The development of parotid salivation in the lamb

Abstract

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.