Abstract
Objective—To compare results of body condition scoring by use of a 9-point scale with body composition determined by dual-energy x-ray absorptiometry (DEXA) in indoor-confined neutered domestic shorthair (DSH) pet cats.
Animals—72 indoor-confined, adult neutered DSH pet cats (38 females and 34 males).
Procedures—All cats underwent a physical examination including assessment of body weight (BW), body condition score (BCS; 1 = emaciated, 5 = ideal, and 9 = grossly obese), and girth. Urinalysis, CBC, and serum biochemical analysis were also performed. After the cats were confirmed healthy, they were anesthetized for body composition measurement via DEXA. Lean body mass, fat mass, and percentage body fat (%BF) were then evaluated.
Results—The correlation between %BF and BCS (r = 0.87) was superior to the correlations between %BFand BW (r = 0.74) and between %BF and girth (r = 0.78). Values for %BF differed significantly between all pairs of BCSs except BCSs 8 and 9. Within a BCS, the %BF was similar for male and female cats. The mean %BF for cats with a BCS of 5 was 32, which exceeded the upper reference limit of %BF generally considered ideal (30).
Conclusions and Clinical Relevance—The 9-point BCS scale appears useful for assessing %BF in DSH pet cats. Nevertheless, study findings could indicate a need for redefining the ideal BCS for inactive neutered cats to include a BCS of 4.
Maintaining an ideal BW is an integral component of a healthy lifestyle. Among the adult pet cat population, 35% to 40% are overweight or obese,1–4 and it is recognized that obesity in cats predisposes them to diseases such as lower urinary tract disease, lameness, hepatic lipidosis, nonallergic skin diseases, and diabetes mellitus.1,5
Objective identification and quantification of the degree of adiposity in individual animals is important for measuring the success of nutritional intervention programs and for obtaining reliable results in obesity-related research. Dual-energy x-ray absorptiometry is considered the reference (gold) standard for estimating body composition and is often used in body composition studies in cats.6–10 However, DEXA is only available at large research institutions, and cats require sedation or anesthesia so that measurements can be obtained.
Body weight is a precise, repeatable, and objective measurement. It is useful for follow-up in weight loss programs but fails to provide any indication of body composition or lean-to-fat mass ratio, nor is it a good value for comparisons across patient populations. Only when BW is related to an individual's height, length, or circumference is it possible to extrapolate body composition. The BMI, which is calculated on the basis of BW and height in humans, is clinically relevant, is objective, and provides parametric data for use in research.11 Although cats have a more uniform body configuration than humans, the ideal BW of an adult cat can range between 2 and 7 kg.1
Several systems have been proposed to estimate body composition in cats.12–15 A feline BMI, based on ribcage circumference and limb length, has been introduced, but it has not yet gained wide acceptance in general veterinary practice or research.12 This may be partly because accurate measurements are difficult to obtain from an awake, active cat. Instead, veterinary clinicians and researchers typically use 1 of 2 semiquantitative scoring systems for body condition, both of which are based on visual and palpatory findings.1,4,5,9,14–17 The most widely used system in cats is the 9-point system developed and validated by researchers at Purina in 1997.14 Importantly, this system has been integrated into determinations of nutrient requirements of dogs and cats18 as reported by the National Research Council, making calculations of energy requirements for cats reliant on their BCS.
Despite the widespread adoption of the 9-point system, it has only been evaluated twice since its validation and introduction 12 years ago. The system was first evaluated in 48 adult male and female DSH colony cats of unreported reproductive status and activity level.14 It was later applied to 60 genetically related DSH colony cats for a patent application, but these data were not published or subjected to peer review.12 As part of a description of an alternative BCS system, a small number (20) of healthy neutered male and female DSH and purebred pet cats were evaluated in another study.15 Although the 9-point system is a subjective, semiquantitative method for evaluating body composition, the aforementioned studies revealed low interobserver variation (reproducibility, 0.87 to 0.89) and a significant correlation between DEXA values and BCSs (r = 0.86 to 0.91) in the cats evaluated.
