Nutrition and Nutritional Diseases of Marine Mammals - Exotic and Laboratory Animals - MSD Veterinary Manual (2023)

Generally, captive animals that have a diet solely or primarily of fish are fed dead fish that has been frozen. The logistics and difficulty in providing this diet can create some unique nutritional issues. Not all fish have the same nutritional value; A diet consisting of a single species of fish is unlikely to provide a balanced diet for any animal. Likewise, one diet will not serve all piscivores equally, and the potential collapse of a fishery can leave some fish species unavailable. Only fish suitable for human consumption should be fed. (See alsoDiet: Exotic and zoo animals Diet: Exotic and zoo animals .)

Storage and thawing of frozen fish must be carefully monitored. Forage fish should be maintained at or below -28 °C (-19 °F) to slow the deterioration of their nutritional value through oxidation of amino acids and unsaturated lipids. Frozen fish dehydration can also be a problem for animals that get their water from food. Fatty fish should not be stored for more than 6 months. Few fish, with the possible exception of capelin, should be stored for more than 1 year. To maintain optimal vitamin levels and reduce moisture loss, frozen fish should be air thawed under refrigeration. Thawing in water depletes water-soluble vitamins. Thawing at room temperature encourages bacterial growth and spoilage.

The energy needs of marine mammals vary with age, ambient temperature and condition. Young, growing bottlenose dolphins and smaller pinnipeds generally require 9-15% of their body weight of quality fish per day. Older animals may only need 4-9% of their body weight for maintenance. Larger species (eg, whales and elephant seals) generally require less food per unit body weight (2%–5% of body weight) than adults. Obesity can develop in captive animals with excessive caloric intake and reduced exercise; Caloric intake should be closely monitored.

Sirens are herbivores, eating numerous species of marine and freshwater plants in the wild but can thrive on a diet of hydroponic weed and various salads, vegetables and fruits such as carrots and bananas. The diet can also be supplemented with manatee-specific pellets from commercially available herbivorous primate pellets, and multivitamin-mineral supplements can be used in particular to balance the calcium to phosphorus concentration ratio. It is believed that sirens ingest considerable animal protein while grazing in the wild. The daily intake requirement has been estimated at 7-9% of body weight, but varies with age and growth. Sirens are generally fed at least several times a day to accommodate their feeding pattern, and food should be offered both underwater and on the surface.

Sea otters are typically fed a diet consisting of various invertebrates (e.g., echinoderms, mollusks, and occasionally crustaceans) and fish. Adult animals require about 25-30% of their body weight in food every day. Rehabilitating wild sea otters may not readily tolerate frozen foods and may need to be offered live foods such as clams and mussels to encourage feeding.

Polar bears in the wild have a high-fat diet, especially in winter when they feed heavily on seals. They are thought to have exceptional vitamin A requirements, and some dermatological conditions respond to daily dietary supplementation of 20,000-1,000,000 U. Polar bears in captivity are usually fed large amounts of fish, but their diets are often supplemented with commercial omnivore diets for nutritional and enrichment diversity. Vitamin D should also be supplemented with 1000 U/kg feed. Kidney disease is common in older bears and in some cases reduced dietary protein may be recommended.

Neonatal nutrition in marine mammals

Young, unweaned marine mammals are often found stranded and need to be fed a diet similar to mother's milk. In captivity, newborns can be abandoned by their parents and require artificial rearing. Marine mammal milk is generally high in lipid content, but there is considerable variability and lipid content often varies during lactation. Most species are carbohydrate intolerant, and newborns fed carbohydrates develop severe, life-threatening bacterial gastroenteritis. Most newborn marine mammals also require immense caloric density in milk substitutes. Milk replacement formulas based on commercially available component-based milk substitutes have begun to replace some of the very complex home-made formulas used in the past. Weight should be monitored closely during hand-rearing, and most animals can begin weaning and offering solid food once teeth have erupted. If you are faced with a newborn marine mammal to raise, it is recommended that you contact one of the major marine mammal rescue centers for species-specific advice and updated methods.

