Dynamics of vitamin A in grey seal (Halichoerus grypus) mothers and pups throughout lactation

Vitamin A concentrations were measured in milk and serum of grey seal (Halichoerus grypus) mothers and in the serum of their pups sampled 2-6 times between parturition and weaning on the Isle of May, Scotland, in 1998 and 2000. Changes in serum vitamin A concentration were also followed in pups during the postweaning fast. During their 18-day lactation period, fasting mothers produced a milk very rich in vitamin A. Concentrations of 6.3 +/- 1.6 and 10.1 +/- 4.5 mg/kg (mean +/- SD) were measured in colostrum (day 0) and in milk at late lactation (greater than or equal to11 days), respectively. Surprisingly, the vitamin A concentration increased at late lactation, even when it was expressed per unit of milk lipids. The vitamin A concentration in mothers' serum was 329 +/- 65 mug/L at day 0. The concentration dropped at day 3 (228 +/- 21 mug/L serum), but increased to 400 +/- 121 mug/L serum at late lactation. At birth, the serum vitamin A concentration of pups (111 +/- 5 mug/L) was much lower than that of their mothers, revealing limited placental transfer. The vitamin A concentration in pup serum then increased throughout lactation to 499 +/- 96 mug/L at the end of the nursing period. At that time, the pups' serum was more concentrated than the mothers' serum, reflecting the great vitamin A ingestion. After weaning, serum vitamin A concentrations of pups dropped over several days and then stabilized at 336 +/- 45 mug/L.