Lactation in whales and dolphins: evidence of divergence between baleen- and toothed-species.
ABSTRACT Although it has been more than one hundred years since the first publication on the milks of whales and dolphins (Order Cetacea), information on lactation in these species is scattered and fragmentary. Yet the immense size of some cetaceans, and the recent evidence that another group of marine mammals, the true seals, have remarkable rates of secretion of milk fat and energy, make this group of great comparative interest. In this paper information on lactation patterns, milk composition and lactation performance is reviewed. Two very different patterns are evident. Many of the baleen whales (Suborder Mysticeti) have relatively brief lactations (5-7 months) during which they fast or eat relatively little. At mid-lactation they produce milks relatively low in water (40-53%), high in fat (30-50%), and moderately high in protein (9-15%) and ash (1.2-2.1%). From mammary gland weights and postnatal growth rates, it is predicted that their energy outputs in milk are exceptional, reaching on the order of 4000 MJ/ d in the blue whale. This is possible because pregnant females migrate to feeding grounds where they can ingest and deposit great amounts of energy, building up blubber stores prior to parturition. On the other hand, the toothed whales and dolphins (Suborder Odontoceti) have much more extensive lactations typically lasting 1-3 years, during which the mothers feed. At mid-lactation their milks appear to be higher in water (60-77%) and lower in fat (10-30%) and ash (0.6-1.1%), with similar levels of protein (8-11%). At least some odontocetes resemble primates in terms of low predicted rates of energy output and a long period of dependency of the young. However, these hypotheses are based on small numbers of samples for a relatively small number of species. Much of the available data on milk composition is of rather poor quality; for example, it is not possible to determine if milk composition changes over the course of lactation among odontocetes. Additional research on cetacean mammary glands and their secretions is needed to understand the reproductive strategies of these fascinating animals.
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ABSTRACT: Female Juan Fernandez fur seals, Arctocephalus philippii, undertake long foraging trips during lactation, resulting in intersuckling intervals that are among the longest ever recorded for a mammal. We collected 44 samples of milk from this fur seal to determine if milk would have a high concentration of fat, as predicted from the hypothesized relation between milk concentration and intersuckling interval. Milk of Juan Fernandez fur seals contained on average 55.1% dry matter, 41.4% fat, 11.9% protein, 1.2% sugar, 0.7% ash, 780 mg/kg calcium, and 840 mg/kg phosphorous. Content of fat and energy were the highest reported for a fur seal or sea lion (Family Otariidae) in the 1st month of lactation. Energetic content was 17.95 kJ/g, and 74% of fatty acids were unsaturated. Data from seven species and subspecies of otariid seals indicated that length of foraging trip explained 66% of the variation in content of fat in milk among taxa. Content of energy in milk of otariid seals also was explained primarily by the duration of trips to sea.Journal of Mammalogy 08/1999; 80(3):758. DOI:10.2307/1383245 · 2.23 Impact Factor
Marine Mammal Science 07/2014; 31(1). DOI:10.1111/mms.12155 · 1.82 Impact Factor