Studies on the alimentary tract of the Merino sheep in South Africa. II. Investigations on the physiology of deglutition

Abstract

(1) A solution of copper sulphate stimulates reflex closure of the oesophageal groove in sheep so that drugs subsequently administered will pass into the abomasum. (2) Preliminary starvation has no favourable influence, unless the sheep are starved for such a long period that the ruminal contents become fluid, in which case the latter condition is favourable. Starvation is, however, contra-indicated for reasons which are discussed. (3) The method of administration and the position in which the animal is held are of no importance. (4) The reflex is established immediately after the stimulant touches the mucosa of the pharynx. (5) The groove remains closed for 15 seconds, sometimes longer, after stimulation. (6) Other conditions being favourable, the stimulus can definitely be produced by a 0.25 per cent. copper sulphate solution. Unfavourable factors are advanced age, poor condition and dryness of ruminal contents. It is shown that a 10 per cent. solution is necessary to overcome the counteracting effects of these adverse factors. (7) It has not been definitely proved whether acidity of the ruminal contents is an unfavourable condition, but there are indications that this is not the case. (8) Copper salts other than the sulphate produce the reflex, but it has not been definitely proved that the stimulus may not be due to astringency of the stimulant. (9) There are indications that the related metals zinc and silver may also produce the reflex. (10) Various drugs administered after the stimulant did not reverse the reflex. Small pills may be swallowed into the abomasum after stimulation but larger objects (small capsules) are not. (11) Preliminary tests indicate that a drug administered into the abomasum may reach the colon in about five hours and that it may be passed in the faeces from about the 15th hour. (12) Since the abomasal mucosa is very tender, care must be exercised in administering drugs in the way indicated.