Determining if lactating Weddell seal mothers are indeed fasting

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.