Studies19–21 performed in the United States, Europe, and Australia show that since the introduction of the 9-point BCS system, neutering of pet cats has become routine and complete indoor confinement is increasingly common. Whether gonadectomy decreases energy expenditure is equivocal; however, it has been speculated that in feeding-controlled gonadectomized cats, lean mass may contract, whereas fat mass may expand.22 Together with a further lean body mass decrease due to physical inactivity, this may result in a skewing of the lean body mass-to-fat mass ratio, resulting in a higher %BF for indoor pet cats relating to a specific BCS relative to a colony cat population. The term skinny fat has been introduced for physically inactive people of healthy BW who, because of a decrease in lean body mass, have a high %BF. Indoor-confined neutered pet cats may also possess this characteristic, which affects the interpretation of research findings in feline nutrition and obesity, in which the BCS system is an important research tool. The purpose of the study reported here was to evaluate whether the 9-point BCS system and the %BF assigned to each BCS based on data from colony cats is valid for privately owned, indoor-confined, adult neutered DSH cats.
Materials and Methods
Animals—Owners were invited to enroll their cats in the study through advertisements in a university magazine and a local weekly newspaper. Informed consent was obtained from all owners, and the study protocol was reviewed and approved by the National Committee on Animal Experimentation in Denmark.
Food was withheld from each cat 8 to 12 hours before admission to the Small Animal Veterinary Teaching Hospital, University of Copenhagen, Denmark, where they underwent a thorough health examination, including physical examination, urinalysis, CBC, and serum biochemical analysis as well as serum thyroxine concentration measurement and testing for FIV and FeLV infection.a Owners completed a questionnaire that included questions on the cat's disease history, feeding practices, and living environment. They were also asked to subjectively estimate their cats' activity level on a 4-point scale (1 = inactive, sleeps most of the time; 2 = mostly inactive, sleeps a lot but plays some; 3 = active, plays with toys and owner; and 4 = very active). In all cats, actual BW was measured with a calibrated scale,b and girth was measured with a measuring tape as the circumference at the level of L4, just caudal to the last rib. A BCS was assigned by 1 experienced clinician (CRB) according to the 9-point BCS system.14 Cats that were intolerant to handling as well as cats with abnormal findings on the physical examination or clinicopathologic tests were deemed ineligible for the study and excluded.
Anesthesia—Each participating cat was anesthetized for DEXA by use of the following standard protocol: sedation with butorphanol tartratec (0.2 mg/kg, IM) and diazepamd (0.2 to 0.3 mg/kg, IV), followed by propofole for anesthetic induction (4 to 6 mg/kg, IV) and maintenance (10 mg/kg/h, IV). To maintain hydration and blood pressure, all cats received lactated Ringer's solutionf (2 mL/kg/h, IV) while anesthetized. To avoid heat loss during anesthesia, a heating lamp was placed beside and above the DEXA table. All cats were monitored throughout anesthesia by use of a pulse oximeter.g
DEXA—The DEXA unith was calibrated prior to each scanning session by use of the calibration phantom provided by the manufacturer and manufacturer's suggested protocol. To minimize the duration of anesthesia, each cat was positioned in ventral recumbency with hind limbs and tail drawn cranially. Because this is a novel position for DEXA scanning, 5 recently euthanized cats were scanned first in this position and in ventral recumbency with limbs placed in a spread-eagle position to evaluate reproducibility and possible position-related bias. These positions yielded similar results (Student t test; P = 0.40). To avoid bias from monitoring systems and intubation, the cat's head was excluded from the calculations. For every scan, the scanner software yielded estimates of total body tissue mass, fat mass, lean body mass, and %BF. After DEXA scanning and recovery from anesthesia, cats were discharged to the care of their owners.
Statistical analysis—Linear regression was used to determine the correlations between actual BW and BWDEXA, %BF and BCS, %BF and actual BW, %BF and girth, and %BF and lean body mass. Because BCSs are nonparametric, semiquantitative data, the method described by Jensen et al23 was used to compare BCS data with the continuous data for cat age, %BF, BW, and girth. For each BCS, the mean, median, SD, and range were calculated, and the differences between means were statistically evaluated by means of 1-way ANOVA. Because a sex-linked difference in body composition was possible, data for male and female cats were compared with each other for all variables, and sex and age were included as covariates in all statistical evaluations. Data were analyzed with the aid of statistical software.i,j A value of P < 0.05 was considered significant for all analyses. Values are reported as mean ± SD or as median (range), depending on the variable.
