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Milk of Marine MammalsO T Oftedal, Smithsonian Environmental Research Center, Edgewater, MD, USA

ª 2011 Elsevier Ltd. All rights reserved.

The Origin and Evolution of MarineMammal Lactation

Lactation is a diagnostic mammalian trait, involving the

synthesis of a nutrient-rich secretion by specializedmammary glands. Since its initial evolution during the

Mesozoic, perhaps more than 200 million years ago

(mya), lactation has undergone profound evolutionary

divergence among mammalian taxa, resulting in a

diversity of lactation patterns characterized by major dif-

ferences in milk composition, milk yield, suckling

patterns, and duration of lactation. In comparison to ter-

restrial mammals, nearly all species of marine mammals,including seals (Figure 1) and whales, produce excep-

tionally rich milks high in fat and energy. For example, in

the order Carnivora, the true seals (family Phocidae)

typically produce milks that contain 48–60% fat, while

dolphins and whales (order Cetacea) produce milks that

typically contain 15–50% fat.The species included as marine mammals do not form

a single phylogenetic group but represent several distinct

lineages that made the transition from terrestrial to mar-

ine life at different points in time. Given that seals,

whales, and manatees are not closely related to each

other, one would not expect them, a priori, to produce

milks similar in composition. Any similarities that do

occur represent convergent evolution.The marine mammals include three major lineages.

The dolphins and whales (order Cetacea) derive from

the even-toed ungulates (order Artiodactyla). Genetic

analysis indicates that the cetaceans are nested within

the Artiodactyla, which is therefore sometimes termed

the Cetartiodactyla, including cetaceans. The stem

group of ancestral cetaceans, the ‘Archaeocetes’, appearsin the fossil record from early to middle Eocene, 52–42

mya. Thus, the milks of cetaceans and other artiodactyls

have diverged for at least 52 million years. Subsequently,

two major groups of cetaceans, the odontocetes or toothed

whales and dolphins, and the mysticetes or baleen whales,

diverged about 35 mya. Among living mammals, the

odontocetes are much more species-rich (71 species)

than the baleen whales (13 species) and typically havelonger lactations (Table 1). Among mammals, lactation

duration typically increases in length with body mass, but

the largest mammals of all, the large baleen whales, depart

from this trend and have lactation durations of only

5–12 months, as compared to 1–4 years or longer in

much smaller odontocetes. All cetaceans give birth in the

water to single offspring, which nurse from nipples buriedwithin mammary slits on the posterior abdomen. At least

fragmentary data are available on the milk composition of17 odontocete species and 8 mysticete species (Table 1).

A second lineage of marine mammals, the orderSirenia (manatees and dugongs), first appears as early

and middle Eocene fossils from 50 mya, or shortly afterthe appearance of the ‘Archaeocetes’. The herbivorous

Sirenia are not closely related to either cetaceans or

marine taxa of the Carnivora, but are rather nested withina group of African mammals known as the Afrotheria.

Among living taxa, the sirenians are most closely relatedto the Proboscidea (elephants). The placement of the

single pair of mammae in the axillary region (armpits) isdistinctive. Although there are only four living species of

Sirenia (three manatees and the dugong), another much

larger species, the c. 4–10 tonne Steller’s sea cow(Hydrodamalis gigas), grazed on algae in the North Pacific

until discovered by Europeans in 1741 and then hunted toextinction by 1768. Apparently, milk was never collected

from this ‘sea cow’. Milk composition has been reportedonly for the West Indian manatee.

A third lineage of marine mammals evolved within theorder Carnivora. The seals, sea lions, and walruses (collec-

tively termed pinnipeds) are represented by three families,Phocidae (true seals), Otariidae (fur seals and sea lions), and

Odobenidae (walrus). The pinniped lineage diverged fromarctoid carnivores in the late Oligocene (27–25 mya); pinni-

peds are most closely related to raccoons (Procyonidae),

bears (Ursidae), and weasels (Mustelidae). The phocidsappear in the late Oligocene, the walruses (formerly a

more diverse group) in the middle Miocene (16–14 mya),and the otariids in the late Miocene (11 mya). The phocids,

otariids, and odobenids are currently represented by 18, 16,and 1 species, respectively; the Caribbean monk seal is

extinct (Table 1). Lactation duration varies greatly among

species, from 4 days in the hooded seal to 17 months inAustralian sea lions and 24 or more months in the walrus; in

general, otariids have longer lactation periods than phocids(Table 1). Pinnipeds have 2–6 mammae, primarily abdom-

inal in location and typically inverted. All pinnipeds give

birth on land or ice, and as all except the walrus nurse theirpups out of the water, they are more accessible for lactation

research than other marine mammals. Lactation has beenmore thoroughly studied in pinnipeds than in any other wild

mammal group. At least fragmentary milk composition data

563

Figure 1 The Weddell seal, the world’s southernmost milk-producing animal. Mother and suckling pup at Hutton Cliffs, Ross Island,McMurdo Sound, Ross Sea, Antarctica (78� S, 166� E). Photograph taken by Olav Oftedal under marine mammal permit 763-1485-00

issued by U.S. National Marine Fisheries Service.

Table 1 Lactation in marine mammals

Family Common name Scientific binomialMilksamples

Age at first majorsolids

Duration oflactation

Order Carnivora (carnivores, 286 spp.)

Mustelidae (weasels, otters, 59 spp., 2 marine)Sea ottera Enhydra lutris Yes 1 month 6 months

Marine otter Lontra felina No ?? ??

Ursidae (bears, 8 spp., 1 marine)

Polar bear Ursus maritimus Yes 3–6 months 18–34 monthsOdobenidae (walruses, 1 sp., marine)

Walrus Odobenus rosmarus Yes 5–6 months 12–24 months

Otariidae (fur seals, sea lions, 16 spp., all marine)South American fur

seal

Arctocephalus australis Yes ?? 12 months

New Zealand fur seal Arctocephalus forsteri Yes ?? 12 months

Galapagos fur seal Arctocephalusgalapagoensis

Yes ?? 11 months

Antarctic fur seal Arctocephalus gazella Yes At weaning 4 months

Juan Fernandez fur

seal

Arctocephalus philippii Yes ?? 7 months

Australian/Cape fur

seal

Arctocephalus pusillus Yes 4–7 months 9 months

Subantarctic fur seal Arctocephalus tropicalis Yes ?? 10 monthsNorthern fur seal Callorhinus ursinus Yes At weaning 4 months

Steller sea lion Eumetopias jubatus Yes ?? 4–12 months

Australian sea lion Neophoca cinerea Yes ?? 17 months

California sea lion Zalophus californianus Yes 4–5 months 11 monthsGalapagos sea lion Zalophus wollebaeki Yes ?? 24 months

Phocidae (true seals. 18 spp., all marine or freshwater)

Hooded seal Cystophora cristata Yes Postweaning 4 days

Bearded seal Erignathus barbatus Yes 13–14 days 24 daysGray seal Halichoerus grypus Yes Postweaning 17 days

(Continued )

564 Milk | Milk of Marine Mammals

Table 1 (Continued)

Family Common name Scientific binomialMilksamples

Age at first majorsolids

Duration oflactation

Weddell seal Leptonychotes weddellii Yes 45 days? 40–50 days

N. elephant seal Mirounga angustirostris Yes Postweaning 26 days

S. elephant seal Mirounga leonina Yes Postweaning 23 days

Mediterranean monksealb

Monachus monachus No ?? 119 days

Harp seal Pagophilus

groenlandicus

Yes Postweaning 12 days

Harbor seal Phoca vitulina Yes Postweaning 27 daysRinged seal Pusa hispida Yes ?? 39 days

Order Cetacea (dolphins and whales, 84 spp., all marine or freshwater)

Suborder Odontoceti (toothed whales, 71 spp.)Delphinidae (dolphins, 34 spp.)

