 mg/ liter of Carbocaine, Xylocaine, or Oxetha-zaine (local anesthetics), were injected into the dorsal rumen of goats during spontaneous meals. Carbocaine and M acetate depressed feeding less than acetate alone (P<.01). Oxethazaine was ineffective in preventing feed intake decrease caused by acetate (P<.01). Propionate alone decreased feed intake 14% versus controls, but combined with either Carbocaine or Xylocaine feeding decreased further. In Experiment 2, catheters were implanted on the right ruminal nerve. Xylocaine (2%) injected on this nerve tended to increase feeding slightly. Xylocaine combined with intraruminal M acetate injections tended to decrease feeding less than acetate alone. Xylocaine injections combined with intraruminal propionate tended to decrease feeding less than propionate alone. In Experiment 3, Pavlov type pouches with neural and blood supply intact were formed in an area innervated by the left ruminal nerve in goats and sheep. Both rumen and pouch were provided with cannulas. Animals were fed twice daily for 2 hr. Thirty ml m acetate, propionate, acetate plus Carbocaine (400 nig/liter), propionate plus Carbocaine, or rumen fluid for a control were injected into pouches on test days just prior to both feedings. Each type of pouch injection was tested for 5 consecutive days. After the second daily feeding, pouches were filled with fresh rumen fluid and left overnight. Teed intake as a percent of control was decreased with acetate (1%) whereas acetate plus Carbocaine increased feeding by 11%. Propionate tended to decrease intakes more (14.1%) than propionate plus Carbocaine (1%). In Experiment 4 water (control), m acetate or m acetate plus Carbocaine (400 mg/liter) were injected through catheters into the abomasum of goats. Acetate alone decreased feeding (P<.02) more than acetate plus Carbocaine although more acetate was injected during the latter treatment. Results lend further support to the hypothesis of acetate receptors in the ruminal wall of goats and sheep.

¹ Present address: Smith Kline & French Laboratories, 1600 Paoli Pike, West Chester, Pennsylvania 19380.