Results
Animals—Of the 101 cats brought to the hospital for inclusion in the study, 29 were excluded because of intolerance to handling (n = 12), abnormal urinalysis or serum biochemical results (7), audible heart murmur (5), hyperthyroidism (2), blood collection or analysis problems (2), or positive FIV test result (1). All of the 72 remaining cats (34 males and 38 females) had been neutered before 1 year of age. Median (range) values were as follows: age, 6 (3 to 13) years; BW, 5.1 (2.5 to 8.7) kg; girth, 44 (29.5 to 58.5) cm; BCS, 6 (4 to 9); and %BF, 40.0 (21.0 to 55.4).
BCSs—The 72 study cats were assigned BCSs ranging from 4 to 9 (Table 1). Females and males were equally distributed in all BCS categories except for a slight but significant overrepresentation of males with a BCS of 8, compared with females with the same score (Table 2). Cats with a BCS of 4 or 5 were younger than cats with a BCS of 8 or 9.
Median (range) age, scale-measured BW, girth, and DEXA-measured %BF in 72 indoor-confined, adult neutered DSH pet cats assigned a BCS of 4 to 9 on the basis of visual and palpatory evaluation and use of a 9-point BCS system scale.
| BCS | Age (y) | BW (kg) | Girth (cm) | %BF |
|---|---|---|---|---|
| 4 (n = 2) | 6 (4–8) | 2.9a (2.5–3.2) | 31a (29–32) | 21.4a(21.0–21.7) |
| 5 (n = 19) | 5 (3–12) | 4.3b (3.1–6.5) | 41b (33–46) | 31.8b (23.6–38.4) |
| 6 (n = 16) | 6 (3–11) | 4.8c (3.8–6.5) | 42b (38–48) | 37.4c (28.3–43.8) |
| 7 (n = 14) | 7 (3–12) | 5.6d (4.3–7.2) | 45c (37–52) | 42.3d (34.4–49.0) |
| 8 (n = 17) | 7 (3–13) | 6.9e (5.3–8.2) | 49d (43–54) | 48.2e (39.5–52.2) |
| 9 (n = 4) | 8 (8–11) | 7.2e (5.8–8.7) | 54e (50–58) | 48.9e (48.1–55.4) |
A BCS of 1 represents emaciated, a BCS of 5 represents ideal, and a BCS of 9 represents grossly obese.
a–eValues with different superscript letters differ significantly (P < 0.05) from values within the same column.
Girth was measured with a measuring tape as the circumference at the level of L4, just caudal to the last rib.
Mean ± SD DEXA-measured %BF of male and female DSH colony cats in a 1997 study13 and indoor-confined, adult neutered DSH pet cats (2011) with a BCS of 4 to 9 assigned on the basis of visual and palpatory evaluation and use of a 9-point BCS system scale.
| Male | Female | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| 1997 | 2011 | 1997 | 2011 | ||||||
| BCS | No. of cats | %BF | No. of cats | %BF | No. of cats | %BF | No. of cats | %BF | P value* |
| 4 | 4 | 19.8 ± 4.7 | 0 | — | 0 | — | 2 | 21.4 ± 0.5 | — |
| 5 | 10 | 21.8 ± 1.7 | 8 | 30.1 ± 4.1 | 0 | — | 10 | 31.6 ± 4.6 | 0.55 |
| 6 | 9 | 28.7 ± 3.8 | 7 | 34.6 ± 2.1 | 1 | 42.8 | 10 | 39.3 ± 4.8 | 0.06 |
| 7 | 5 | 36.9 ± 5.4 | 5 | 41.8 ± 5.9 | 4 | 44.1 ± 1.3 | 9 | 42.3 ± 3.9 | 0.85 |
| 8 | 4 | 39.2 ± 5.9 | 14 | 46.9 ± 3.8 | 6 | 47.4 ± 2.1 | 4 | 48.6 ± 3.2 | 0.48 |
| 9 | 0 | — | 1 | 49.0 | 5 | 53.4 ± 2.9 | 3 | 50.7 ± 4.1 | 0.65 |
*P values are for comparisons of BCSs between male and female cats for 2011 data only.
— = Not applicable.