Phocid and Otariid seals can be raised using the same milk replacer based formulas. Pinnipe puppies should be fed about every 4 hours during their first week of life; gradually the amount of formula fed should be increased and feedings can be reduced to three to five per day. The transition from the formula diet to the fish diet should be gradual to ensure adequate calorie intake during this time; Fish oil is often added to formulas to increase caloric value. port seal (Phoca Kalb) Hatchlings should be tube fed until at least 2–3 weeks of age, when they can become accustomed to small pieces of fish. Elephant seal pups will need tube feeding until they are at least 4 weeks old, at which point weaning can begin. Otariids generally have a longer lactation period, so bottle feeding may be preferable for newborns to reduce handling and the risk of accidental insertion of a feeding tube into the airway. Most Otariid puppies can be offered fish as early as 4 weeks of age, but as they can nurse for a year or more it may take time to fully transition to fish. California sea lion (Zalophus californianus) Hatchlings can be supported with fish as early as 4 weeks of age and fed freely from 6 weeks.

newborn walruses (Odobenus rosmarus) were bred with milk substitute based formulas as well as whipped cream based ones enhanced with ground mollusks (clams) instead of fish. Walruses have a much longer lactation period than other pinnipeds, up to 19 months.

Newborn whales have longer breastfeeding periods than pinnipeds. Success in bottle rearing has improved with experience, and individuals of species inferior to common dolphins (Dolphin Dolphin) in gray whales (strong writing) were raised successfully. The fat content of whale milk varies significantly; bottlenose dolphin (Tursiopsspp) milk contains about 17% fat (half that of most fin milk), beluga whale (Delphinapterus Leukas) milk is 27%, porpoise (come on, come on) Milk is 46% and Mysticete Blue Whale (Baleanoptera musculus) Milk is 42%. Formulas based on commercial milk replacers supplemented with ground fish and oils have been successfully fed to bottlenose dolphins and porpoises using a lamb nipple or gastric tube.

Newborn sirens begin nibbling on seaweeds shortly after birth, but may continue nursing for up to 18 months. They can be raised on artificial milk if weaned early; However, gastrointestinal problems such as diarrhea, constipation and enterocolitis are common with inappropriate formulations.

Newborn sea otters have also been successfully raised on artificial formula from birth. They should be bottle fed initially and solid food can be offered in addition to formula at around 4-6 weeks of age. Hand-rearing sea otters is particularly challenging, and because otters are highly susceptible to imprinting, specialists should be consulted if hand-rearing is attempted.

Newborn polar bears are extremely altricial and present challenges due to an apparently immature immune system. Most hand-reared cubs are given polar bear serum orally and parenterally to support the immune response. Polar bear milk is high in fat (31%) and contains little lactose. Polar bears have been successfully raised with formulas based on whipped cream or oil, or using a commercial canine formula as the main ingredient.

Thiamine deficiency in marine mammals

Because thiamine deficiency can occur in any fish-eating animal, any animal fed primarily frozen fish should be supplemented with thiamine. Thiamine in feed is destroyed by the activity of thiaminase enzymes or antithiamine substances in the fed fish. These active enzymes can also destroy extra thiamine added to fish when the fish sits for a long time before feeding.

Clinical signs of thiamine deficiency are primarily CNS disorders. Affected animals may develop anorexia, regurgitation, or ataxia. The condition can lead to seizures, coma, and death.

Animals showing signs of thiamine deficiency respond rapidly (usually within 24 hours) to injection of thiamine hydrochloride (up to 1 mg/kg, IM) followed by oral supplementation. The control normally includes supplemental thiamine at a level of 25 mg/kg feed, preferably administered 2 hours prior to a main feed.

