The Relationship Between Milk Composition and Reproductive Status in Bottlenose Dolphins
Milk composition reflects the nutritional status of lactating mothers. Bottlenose dolphins can
become pregnant while lactating, and this study aimed to investigate milk compositional changes throughout lactation and
the relationship between variations in milk composition and reproductive status.
Three lactating female bottlenose dolphins were sampled, two from Dolphin Quest Hawaii and one from
Dolphin Quest Bermuda. Milk samples were collected on a daily basis for a 2-yr period starting approximately 1 mo
following parturition. Reproductive statuses of individual bottlenose dolphins were monitored by progesterone
concentrations obtained from these daily milk samples. The dolphin monitored at Dolphin Quest Bermuda did not become
pregnant during the study period, but both dolphins from Dolphin Quest Hawaii became pregnant at the same time.
Milk samples collected daily were pooled for a monthly sample from each individual for compositional
analysis. Percentages of milk fat, protein, water, and total solids were determined for each sample. Fluctuations in milk
fat were apparent during the course of lactation. In all three animals sampled, a significant rise occurred 9 mo after
parturition. Fat percentage generally increased during lactation in all individuals, although some rise and fall was
evident. Fat percent also appeared to be higher during pregnancy, as an increase in fat content accompanied the increased
progesterone concentrations associated with pregnancy. During non-pregnancy, milk fat averaged approximately 13% versus
18% during pregnancy. Percentage of protein averaged around 9% and only slightly fluctuated during the course of lactation
or between pregnant and non-pregnant dolphins. Percentage of water ranged between 65% and 80%, and total solids between
20% and 35% in the individuals studied. Although water and total solids percentages did fluctuate, patterns associated
with the course of lactation or the reproductive status of the dolphin were not clear.