Seasonal variation in the concentration of vitamins A and E in the blood plasma of fat-tailed sheep.

Six non-pregnant ewes and 6 rams (age: 3-4 years) of an Iranian fat-tailed sheep breed (Shal) were used. Blood samples were collected monthly for 12 months, and the concentrations of retinol and alpha-tocopherol were determined by high-performance liquid chromatography (HPLC). A limited ration of standard composition was fed throughout the year. The ration was supplemented with 25-32 IU alpha-tocopherol/animal/day. Vitamin A concentrations in the blood plasma of ewes were lower in the spring (442 +/- 9 micrograms/L) and summer (452 +/- 7 micrograms/L) and higher in the autumn (467 +/- 5 micrograms/L). In the rams, the plasma concentration of vitamin A was the lowest in the spring (436 +/- 6 micrograms/L) and the highest in the summer (471 +/- 5 micrograms/L). A seasonal comparison did not show statistical differences between consecutive seasons for the ewes (P > 0.05). The differences were significant between winter and spring (P < 0.05) and spring and summer (P < 0.001) for the rams. The blood plasma concentration of vitamin E was 1.21 +/- 0.05, 1.04 +/- 0.05, 1.24 +/- 0.05 and 1.24 +/- 0.08, mg/L in spring, summer, autumn and winter, respectively, for the ewes and 1.24 +/- 0.05, 1.11 +/- 0.06, 1.09 +/- 0.04 and 1.38 +/- 0.07 mg/L in spring, summer, autumn and winter, respectively, for the rams. The values were significantly different between spring and summer (P < 0.05) and summer and autumn (P < 0.01) for the ewes. In rams, the values obtained in autumn also showed a significant difference (P < 0.001) from those found in winter. Differences between values found in other seasons were not significant (P > 0.05). The retinol and alpha-tocopherol concentrations of the blood plasma were highly similar in the two sexes. The concentrations of retinol in the summer (P < 0.01) and alpha-tocopherol in the autumn (P < 0.05) showed significant differences between the two sexes. The results show that the concentrations of vitamins A and E are relatively constant in the blood plasma of fat-tailed sheep kept on a standardised feed. However, some differences due to the influence of season and sex were observed.