Studies on the alimentary tract of Merino sheep in South Africa. V. The motility of the rumen under various conditions

Abstract

Experiments conducted on sheep with ruminal fistula have shown that normal ruminal movement may undergo very considerable variations from any rhythm that may be temporarily established. In this respect it is essentially the strength of the individual contractions as well as the spacing of the movement s which may undergo a sudden change rather than the rate and the tonus of the rumen, both of which remain far more constant. An interesting feature is the extensive degree of relaxation undergone by the ruminal musculature between the actual contractions. During these periods of rest the intra-ruminal pressure usually falls well below zero, values of -5 to -15 mm. H₂O pressure being frequently encountered, At the height of contraction the intra-luminal pressure may rise from +20 to +129 mm. H₂O, with an average of ±70 mm. Feeding in every instance causes a very significant acceleration in the movement of the rumen, this being due in all probability to vagus reflexes initiated in the pharynx and oesophagus, and closely associated with mastication and deglutition. In some animals the mere sight of food may initiate reflex acceleration of ruminal movement. This effect is, however, neither as constant nor as strong as that noticeable during actual feeding. The type of food exerts little, if any, effect on the ruminal rhythm, although contractions tend to become small when animals are kept on a ration comprised exclusively of concentrates. Complete starvation as a rule causes no definite change in the rate of ruminal movement up to the third or even fourth day, although the excursions may become progressively smaller. After this period all movements may, however, disappear completely. Following renewed feeding after such prolonged starvation, definite delay in the return of movements and also of the appetite is frequently noticeable. The influence of water on the rumen is much less specific seeing that neither the sight of water nor actual drinking causes any appreciable change in the motility of the rumen. Moreover, wide extremes of temperature ranging from 0 °C. to 50 °C. following the dosing of 1 litre of either iced or warm water cause very little change in normal motility. With regard to the influence of various mineral salts, it has been established that small doses of a copper sulphate solution, as well as similar solutions of silver nitrate and nicotine sulphate, when dosed on to the back of the tongue all cause very profound changes in ruminal rhythm, due again probably to a vagal reflex. Al other mineral salts tested out so far have failed to provoke this characteristic response from the rumen. Potassium cyanide in small doses per os causes a rapid though transitory paralysis of all ruminal movements. In addition to the mineral salts, various other substances have also been tested for their action on the rumen. Of these, Lentin (Merck) and Esmodil (Bayer) have been found to cause a well-marked stimulation of ruminal movement, while acetyl-choline causes an acute though transitory paralysis. Pilocarpine and arecoline also cause significant stimulation of ruminal movement. Adrenaline subcutaneously in doses of 2 c.c. (1 : 1000) was found to exert little, if any, change in ruminal motility.