Vitamin E deficiency (steatitis, white fat disease) in marine mammals

The antioxidant properties of vitamin E are believed to play an important role in maintaining the integrity of cell membranes. Oxidative processes during storage of fish destroy vitamin E and other antioxidants. Steatitis has been experimentally induced in phocid seals, and relationships between vitamin E deficiency and hyponatremia are suggested.

Captive piscivores are commonly supplemented orally with vitamin E at levels up to 100 mg/kg diet, which generally maintains high serum concentrations of the vitamin. This does not seem necessary if forage fish are properly stored and thawed.

Hyponatremia (salt deficiency, Addison's disease) in marine mammals

Hyponatremia in pinnipeds is closely associated with adrenal exhaustion and the development of Addison's disease, which links the syndrome to environmental stressors rather than simple primary salt deficiency. It is most common in pinnipeds kept in freshwater enclosures, but can also be seen in animals kept in saltwater. It is more common in phocid seals but occurs in otariids and other marine mammals, particularly when food is thawed in water, as sodium is lost in this way.

Signs include periodic weakness, anorexia, lethargy, incoordination, tremors, and convulsions. The serum sodium concentration can fall to < 140 mEq/L. Severely affected animals can collapse in an Addisonian crisis, which can be fatal.

Emergency therapy consists of sodium chloride infusion and substitutionCorticosteroids Corticosteroids in Animals Two classes of steroid hormones, mineralocorticoids and glucocorticoids, are naturally synthesized in the adrenal cortex from cholesterol. (See also The Adrenal Glands.) more . Long-term management of advanced cases requires mineralocorticoid supplementation in conjunction with oral sodium chloride supplements and regular monitoring of serum sodium concentrations. Providing saltwater pools and supplementing sodium chloride (3 g NaCl/kg feed) in the diet of pinnipeds kept in freshwater pools should be considered a poor second choice. Salt-supplemented animals should have constant access to fresh water.

Histamine poisoning (scombroid poisoning, mackerel poisoning) in marine mammals

Scombroid fish (e.g. mackerel and tuna) and other dark-fleshed fish have a short shelf life, even when frozen at low temperatures. A complex of substances that also includes histamine, which is formed by bacterial decarboxylation of the large amount of histidine in fish meat, is responsible for the signs of histamine poisoning in affected marine mammals. Histamine toxicosis can also occur in non-scombroid fish, including poorly treated herring, anchovies, or sardines. It is most common in pinnipeds but is also seen in other marine mammals.

Clinical signs include anorexia; Lethargy; a red, sore mouth or throat; conjunctivitis and increased lacrimation; and palpitations. Occasionally, vomiting, diarrhea, itching, urticaria, or postures suggestive of abdominal pain are observed.

Antihistamines, including cimetidine, can relieve clinical signs, but the condition is generally self-limiting and the animal begins feeding within 2 to 3 days. In more severe or acute cases, epinephrine counteracts the histamine response. Cortisone and diphenhydramine hydrochloride can help with breathing problems. The control is to avoid scombroid fish in the diet or to pay careful attention to their quality, storage and handling when using.

Iron storage disease (hemochromatosis) in marine mammals

Iron storage disease is most common in captive cetaceans and pinnipeds and is associated with an iron-rich diet. Excess iron is naturally stored in the liver as ferritin and hemosiderin, and excessive amounts can lead to liver disease (eg, hepatitis or hemochromatosis). The disease is most common in bottlenose dolphins and has also been reported in fur seals and California sea lions.

Iron storage disease is characterized by high serum iron and ferritin levels with >50% transferrin saturation. The activities of liver enzymes (ALT and AST) and the concentrations of triglycerides, cholesterol and globulins are also frequently increased.

Treatment is to reduce the amount of iron in the diet, mainly through dietary changes, including reducing vitamin C intake. Phlebotomy has been used for faster iron reduction and may be effective in the short term, but long-term dietary changes are also needed to prevent recurrence.

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