See Table 1 for remainder of key.
Correlations—The correlation between the scale-measured BW and that calculated by use of DEXA data was 0.99 (P < 0.001). There was a systematic overestimation of the DEXA-measured BW by 4%, compared with scale-measured values. When BW and %BF were compared between pairs of BCSs, their values increased significantly with increasing BCS, except for comparisons between a score of 8 and a score of 9. Girth increased significantly with increasing BCS.
A stronger correlation was evident between BCS and %BF (Figure 1; r = 0.87; P < 0.001) than between BCS and BW (r = 0.81; P < 0.001), BCS and girth (r = 0.79; P < 0.001), %BF and BW (Figure 2; r = 0.74; P < 0.001), and %BF and girth (Figure 3; r = 0.78; P < 0.001). Lean body mass was positively correlated with fat mass (r = 0.33; P = 0.005), and obese cats (ie, BCS of 8 or 9) had significantly more lean body mass (mean ± SD, 3.77 ± 0.42 kg; n = 21) than did overweight cats (ie, BCS of 6 or 7; 3.27 ± 0.52 kg; 30) and lean cats (ie, BCS of 4 or 5; 3.08 ± 0.55 kg). According to the subjective owner activity estimate, there was no difference in physical activity among BCS groups (mean ± SD activity score, 2.4 ± 0.9).
Figure 1—Dot plot of the correlation between BCS assigned by use of a 9-point body condition scoring system and %BF as measured via DEXA in 72 indoor-confined, adult neutered DSH pet cats (r = 0.87; P < 0.001).
Citation: American Journal of Veterinary Research 72, 4; 10.2460/ajvr.72.4.433
Figure 2—Dot plot of the correlation between scale-measured BW and %BF as measured via DEXA in 72 indoor-confined, adult neutered DSH pet cats (r = 0.74; P < 0.001).
Citation: American Journal of Veterinary Research 72, 4; 10.2460/ajvr.72.4.433
Figure 3—Dot plot of the correlation between girth measured just caudal to the last rib and %BF as measured via DEXA in 72 indoor-confined, adult neutered DSH pet cats (r = 0.78; P < 0.001).
Citation: American Journal of Veterinary Research 72, 4; 10.2460/ajvr.72.4.433
Discussion
The present study revealed that the 9-point BCS system14 reflected actual body composition well in pet DSH cats. However, particularly for male cats, the %BF associated with each BCS was higher in our study than was reported for colony cats.14 The correlation between measured %BF and BCS reported here (r = 0.87) was superior to %BF correlations with BW or girth, and it was in agreement with data reported for colony DSH cats (r = 0.91),14 20 DSH or purebred pet cats (r = 0.9),15 and young adult colony DSH cats (r = 0.86).12 Contrary to the findings in colony cats,14 male cats in the present study had a %BF equivalent to that of female cats for a given BCS. All cats in the present study had been neutered at < 1 year of age; however, information regarding reproductive status and activity level of the colony cats in the 1997 study is not available. Neutered males and females have a more comparable body type than sexually intact male and female cats.16,24 Furthermore, differences in body composition and activity level between sexually intact and neutered cats may cause a higher %BF associated with each BCS in neutered versus sexually intact cats.
