Pig mandibular gland morpho-functional features are affected by feed physical form

Study was performed on the mandibular gland from growing pigs, enrolled in a research to test the effects of different physical forms of the diet on animal’s health, production and welfare, considering that chewing acts are associated with salivary production and that the feed physical forms can affect the mandibular gland function. 48 castrated male growing pigs were fed, for 4 weeks, with different forms of the same diet (grinding intensities/compactions) namely coarsely ground meal (CM), finely ground pelleted (FP) and coarsely ground pelleted (CP) diets. Samples from mandibular glands were analyzed by conventional histochemistry to identify the glycohistochemical profile, and by immunohistochemistry to localize aquaporin 5, apelin and apelin receptor. The stats R-package, version 3.5.3, was used forstatistical elaborations. Pig mandibular gland increased both the quantity and acidity of produced glycoconjugates from CM to FP and CP diets. Mandibular gland increate aquaporin 5 positivity in the CP diet. Based on apelin/receptor localization, it was hypothesized that in pig mandibular gland the apelinergic system likely performs an endocrine control on the demilunes activity and a paracrine control on ducts. The intense chewing activity linked to the highest feed compaction/hardness promotes an increase in pig mandibular gland secretion. Saliva becomes more fluid and richer in acid glycoconjugates in order to better lubricate the bolus and protect the mouth mucosae. The apelinergic system is likely involved in the above modifications enhancing both the fluidity and the quantity of serous saliva in pig mandibular gland. The project was approved by the Ethics Committee on Animal Welfare of the Hannover District Government in accordance with the German legislation on animal welfare.