Energy Requirements
Energy Requirements for Maintenance and Growth of Wild Mammals, Birds and Reptiles in Captivity1 JAMES K KIRKWOOD2 Department of Veterinary Science, Institute of Zoology, Zoological Society of London, Regent's Park, London NW1 4RY, United Kingdom
turn feeding is generally a suitable system because most animals are better able to judge their require ments than their keepers. However, there are cir cumstances when estimates of energy requirements are useful, for example, when treating or preventing obesity, when treating inanition or anorexia and in the artificial rearing of neonates of some species. The aim of this paper is to review the bases for estimating the energy requirements of reptiles, birds and mam mals for maintenance and growth. Although objective criteria for assessment of obe sity in wild animals are lacking, it is clear that in dividuals of some species can become abnormally fat in captivity. Animals in captivity tend to main tain higher body weights and fat contents than in the wild. The point at which fatness is judged to be pathological is subjective. When an individual is manifestly grossly fatter than typical for the species, it is useful to have an estimate of maintenance en ergy requirement to devise a ration likely to promote weight loss. Anorexia can be due to systemic illness, dental or other oral diseases or injuries causing pain, or pro vision of unfamiliar or inappropriate diets. It can also be a normal part of the biology and associated with season or reproductive status. When the cause is pathological, in addition to treating the cause of the anorexia, it is important to have an estimate of energy requirements so that nutritional support can be given, if necessary by stomach tube or intrave nously. Anorexia is a common complication of dis eases of reptiles. Inanition due to provision of in sufficient food occurs sometimes because of igno-
ABSTRACT A wide range of wild animals are main tained in captivity as pets and an increasing number are likely to become dependent on captive breeding for conservation. Generally, these animals are fed ad libi tum and a knowledge of their energy requirements is not essential. However, estimates of energy require ments are helpful in several situations: treating obesity, providing nutritional support to anorexic animals and feeding neonates. Data on basal metabolic rates (BMR) are available for ~5% of avian and 17% of mammalian species, and the maintenance requirement can be es timated at twice BMR. Estimates for other species can be based on allometric equations relating energy ex penditure to body weight in the species that have been studied. Although between species time taken to grow increases with adult mass, wide variation remains after the effect of adult mass is considered. A model is de veloped which illustrates the impact of variation in time taken to grow on daily growth rate (per metabolic mass) at all stages of maturity. This model may assist in es timating the lower limit to energy requirements during growth. J. Nutr. 121: S29-S34, 1991. INDEXING KEY WORDS:
•symposium •mammals •energetics «growth
•birds •vertebrates
Loss of habitat and changes in environmental qual ity have lead to drastic declines in the populations of some species of wild animals. For an increasing num ber of species, survival will depend upon active inter vention, either by managing populations in the wild or by captive breeding. Nutrition is a fundamental part of captive man agement and devising appropriate diets for the great variety of species maintained in captivity presents a major challenge. There is very little specific infor mation on the nutrient requirements of nondomesticated animals. Most wild animals kept in zoos or as pets are fed ad libitum, and it is not usually nec essary to know their energy requirements. Ad libi-
1Presented as part of the Waltham International Symposium on Nutrition of Small Companion Animals, at University of California, Davis, CA 95616, on September 4-8, 1990. Guest editors for the symposium were James G. Morris, D'Ann C. Finley and Quinton R. Rogers. 1To whom correspondence should be addressed: Department of Veterinary Science, Institute of Zoology, Zoological Society of Lon don, Regent's Park, London NW1 4RY.
0022-3166/91 $3.00 ©1991 American Institute of Nutrition.
