ABSTRACT: 3, 4-Didehydroretinol (DR) metabolism was previously followed in vitamin A (VA)-replete lactating sows. This study followed DR appearance and clearance after dosage in serum and milk during 2 lactation cycles in sows (n = 8) fed VA-free feed for 3 gestation-lactation cycles. During lactations 2 and 3, 35 μmol 3, 4-didehydroretinyl acetate was given orally after overnight food deprivation. Blood and milk were collected at 0, 1.5, 3, 5, 7, 9, 16, 24, 36, 48, 60, and 72 h; livers were obtained at kill. Samples were analyzed for DR, retinol (R), and 3, 4-didehydroretinyl esters. During lactations 2 and 3, the 5-h serum DR:R ratios were 0.028 ± 0.017 and 0.069 ± 0.042, respectively, and serum R concentrations were 0.75 ± 0.23 and 0.86 ± 0.37 μmol/L, respectively. The DR:R ratio and serum R were
