Evaluation of several indices for assessment of coyote (Canis latrans) body composition

Jean Huot, Marie-Lazarine Poulle, and Michel Crate

Abstract: The body composition of 27 coyotes (Canis latrans) of different ages and both sexes was determined on the basis of chemical analyses of homogenized samples of viscera, carcass, and skin. Regression analyses were used to identify the best indices for estimating fat (lipid reserves), protein, and water body contents. A combined index based on the kidney fat index and the percentage of femur marrow fat was the best indicator of fat reserves. Body mass (whole or skinned carcass) and eviscerated carcass mass were the best predictors of total body protein and total body water contents. A combination of indices is proposed to provide postmortem or in vivo estimates of coyote body composition.

R6sum6 : La composition corporelle de 27 Coyotes (Canis latrans) miiles et femelles d'8ges divers, a kt6 dkterminke par analyse chimique d'kchantillons broyks des visckres, de la carcasse et de la peau. Des analyses de rkgression ont permis d'identifier les meilleurs indices d'estimation des graisses (lipides de rkserves), des protkines et du contenu en eau. Une indice combink bask sur l'indice des graisses du rein et sur le pourcentage de graisses dans la moelle du fkmur a kt6 reconnu comme le meilleur indicateur des rkserves des graisses. La masse corporelle (totale ou sans la peau) et la masse de la carcasse kvisckrke se sont averkes les meilleurs indicateurs du contenu total en protkines et en eau. Nous suggkrons une combinaison d'indices permettant d'obtenir des estimations post mortem ou in vivo de la composition corporelle du Coyote.

Introduction et al. 1974; Ringberg et al. 1981; Huot 1982; Huot and

Habitat evaluation has become a major focus of attention for ecologists and managers in recent years. To assess the per- formance of birds and mammals in relation to their envi- ronment, biologists have developed numerous indices for assessing the body condition of wild animals. Most indices are related to fat reserves, which are the principal stored form of energy in many species (Lehninger et al. 1993, p. 240). These indices, especially femur marrow and kidney fat indices, were first developed for ungulates (see review in Huot 1988). More recently, some of these, as well as new indices, have been applied to carnivores (Lindstrom 1983 ; Todd and Keith 1983; Litvaitis et al. 1986; Quinn and Thompson 1987; Thompson and Colgan 1987; Buskirk and Harlow 1989; Windberg et al. 1991).

Nevertheless, few researchers have tested the relation- ships between the indices they used and body composition as assessed by chemical extraction of the entire carcass (Robbins

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Received April 26, 1994. Accepted April 12, 1995.

J. Huot. Dkpartement de Biologie, Pavillon Alexandre-Vachon, Universitk Laval, Sainte-Foy, PQ G 1K 7P4, Canada and Centre d'ktudes nordiques, Universitk Laval, Sainte-Foy, PQ GlK 7P4, Canada. M.-L. Poulle. Centre d'ktudes nordiques, Universitk Laval, Sainte-Foy, PQ GlK 7P4, Canada. M. Cr2te. Service de la faune terrestre, Ministkre de 1'Environnement et de la Faune, 150 boulevard Saint-Cyrille Est, Qukbec, PQ GlR 4Y 1, Canada, and Centre d'ktudes nordiques, Universitk Laval, Sainte-Foy, PQ GlK 7P4, Canada.

Picard 1988; van der Merwe and Racey 1991; Virgil and Messier 1992). This validation is essential to an accurate understanding of the dynamics and ecological importance of fat reserves and other body components. Chemical validation of body composition indices has been completed for only two species of carnivore, the American marten (Martes ameri- cana; Buskirk and Harlow 1989) and the arctic fox (Alopex lagopus; Prestrud and Nilssen 1992), and has never been completed for the coyote.