S29 Downloaded from https://academic.oup.com/jn/article-abstract/121/suppl_11/S29/4744042 by guest on 27 February 2018
S30
KIRKWOOD
TABLE 1
Maintenance or average daily metabolizable energy requirements for some groups of animals in relation to body mass
METABOLIZABLE ENERGY REQUIREMENTS FOR MAINTENANCE
The metabolizable energy requirements for main tenance of adult animals in energy balance and kept in a comfortable thermal environment approximate Requirementk]/d-45 GroupCaptive twice the basal metabolic rate (BMR) (6) and recom mendations for maintenance are often based on this M075481 (7).This is a useful guide in practice because, although snakes'Passerine Kirkwood,unpublisheddataRef. & energy requirements for maintenance or captive ex istence have been measured in relatively few species, 30°CNon-passerines, birds, M°«41 10Ref. 30°CCaptive 4M075456 data on BMR are available for many. For example, 10Ref. •"•607 M° 11Ref. raptorsCaptive Bennett and Harvey (8) collected data on resting met eutherianmammalsCaptive abolic rate for 399 species of birds from the literature •"586 M° 12Ref. for a review of the effects of body size and other fac eutherianmammalsRodents, •"356 M° 6Ref. tors, and Heusner (9) studied data from 685 mammal ADMR1Insectivores, captive M°"280 13Ref. species. captiveADMR2Captive M043406 Allometric equations relating maintenance energy 13Ref. "264-573 M° 14Ref. primatesCaptive requirements or the average daily metabolism in cap M°"SourceGili 15 prosimiansEnergy tivity in relation to body mass for several groups of animals are shown in Table 1. The BMRs of mono1Snakes maintained at temperatures close to 28°C. 2 Average daily metabolic rate. tremésand marsupials are lower than typical for eu therian mammals (16, 17) and their maintenance re quirements are likely to be correspondingly low. The mean maintenance energy requirement per metabolic ranee of requirements and failure to recognize the mass of three species of macropod marsupials for effects. which data are cited by Loudon (18) was 427 kj/d. The It is quite often necessary to artificially rear wild prosimians also tend to have lower metabolic rates animals born in captivity either because mother or than the mean for eutherian mammals (15, 19). baby are ill or because of inadequate maternal behav Average daily metabolic rates have been measured ior. The need also arises when eggs are removed for in free-living individuals of quite a wide range of spe artificial incubation to increase clutch size and pro cies and some allometric equations are listed in Table ductivity (1). In some species, clutch or litter sizes of 2. Where the captive conditions mimic the wild en ten exceed the number that the mother can rear. For vironment closely, estimates of requirements based example, common marmosets often have triplet litters on these equations may be more appropriate. but can rear only two babies (2), giant pandas fre quently have twins but rear only one (3) and some eagles incubate two eggs but rear only one hatchling (4). In these cases the surplus neonates can be handENERGY REQUIREMENTS DURING GROWTH reared. It can be difficult to judge how much food to provide and an estimate of what the requirements are During growth, energy is required both for mainte likely to be is useful so that gross over- or underfeeding nance functions and also for deposition of new tissue. is avoided. The amount by which the total daily requirement ex Estimates of energy requirements can therefore be ceeds the maintenance requirement depends upon the useful, but can useful estimates be made? Intra- and rate of tissue deposition and the composition of tissue interspecies variation makes the precise prediction of the energy requirements of an individual impossible, but enough is known about the influence of body size TABLE 2 and taxonomic position for it to be possible to make adequate first approximations. Intakes in excess of Average daily metabolic rate ¡ADMR]of free-living animals ~ 1700 kj/d per metabolic mass (M in kg raised to the Species ADMR Source I power) are very unlikely under any circumstances since there seems to be a limit to intake at about this ki/d level (5). In this paper, information relevant to the es 54 Ma>0 Free-living lizards timation of energy requirements for maintenance is Ref. 20 854 M0
Energy Requirements for Maintenance and Growth of Wild Mammals, Birds and Reptiles in Captivity1 JAMES K KIRKWOOD2 Department of Veterinary Science, Institute of Zoology, Zoological Society of London, Regent's Park, London NW1 4RY, United Kingdom
turn feeding is generally a suitable system because most animals are better able to judge their require ments than their keepers. However, there are cir cumstances when estimates of energy requirements are useful, for example, when treating or preventing obesity, when treating inanition or anorexia and in the artificial rearing of neonates of some species. The aim of this paper is to review the bases for estimating the energy requirements of reptiles, birds and mam mals for maintenance and growth. Although objective criteria for assessment of obe sity in wild animals are lacking, it is clear that in dividuals of some species can become abnormally fat in captivity. Animals in captivity tend to main tain higher body weights and fat contents than in the wild. The point at which fatness is judged to be pathological is subjective. When an individual is manifestly grossly fatter than typical for the species, it is useful to have an estimate of maintenance en ergy requirement to devise a ration likely to promote weight loss. Anorexia can be due to systemic illness, dental or other oral diseases or injuries causing pain, or pro vision of unfamiliar or inappropriate diets. It can also be a normal part of the biology and associated with season or reproductive status. When the cause is pathological, in addition to treating the cause of the anorexia, it is important to have an estimate of energy requirements so that nutritional support can be given, if necessary by stomach tube or intrave nously. Anorexia is a common complication of dis eases of reptiles. Inanition due to provision of in sufficient food occurs sometimes because of igno-
ABSTRACT A wide range of wild animals are main tained in captivity as pets and an increasing number are likely to become dependent on captive breeding for conservation. Generally, these animals are fed ad libi tum and a knowledge of their energy requirements is not essential. However, estimates of energy require ments are helpful in several situations: treating obesity, providing nutritional support to anorexic animals and feeding neonates. Data on basal metabolic rates (BMR) are available for ~5% of avian and 17% of mammalian species, and the maintenance requirement can be es timated at twice BMR. Estimates for other species can be based on allometric equations relating energy ex penditure to body weight in the species that have been studied. Although between species time taken to grow increases with adult mass, wide variation remains after the effect of adult mass is considered. A model is de veloped which illustrates the impact of variation in time taken to grow on daily growth rate (per metabolic mass) at all stages of maturity. This model may assist in es timating the lower limit to energy requirements during growth. J. Nutr. 121: S29-S34, 1991. INDEXING KEY WORDS:
•symposium •mammals •energetics «growth
•birds •vertebrates
Loss of habitat and changes in environmental qual ity have lead to drastic declines in the populations of some species of wild animals. For an increasing num ber of species, survival will depend upon active inter vention, either by managing populations in the wild or by captive breeding. Nutrition is a fundamental part of captive man agement and devising appropriate diets for the great variety of species maintained in captivity presents a major challenge. There is very little specific infor mation on the nutrient requirements of nondomesticated animals. Most wild animals kept in zoos or as pets are fed ad libitum, and it is not usually nec essary to know their energy requirements. Ad libi-
1Presented as part of the Waltham International Symposium on Nutrition of Small Companion Animals, at University of California, Davis, CA 95616, on September 4-8, 1990. Guest editors for the symposium were James G. Morris, D'Ann C. Finley and Quinton R. Rogers. 1To whom correspondence should be addressed: Department of Veterinary Science, Institute of Zoology, Zoological Society of Lon don, Regent's Park, London NW1 4RY.