Common dolphin Delphinus delphis Yes ?? 16 months

Long-finned pilot

whale

Globicephala melas Yes 6–9 months 24 months?

Humpback dolphin Sousa chinensis Yes ?? ??

Spotted dolphin Stenella attenuata Yes 3–7 months 20 months

Atlantic spotted

dolphin

Stenella frontalis Yes ?? ??

Spinner dolphin Stenella longirostris Yes ?? 11–34 months

Bottlenose dolphin Tursiops truncatus Yes 4–11 months 19 months

Iniidae (river dolphins, 3 spp.)

Amazon River dolphin Inia geoffrensis Yes ?? ??Franciscana dolphinc Pontoporia blainvillei Yes ?? 9 months

Monodontidae (beluga, narwhal, 2 spp.)

Beluga whale Delphinapterus leucas Yes 12 months 20–24 monthsPhocoenidae (porpoises, 6 spp.)

Harbor porpoise Phocoena phocoena Yes 2–3 months 8–12 months

Dall’s porpoise Phocoenoides dalli Yes ?? ??

Physeteridae (sperm whales, 3 spp.)Pygmy sperm whale Kogia breviceps Yes ?? ??

Dwarf sperm whale Kogia simus Yes ?? ??

Great sperm whale Physeter

macrocephalus

Yes 12 months 25 months

Ziphiidae (beaked whales, 21 spp.)

Bottlenose whale Hyperoodon sp. Yes ?? ??

Stejneger’s beakedwhale

Mesoplodon stejnegeri Yes ?? 12 months

Suborder Mysticeti (baleen whales, 13 spp.)

Balaenidae (right whales, 4 spp.)

Bowhead whale Balaena mysticetus Yes ?? 9–12 monthsBalaenopteridae (rorquals, 7 spp.)

Minke whale Balaenoptera

acutorostrata

Yes 5–6 months 5–6 months

Sei whale Balaenoptera borealis Yes 6–7 months 6–7 monthsBryde’s whale Balaenoptera edeni Yes ?? ??

Blue whale Balaenoptera musculus Yes 6–7 months 6–7 months

Fin whale Balaenoptera physalus Yes 6–7 months 6–7 months

Humpback whale Megaptera novaeangliae Yes 5–6 months 10–11 monthsEschrichtiidae (gray whale, 1 sp.)

Gray whale Eschrichtius robustus Yes 6–7 months 7–8 months

Order Sirenia (manatees, dugongs, 5 spp.,all marine or freshwater)

Trichechidae (manatees, 3 spp.)

West Indian manatee Trichechus manatus Yes 3–5 months 12–24 months

aPayne SF and Jameson RT (1984) Early behavioral development of the sea otter, Enhydra lutris. Journal of Mammalogy 65: 527–531.bAguilar A, Cappozzo LH, Gazo M, Pastor T, Forcada J, and Grau E (2007) Lactation and mother–pup behaviour in the Mediterranean monk sealMonachus monachus: An unusual pattern for a phocid. Journal of the Marine Biological Association of the United Kingdom 87: 93–99.cCaon G, Secchi ER, Capp E, and Kucharski LC (2008) Milk composition of franciscana dolphin (Pontoporia blainvillei) from Rio Grande do Sul,southern Brazil. Journal of the Marine Biological Association of the United Kingdom 88: 1099–1101.Unless otherwise specified, data from Oftedal OT, Boness DJ, and Tedman RA (1987) The behavior, physiology, and anatomy of lactation in thePinnipedia. Current Mammalogy 1: 175–245; Oftedal OT (1997) Lactation in whales and dolphins: Evidence of divergence between baleen- andtoothed-species. Journal of Mammary Gland Biology and Neoplasia 2: 205–230.

Milk | Milk of Marine Mammals 565


are available for 12 of 16 otariids, 9 of the 18 phocids, and onthe sole odobenid (the walrus) that is, on 63% of the extantpinniped species. By comparison, among the approximately250 species of non-pinniped carnivores, in only 12 species(5%) have at least 3 samples of mid-lactation milk beenassayed (Table 2).

The order Carnivora also includes three ‘newer’ mar-ine mammals, the marine and sea otters and the polar bear(Table 1). They arose in the Pleistocene (c. 1–3 mya), butremain closely related to other lutrine otters and otherbears of the genus Ursus, respectively. Milk data areavailable for sea otters and polar bears.

Factors Affecting the Composition ofMarine Mammal Milks

The collection of milk samples from wild mammalsrequires that animals be captured and restrained(Figure 2), or chemically immobilized. Marine mammalsoften react adversely to chemical immobilization, butwhether this affects the composition of collected milk isnot known. During the heyday of whaling, milk sampleswere taken during the processing of carcasses, and sam-ples have been obtained from stranded animals. For suchsamples, there is always concern that post-mortem orpathological changes may result in abnormal results,especially for labile constituents such as carbohydratesor constituents that may diffuse into or out of damagedmammary glands, such as sodium and potassium. Morerecently, captive animals, such as bottlenose dolphins,have been trained to present for milk collection. Even inthis situation, seawater contamination can occur, leadingto elevated levels of water, sodium, and magnesium.Another potential error could arise from incompletemammary evacuation, which in some terrestrial speciescan lead to underestimation of milk fat. In seals, milkcomposition does not change during the course of mam-mary evacuation, but this has not been examined in otters,bears, cetaceans, or sirenians. Thus, the magnitude ofsampling bias in the data in Tables 2–4 is unknown.

Marine mammal milks change in composition accord-ing to lactation stage. In most species of pinnipeds andcetaceans, fat and energy contents rise, and water contentfalls, from early to mid-lactation (Figure 3). In somespecies, fat and energy contents then remain high to theend of lactation, while in others a modest decline in fatand energy content may occur toward the end of lacta-tion. In polar bears, milk fat content is constant at about32–36% from 3 to 4 months until weaning, or may declinewhen bears return onto land from the sea ice.

Other constituents may also change with lactationstage. The protein content of pinniped and cetaceanmilks may rise somewhat over lactation, but the degree

and direction of change vary among species and may evenvary with maternal condition. In general, milk composi-tion should be compared across species at similar stages oflactation to avoid confounding effects.

An additional complication occurs in sea lions and furseals (family Otariidae). After a short (c. 1 week) post-parturient period ashore, mothers undertake foragingtrips to sea. The pups remain on land or in shallow pools,fasting, until the mothers return. Foraging trip length variesby species, breeding population, and maternal condition,with trips lasting less than a day in some sea lions or asmuch as 23 days in the sub-antarctic fur seal. During theforaging trip, the rate of milk protein synthesis and overallmilk production declines and the composition of secretedmilk changes. On return to the breeding colony, the firstmilk provided to the pup is considerably higher in fat andprotein than milk provided on subsequent days ashore.Some authors consider this a case of two separate milks(milk on arrival vs. milk obtained by subsequent suckling),but it is more likely a continuous process whereby secre-tory processes are up- and down-regulated according tothe stage of the foraging/nursing cycle. Nonetheless,this complicates determination of the ‘average’ milkcomposition.

The Proximate Composition of MarineMammal Milks

The summary data in Tables 2–5 were selected fromavailable data as those that best represent milk composi-tion at the period of maximal milk production or peaklactation. Although milk production has been measured atdifferent lactation stages only in a few pinniped species,peak production can be inferred from the pattern of off-spring growth and behavior. Offspring growth can besustained only if the increased energy needs associatedwith increasing size are matched by an increase in milkyield, an increase in milk energy/nutrient density, or theingestion of solid foods. Peak lactation is estimated as theperiod preceding the onset of substantial food intake bythe young (Table 1), as determined by observation orexamination of stomach contents.

