The effect of diet on the secretion of parotid saliva by sheep. III. Observations of the secretion of saliva by grazing sheep

The parotid saliva secreted by three grazing sheep was recorded by exteriorizing and cannulating one parotid duct of each sheep, and collecting the saliva into carts that were harnessed to the sheep. The sheep were grazed on an annual pasture in a Mediterranean climate and collections were made during spring, summer, autumn, and winter. In each season, recordings were also made of the pasture intake, pasture availability, and the behaviour of the grazing sheep. The mean daily secretion of saliva from one gland was 3.42 l. in autumn, 4.05 l. in winter, 6.69 l. in spring, and 4.07 l. in summer. In spring, the mean secretion from one sheep was 7.92 l./day. The changes in secretion did not appear to be related to the pasture intake, or to the grazing behaviour of the sheep.

The effect of diet on the secretion of parotid saliva by sheep. II. Variation in the rate of salivary secretion

The rates of parotid salivation of two sheep were recorded during periods of resting (when not eating or ruminating), eating, and ruminating. Diets differing in both quality and quantity were offered to the sheep, and continuous recordings of the salivation rates of each sheep were made for 24 hr during each dietary period. The mean rate of secretion during rest was lowest at the beginning of a rest period and increased gradually to a peak at the end of the rest period. The mean secretion rate at rest was lowest during the rest period following a meal, and increased gradually to reach a peak during the rest period before the next meal. The secretion rat e during rest was increased by partially evacuating the rumen, and decreased by introducing fluids into the rumen. The mean secretion rates during rest and rumination were higher when the sheep were fed ground hay than when they were fed long hay. The mean secretion rate during rest was increased when the food intake was increased.

The influence of diet on the development of paratid salivation and the rumen of the lamb

The development of the parotid glands and the rumen were studied in four groups of lambs, 91–98 days old, each group being reared on a different diet. One group received an all milk diet; and the others received — in addition to milk — hay, wood shavings, or a purified diet consisting of starch, fortified whole milk powder, and 3% sodium bicarbonate. The criterion of parotid development was the stimulated secretion rate per gram of parotid gland, in anaesthetized lambs. Rumen development was recorded in terms of the growth of mucosa and muscle, the growth of the papillae, and the changes in the volume of rumen contents and the rumen capacity. In another experiment the same comparisons were made between lambs of 63 days of age which had grazed with their mothers, and lambs that were grazed until 63 days of age, but were then confined to a milk diet for a further 70 days. The parotids of the lambs fed on wood shavings secreted 0.50 g saliva/g parotid/min, compared with a secretion of 0.51 g/g/min by the lambs fed with hay. The parotids of the lambs fed on the purified diet secreted 0.27 g/g/min, which was little more than the secretion of 0.20 g/g/min by the lambs fed on milk alone. The lambs receiving the milk or purified diets secreted significantly less saliva than those receiving the hay or shavings diets (P < 0.01). The parotids of the grazing lambs secreted 0.44 g/g/min, which was significantly greater (P < 0.05) than the secretion by the lambs returned to the milk diet (0.26 g/g/min). It was concluded that the parotid glands developed in response to the mechanical stimulation of the food, and that there was a regression of gland development when this stimulation was removed. The rumen mucosa developed in the lambs fed on the hay, grazing, and purified diets, but not in those lambs fed on the milk or shavings diets. There was a regression of the mucosa in those lambs returned to the milk diet.

The effect of diet on the secretion of parotid saliva by sheep. I. The daily secretion of saliva by caged sheep

Two sheep with unilateral parotid fistulae were used to record the effect of individual dietary factors on parotid salivary secretions. The volume of saliva secreted was not affected by the addition of urea and molasses to a straw diet, by the drying of pasture containing 20% dry matter, or by restricting or increasing the water intake. Parotid secretion was increased by increasing the dry matter intake. With a constant food intake, the secretion was increased by 25% when the hay ration was ground through a 1/16 in. screen, but was decreased by 61% when ground through a finer screen. The intraruminal infusion of artificial saliva or 1%sodium chloride decreased the secretion by a mean of 59%. Food intake was of greater importance than other dietary factors, excluding fine grinding, in determining the volume of parotid saliva secreted.

The development of parotid salivation in the lamb

The development of the parotid gland was studied in lambs reared under the following three dietary conditions: (a) lambs freely grazed with their ewes; (b) lambs hand-reared on milk and hay; (c) lambs hand-reared on milk alone. Weekly measurements were made of the saliva flowing from the cannulated parotids of two anaesthetized lambs from each group, during reflex and electrical stimulation of their glands. The fresh weights of the parotid and submaxillary glands and of the four stomachs were also recorded. Before 4 weeks of age, all the parotid glands were physiologically immature, secreting only 0.1–0.2 g saliva/g parotid tissue/min. The parotids of the grazing lambs developed rapidly from 4 to 6 weeks of age and reached adult capacity of 0.50–0.65 g/g/min between 7 and 10 weeks of age. The parotids of the lambs receiving millr and hay developed more slowly than the grazing lambs, while the parotids of the lambs receiving milk only scarcely developed at all. The histological examination of these glands showed that the parotids of the 2-week-old lambs were immature. Differentiation in the grazing group occurred at 4–6 weeks of age, while no differentiation occurred in the lambs fed milk only. The rate of flow of parotid saliva from all lambs was significantly correlated with the fresh weight of rumen tissue. The parotid gland increased in weight in relation to the rumen weight and not to the body weight.