Volume 21 | Issue 2 Article 8

1959 The Theories and Physiology of Hibernation Charles Haight Iowa State College

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Recommended Citation Haight, Charles (1959) "The Theories and Physiology of Hibernation," Iowa State University Veterinarian: Vol. 21 : Iss. 2 , Article 8. Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol21/iss2/8

This Article is brought to you for free and open access by the Journals at Iowa State University Digital Repository. It has been accepted for inclusion in Iowa State University Veterinarian by an authorized editor of Iowa State University Digital Repository. For more information, please contact [email protected]. The Theories and Physiology of Hibernation Charles Haight, B.S.

NE of the most interesting. phas~s .of out, their bodies, legs and wings held O the life history of any ammal IS ItS stiffly parallel. Hibernating animals life 'in the winter when conditions of breath slowly and unevenly, their tem­ temperature and food supply are gener­ peratures approaching that of the envi­ ally very adverse. The fact that some ani­ ronment and fluctuating with it. In his mals have the ability to meet these con­ studies of the 13-lined squirrel, Johnson ditions by hibernating gives them a par­ in 1928 found that during ordinary active ticular interest to not only the naturalist, life this squirrel respires 100 to 200 times but the physiologist and anatomist as per minute; its heart beats 200 to 350 well. In recent years a great deal of in­ times per minute; and its body tempera­ terest has been given to this field in re­ ture ranges from 32 to 41 0 C. However, spect to its surgical application, espec­ during hibernation it may breathe as ially in the field of cardio-vascular and seldom as once or twice per minute or cerebral surgery. even less; its heart beats only about five times per minute and its temperature THE PHENOMENON OF drops almost as low as that of the air HIBERNATION surrounding it. Although they may appear entirely The life processes of a hibernating ani­ lifeless, hibernators are in general quick­ mal are slow. They take little or no food ly sensitive to handling and to changes and only a fraction of their normal re­ of temperature or other stimuli. Torpid quirement of oxygen. There is a com­ woodchucks grasped suddenly and parable summer dormancy, called est'iva­ thrown into water have begun to swim tion, resorted to by various animals dur­ immediately. According to one worker, ing periods of excessive drought and heat. hibernating bats that were brought into Very distantly-related animals may a warm room began drinking water be­ respond similarly to winter temperature. fore their temperature had risen to that Whirligig beetles and black bears agree of the room. in being "light sleepers," though their A loss in the water content of the body mid-winter stirrings hardly compare in is a characteristic preparation for hiber­ results. Closely related species, on the nation and has been rather widely ob­ other hand, may react very differently to served. In insects this preliminary drying temperature. Chipmunks may remain out of the tissues is apparently a neces­ continuously dormant through their sary preparation for dormancy. Insects whole hibernating period; red squirrels can endure continuous freezing. Snails, now and again awake from their sleep spiders and insects that have been en­ and come out in mid-winter, while grey cased in ice crystals and solid masses of squirrels are out and about the entire frozen soil for weeks at a time become season. normally active when thawed out. But True hibernators appear to be in a deep they cannot survive alternate freezing sleep. While they are dormant, chip­ and thawing as well. No vertebrates have munks and ground squirrels lie with been known to survive having been com­ their eyes closed and their bodies tightly pletely frozen. Frogs frozen into the solid curled up. On the other hand, dormant ice of shallow ponds have often been wasps hold themselves strictly straigtened known to survive; however, in experi­ mental tests the bodies of those similarly Mr. Haight is a sophomore in v~terinar~ med­ frozen into blocks of ice have been found icine at Iowa State College. He 1S workmg on a M.S. in veterinary physiology. to be only incompletely frozen.