The adaptation to marine life has apparently entailedchanges in milk composition, but to discriminate suchchanges from simple phylogenetic variation due to longperiods of separate evolution, milk composition needs tobe compared to the closest living relatives of marinemammals. Thus in Tables 2–4 compositional data areprovided for terrestrial carnivores, a subset of the artio-dactyls, and elephants as the closest living relatives ofmarine carnivores, cetaceans, and sirenians, respectively.

Both the polar bear and sea otter, species that haverecently diverged from terrestrial counterparts, producemilks that are higher in fat and energy than other

Table 2 Milk composition of terrestrial and marine Carnivora

Family and species NLactation stage(days)

Water(%)

Dry matter(%)

Fat(%)

Crude protein(%)

Sugar(%)

Ash(%)

Gross energyMJ kg�1

Canidae (wolves, foxes, 35 spp.)

Arctic fox �100 Mid? 71.4 28.6 13.5 11.1 3.0 1.0 8Dog (domestic) 25 7–37 77.3 22.7 9.5 7.5 3.8 1.1 6

Raccoon dog 22 7–59 81.4 18.6 3.4 7.8 1.1

Red fox 3 28–35 81.9 18.1 5.8 6.7 4.6 0.9 5Ursidae (bears, 8 spp.)

Brown bear 9 60–98 68.1 31.9 17.1 9.2 2.2 1.5 9

Black bear 6 60–90 62.4 37.6 25.1 7.0 3.0 1.8 12

Polar beara 7 210–550 52.0 48.0 33.0 11.1 0.3 1.4 16Mephitidae (skunks, 13 spp.)

Striped skunk 15 20–48 69.4 30.6 13.8 9.9 3.0 8

Mustelidae (weasels, otters, 59 spp.)

Ferret 18 11–25 9.7 6.9 3.8 6American mink 20 10–27 78.3 21.7 7.3 5.6 4.5 1.0 5

Sea otterb 3 Mid-late 59.8 40.2 23.7 11.7 0.9 0.8 12Felidae (cats, 40 spp.)

Cat (domestic) 15 6–38 10.8 10.6 3.7 1.0 7

Serval 3 56–77 70.7 29.3 15.3 15.8 0.7 10

African lion 6 45–90 73.2 26.8 8.7 11.8 3.2 7

Odobenidae (walruses)Walrusc 3 Early (<30) 61.0 39.0 24.1 9.2 0.0 0.6 12

Otariidae (fur seals, sea lions)South American fur seal 4 �150 45.6 54.4 44.4 9.7 20Antarctic fur seald 27 �20–100 42.3 57.7 42.4 10.5 0.1 19Juan Fernandez fur

seale23–44 1–110 44.9 55.1 41.4 11.9 1.2 0.7 19

Australian fur sealf >20 �80–150 43.6 56.4 42.8 10.2 0.8 19Subantarctic fur sealg 74–103 20–180 38.2 61.8 47.1 12.8 21Northern fur seal 5 30–120 36.7 63.3 50.7 10.3 0.1 22Australian sea lion 20–38 14–125 62.4 37.6 25.4 10.5 0.9 12Southern sea lionh 4 18–20 63.5 25.8 8.6 1.1 12California sea lion 12 90–120 45.8 54.2 43.7 8.9 0.6 19

Phocidae (true seals)Hooded seali 15 2–4 30.2 69.8 61.1 4.9 1.0 0.5 25Bearded sealj 3 �10–20 41.0 59.0 48.0 10.0 21Gray seal 13 8–15 28.9 71.1 59.8 8.9 25Weddell seal 7 10–45 33.8 66.2 53.6 8.9 0.0 - 23

(Continued )

Table 2 (Continued)

Family and species NLactation stage(days)

Water(%)

Dry matter(%)

Fat(%)

Crude protein(%)

Sugar(%)

Ash(%)


N. elephant seal 20–24 20–28 34.2 65.8 51.9 10.2 <0.025 23S. elephant sealk 26 10–20 37.0 63.0 47.9 9.6 2.6 0.7 21Harp seall 8 10–13 34.3 65.7 53.5 7.7 0.8 23Harbor sealm 42 7–21 37.8 62.2 49.8 9.1 22Ringed sealn 3 �15–35 48.6 51.4 38.1 9.9 1.0 17

aDerocher AE, Andriashek D, and Arnould JPY (1993) Aspects of milk composition and lactation in polar bears. Canadian Journal of Zoology 71: 561–567.bJenness R, Williams DT, and Mullin RJ (1981) Composition of milk of the sea otter (Enhydra lutris). Comparative Biochemistry and Physiology 70A: 375–379.cFay FH (1982) Ecology and Biology of the Pacific Walrus, Odobenus rosmarus divergens. North American Fauna No. 74, pp. 1–279. Washington, DC: U.S. Fish and Wildlife Service.dArnould JPY and Boyd IL (1995) Inter- and intra-annual variation in milk composition in Antarctic fur seals. Physiological Zoology 68: 1164–1180.eOchoa-Acuna H, Francis JM, and Oftedal OT (1999) Influence of long intersuckling interval on composition of milk in the Juan Fernandez fur seal, Arctocephalus philippii. Journal ofMammalogy 80: 758–767.fArnould JPY and Hindell MA (1999) The composition of Australian fur seal (Arctocephalus pusillus doriferus) milk throughout lactation. Physiological and Biochemical Zoology72: 605–612.gGeorges J-Y, Groscolas R, Guinet C, and Robin J-P (2001) Milking strategy in subantarctic fur seals Arctocephalus tropicalis breeding on Amsterdam Island: Evidence from changesin milk composition. Physiological and Biochemical Zoology 74: 548–559.hWerner W, Figueroa-Carranza A-L, and Ortiz CL (1996) Composition and energy content of milk from Southern sea lions (Otaria flavescens). Marine Mammal Science 12: 313–317.iOftedal OT, Boness DJ, and Bowen WD (1988) The composition of hooded seal (Cystophora cristata) milk: An adaptation to postnatal fattening. Canadian Journal of Zoology66: 318–322. Lydersen C, Kovacs KM, and Hamill MO (1997) Energetics during nursing and early postweaning fasting in hooded seal (Cystophora cristata) pups from the Gulf of St.Lawrence, Canada. Journal of Comparative Physiology B 167: 81–88.jLydersen C, Kovacs KM, Hammill MO, and Gjertz I (1996) Energy intake and utilisation by nursing bearded seal (Erignathus barbatus) pups from Svalbard, Norway. Journal of ComparativePhysiology B 166: 405–411.kCarlini AR, Marquez MEI, Soave G, Vergani DF, and Ronayne de Ferrer PA (1994) Southern elephant seal Mirounga leonina: Composition of milk during lactation. Polar Biology14: 37–42.lOftedal OT, Bowen WD, and Boness DJ (1996) Lactation performance and nutrient deposition in pups of the harp seal, Phoca groenlandica, on ice floes off southeast Labrador.Physiological Zoology 69: 635–657.mLang SLC, Iverson SJ, and Bowen WD (2005) Individual variation in milk composition over lactation in harbour seals (Phoca vitulina) and the potential consequences of intermittentattendance. Canadian Journal of Zoology 83: 1525–1531.nLydersen C, Hammill MO, and Ryg MS (1992) Water flux and mass gain during lactation in free-living ringed seal (Phoca hispida) pups. Journal of Zoology, London 228: 361–369.Unless otherwise specified, data from Oftedal OT and Iverson SJ (1995) Phylogenetic variation in the gross composition of milks. In: Jensen R (ed.) Handbook of Milk Composition,pp. 749–789. New York: Academic Press.Species in bold are considered marine mammals. See Table 1 for scientific binomials. N refers to number of milk samples assayed.

