An Energy-Rich Diet Causes Rumen Papillae Proliferation Associated with More IGF Type 1 Receptors and Increased Plasma IGF-1 Concentrations in Young Goats

We tested the hypothesis that the dietary energy–dependent alterations of the rumen papillae size are accompanied by corresponding changes in systemic insulin-like growth factor (IGF)-1 concentration and in rumen papillary IGF type 1 receptors (IGF-1R). Young male goats (n = 24) were randomly allocated to two groups (n = 12) and fed a high level (HL) metabolizable energy [1200 kJ/(kg0.75 · d)] or a low level (LL) [500 kJ/(kg0.75 · d)] diet for 42 d. The concentration of ruminal total SCFA did not differ between the groups, but the molar proportion of butyric acid was enhanced by 70% in the HL group (P < 0.05). Both the length and width of the papillae were greater (P < 0.05) in the HL group, and the surface was 50–100% larger (P < 0.05) in the tissue sampled from the artrium ruminis, the ventral ruminal sac and the ventral blind sac. Transport of Na+ across the rumen epithelium, which is amiloride sensitive, was higher (P < 0.05) in the HL than in the LL group. Furthermore, the plasma IGF-1 concentration was about twofold higher in the HL group (P < 0.05), and the maximal rumen epithelial IGF-1R binding was also higher in the HL (P < 0.05) than in the LL group. IGF-1R mRNA and IGF-1 mRNA were detected in rumen papillae; however, they were unaffected by dietary treatments. DNA synthesis and cell proliferation of cultured rumen epithelial cells were higher (P < 0.05) after IGF-1 treatment (25 or 50 μg/L) compared with those in the medium without IGF-1. Thus dietary energy–dependent alterations of rumen morphology and function are accompanied by corresponding changes in systemic IGF-1 and ruminal IGF-1R.