Dietary Vitamin D Supplementation Improves Hair Follicle Development and Affects Fatty Acid Metabolism in Rex Rabbits

An experiment was conducted to investigate the effect of different levels of vitamin D (VD) supplementation in rabbit diets on hair follicle development and fatty acid metabolism. Two hundred Rex rabbits with similar body weight were divided randomly into five groups (40 replicates per group and 1 rabbit per replicate): control group fed a basic diet; experimental groups fed respectively a basic diet with an addition of 700, 1400, 2100, or 2800 IU/kg VD. Dietary addition of 2800 IU/kg VD significantly increased hair length (p < 0.05). Dietary addition of 700-2100 IU/kg VD significantly decreased average hair fineness (p < 0.05). Dietary addition of 1400-2800 IU/kg VD significantly increased total hair follicle density and secondary hair follicle density (p < 0.05). Dietary addition of VD (2100 IU/kg) significantly increased the mRNA levels of Wnt10b, β-catenin, insulin-like growth factor 1 (IGF1), epidermal growth factor (EGF), sonic hedgehog (SHH), and Notch in rabbit skin (p < 0.05). Dietary addition of VD (2100 IU/kg) significantly increased the mRNA levels of Carnitine palmitoyl transferase (CPT1) 1 and CPT2 in fat, CPT1, CPT2, and peroxisome proliferator-activated receptor-α in liver, and fatty acid-transport protein and fatty acid-binding protein in skeletal muscle, but significantly decreased the mRNA level of acetyl coenzyme A carboxylase in fat (p < 0.05). Dietary VD addition promotes hair follicle development. Wnt10b/β-catenin, Notch, SHH, IGF1, and EGF signaling pathways or factors may participate in the regulatory process. Dietary VD addition increases the fatty acid oxidation process in fat tissue and liver, and fatty acid uptake in muscle, and inhibits the fatty acid synthesis process in fat tissue. Dietary addition of 1400-2100 IU/kg VD is a better appropriate dose for hair density for Rex rabbits.