The Effect of Dietary Grain Inclusion and Zn Concentration on Rumen Epithelial Structure and Zn Transporter Expression in Sheep

The objective of this study was to evaluate the effect of dietary grain inclusion and supplemental Zn on rumen epithelial structure and Zn transporter expression in ruminants. Twenty crossbred wethers (34 ± 5.3 kg) were individually fed in a 2×2 factorial with two diet types, 50% forage, 50% concentrate (HF) or 10% forage, 90% concentrate (HG), and two supplemental Zn concentrations, 0 (CON) or 120 mg Zn/kg DM from ZnSO₄ (ZINC). After 60 d, sheep were euthanized and blood, liver and rumen sections from the ventral sac were collected and preserved for trace mineral analysis, histology, tight junction protein expression, and in-situ RNA hybridization of Zn transporters. Data were analyzed as a 2×2 factorial, with the fixed effects of diet type and Zn concentration, and wether was the experimental unit. Plasma Fe and Zn concentrations were greater in HG (P ≤ 0.005), and plasma Zn was greater (P = 0.004) and Cu tended to be greater (P = 0.08) in ZINC. There was a tendency for an interaction for liver Cu (P = 0.08), where within ZINC, HG was greater than HF (P = 0.01). The HF had greater liver Fe (P = 0.01) and liver Zn was not affected by either diet or Zn concentration (P ≥ 0.17). There was an interaction within rumen epithelial Zn concentration (P = 0.05) where HG+ZINC were greatest followed by HF+ZINC while CON were not different (P = 0.63). The HG had greater rumen tissue Cu and lesser Fe concentrations (P = 0.004). Rumen papillae width, epithelial, non-keratinized, and keratinized layers were not affected by treatments (P ≥ 0.13). There was an interaction within papillae length (P = 0.05) where HG+CON were greater (P = 0.008) than HG+ZINC, both of which were greater than HF (P < 0.01). Claudin-1, Claudin-4, and Occludin protein expression was not affected by treatments (P ≥ 0.32). Claudin-7 protein expression was greater in HG (P = 0.002) and tended to be greater in CON (P = 0.09). In situ RNA expression of zip4 and zip5 were not affected by treatments (P ≥ 0.24) but there was an interaction in RNA expression of znt1, a Zn exporter (P = 0.04), where HG+CON was greater than other treatments. These data suggest dietary Zn has minimal effect on rumen histology, but may influence tight junction protein and znt1 expression in ruminants fed a high grain diet.