What We Knew Then & Now
What we knew before…
Milk composition has been described for hundreds of species of mammals. Dolphin milk composition was first studied in the 1890’s in milk collected from a dead dolphin mother, but the scientists conducting these studies did not know the age or status of that female’s nursing calf.
Marine mammal milk is especially high in fat content, much higher than that of any terrestrial mammal. The terrestrial mammal milk that we are most familiar is the dairy cow’s, the stuff you buy it at your local grocery store at between 0% (nonfat skim) and 5% fat content. Some species of seals and large whales have milk fat content over 50%; the highest percentage of fat recorded in marine mammals is 65% in the hooded seal.
Scientists have determined that there is a general relationship between the percentage of fat in marine mammal milk and the length of lactation - the shorter the period of lactation in the species, the higher the fat content of the milk. Once lactation ends and a young is weaned, it must be physically able to find and catch prey on its own to survive. In the short, four-day lactation of the hooded seal, the young pup bulks up extremely quickly to store the energy it needs to grow to the point where it has a good chance of fending for itself. Hooded seal milk is extremely high in energy-rich fat and a huge amount of energy transfers between mother and young in the four short days of lactation. In species with longer lactations, fat content tends to be considerably lower as there is more time to transfer the energy young require to grow to independence. Bottlenose dolphins typically lactate for 3-5 years and the few milk samples collected from this species, probably at very different stages of lactation, have reported milk fat percentages of between 10% and 30%.
While there have been many reports in the past 100 years describing the high fat content of marine mammal milk, much still remains to be learned about dolphin milk. Prior to research performed by our team, no one had investigated whether milk composition changes over the course of lactation in dolphins as it does in many other mammals. Nor had milk produced by wild and captive dolphins been compared and there were no values available for “normal” versus “abnormal” dolphin milk.
What we know now…
Through our team’s research efforts, we have discovered that bottlenose dolphin milk composition does change over the long lactation period. Fat content steadily increases from the time the calf is born (around 10% fat) until it is weaned (about 20% fat). Protein content of milk also steadily increases over the course of lactation while water content declines. We also now know that there is variability in the amount of milk fat, milk protein and milk water among different dolphin moms, although changes over the duration of lactation follow the same trend mentioned above. Our team also had the opportunity to compare milk samples collected from healthy wild dolphins with those of captive counterparts. Wild dolphins have higher levels of milk protein than captive dolphins while all other milk components appear to be similar.
Our team has analyzed over 100 bottlenose dolphin milk samples in the laboratory and we are now able to identify “normal” and “abnormal” milk. Abnormal milk samples are sometimes collected from mothers that have recently lost a calf or from the carcasses of a dead lactating females. Our ability to identify abnormal samples will be helpful in attempting to analyze dolphin milk from carcasses or from females where calf status is unknown. It will also help veterinarians to evaluate milk quality in mothers with health problems or other issues that may affect the nutrition of dependent calves.