Figure 2 Milk collection from the Weddell seal in Antarctica. Lactating seal (c. 450 kg) is manually restrained in a head bag, injected

intramuscularly with oxytocin, and milk is collected by pumping a cutoff 60 ml syringe placed over the inverted nipple. Drawing by

Regina Eisert.


terrestrial carnivores, except bears (Table 2). The high

fat and low sugar contents of bear milk are believed to beimportant to preservation of lean body mass during‘hibernation’, when bears are simultaneously lactatingand fasting. Bear milk was thus ‘preadapted’ to a marine

lifestyle (see below); such a process is termed exaptationin evolutionary biology. Unfortunately, there are no reli-able data on milks of other otters with which to comparesea otters, although mink, which are quite aquatic, do nothave high milk fat levels.

Seven of nine otariids (fur seals and sea lions) and eightof nine phocids (true seals) that have been studied produceextremely high-fat (40–60%) and high-energy

(19þMJ kg�1) milks (Table 2). No other terrestrial mam-mals produce milks that come close to these levels,although some shrews, tree shrews, bears, and bats producemilks containing about 30% fat and 12–15 MJ kg�1 energy.

Even walrus, Australian sea lion, and southern sea lionmilks, although not as energy dense as other otariids orphocids, are still high in fat (24–26%) and energy(12 MJ kg�1) compared to terrestrial carnivores. Pinnipedmilks are less variable in protein content (about 9–12%)

and these levels are matched by such terrestrial carnivoresas Arctic fox, striped skunk, and various cats (Table 2).The reported sugar levels are usually low (0.1–1.2%),although at least one species appears to have more than

2% (Table 2).The milks of the cetaceans differ greatly from those of

the terrestrial Artiodactyla to which they are related(Table 3). Artiodactyl milks typically contain 4–10% fat

and 3–8 MJ kg�1 energy, as compared to 10–30% fat and7–14 MJ kg�1 energy in dolphins and toothed whales

(Odontoceti), and 30–44% fat and 15–19 MJ kg�1 energy

in baleen whales (Mysticeti) (Table 3). Like the pinni-peds, cetaceans produce milks containing about 8–12%

protein (as compared to 3–9% in artiodactyls). Cetaceanmilks are also low in total sugar (1–2.5%).

Manatee milk is higher in fat, protein, and energy, butlower in sugar, than the milks of elephants, to which it is

related (Table 4); manatee milk resembles the milks ofdolphins and toothed whales in gross composition

(Table 3).Thus, all marine mammals produce milks that are

higher in fat and energy than the terrestrial taxa to which

they are most closely related. It is likely that this is anecessity due to the thermoregulatory challenge of a

marine environment. A newborn mammal is not onlysmall but typically has less subcutaneous body fat that

can provide insulation against heat loss upon immersionin water. High-fat, high-energy milks allow rapid postnatal

fat deposition, generating insulation, and also supplyenergy that can be used to sustain high metabolic rates in

a thermally demanding environment. Polar bears use snowdens to provide a more benign climate for neonates. Many

pinnipeds live in cold temperate or polar environments andpups delay water entry until a substantial blubber layer is

developed. Some polar cetaceans, such as the large baleenwhales, migrate to warm temperate or subtropical waters

for parturition and early nursing. The distribution ofmanatees is restricted by cold water temperatures.

The highest milk fats (48–61%) are found in phocidseals, which have relatively short lactations, and deposit fatrapidly after birth. Phocid seals that pup on unstable float-

ing ice (such as hooded and harp seals) have particularly

Figure 3 Changes in milk fat composition over the course of lactation in marine mammals. (a) Phocid seals with short lactation periods(<1 month). (b) Other marine mammals with long lactation periods (4–16 months). Data are from references listed for these species in

Tables 2 and 3, plus Kretzmann MB, Costa DP, and Le Boeuf BJ (1993) Maternal energy investment in elephant seal pups: Evidence for

sexual equality? The American Naturalist 141: 466–480; Lydersen C and Kovacs KM (1996) Energetics of lactation in harp seals (Phoca

groenlandica) from the Gulf of St. Lawrence, Canada. Journal of Comparative Physiology B 166: 295–304; Mellish JE, Iverson SJ, andBowen WD (1999) Variation in milk production and lactation performance in grey seals and consequences for pup growth and weaning

characteristics. Physiological and Biochemical Zoology 72: 677–690.


short and intensive lactations. Hooded seal pups gain 7 kgmass per day, most of which is fat, and are weaned in

4 days, the shortest lactation of any mammal. Hoodedseals also produce milk which has the highest fat content(61%) of any mammalian milk. As the mothers of manyphocid species fast during lactation, the secretion of high-

fat, low-sugar milk may also be important in reducing theglucose demand of the mammary gland, thereby conser-ving gluconeogenic substrates (especially body proteins).

Most fur seals and sea lions also have high-fat, high-energy milks (Table 1). This may be related, in part, to

the fact that mothers undertake extended foraging trips tosea during the long lactation period. The pups of otariidseals do not deposit fat as rapidly as phocid pups, partlybecause when their mothers depart to sea they must usestored energy to cover metabolic costs until she returns.In some species (such as subantarctic and Juan Fernandezfur seals), these maternal foraging trips may be 2–3 weeksin duration, as the mother travels hundreds of kilometersto find suitable prey densities. The high-fat, high-energymilks of otariid seals allow rapid energy transfer duringthe short period the mother is on land with her pup. Thus,

Table 3 Milk composition of the Artiodactyla and Cetacea

Species Scientific binomial NLactation stage(days)

Water(%)

Dry matter(%)

Fat(%)

Crudeprotein(%)

Sugar(%)

Ash(%)


Order Artiodactyla (even-toed ungulates, 240 spp.)

Bovidae (antelope, goats, sheep, etc., 143 spp.)

Gayal Bos frontalis >4 11–50 80.0 20.0 7.0 6.3 5.2 5Cattle (domestic) Bos taurusa >2000 Mature 87.6 12.4 3.7 3.2 4.6 0.7 3

Goat (domestic) Capra hircusa 120 14–56 88.0 12.0 3.8 2.9 4.7 0.8 3

Sable antelope Hippotragus niger 6–8 �30–107 82.1 17.9 5.0 6.2 5.3 0.9 4

Muskox Ovibus moschatus 6 �100 71.5 28.5 14.3 8.7 3.6 1.2 8Rocky mountain

goat

Oreamnos

americanus

28 14–35 82.0 18.0 7.0 6.5 4.5 0.7 5

þ7 spp.

Camelidae (camels, 4 spp.)Bactrian camel Camelus bactrianus 30 23–91 84.8 15.2 4.3 4.3 0.9

Cervidae (deer, 51 spp.)

N. American elk Cervus elaphus 28 14–77 81.0 19.0 6.7 5.7 4.2 1.3 5Mule deer Odocoileus hemionus 24 14–35 81.5 18.5 5.5 7.0 4.5 1.4 5

Reindeer Rangifer tarandus 6 21–30 73.7 26.3 10.9 9.5 3.4 1.3 7

þ3 spp.

Giraffidae (giraffe, okapi, 2 spp.)Giraffe Giraffa camelopardalis 3 Mid 85.5 14.5 4.8 4.0 0.8

Suidae (pigs, 19 spp.)

Pig (domestic) Sus scrofaa >300 14–35 79.9 20.1 8.3 5.6 5.0 0.9 5

Tayassuidae (peccaries, 3 spp.)Collared peccary Tayassu tajacu 4 21–48 83.8 16.2 4.2 5.1 6.2 4

Order Cetacea (84 spp.)Suborder Odontoceti (toothed whales)

Delphinidae (dolphins, n¼34 spp.)Common dolphin Delphinus delphis 1 Mid 58.6 41.4 30.0 10.3 0.8 14Humpback dolphin Sousa chinensis 1 Mid 76.7 23.3 10.2 11.3 0.8 7Spotted dolphin Stenella attenuata 3 Mid-late 22.5 8.4 1.2 11Bottlenose dolphin Tursiops truncatusb 17 210–360 73.0 27.0 12.8 8.9 1.0 7

Iniidae (river dolphins, n¼3 spp.)Franciscana dolphin Pontoporia

blainvilleic3 Mid-late 15.6 10.3 2.5 9

Physeteridae (sperm whales, n¼ 3 spp.)