82 Iowa State College, Veterin((rian PHASES OF HIBERNATION hibernation remain in a comatose condi­ tion throughout their period of confine­ The Entering Phase. The process of en­ ment. tering into hibernation is not a rapid one. Bears differ greatly from the wood­ It does not take place within an hour or chuck. Even when asleep and unirri­ two, and the attainment of the actual table, they cannot be in true hibernation deep hibernating state may take any­ because they do not have a low body where from a few days to a month. Ben­ temperature and low heat production. edict in his book, Hibernation and Mar­ The A wakening Phase. The process of mot Physiology, mentions some obser­ awakening from hibernation involves a vations made on woodchucks which were marked increase in metabolism. In the It entering into hibernation. was found ground squirrel, the body temperature that the animals first became lethargic may rise from 2° to above 30° C., respira­ and uninterested in the general sur­ tions may increase from one per minute roundings, as long as they were not in to about 150 per minute and the pulse danger. Usually the animal's eyes were rate may rise from 5 per minute to about open and ,it was not in the characteristic 300 per minute. The anterior part of the curled-up or ball-shaped position of deep body recovers from lethargy earlier than hibernation. Frequently the animal would the posterior part. There is violent trem­ appear to be sleeping but the noise of bling and shaking. The awakening phase someone entering the room would cause is completed within one or two hours it to raise its head. from its initiation. The animal is con­ The process of entering hibernation sidered to be fully awake when the eyes may be considered to take place in steps, are opened; however, they appear to for the woodchuck returns to its origin­ gain control of their other senses by as al awake condition at least once after much as five or six minutes earlier. its initial drowsiness. The period of ini­ tial lethargy varied from a few hours to PHYSIOLOGY OF HIBERNATION four days, after which the animals re­ turned to the normal awake state. Usu­ Body Weight. Many references in the ally the second step into the semi-hiber­ literature indicate actual gains in weight nation state occurred from one to five have been made during deep hibernation days after this first drowsy period. Some when the animal is not partaking of any of the woodchucks maintained this sec­ food. These earlier observations implied ond drowsy state for only a day or two that there is a great consumption of oxy­ and thereafter the condition reappeared gen during hibernation, so great that every two or three days. The time after there is an absorption and retention of the initial period, until the animals went oxygen in the body. Later, it was shown into deep hibernation, varied from three that any gain in weight is primarily due days to a month. At no time did the ani­ to adsorption of water on the fur of the mals hibernate before food was removed animals. Benedict measured the weight from their cages. loss of woodchucks during the time the Benedict, from his experience with the animals were actually hibernating and woodchuck in hibernation, would base found that it amounted to 0.2 grams per his definition of hibernation on a lower­ day per kilogram of body weight. ing of the body temperature to within a Body Temperature and B. M. R. The rectal temperature of hibernators when few degrees of the environmental temp­ not in hibernation is quite labile. In the erature and accompanied by a profound woodchuck it ranges from 34-39° C. On decrease in the heat production. Deep the other hand, in normal hibernation torpor representing these conditions is the rectal temperature of the woodchuck, usually found only with small animals at a constant environmental temperature, ranging from the ground squirrel to the is always found to exceed the surround­ woodchuck. True hibernators in deep ing temperature by from one to three

