Factors affecting the voluntary intake of food by sheep. 4. The effect of additives representing the primary tastes on sham intakes by oesophageal-fistulated sheep.

1. Sheep with oesophageal fistulas were sham-fed on pelleted lucerne (Medicago sativa) hay to assess the palatability of added chemicals representing the tastes of sweet (sucrose), sour (hydrochloric acid), salt (sodium chloride), bitter (urea) and umami (monosodium glutamate; MSG). 2. Plain pellets and four concentrations of each chemical were sham-fed for 30 min after 5.5 h deprivation in 5 x 5 Latin-square experiments following a period of adaptation feeding. 3. Sucrose, at concentrations of 15-120 g/kg air-dried pellets, depressed intakes with a linear relation between intake (I; g) and concentration (C; g/kg): I = 1001-3.42C. 4. HCl at 6.25-25.0 g/kg pellets had no effect on sham intakes but at 50 g/kg reduced them by 50% of control (P less than 0.05). 5. NaCl at 50 200 g/kg increased sham intakes by 26% (P less than 0.01) with no evidence of a dose-related effect. 6. Urea at 10-80 g/kg decreased sham intakes by 26.9% (P less than 0.01) with no evidence of a dose-related effect. 7. MSG at 5-40 g/kg in two experiments increased sham intakes by 16.1 and 40.8% (P less than 0.05). In another experiment at 1-8 g/kg there was no significant effect. 8. When palatability and post-ingestive effects are separated by sham-feeding, the effect of added chemicals on intake may be completely different from when they are ingested normally (e.g. NaCl and sucrose). This newly developed technique enables the palatability effect of feed additives to be tested critically and economically.

Abomasal intubation of young calves.

A nonsurgical method for passing a tube into the abomasum of young calves was developed. The tube described may be used for infusion into, or sampling from, the abomasum. The tube was successfully passed into the abomasum of all eight calves used. In two calves two to four days old and in two neonatal calves (greater than 24 h old) reticular groove closure was stimulated by providing a suckling stimulus but in four neonatal calves, passage of the tube was successful without the suckling stimulus. Placement of the tip of the tube was verified by auscultation and, in two calves, by radiography.

The route of liquids administered to calves by esophageal feeder.

An esophageal feeder and a rubber nasoesophageal tube were used to administer fluids to calves. Radio-opaque fluids were given and their destination determined by fluoroscopy and radiography. Fluids containing glucose and xylose were also given and plasma glucose and xylose concentrations measured. In at least 93% of calves, the radio-opaque fluids entered the reticulum, indicating that the reticular groove did not close. Oral administration of sodium bicarbonate, copper sulfate and guanidine HCl did not influence groove closure in calves that received fluids through an esophageal feeder. As administration of the fluids continued, overflow to the abomasum occurred after about 400 mL had been given. When 2.0 L of glucose and electrolyte solution was given by esophageal feeder, plasma glucose levels rose significantly (p less than 0.01), showing that absorption had occurred. Plasma xylose levels rose in seven out of eight calves 30 minutes after a second 2.0 L dose (containing xylose) had been administered. Thus, even though esophageal feeders do not cause reticular groove closure, they can be used to administer fluids for enteric absorption, provided large quantities are given.

Pentagastrin in the circulation acts directly on the brain to depress motility of the stomach in sheep.

The mechanism whereby pentagastrin inhibits the frequency of contractions of the reticulo-rumen in conscious sheep was studied by comparing the effects of a range of doses given by continuous infusion into the jugular vein and the carotid artery. The intracarotid infusions at rates of 1 and 2 micrograms/kg per h were more effective than the jugular infusions (P less than 0.05). This is the first report that pentagastrin administered intravenously acts directly on the brain to alter the motility of a portion of the digestive tract. This agrees with the fact that in sheep and other ruminants, the gastric centres in the medulla dictate the frequency of cyclical motility in the reticulum.