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

Abstract

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.