The eastward range expansion of the coyote through the northeastern United States, Quebec, and the Maritime Prov- inces (Richens and Hugie 1974; Georges 1976; Hilton 1978; Harrison 1986; Voigt and Berg 1987) potentially affects endemic prey species in the Northeast (especially the white- tailed deer, Odocoileus virginianus) , as well as native carni- vores such as the bobcat (Lynx rufus; Litvaitis and Harrison 1989). Coyote productivity may be affected by the status of its energy reserves (Todd and Keith 1983), so ecologists need reliable information on seasonal and local variation in coyote nutrition and body reserves in order to assess coyote - prey relationships.

The objective of this research was to evaluate several indices used in determining coyote body composition. The indices tested were those that appeared to be the most sensi- tive to minor variations in body condition, specifically changes in fat and protein contents, and to be robust and practical for use under field conditions, as recommended by LeResche et al. (1974) and Harder and Kirkpatrick (1980). Indices were tested for their relationships to whole-body components of coyotes (water, protein, fat), as assessed by chemical analysis.

Can. J . Zool. 73: 1620- 1624 (1995). Printed in Canada 1 Imprimk au Canada

Huot et al.

Table 1. Coefficients of determination (r2) for simple linear regressions relating whole-body components of coyotes (water, protein, fat) to various measurements taken during necropsy.

Independent variable Dependent variable

Total body mass (BM), kg Skinned body mass (SBM), kg

Loge (SBM) Eviscerated carcass mass (ECM) M. gracilis mass (GM)

Kidney mass (KM)

Heart mass (HM)

Heart fat mass (HFM) Kidney fat mass (KFM) Log, (KFM) Heart and kidney fat mass (HKFM) Kidney fat index (KFI; Riney 1955)

(KFM x 1001KM) Heart fat index (HFI)

(HFM x 1001HM) Heart and kidney fat index (HKFI)

(HKI + KFI) Kidney - M. gracilis fat index (KGFI)

(KFMIM. gracilis mass) Heart - M. gracilis fat index (HGFI)

(HFMIM. gracilis mass) Femur marrow fat (FMF), % Kidney -femur fat index (KFFI)

(KFI + FMF) Body mass (BM)/body length (BL)

(BMBL) BMl(BL)3 (BMBL3) Percentage of water (WP)

Total water mass (0.85); total protein mass (0.86) Total water mass (0.86); total protein mass (0.86); total

fat mass (0.64) Total water mass (0.85); total protein mass (0.88); total

fat mass (0.62) Total protein mass (0.88) Total water mass (0.85) Total water mass (0.76); total protein mass (0.79); carcass

protein mass (0.83); visceral protein mass (0.41) Total protein mass (0.46); carcass protein mass (0.42);

visceral protein mass (0.41) Total protein mass (0.6 1); carcass mass (0.6 1); visceral

protein mass (0.53) Total fat mass (0.67) Total fat mass (0.67) Percent total fat (0.76) Total fat mass (0.71)

Percent total fat (0.69)

Percent total fat (0.55)

Percent total fat (0.67)

Total percent fat (0.53)

Total percent fat (0.42) Total percent fat (0.56)

Total percent fat (0.86)

Total percent fat (0.45) Total percent fat (0.23) Total percent fat (0.96)

Methods Sample collection We collected 27 coyotes (16 males and 11 females) from trap- pers and conservation officers in southeastern Quebec: 10 between 17 July and 8 September 1990 and 17 between 24 December 1990 and 23 January 1991. The coyotes were caught in snares and then stored at -20°C until the labora- tory analyses were carried out.

Necropsies Of the various indices described in the literature, 22 were selected for the present study (Table 1). Necropsies were conducted as described by Huot and Picard (1988). The specimens were thawed, weighed (body mass, BM), and then skinned, leaving as much subcutaneous fat as possible on the carcass. Skinned carcasses, including the viscera, were weighed again (skinned body mass, SBM), as were the hides. All viscera in the thoracic and gastrointestinal cavity were removed and weighed. Fat attached to the heart and

both kidneys was removed and weighed separately; the heart and kidneys were also weighed. One femur was removed and a piece of marrow, 3 cm long, was collected and frozen (Neiland 1970). The M. gracilis muscle was dissected out and weighed fresh. The eviscerated carcass mass (ECM) was calculated as the difference, i.e., the whole carcass minus the viscera and hide. The carcass and viscera were refrozen separately.