0022-3166/91 $3.00 ©1991 American Institute of Nutrition.
S29 Downloaded from https://academic.oup.com/jn/article-abstract/121/suppl_11/S29/4744042 by guest on 27 February 2018
S30
KIRKWOOD
TABLE 1
Maintenance or average daily metabolizable energy requirements for some groups of animals in relation to body mass
METABOLIZABLE ENERGY REQUIREMENTS FOR MAINTENANCE
The metabolizable energy requirements for main tenance of adult animals in energy balance and kept in a comfortable thermal environment approximate Requirementk]/d-45 GroupCaptive twice the basal metabolic rate (BMR) (6) and recom mendations for maintenance are often based on this M075481 (7).This is a useful guide in practice because, although snakes'Passerine Kirkwood,unpublisheddataRef. & energy requirements for maintenance or captive ex istence have been measured in relatively few species, 30°CNon-passerines, birds, M°«41 10Ref. 30°CCaptive 4M075456 data on BMR are available for many. For example, 10Ref. •"•607 M° 11Ref. raptorsCaptive Bennett and Harvey (8) collected data on resting met eutherianmammalsCaptive abolic rate for 399 species of birds from the literature •"586 M° 12Ref. for a review of the effects of body size and other fac eutherianmammalsRodents, •"356 M° 6Ref. tors, and Heusner (9) studied data from 685 mammal ADMR1Insectivores, captive M°"280 13Ref. species. captiveADMR2Captive M043406 Allometric equations relating maintenance energy 13Ref. "264-573 M° 14Ref. primatesCaptive requirements or the average daily metabolism in cap M°"SourceGili 15 prosimiansEnergy tivity in relation to body mass for several groups of animals are shown in Table 1. The BMRs of mono1Snakes maintained at temperatures close to 28°C. 2 Average daily metabolic rate. tremésand marsupials are lower than typical for eu therian mammals (16, 17) and their maintenance re quirements are likely to be correspondingly low. The mean maintenance energy requirement per metabolic ranee of requirements and failure to recognize the mass of three species of macropod marsupials for effects. which data are cited by Loudon (18) was 427 kj/d. The It is quite often necessary to artificially rear wild prosimians also tend to have lower metabolic rates animals born in captivity either because mother or than the mean for eutherian mammals (15, 19). baby are ill or because of inadequate maternal behav Average daily metabolic rates have been measured ior. The need also arises when eggs are removed for in free-living individuals of quite a wide range of spe artificial incubation to increase clutch size and pro cies and some allometric equations are listed in Table ductivity (1). In some species, clutch or litter sizes of 2. Where the captive conditions mimic the wild en ten exceed the number that the mother can rear. For vironment closely, estimates of requirements based example, common marmosets often have triplet litters on these equations may be more appropriate. but can rear only two babies (2), giant pandas fre quently have twins but rear only one (3) and some eagles incubate two eggs but rear only one hatchling (4). In these cases the surplus neonates can be handENERGY REQUIREMENTS DURING GROWTH reared. It can be difficult to judge how much food to provide and an estimate of what the requirements are During growth, energy is required both for mainte likely to be is useful so that gross over- or underfeeding nance functions and also for deposition of new tissue. is avoided. The amount by which the total daily requirement ex Estimates of energy requirements can therefore be ceeds the maintenance requirement depends upon the useful, but can useful estimates be made? Intra- and rate of tissue deposition and the composition of tissue interspecies variation makes the precise prediction of the energy requirements of an individual impossible, but enough is known about the influence of body size TABLE 2 and taxonomic position for it to be possible to make adequate first approximations. Intakes in excess of Average daily metabolic rate ¡ADMR]of free-living animals ~ 1700 kj/d per metabolic mass (M in kg raised to the Species ADMR Source I power) are very unlikely under any circumstances since there seems to be a limit to intake at about this ki/d level (5). In this paper, information relevant to the es 54 Ma>0 Free-living lizards timation of energy requirements for maintenance is Ref. 20 854 M0