Issue 2, 1958-59 83 degrees. The body temperamre may go PREDISPOSING FACTORS TO as low as 3° C. after which it is pos­ HIBERNATION sible for the animal to return to its warm­ blooded state. It reacts slowly to the en­ Environmental Temperature. Of all the vironmental temperature, but follows it major contributing factors inducing hi­ in a general way. bernation, cold and the lack of food or hunger have received the most attention. The minimum basal metabolism of the non-hibernating animal is 410 calories It is agreed by all workers that the ani­ mals must be placed in a cold environ­ per unit of body surface per 24 hours. ment. The optimum temperature is com­ During hibernation the absolute mini­ monly stated to be from 10 to 11°C. mum heat production is 17 calories per However, animals have been kept for unit of body surface per 24 hours; al­ weeks and even months at temperatures though, 27 calories per unit of body sur­ face is the average minimum attained by of 10 degrees without hibernating. This emphasizes the point noted by many most of the animals. The low values of the heat production are not accompanied writers that cold is not certain to pro­ by the lowest rectal temperatures, but duce hibernation and that some other frequently are observed at rectal tem­ factor or factors enter into the initiation peratures of 8 to 12° C. of this phenomenon. The conclusion can be drawn that cold, per se, is in general Insensible Water Loss. The water loss due to insensible perspiration in the nor­ a contributory factor but not of itself mal non-hibernating animal at an en­ sufficient to cause hibernation. vironmental temperature of about 17° C. Lack of Food. The second most gener­ averages 7.2 grams per kilogram of body ally accepted condition is that the animal weight per 24 hours and 15.7 grams per should be without food. This is almost kilogram of body weight at 31°C. For invariably mentioned as a cause, yet, the the woodchuck in deep hibernation the opposite point of view is frequently held. insensible water loss is approximately It is a well-known fact that animals rare­ 0.2 grams per kilogram of body weight ly hibernate in zoological parks. The per 24 hours. Although an average is normal explanation of this is that the ani­ given here for the insensible water loss mals always have plenty of food before them. This would suggest that when it is so small that ,it is of little significance since it is profoundly influenced by food is available there would be no hi­ changes in the humidity. bernation. A close study of the natural habits of the woodchuck shows that they Heart and Respiration Rate. The non­ frequently take edible material such as hibernating woodchuck has a minimum hay into their burrows for bedding. In heart rate of 80 beats per minute and an fact, they have been known to bring hay average minimum respiration rate of to the mouth of their den to be eaten on from 25 to 30 per minute. In deep hiber­ awakening, thus anticipating the need nation the minimum heart rate is 4 to 5 for food. Present evidence indicates that beats per minute and the minimum res­ the absence of food is probably on the piration rate is 0.2 per minute, the aver­ whole contributory, but not absolutely age being not more than 1 per minute. essential to hibernation. Respiratory Quotients. In the non-hi­ External Stimuli and CO2, The absence bernating woodchuck 48 hours must of external stimuli, either touch or sound has been advanced as a contributor; elapse after the animal eats to insure res­ cause to induce or maintain hibernation. piratory quotients of 0.71 which is the The theory that the accumulation of car­ quotient one observes when fat is the bon dioxide in the burrow, producing an sole SOurce of energy. A respiratory quo­ autonarcosis, as an important factor in tient of 0.70 is obtained in the hibernating hibernation has largely been refuted by woodchuck which would indicate that Benedict as has the theory of complete the sole source of energy is fat. darkness being a facilitating factor.

84 Iowa State Colleget Veterinarian THEORIES OF HIBERNATION any adequate explanation of the me­ canism of this phenomenon, nor how it Many theories have been offered on became established in certain animals. the phenomena of hibernation. Early workers believed there was a so-called References "hibernating gland" in the vicinity of the 1. Benedict, F . G. Hibernation and Marmot thymus in the cervical region. This is Physiology. Carnegie Institution of Wash­ now generally regarded as adipose tissue ington. Washington, D. C. 1938. 2. Buchanan, F., The initiation of the State of which aids the animal to survive the long hibernation in mammals. J. Physiol. 57:76- confinement period. Some investigators 77. 1923. 3. Johnson, G. E. Hibernation of the 13-lined have associated hibernation with the ground squirreL I. A comparison of the nor­ nervous system, while others consider mal and hibernating states. J. Exp. Zool. 50: an inefficient heat regulating mechanism 15-30. 1928. 4. --. Hibernation of the 13-lined ground to be the true explanation. Others have squirrel. II. The general process of waking thought certain anatomical peculiarities from hibernation. Amer. Nat. 63:171-180. such as the enlarged character of the 1929. 5. --. Hibernation of the 13-lined ground heart, thorax and central blood vessels squirrel. III. The rise in respiration, heart­ or the smallness of the peripheral vessels beat and temperature in waking from hi­ and lungs to be the cause. More recent bernation. BioI. Bull. 57:107-129. 1929. 6. --. The process of awakening from hi­ evidence would indicate that the endoc­ bernation in the 13- lined ground squirrel. rine glands probably should be included Anat. Rec. 29:94. 1924. under a general theory of a hypo o,r hy­ 7. Lyman, C. P ., and Chatfield, P . O. Physiol­ ogy of hibernation in mammals. Physiol. perfunction as the cause of hibernation. Rev. 35:403-425. 1955. However, there is no convincing evi­ 8. Morgan, A . H . Field Book of Animals in Winter. G. P. Putnam's and Sons, New dence that the endocrines exert a domin­ York. 1939. ant role in the onset of hibernation. It is 9. Newby, W. W. Respiration of the ground quite obvious that scientists do not have (Continued on Page 89)