Six samples (50 x 50 mm) were cut from the hide. The hair was shaved off and the skin was cut into small pieces. The frozen viscera and shaved skin samples were ground separately twice in a Hobart meat grinder (model A-200, Hobart Co., Don Mills, Ontario) equipped with a 3-mm sieve. The frozen carcasses were passed through a large meat grinder (Model 801-CP, Autio Co., Astoria, Oregon) equipped with a 5 mm mesh sieve. Minced carcass material was thoroughly mixed and passed through the Hobart grinder with a 3 mm mesh sieve. Samples of approximately 1-2 kg of minced carcass and viscera were collected and frozen and

1622 Can. J. Zool. Vol. 7 3 , 1995

Table 2. Best simple regression models (r2 > 0.85) predicting total body water and protein masses (g) of adult coyotes from eastern Quebec, July -January 1990 - 199 1.

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Regression Independent variable

- SE of Dependent variable Parameter x SD Intercept Slope r2 estimate n

Total water mass Total water mass Total water mass Total protein mass Total protein mass Total protein mass Total protein mass Carcass protein mass Log,(carcass protein mass)

SBM 11 700 BM 13 200 ECM 9 650 Loge (BM) 4.11 Loge (SBM) 4.06 BM 13 200 SBM 11 700 Loge (BM) 4.11 M. gracilis mass 36.3

Table 3. Best simple regression models (r2 > 0.85) predicting the total, carcass, and visceral fat masses (g) and percentages for adult coyotes from eastern Quebec, July -January 1990 - 199 1.

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Regression Independent variable

- SE of

Dependent variable Parameter x SD Intercept Slope r2 estimate n

Total fat mass KFFI 142 94.3 -348 13.3 0.86 523 2 1 Total percent fat KFFI 142 94.3 0.46 7.18 x 0.86 2.91 21 Carcass fat mass KFFI 142 94.3 -317 9.56 0.88 355 2 1 Percent carcass fat KFFI 142 94.3 -0.15 6.88 X 0.89 2.36 21 Percent visceral fat KFFI 142 94.3 -0.15 7.73 X 0.88 2.88 21 Total percent fat Total water (%) 59.8 5.35 93.9 -1.37 0.96 1.62 27

three subsamples weighing 5 -6 g were taken for chemical analysis.

Composition analyses Water content was obtained by freeze-drying the samples of minced material and femur marrow for 72 h (Labconco freeze-drier No. 5, Kansas City, Missouri). Femur marrow was considered to be the residue after dehydration (Neiland 1970). Fat was extracted from minced material with petro- leum ether in a Rafatec apparatus (Randall 1974). Petroleum ether is an efficient solvent of storage lipids that leaves non- lipids and structural lipid intact (Christie 1982; Dobush et al. 1985). Here we consider storage lipids and fat to be synony- mous. Ash content was determined after combusting two samples of material in a muffle furnace for 6 h at 500OC. The hair was combusted without preliminary fat extraction. We defined the protein content (%) as 100 minus the percentage of water, ash, and fat. All analyses were duplicated and, when differences between replicates exceeded 5 % , a third analysis was performed.

Composition estimates based on minced samples were considered to be true values for the carcass, viscera, and skin (Huot and Picard 1988). Body composition in terms of water, ash, fat, and protein was obtained by summing the amounts (kg) of each element in all body components.

Statistical analyses Coefficients of determination (r2, from least squares regres- sion analysis) were calculated between indices and validation

measurements for either the total mass or the percentage of BM or SBM (Table 1). Sample sizes varied slightly from one regression to another, because some measurements were missing. Correlations were considered to be significant at P < 0.0001. We selected the indices providing the highest r2 value and normal and independent distribution of resid- uals for the regression. Multiple correlation coefficients, including sex (1 = M, 0 = F) as a qualitative variable, were also computed for the regressions concerning fat indices. We decided to retain as reliable indices only those with r2 > 0.85.

