Influence of increased vitamin A supplements on alpha-tocopherol and retinoids in serum and lipoproteins of Shetland ponies

The effects of feeding 75 versus 750 IU vitamin A/kg body mass (BM) per day to eight healthy pony geldings were studied in a cross-over design experiment for 20 weeks. The vitamin E intake was 2 mg/kg BM per day. cc-tocopherol and retinoid distribution was examined in serum and lipoproteins. No effect was seen on retinol, alpha -tocopherol, cholesterol, triglycerides, phospholipids and protein. The alpha -tocopherol was distributed between high-density lipoprotein (69%), low-density lipoprotein (LDL; 22%) and very-low-density lipoprotein (VLDL; 9%). A retinol dose response (RDR)-test was carried out in both experimental groups to analyse the vitamin A status. The RDR-test indicated in some cases a false insufficient supply in spite of increased dietary vitamin A. However increased retinyl ester concentrations were found in serum and lipoproteins. Therefore concentrations of retinyl esters seems to be an excellent indicator for the vitamin A status of ponies. In lipoproteins, retinyl ester were measurable in VLDL and LDL. The main ester was retinyl stearate followed by retinyl palmitate. Data suggest that feeding increased concentration of vitamin A did not influence the serum vitamin E status and lipid parameters in ponies, but increased the retinyl esters in serum, VLDL and LDL.