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Issue 2, 1958-59 85 4. Subcutaneous tissue: lipoma. 4. Mycetomycoses. actinomycosis, ac­ Skin Manifestations in the Course of tinobacillosis, farcy of cattle, strepto­ Infectious Diseases. thricosis in dogs, botryomycosis. 1. Virus infections: pox, virus papular 5. Sporotrichosis. dermatitis in horses, contagious ec­ Skin Manifestations of Protozoal Ori­ thyma, infectious goat dermatitis, gin. foot and mouth disease, vesicular 1. Babesiosis. 2. Surra. 3. Mal de Caderas. stomatitis, vesicular exanthema of 4. Dourine. 5. Leshmaniosis. 6. Spiro­ swine, coital vesicular exanthema in chaetosis. horses, rinderpest, cutaneous strang­ Dermatoses Associated with Hel­ les, hog cholera, distemper complex, minthes. pemphigus, scrapie. 1. Nematodiases: rhabditidiasis, ancy­ 2. Bacterial infections: impetigo, pyo­ lostomiasis, bunostomiasis, parafilar­ genic dermatitis, contagious derma­ iasis, stephanofilariasis, habronemia­ titis in horses, swine erysipelas, an­ sis, dirofilariasis, dracunculiasis, on­ thrax, malignant edema, tuberculosis, chocerciasis. glanders, ulcerous lymphagitis in 2. Trematodiasis. horses and dogs (Nocardiosis). Acarine Dermatoses Associated with Ticks and Mites. 1. Ixodes acariasis. 2. Dermanysus acar­ iasis. 3. Trombiculidiasis. 4. Sarcoptic acariasis: Genus sarcoptes, genus cnemi­ docoptes, genus notoedres, genus psorop­ tes, genus chorioptes, genus otodectes. 5. Demodectic acariasis. Dermatoses Caused by Insects. 1. Pediculosis. 2. Siphonaptera. 3. Dip­ tera. 4. Hemiptera. 5. Coleoptera. 6. Hy- menoptera. 7. Lepidoptera. .F:".a

Pyogenic dermatitis Skin Disorders Caused by Fungi. Der­ matoses of fungal origin may be classi­ fied as follows: Pustular and phlegmonous form of Demodectic 1. Blastomycoses: equine blastomycosis, mange. canine blastomycosis. 2. Dermatomycoses: ringworm-tinea. (Continued from page 85) squirrel during hibernation. Master of Sci­ Microsporum group: Microsporum ence Thesis. Iowa State College Library, canis, M. gypseum, M. audouini. Ames. 1927. Trichophyton group: Trichophyton 10. Rasmussen, A. T. Theories of hibernation. Amer. Nat. 50:609-662. 1916. equinum, T. mentagrophytes, T . ver­ 11. Sheldon, E. F . The so-called hibernating rucosum, T. schoenleini, T. gallinae. gland in mammals: a form of adipose tis­ 3. Cutaneous moniliasis: Monilia albi­ sue. Anat. Rec. 28:331-343. 1924. 12. Simpson, S. The food factor in hibernation. cans. Proc. Soc. Exp. BioI. Med. 9:92-93. 1912.

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