Pigs use endogenous proline to cope with acorn (Quercus pubescens Willd.) combined diets high in hydrolysable tannins

Abstract

Detrimental effects due to high intake of dietary tannins are described in the literature in different animal species after acorn (fruit of Genus Quercus) ingestion. By contrast, pigs seem to tolerate dietary regimes with considerable amounts of acorns. This study investigates whether the esophageal mucosa (pars non glandularis) of the stomach might be a susceptible target for the onset of injuries and whether salivary proline rich proteins (PRPs) can be a valid defense to preserve its integrity, when a large amount of ripe shredded acorns (Quercus pubescens Willd.) is combined in the diet for growing pigs. A matched pair approach was used to divide a total of 16 crossbred growing pigs (14.2–27.6kg BW) into 2 groups (n=4 in each, homogeneous for BW) for 8 days of experimental feeding (two replicates): the control group was fed with a conventional complete diet for pigs (pelleted; 890g DM/kg; based on cereals and soybean meal). The acorn-fed group was offered a combined diet, 70% of ripe shredded acorns (612g DM/kg of fresh matter; Tannic Acid Equivalent, 0.516g TAE/kg DM) and 30% of the complete pelleted diet, as fed. Stomach ingesta were analyzed for chemical composition and proline content; on gross inspection, the gastric mucosa was exteriorized and scored (on a 0–5 point scale) for prevalence and severity of injuries. A sort of “tanning effect” underlined the edges of the cardiac gland region (CGR) in all the stomachs from the acorn-fed group, inducing to consider the high affinity of acorn tannins for PRP, such as gastric mucins. No signs of injury could be identified after both dietary treatments. The differential between the dietary proline intake and proline content in the stomach constantly showed a negative value (−46.1±9.72%) in the acorn-fed group, in contrast to the positive disappearance of proline in control group (39.3±25.4%). Therefore, endogenous proline for “buffering” purposes was considered to be a defense mechanism, either as a salivary or gastric mucus component.