Effects of dietary vitamin A supplementation or restriction and its timing on retinol and α-tocopherol accumulation and gene expression in heavy pigs

• A long-term high level vitamin A supplementation increased the expression of ADH1C and LRAT.
• Growth time influenced vitamin A and vitamin E metabolism-related genes.
• A long-term dietary vitamin A withdrawal did not affect final pig weight at 11 months of age.
• Short- or long-term vitamin A withdrawal increased fat and liver α-tocopherol.

Vitamin supplementation is a widely extended practice in swine nutrition. Certain vitamins such as vitamins A and E are related to meat quality and have been reported as antagonists. Thus, their tissue levels are of interest for swine producers and consumers. This experiment was undertaken to study the effect of dietary vitamin A supplementation or withdrawal duration and timing on the evolution of vitamin A deposition in tissues, α-tocopherol accumulation and gene expression in heavy pigs. Eighty weaned Iberian piglets (16.3 ± 2.5 kg) were either fed a vitamin A-enriched diet (10,000 IU vitamin A/kg) (CONTROL) or given a diet without added vitamin A applied from the beginning of the trial at 16.3 kg (early restriction group, ER) or from an average weight of 35.8 kg (late restriction group, LR). Pigs fed ER and LR had lower ADG and worse feed efficiency than those from the CONTROL group at 101.4 kg (P=0.001 and P=0.034, respectively). However, final weight, average daily gain, average daily intake and feed conversion efficiency were not statistically affected by dietary treatment during the starter (<35.8 kg), fattening period (101.4–157.9 kg) or overall (16.3–157.9 kg). Retinol concentration in tissues reflected the dietary vitamin A level. Retinol and retinyl palmitate accumulation in hepatic and fat depots of control animals was more marked during the growing than during the finishing period. Retinol depots decreased in restricted groups and showed different sensitivity for mobilization between tissues, with faster retinol mobilization from the liver. The ER group had a higher hepatic α-tocopherol increase than the LR group (P<0.0001). However, in fat the increase in α-tocopherol levels were more marked in the LR than in the ER group (P<0.0001). ADH1C gene expression was higher (P=0.0237) in CONTROL than in ER at 101 kg and LRAT gene expression showed a dose-dependent decrease in the ER group at 101 and 158 kg LW (P<0.0001). There were no differences in RBP4, ALDH1A1, MTTP and TTP gene expression as affected by dietary treatment. Growth time influenced gene expression, with ADH1C and RBP4 genes being mainly expressed at 101 kg LW compared to pigs at 36 or 158 kg LW (P<0.05). Relative expression of MTTP and TTP was also affected by time and showed an opposite pattern to that observed for vitamin A-related genes. The results suggest that removing vitamin A from the diet for long or short periods in heavy pigs has the potential to reduce feed costs, increasing tissue α-tocopherol levels without affecting slaughter weight or feed efficiency.