(Continued )

Table 3 (Continued)

Species Scientific binomial NLactation stage(days)

Water(%)

Dry matter(%)

Fat(%)

Crudeprotein(%)

Sugar(%)

Ash(%)


Pygmy sperm whale Kogia breviceps 1 Mid 74.3 25.7 15.3 8.2 2.2 0.8 8Dwarf Sperm whale Kogia simus 1 Early-mid 62.2 37.8 18.5 10.6 1.1 10Great sperm whale Physeter

macrocephalus7 90–180 63.8 36.2 25.7 8.5 0.6 12

Suborder Mysticeti (baleen whales, n¼ 13 spp.)Balaenopteridae (rorquals, n¼ 7 spp.)

Minke whale Balaenopteraacutorostrata

16 �120–150 51.9 48.1 30.2 13.6 1.7 15

Blue whale Balaenopteramusculus

4–7 �150–210 45.5 54.5 39.4 11.3 1.3 1.4 18

Fin whale Balaenopteraphysalus

10–12 180–210 53.2 46.8 33.4 10.6 2.1 1.2 16

Humpback whale Megapteranovaeangliae

�3–5 �120–210 42.9 57.1 43.8 9.1 0.7 2.1 19

aOftedal OT (1984) Milk composition, milk yield and energy output at peak lactation. A comparative review. Symposia of the Zoological Society of London 51: 33–85.bWest KL, Oftedal OT, Carpenter C, Krames BJ, Campbell M, and Sweeney JC (2007) Effect of lactation stage and concurrent pregnancy on milk composition in the bottlenose dolphin (Tursiops truncatus).Journal of Zoology 273: 148–160.cCaon G, Secchi ER, Capp E, and Kucharski LC (2008) Milk composition of franciscana dolphin (Pontoporia blainvillei) from Rio Grande do Sul, southern Brazil. Journal of the Marine Biological Association ofthe United Kingdom 88: 1099–1101.Unless otherwise specified, data from Oftedal OT and Iverson SJ (1995) Phylogenetic variation in the gross composition of milks. In: Jensen R (ed.) Handbook of Milk Composition, pp. 749–789. New York:Academic Press; Oftedal OT (1997) Lactation in whales and dolphins: Evidence of divergence between baleen- and toothed-species. Journal of Mammary Gland Biology and Neoplasia 2: 205–230.Marine mammals are indicated in bold.

Table 4 Milk composition of the Sirenia and Proboscidea

SpeciesScientificbinomial N

Lactation stage(days)

Water(%)

Dry matter(%)

Fat(%)

Crude protein(%)

Sugar(%)

Ash(%)


Order ProboscideaElephantidae

Asian elephant Elephas maximus 3 60–120 82.3 17.7 7.3 4.5 5.2 0.6 5

African elephant Loxodonta

africana

6 60–80 82.7 17.3 5.0 4.0 5.3 0.7 4

Order SireniaTrichechidae

West Indianmanateea

Trichechusmanatus

5 210–720 76.9 23.1 14.8 8.1 0.4 1.0 8

aBachman KC and Irvine AB (1979) Composition of milk from the Florida manatee, Trichechus manatus latirostris. Comparative Biochemistry and Physiology A 62: 873–878. Pervaiz S and Brew K (1986)Composition of the milks of the bottlenose dolphin (Tursiops truncatus) and the Florida manatee (Trichechus manatus latirostris). Comparative Biochemistry and Physiology A 84: 357–360.Unless otherwise specified, data from Oftedal OT and Iverson SJ (1995) Phylogenetic variation in the gross composition of milks. In: Jensen R (ed.) Handbook of Milk Composition, pp. 749–789. New York:Academic Press. Marine mammals are indicated in bold.


otariid pups experience a feast–famine–feast patternthroughout lactation; those species with the longest fora-ging trips tend to produce the highest fat milks. The highfat and energy density of otariid milks may also be impor-tant in maximizing milk energy storage in the mammaryglands during the prolonged foraging trips. It appears thatrates of milk protein synthesis and milk productiondecline during otariid foraging trips, but recover oncesuckling is reinitiated upon return to the pup. The amaz-ing fact that otariid mammary glands do not involuteduring these prolonged periods between suckling maybe related to milk composition (see below). In contrast,phocid mammaries begin to involute if not suckled for aday or more.

Both cetaceans and manatees give birth in the water,and the calf accompanies its mother while she forages.High-fat milk is presumably important both for deposi-tion of insulating blubber and for supporting the energetic(and thermoregulatory) costs of living in water. Amongthe cetaceans, the toothed species (odontocetes) have longlactations and grow slowly, and therefore fat deposition isalso slow. As there is no added burden of a concurrent fastby mother or calf, and no need for rapid fat accumulationby calves prior to weaning, it is perhaps to be expectedthat the fat and energy levels in odontocete milks are notas high as in most pinniped milks. The baleen whales,including the gargantuan blue whale (the largest livingvertebrate), have higher milk fat levels than odontocetes,but unlike odontocetes most species eat little if anythingduring the first 6 months of lactation. During this period,milk production derives mostly from body reserves, andhigh-fat, low-sugar milks may limit protein catabolism viaminimizing mammary glucose demand, as in phocids andpolar bears that fast while lactating.

Other Milk Constituents

Most recent research on marine mammals has focused onunderstanding reproductive energetics and relatively lit-tle attention has been paid to milk constituents other thanthe primary energy sources.

Lipids

Lipids are by far the most abundant organic component ofmarine mammal milks, and in some cases the lipidsexceed water content (Tables 2 and 3). As in othermammals, the milk lipids are packaged into membrane-bound milk fat globules, and at least in the Weddell sealthese milk fat globules are relatively large. There hasbeen considerable interest in the fatty acid compositionof the lipids (Table 5), in part because this may provideindirect information on the prey species eaten by lactat-ing females. Most marine mammal milks are high in long-

chain polyunsaturated lipids, including such omega-3fatty acids as 18:3n3, 20:4n3, 20:5n3, 22:5n3, and 22:6n3,as well as such omega-6 fatty acids as 18:2n6 and 20:4n6(Table 5). The differences among species may reflectdifferences in diet more than species differences in lipidprocessing, since the fatty acid composition of marinemammal milks typically reflects both the fatty acid com-position in the diet and the fatty acid composition ofstored lipids (which reflect previously consumed lipid).The extent to which milk or blubber fatty acids arealtered by lipogenesis, preferential mobilization, chainelongation, or desaturation is debated, but this is undoubt-edly important in some species, particularly those thatingest low-fat diets (such as manatees). Manatee milkappears to lack the long-chain (C20 and longer) polyun-saturated fatty acids characteristic of pinniped andcetacean milks, but does have short-chain saturates suchas 8:0, 10:0, 12:0, and 14:0 (not shown in Table 5), as mightbe expected of a herbivore that generates volatile fattyacids via intestinal fermentation.

Proteins

The crude protein in marine mammal milks representsabout 8–12% of the milk by mass, which may seem highby comparison to most terrestrial mammals but is actuallylow relative to total milk energy. The proportion of milkenergy provided by protein is lower in odontocetes andmysticetes than in artiodactyls, and lower in otariids andphocids than in terrestrial carnivores (Figure 4). Theparticularly low percentage of energy provided by pro-tein in phocid milks relates to the pattern of post-natalpup growth, which entails high rates of fat depositionrather than high rates of lean mass gain. About 3–9% ofthe total nitrogen in marine mammal milks is non-proteinnitrogen, and thus crude protein somewhat overestimatestrue protein.

