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-year period starting approximately 1 month 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 months 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.