Feed physical form affects anatomical traits of mandibular gland in growing pigs

The study was carried out on growing pigs fed with different dietary treatments based on different grinding intensities and compactions of the same diet, to test the effects of chewing acts on salivary production and fluidity. Therefore, the glycohistochemical profile and the presence of aquaporin 5, a canne protein modulating the saliva fluidity, were investigated. In addition, presence and localization of both apelin and its receptor were studied. Study was performed on the mandibular gland obtained from pigs enrolled in a wide research project [1, 2] aiming to test the effects of different physical forms of the diet on animal's health, production and welfare. The project was approved by the Ethics Committee on Animal Welfare of the Hannover District Government in accordante with the German legislation on animal welfare. 48 castrated male growing pigs (German Landrace x Large White on Duroc sires) were fed, for 4 weeks, with different forms of the same diet, namely coarsely ground meal (CM) finely ground pelleted (FP) and coarsely ground pelleted (CP) diets. Samples were analyzed by conventional histochemistry to identify the glycohistochemical profile, and by immunohistochemistry to localize aquaporin 5, apelin and apelin receptor. Statistical elaborations were performed using the stats R-package, version 3.5.3. Adenomere of pig mandibular gland increased both the quantity and acidity of produced glycoconjugates from CM to FP and CP diets; this probably call forth higher watery saliva, thus promoting a better feed softening facilitating the amalgamation of the bolus. Mandibular gland increased aquaporin 5 positivity in CP diet, supporting the hypothesis of an augmented demand for water. Findings suggest that the differenziate mechanical stimuli linked to different feed physical forms, likely allow to diverse physiological behavior of pig mandibular gland. The intense chewing activity linked to the highest feed compaction and hardness promotes an increase in pig mandibular gland secretion; in addition, saliva becomes more fluid and richer in acid glycoconjugates in order to better lubricate the bolus and protect the mouth mucosae. 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, facilitating the production of serous saliva by pig mandibular gland.