Marine mammal milks contain both caseins and avariety of whey proteins, as do the milks of terrestrialmammals. The relative proportions of caseins:whey pro-teins range from 30:70 (in the southern elephant seal) to70:30 (in fin and blue whales); sea otters (35:65) and polarbears (61:39) are intermediate. It is not known if thesedifferences are associated with differences in the forma-tion and retention of curds in the stomach of the young,although gastric retention of milk solids may be impor-tant to allow gastric lipolysis of high-fat milks. Genetranscript sequencing has identified �S1, �S2, �, and� caseins in fur seal mammaries, although the propor-tions in milk are not known. Genes for the whey proteins�-lactoglobulin 1 and lysozyme C have also been iden-tified in fur seal mammary tissue. Electrophoretic bandswith the mobility of �-lactoglobulin have been found inmilks of the northern fur seal, Stejneger’s beaked whale,and bowhead whale, and two variants of �-lactoglobulin

Table 5 Fatty acid composition of milk lipids of marine mammals, expressed as mass% of total fatty acids

Family and species N

Lactationstage(days) 14:0 16:0 16:1 18:0 18:1 18:2n6 18:3n3 18:4n3 20:1 20:4n3 20:4n6 20:5n3 22:1 22:5n3 22:6n3

Order Carnivora (carnivores)

Otariidae (fur seals, sea lions)New Zealand fur seala 160 ? 3.8 20.2 5.2 2.9 28.2 1.5 nr 0.4 7.6 1.2 1.2 3.6 0.6 2.4 13.4

Antarctic fur seal 8 15–25 10.3 20.6 12.5 1.6 25.2 1.4 0.3 0.4 2.4 0.6 0.5 11.6 0.5 2.2 6.3

Juan Fernandez fur sealb 15 1–110 2.9 18.1 5.4 2.8 29.2 1.1 0.5 0.3 2.3 0.7 1.2 3.7 0.2 3.1 21.3

Australian fur seal 1 90.0 7.0 18.2 6.9 2.5 19.0 1.7 1.0 1.1 6.1 2.3 1.2 5.6 2.3 2.5 16.2California sea lion 2 30–60 4.5 18.1 6.5 3.0 23.2 1.6 0.9 1.0 2.7 1.2 1.0 8.5 1.3 3.9 19.2

Phocidae (true seals)

Hooded seal 10 0–4 4.4 11.7 13.4 2.1 27.0 1.4 0.4 1.2 14.8 0.7 0.3 6.8 4.9 1.9 6.5

Gray sealc 18 �7 4.6 13.1 13.6 1.9 30.2 1.4 0.5 1.1 10.4 nr 0.8 6.7 nr 4.5 10.0Weddell seal 5 10–18 8.7 13.3 11.8 2.0 38.8 1.7 0.4 1.0 7.5 0.4 0.2 4.7 1.6 0.9 4.1

N. elephant seal 3 25–26 2.7 11.3 4.7 3.1 37.9 1.5 0.3 tr 21.0 0.2 0.4 1.1 6.9 0.9 4.2

S. elephant seald 53 1–23 2.7 10.4 5.0 2.8 30.5 1.3 0.4 1.7 8.2 1.7 0.9 8.4 1.5 5.3 15.9Harp seal 5 4–9 4.6 8.8 17.4 1.6 23.0 1.1 0.3 0.8 17.2 0.3 0.4 6.1 5.9 3.2 6.5

Order Cetacea (dolphins and whales)

Suborder Odontoceti (toothed whales)

Delphinidae (dolphins)Bottlenose dolphin 1 Late 3.2 21.1 13.3 3.3 23.1 1.2 0.2 0.2 9.0 0.4 1.4 6.0 2.8 2.0 6.4

Suborder Mysticeti (baleen whales)

Balaenopteridae (rorqual whales)

Fin whale 1 Late 5.5 22.9 6.5 3.9 24.7 1.1 0.6 1.1 3.1 0.7 0.5 13.9 1.9 3.0 5.7Order Sirenia

Trichechidae (manatees)

West Indian manateee 5 >365 6.3 20.2 11.6 0.5 47.0 1.8 2.2

aBaylis AMM and Nichols PD (2009) Milk fatty acids predict the foraging locations of the New Zealand fur seal: Continental shelf versus oceanic waters. Marine Ecology Progress Series 380: 271–286.bOchoa-Acuna H, Francis JM, and Oftedal OT (1999) Influence of long intersuckling interval on composition of milk in the Juan Fernandez fur seal, Arctocephalus philippii. Journal of Mammalogy 80: 758–767.cGrahl-Nielsen O, Hammill MO, Lydersen C, and Wahlstrøm S (2000) Transfer of fatty acids from female seal blubber via milk to pup blubber. Journal of Comparative Physiology B 170: 277–283.dBrown DJ, Boyd IL, Cripps GC, and Butler PJ (1999) Fatty acid signature analysis from the milk of Antarctic fur seals and Southern elephant seals from South Georgia: Implications for diet determination.Marine Ecology Progress Series 187: 251–263.eManatee milk also contains shorter-chain fatty acids (see text).Unless otherwise specified, data from Iverson SJ and Oftedal OT (1995) Phylogenetic and ecological variation in the fatty acid composition of milks. In: Jensen R (ed.) Handbook of Milk Composition,pp. 789–827. New York: Academic Press.nr, not reported, i.e. <0.5%.

Figure 4 Percentage of milk energy provided by protein in different mammalian groups. Bars represent means plus standard errors.

Number of species is indicated at the bottom of each bar. Values are calculated from data in Tables 2 and 3.


have been isolated and partially sequenced from bottle-nose dolphin milk. Electrophoretic evidence for thepresence of serum albumin has been observed in grayand southern elephant seals. However, other whey pro-teins observed via electrophoresis of marine mammalmilks have not been characterized. Activity of theenzyme bile salt-stimulated lipase has been observed inhooded seal milk. The milk fat globule membrane of theWeddell seal contains the proteins butyrophilin andxanthine oxidoreductase.

Of particular interest is the apparent lack of lactosesynthase activity in otariid mammary glands. Thisappears to be due both to mutations causing aberrantsplicing during the transcription of the �-lactalbumingene and to great reduction in the transcription andtranslation of �-lactalbumin, which is an essentialcomponent of the lactose synthase complex. Without�-lactalbumin, the �1,4-galactosyltransferase does notutilize glucose as a receptor for galactose, and thus lac-tose is not formed. As noted below, otariid milks lack bothfree lactose and oligosaccharides that incorporate lactose.The failure to produce �-lactalbumin appears to beimportant in preventing mammary involution duringthe long foraging trips that lactating otariids may under-take. The milk of Stejneger’s beaked whale, which lackslactose, also lacks �-lactalbumin in amounts detectableby electrophoresis.

Carbohydrates

Marine mammal milks are typically much lower intotal sugar content than the milks of related terrestrialtaxa (Tables 1–3). Most marine mammals, including

polar bears, phocid seals, and at least some dolphins andwhales, produce milks with low levels of both lactose andother more complex sugars (Table 6). These complexsugars are synthesized by the addition of other monosac-charide units to lactose (Gal(�1-4)Glc), such as thetrisaccharides isoglobotriose (Gal (�1-3)Gal (�1-4)Glc),29fucosyllactose (Fuc(�1-2)Gal(�1-4)Glc), and39sialyllactose (Neu5Ac(�2-3)Gal(�1-4)Glc). Of these,isoglobotriose is the predominant sugar in polar bearmilk (and in the milk of some other bears), and29fucosyllactose is a codominant sugar (with lactose) inat least some phocid seals (hooded seal, harbor seal) andsome baleen whales (minke whale).

