Determining if lactating Weddell seal mothers are indeed fasting

Weddell seals are well adapted polar animals. They give birth to pups in the Antarctic summer when they haul out onto the ice. While feeding their pups, they have a massive fasting weight loss (and fat mobilisation) and their suckling pup has a correspondingly massive weight gain and fat deposition. The question of whether the lactating mothers actually do fast was investigated by testing blood samples for the presence of a chemical, trimethylamine-N-oxide (TMAO), derived from fish in the diet. During the first season of the study, two seals which had not been diving for many hours were given an oral dose of TMAO and blood samples were collected to monitor the change in TMAO concentrations with time. During the second season five seals were given an infusion of TMAO and blood samples were collected for 3.5 hours to monitor the change in TMAO concentrations with time. Single blood samples were taken from 12 other seals for additional biochemical measurements. Ketone bodies such as ß-hydroxybutyrate (BOB) are unexpectedly low in these animals. In order to see if the seals can utilise ketone bodies as soon as they are formed, thereby maintaining low blood concentrations, 12 seals were given infusions of BOB at 3 dose levels (n=4) and blood sampled for 3.5 hours to determine the disappearance rate for BOB. To provide control values for the TMAO and BOB infusion studies, 5 seals were given an infusion of saline solution and blood sampled for 3.5 hours as well.