THE MECHANISM OF RUMINAL STASIS IN LANTANA-POISONED SHEEP

¹ CSIRO Davies Laboratory, Townsville, Queensland 4810, Australia
² Department of Physiology and Pharmacology, University of Queensland, St Lucia, Queensland 4067, Australia

The effect of poisoning by the plant Lantana camara L. on reticulo-ruminal motility was investigated in sheep. There was a marked decrease in forestomach motility 4-6 h after dosing with the plant and motility continued to be depressed throughout the course of the disease. The effect of lantana on motility was characterized by a decrease in the number and median amplitude of forestomach movements. This was in contrast to the effect of starvation which caused a decrease in only the number of forestomach movements and even this effect was less severe than in lantana-poisoned animals. The effects of lantana on the components of the reflex which controls rumen motility were examined. No evidence was found for a direct effect of lantana toxins on the stretch and tactile receptors in the reticulum; on the vagus nerves; on the gastric centre or on the muscle of the forestomach. However, evidence was found to support an hypothesis that stasis of the rumen in lantana poisoning is due to inhibitory influences arising from the damaged liver. The evidence included a correlation between the onset of ruminal stasis and liver injury; a relationship between the severity of liver injury and ruminal stasis and the finding that denervation of the liver converted the pattern of forestomach movements in intoxicated animals to that seen in starved animals. It is concluded that stasis of the rumen in lantana-poisoned animals is due at least initially, to inhibitory neural impulses arising from the damaged liver and to the effects of anorexia.