Most marine mammals with the ability to synthesizelactose also synthesize an array of longer chain oligosac-charides (up to octa- and nonasaccharides) that includelactose (i.e., Gal(�1-4)Glc) at the reducing end as well asvarying combinations of galactose, N-acetyl galactosa-mine, N-acetyl glucosamine, fucose, and sialic acid (orN-acetyl neuraminic acid (Neu5Ac)) (Table 6). Thus,7–10 oligosaccharides have been identified in the milksof polar bears, hooded seals, harbor seals, and minkewhales, but not the same oligosaccharides in each species.The biological significance of this array of oligosacchar-ides is not clear, although by analogy to human milkoligosaccharides, antimicrobial functions in either themammary gland or the neonatal digestive tract havebeen hypothesized.

Some marine mammals, including otariids, the wal-rus, and Stejneger’s beaked whale, appear to producemilks devoid of lactose, the primary sugar in the milksof most mammals. In otariids and the walrus, gene muta-tions and/or changes in transcription rates effectively

T le 6 Oligosaccharides in marine mammal milks

Number of sugar units per oligosaccharide Marine mammal species

Total of

sugar units Glucose Galactose

N-Acetyl

glucosamine

N-Acetyl

galactosamine Fucose

N-Acetyl

neuraminic

acid Polar beara

Australian

fur sealbNorthern fur

sealcHooded

sealbBearded

sealdHarbor

sealeBottlenose

dolphinf

Beluga

whaleg

Minke

whaleg

In itol 1 xx xx x x x

L tose 2 1 1 x xx xx xx xx trace xx

Is lobotriose 3 1 2 xx

G otriose 3 1 2 x

2 cosyllactose 3 1 1 1 x xx xx xx xx

3 ialyllactose 3 1 1 1 x x x

6 ialyllactose 3 1 1 1 x

L to-N-neotetraose 4 1 2 1 x x x

B etrasaccharide 4 1 2 1 x

3 ucosylisoglobotriose 4 1 2 1 x

A etrasaccharide 4 1 1 1 1 x x

M osialyltetrasaccharide 4 1 1 1 1 x

A entasaccharide 5 1 1 1 2 x

B entasaccharide 5 1 2 2 x

S yl lacto-N-

eotetraosea

5 1 2 1 1 x x

L to-N-fucopentaose IV 5 1 2 1 1 x

S yl lacto-N-neotetraoseb

5 1 2 1 1 x

L to-N-neohexaose 6 1 3 2 x x

P lacto-N-neohexaose 6 1 3 2 x x

M ofucosyl para lacto-N-

eohexaose

7 1 3 2 1 x

M osialyl lacto-N-

eohexaose

7 1 3 2 1 x

(Continued )

ab

os

ac

og

lob

-Fu

9-S

9-S

ac

-T

9-F

-T

on

-P

-P

ial

n

ac

ial

c

ac

ara

on

n

on

n

Table 6 (Continued)

Number of sugar units per oligosaccharide Marine mammal species

Total of

sugar units Glucose Galactose

N-Acetyl

glucosamine

N-Acetyl

galactosamine Fucose

N-Acetyl

neuraminic

acid Polar beara

Australian

fur sealbNorthern fur

sealcHooded

sealbBearded

sealdHarbor

sealeBottlenose

dolphinf

Beluga

whaleg

Minke

whaleg

Sialyl para lacto-N-

neohexaose

7 1 3 2 1 x

Monofucosyl lacto-N-

neohexaose a

7 1 3 2 1 x x

Monofucosyl lacto-N-

neohexaose b

7 1 3 2 1 x x

Difucosyl lacto-N-

neohexaose

8 1 3 2 2 x x x

Monosialyl monofucosyl

lacto-N-neohexaose

8 1 3 2 1 1 x

Disialyl lacto-N-

neohexaose

8 1 3 2 2 x

Monosialyl difucosyl lacto-

N-neohexaose

9 1 3 2 2 1 x x

Difucosyldecasaccharide 10 1 4 3 2 x

Unnamed 11 1 4 3 2 1 x

aUrashima T, Nagata H, Nakamura T, et al. (2003) Differences in oligosaccharide pattern of a sample of polar bear colostrum and mid-lactation milk. Comparative Biochemistry and Physiology B 136: 887–896.bUrashima T, Arita M, Yoshida M, et al. (2001) Chemical characterization of the oligosaccharides in hooded seal (Cystophora cristata) and Australian fur seal (Arctocephalus pusillus doriferus) milk. Comparative Biochemistry and Physiology B

128: 307–323.cDosako S, Taneya S, Kimura T, et al. (1983) Milk of northern fur seal: Composition, especially carbohydrate and protein. Journal of Dairy Science 66: 2076–2083.dUrashima T, Nakamura T, Nakagawa D, et al. (2004) Characterization of oligosaccharides in milk of bearded seal (Erignathus barbatus). Comparative Biochemistry and Physiology B 138:1–8.eUrashima T, Nakamura T, Yamaguchi K, et al. (2003) Chemical characterization of the oligosaccharides in milk of high Arctic harbor seal (Phoca vitulina vitulina). Comparative Biochemistry and Physiology B 135: 549–563.fUemura Y, Asakuma S, Nakamura T, Arai I, Taki M, and Urashima YT (2005) Occurrence of a unique sialyl tetrasaccharide in colostrum of a bottlenose dolphin. Biochimica et Biophysica Acta 1725: 290–297.gUrashima T, Sato H, Munakata J, et al. (2002) Chemical characterization of the oligosaccharides in beluga (Delphinapterus leucas) and minke whale (Balaenoptera acutorostrata) milk. Comparative Biochemistry and Physiology B 132: 611–624.

Predominant sugar is identified by xx; others by x.


produce milks lacking functional �-lactalbumin, and

�-lactalbumin is reported missing from Stejneger’s

beaked whale. The West Indian manatee also produces

milk in which lactose was not detected by paper chro-

matography or enzymatic methods, although trace

levels of lactose were found by high-performance liquid

chromatography (HPLC) and very low levels of

�-lactalbumin could be detected. It is not known if

the low level of sugar in manatee milk (Table 3)

represents free sugars or covalently bound sugars that

were hydrolyzed from glycolipids or glycoproteins

during analysis.Sea lions and fur seals that lack the ability to

synthesize lactose produce milks devoid of lactose-

containing oligosaccharides. It appears that the pri-

mary free sugar in these milks is the monosaccharide

inositol (Table 6). Whether inositol or other small

organic osmolytes replace the osmotic role of lactose

in the secretion of the aqueous phase of otariid milks

is not known.

Table 7 Major mineral elements in marine mammal milks

NCag k

Carnivora

Ursidae Polar beara 7 0.2Mustelidae Sea otterb 5 1.0

Otariidae Galapagos fur seal 17 0.6

Northern fur seal 1 0.5

Southern sea lionc 4 0.4California sea lion 7 0.8

Phocidae Weddell seal

N. elephant seal 7–12 0.5S. elephant seal

Harp seal 4 0.7

Cetacea

Delphinidae Common dolphin 2 1.5Humpback dolphin 1 1.7

Spotted dolphin 8

Atlantic spotted dolphin 1 1.5

Bottlenose dolphin 3–4 1.3Physeteridae Pygmy sperm whale 1 1.5

Ziphiidae Stejneger’s beaked whale 1 2.2

Balaenopteridae Blue whale 2 3.3Fin whale 1 3.2

Sirenia

Trichechidae West Indian manateed 1 0.2

aJenness R, Erickson AW, and Craighead JJ (1972) Some comparative aspebJenness R, Williams DT, and Mullin RJ (1981) Composition of milk of the se375–379.cWerner W, Figueroa-Carranza A-L, and Ortiz CL (1996) Composition and enMammal Science 12: 313–317.dBachman KC and Irvine AB (1979) Composition of milk from the Florida maPhysiology A 62: 873–878.Unless otherwise specified, data from Oftedal OT, Boness DJ, and TedmanPinnipedia. Current Mammalogy 1: 175–245; Oftedal OT (1997) Lactation intoothed-species. Journal of Mammary Gland Biology and Neoplasia 2: 205–Data are presented on a whole milk basis.