Results

Body mass averaged 13.93 + 2.81 (SD) kg for males and 12.06 + 2.80 kg for females. Body fat content was highly variable, ranging from 1.70 to 26.72 % (average 1 2.08 + 7.36%). Water (59.79 + 5.35%), protein (24.10 + 1.94%), and ash (4.02 + 0.62%) contents exhibited less variation among individuals.

We tested M. gracilis mass, ECM, BM, and SBM as indices of total water content (Table I). The last three were the most reliable (Table 2).

BM, SBM, M. gracilis mass, ludney mass, heart mass, and heart plus kidney mass were tested as indices of protein mass (Table I). Log,(BM) and log,(SBM) were the best indices of total protein mass, whereas log,(BM) was the best index of protein mass of eviscerated carcasses (Table 2). We found no acceptable (r2 > 0.85) index of visceral protein mass.

Huot et al

The kidney fat index (KFI), the heart fat index (HFI), BM, and the kidney - femur fat index (KFFI) were the main indices tested as indicators of the total percentage of fat (Table 1). Heart fat mass (HFM), kidney fat mass (KFM), BM, and KFFI were also tested as indicators of the mass of fat reserves. Because the relative distribution of fat between the carcass and viscera varied among individuals and was poorly correlated with total fat mass (r2 = 0.14, 25 df, P > 0.005), regressions were also calculated to predict carcass and visceral fat masses or percentages independently (Table 3). KFFI provided the most reliable index, the highest r2 value, of both total body fat content (%) and total body fat mass (kg). It was also a reliable index of the percentage of fat in the carcass and viscera. There was a strong negative correla- tion between body water and body fat contents (Table 3). Sex as a supplementary independent variable in multiple regres- sions never added significantly to the fit for any of the variables.

Discussion

Although our sample contained lean as well as fat animals and males and females trapped in different seasons, the coef- ficients of determination obtained for predicting fat, water, and protein contents were relatively high. Moreover, the dis- tribution of residuals was normal and independent for every parameter. Within the range tested, all relationships were linear. We conclude that these indices are versatile enough to allow the body composition of both lean and fat coyotes at different times of the year and for both sexes to be esti- mated. Furthermore, as the coefficients of determination were relatively high, the selected indices are sufficiently sen- sitive to detect changes of interest to ecologists and managers in the nutritional state of an animal or a population. Finally, all selected indices are easy to obtain.

Ash content, at approximately 4..0% of BM, is a minor component in absolute value and can be considered constant, as its variation cannot affect estimates of water, protein, or fat contents. Water and protein contents can be estimated post mortem or in vivo from body mass. Fat content can be accurately estimated post mortem using KFFI. Our attempt to estimate fat mass from differences between BM and pre- dicted protein plus water content produced unreliable results. Thus, we found no direct index of fat content that can be used for live animals. As water and fat contents are highly cor- related, fat content could be estimated in vivo from a precise estimation of water content using dilutions of isotopically labelled water (e .g . , oxygen- 18 or tritium labels). However, there are still large potential errors in the estimation of total body water using this method (Sheng et al. 1979).

Acknowledgments

Financial support for this project was provided by the Ministkre de 1'Environnement et de la Faune (Quebec), World Wildlife Fund Canada, Outdoor CanadaIThe Sport- men's Shows, the Canadian Wildlife Service, and a Natural Sciences and Engineering Research Council of Canada grant to J. Huot. We sincerely thank C. Bainville and G. Landry for their cooperation in the carcass collection. We also acknowledge the invaluable assistance of R. Lemieux and B. Picard, who made the necropsy, and M. Lalibertk, who

performed the chemical analyses. Two anonymous reviewers helped to improve the manuscript.

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