Effect of whole acorns (Quercus pubescens) shred based diet on parotid gland in growing pigs in relation to tannins

The amounts and composition of saliva produced in parotid glands can be influenced by dietary biologically active substances. Among phenolic compounds naturally present in some feedstuffs, particularly condensed tannins and hydrolysable tannins and derivates appear to play a role for the induction of Proline Rich Protein secretion in the parotid saliva of some animal species: this might be considered as a first evolutionary defence mechanism against the protein precipitating activity of tannins, preferably bond to proline and histatins in saliva. This is the first paper to report the preliminary results on the effects of full ripe acorns ( Q. pubescens ) polyphenols measured as Tannic Acid Equivalents on the parotid gland of growing pigs. A total of 8 growing pigs were divided into 2 experimental groups (each n = 4): the control group was fed a conventional complete diet for pigs (pelleted; 890 g DM/kg; based on cereals and soybean extraction meal). The acorn-fed group was offered a combined diet, 70% of ripe whole acorns shred (612 g DM/kg of fresh matter, 0.516 g TAE/kg DM) and 30% of the complete diet. One additional pig was fed the experimental diet for 24 h only. All 8 animals from the 2 experimental groups were sacrificed at 1 week after consumption, the additional pig, 24 h after consumption. Both parotid glands of each pig were removed and weighed. Maximum length and width were measured and the right parotids were used in toto to determine dry matter, crude protein and total proline content. Each left parotid gland was processed for microscopic check. Increased size (+ 53.8% length; + 19.9% width), mass (+ 68.5% fresh weight) and proline content (+ 33.8% based on DM) were observed in animals fed the 70% acorns diet after 7 days. These results inspire to perform further investigations on the rapid adaption of pigs to counteract the effects of tannins in whole acorns as found after only one day of exposure.