Mineral Elements

The milks of marine mammals presumably supply thewide variety of macrominerals, trace elements, and vita-mins that growing young require for tissue growth andmetabolic function, but these constituents are not wellstudied. Some of the early work on whale milks collectedduring whaling operations used what are now outdatedmethodologies, and as the results may not be reliable theyare not included herein. As noted above, contamination ofmilks with water, sodium, and magnesium from seawateris of concern, and contamination of milk with dirt or fecalmaterial may be hard to avoid when working with land-breeding seals in large colonies.

Among terrestrial mammals, the ratio of calcium tophosphorus (Ca:P) in milk is typically above 1:1, reflect-ing a greater post-natal requirement for calcium than forphosphorus, primarily due to calcium deposition in grow-ing bone. Ca:P ratios above 1 are also found in the milks ofthe polar bear, sea otter, some dolphins and whales, andthe West Indian manatee (Table 7). However, both the

g�1Pg kg�1

Ca:Pratio

Kg kg�1

Nag kg�1

K:Naratio

9 0.23 1.267 0.84 1.27

3 1.67

7 1.19 0.48 0.84 0.52 1.61

0 1.00 0.400 1.03 0.78 1.21 0.89 1.36

0.57 0.53 1.08

1 0.94 0.54 0.56 0.86 0.651.36 0.99 1.37

2 1.20 0.60 1.08 0.62 1.75

2.3 0.651.4 1.21

1.2

1.7 1 1.70

1.1 1.18 0.8 1.6 0.501.7 0.88

0.7 3.14 1.1 1.3 0.85

2.1 1.57 1.5 1 1.504.1 0.78

6 0.22 1.18 0.51 3.1 0.16

cts of milk from four species of bears. Journal of Mammalogy 53: 34–47.a otter (Enhydra lutris). Comparative Biochemistry and Physiology 70A:

ergy content of milk from Southern sea lions (Otaria flavescens). Marine

natee, Trichechus manatus latirostris. Comparative Biochemistry and

RA (1987) The behavior, physiology, and anatomy of lactation in thewhales and dolphins: Evidence of divergence between baleen- and230.


otariids and the phocids produce milks with an inverseCa:P ratio, that is, more phosphorus than calcium. Thefunctional significance of this is not known. In captivity,seal pups allowed to suckle beyond normal weaning datesmay develop pathological bone demineralization.

In terrestrial mammals, milk is higher in potassiumthan sodium, reflecting the existence of sodium andpotassium gradients maintained across the basal mem-branes of mammary secretory epithelial cells. The sameis probably true of marine mammals, although data arelimited (Table 7). The high sodium values reported forsome cetacean and manatee milks are suspect due to thepossibility of seawater contamination. Based on data on ahandful of species, marine mammal milks are reported tocontain about 1000–1700 mg kg�1 chloride, 120–200 mgkg�1 magnesium, and trace levels of iron (5–36 mg kg�1),copper (2–3 mg kg�1), zinc (1–8 mg kg�1), and selenium(0.4–0.5 mg kg�1).

Vitamin data on marine mammal milks are sparse.The milks of blue and fin whales reportedly contain,per kg fresh milk, the following vitamins: 3100–7800 IUvitamin A, 1.1–1.6 mg total thiamin, 0.2–1.6 mg ribofla-vin, 7–26 mg niacin, 0.9–1.1 mg vitamin B6, 3–18 mgpantothenic acid, 12–65 mg biotin, and 8–130 mg vitaminB12. Fairly fresh (<6 h post-mortem) fin whale milkreportedly contains 70 mg l�1 ascorbic acid (vitamin C).In harp and hooded seals, vitamin E content of colostrumis high but then falls to stable levels of about 20–50 mgkg�1 at mid-lactation; by contrast, vitamin A levels areconstant throughout lactation. Similar patterns have beenseen in gray seals. Further research is needed on freshlycollected and well-preserved marine mammal milks todetermine if the above values are representative orinclude errors due to vitamin losses during collection,storage, and analysis.

See also: Lactose and Oligosaccharides: Indigenous

Oligosaccharides in Milk. Mammary Gland: Growth,

Development and Involution. Mammary Gland, Milk

Biosynthesis and Secretion: Lactose; Milk Fat; Milk

Protein; Secretion of Milk Constituents. Milk: Milk of

Monotremes and Marsupials; Milks of Non-Dairy

Mammals; Milks of Other Domesticated Mammals (Pigs,

Yaks, Reindeer, etc.). Milk Lipids: Fatty Acids; General

Characteristics; Nutritional Significance. Milk Proteins:

Casein Nomenclature, Structure, and Association;

Interspecies Comparison of Milk Proteins: Quantitative

Variability and Molecular Diversity; Nutritional Quality of

Milk Proteins; �-Lactalbumin; Milk Salts:

Macroelements, Nutritional Significance; Trace elements,

Nutritional Significance.

Further Reading

Berta A, Sumich JL, and Kovacs KM (2006) Marine Mammals:Evolutionary Biology, 2nd edn. New York: Academic Press.

Iverson SJ and Oftedal OT (1995) Phylogenetic and ecologicalvariation in the fatty acid composition of milks. In: Jensen R (ed.)Handbook of Milk Composition, pp. 789–827. New York:Academic Press.

Lydersen C and Kovacs KM (1999) Behavior and energetics of ice-breeding North Atlantic phocid seals during the lactation period.Marine Ecology Progress Series 187: 265–281.

Oftedal OT (1993) The adaptation of milk secretion to the constraints offasting in bears, seals and baleen whales. Journal of Dairy Science76: 3234–3246.

Oftedal OT (1997) Lactation in whales and dolphins: Evidence ofdivergence between baleen- and toothed-species. Journal ofMammary Gland Biology and Neoplasia 2: 205–230.

Oftedal OT (2000) Use of maternal reserves as a lactation strategyof large mammals. Proceedings of the Nutrition Society59: 99–106.

Oftedal OT, Boness DJ, and Tedman RA (1987) The behavior,physiology, and anatomy of lactation in the Pinnipedia. CurrentMammalogy 1: 175–245.

Oftedal OT and Iverson SJ (1995) Phylogenetic variation in the grosscomposition of milks. In: Jensen R (ed.) Handbook of MilkComposition, pp. 749–789. New York: Academic Press.

Reich CM and Arnould JPY (2007) Evolution of Pinnipedia lactationstrategies: A potential role for �-lactalbumin? Biology Letters3: 546–549.

Schulz TM and Bowen WD (2005) The evolution of lactation strategiesin pinnipeds: A phylogenetic analysis. Ecological Monographs75: 159–177.

Sharp JA, Cane KN, Lefevre C, Arnould JPY, and Nicholas KR(2006) Fur seal adaptations to lactation: Insights into mammarygland function. Current Topics in Developmental Biology72: 275–308.

Sharp JA, Lefevre C, and Nicholas KR (2008) Lack of functional alpha-lactalbumin prevents involution in Cape fur seals and identifies theprotein as an apoptotic milk factor in mammary gland involution.BMC Biology 6: 48.

Urashima T, Arita M, Yoshida M, et al. (2001) Chemicalcharacterization of the oligosaccharides in hooded seal(Cystophora cristata) and Australian fur seal (Arctocephaluspusillus doriferus) milk. Comparative Biochemistry and PhysiologyB 128: 307–323.

Urashima T, Sato H, Munakata J, et al. (2002) Chemical characterizationof the oligosaccharides in beluga (Delphinapterus leucas) and minkewhale (Balaenoptera acutorostrata) milk. Comparative Biochemistryand Physiology B 132: 611–624.

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