A %BF of 20 to 30 is generally accepted as optimal, and cats with such a %BF are expected to have a BCS of 5.14 In the present study, the mean %BF of cats with a BCS of 5 was 31.8. This value is slightly higher than has been reported14,24 and could reflect a low activity level in the pet DSH cat population, resulting in less muscle mass and thus a higher %BF even in the lean cats, compared with physically active colony cats. This finding in inactive, indoor-confined, adult neutered cats appears similar to characteristics of humans categorized as so-called skinny fat. The skinny fat category was introduced to describe individuals with a healthy BMI but a relatively high %BF attributed to physical inactivity and decreased muscle mass.25 Such people are at increased risk for developing cardiovascular diseases and type 2 diabetes, compared with overweight fit people,26 and in cats, obesity and physical inactivity are risk factors for feline diabetes mellitus.27 We propose changing the BCS system for pet cats to accommodate for the so-called skinny fat category or redefining the ideal BCS for inactive neutered cats to include a BCS of 4. The BCS of 4 was originally defined as underweight in the 9-point BCS system for dogs but is now categorized as ideal, together with a BCS of 5.28
A limitation to this study was the risk of investigator bias. The BCS system is a subjective evaluation based on clinical examination but despite its subjective basis, a good correlation of scores reportedly exists between assessors.14 Furthermore, bias could be attributed to DEXA machine, computer software, or protocol differences between this and other studies.7,29,30 However, in earlier validation studies7,8 of the use of DEXA to measure body composition in dogs, DEXA results correlated well with the postmortem total body biochemical analysis, total body mass (r = 1), lean tissue mass (r = 0.99), total body water (r = 0.992), and fat mass (r = 0.982) and there was good reproducibility (coefficients of variance = 0.16% to 5.58%, depending on the variable measured). Of the various tissues quantified by use of the DEXA method, measures for fat mass had the lowest correlation to postmortem chemical analysis and the highest variation in repeated measurements (remaining, however, at < 6%). Factors important for precision and variation are hydration status and subject positioning.7,29 To minimize measurement variation in the present study, all cats received fluids at a standard rate for 14 to 16 hours before DEXA scanning, and the positioning was standardized. There was no difference in DEXA values between 2 ventral recumbency positions in a small number of cats in preliminary testing. This likely indicated that hind limb positioning did not affect the measurements. The excellent correlation between actual and DEXA-calculated BW values signified that the DEXA scans were representative of actual body composition, since the BWDEXA was calculated on the assumption that muscle, fat, and bones differ in weight.
Our findings confirm a rule of thumb that %BF increases by approximately 5% for each unit increase in BCS between a BCS of 4 and 8.14,31 However, similar to findings from other studies,12,14 the measured %BF interval overlapped between BCS categories. This is of relevance to veterinary practice because it illustrates that to detect subtle weight change in individual cats, the BCS system should be combined with regular BW measurements at all veterinary visits.
Other methods of evaluating body condition in cats include BMI and thoracic measurements.12,30 Both require the cat to be in a standing position with its limbs perpendicular to the examination table and its head in a neutral position. In our experience, cats' behavior during clinical examinations makes such measurements difficult to perform consistently. This experience led us to focus the present investigation on the 9-point BCS scale, particularly because it is now included in the National Research Council recommendations for feeding cats. Girth was measured because it was included in the first validation study.14 In the present study, girth did correlate with %BF but it was often a difficult measurement to perform, with measurements dependent on how well a cat stood up on the examination table.
A limitation of our study is that the cats assigned a BCS of 9 may not be true representatives of this BCS category, as more grossly obese cats are evaluated in clinical practice than were volunteered for this study. Underweight to lean cats (ie, BCS of < 5) were also under-represented. Therefore, findings pertain primarily to cats with a BCS of between 5 and 8 only. Because purebred cats, which can vary in frame size considerably, were not included, it may not be justified to extrapolate our findings in DSH cats to cats of other breeds. However, these data should be useful for application to indoor-confined, adult neutered pet DSH cats.
ABBREVIATIONS
| %BF | Percentage body fat |
| BCS | Body condition score |
| BMI | Body mass index |
| BW | Body weight |
| BWDEXA | Body weight estimated via dual-energy x-ray absorptiometry |
| DEXA | Dual-energy x-ray absorptiometry |
| DSH | Domestic shorthair |
Witness FeLV-FIV, Synbiotics Corp, Lyon, France.
Baby/child scale, Soehnle 8310, 0 to 20 kg (0 to 45 lb), Murrhardt, Germany.
Torbugessic, 10 mg/mL, Fort Dodge, Valle de Bianya, Spain.
Stesolid emulsion, 5 mg/mL, Actavis, Gentofte, Denmark.
Rapinovet, Shering Plough Animal Health, Ballerup, Denmark.
Ringer Acetate, Fresenius Kabi, Uppsala, Sweden.
CO2 detector pulse oximeter, model 9847V, Nonin Medical Inc, Minneapolis, Minn.
Small Animal software program, version 4.7e, LUNAR DXP-α Dual-Energy Densitometer, Lunar Corp, Madison, Wis.
GraphPad Prism, version 4.1, GraphPad Software Inc, La Jolla, Calif.
SAS, version 9.1, SAS Institute Inc, Cary, NC.
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