Trained vs untrained evaluator assessment of body condition score as a predictor of percent body fat in adult cats

Abstract

Body condition scoring (BCS) provides a readily available technique that can be used by both veterinary professionals and owners to assess the body condition of cats, and diagnose overweight or underweight conditions. The objective of this study was to evaluate a five-point BCS system with half-point delineations using dual-energy x-ray absorptiometry (DXA). Four evaluators (a veterinarian, veterinary technician, trained scorer and untrained scorer) assessed 133 neutered adult cats. For all scorers, BCS score was more strongly correlated with percent body fat than with body weight. Percent body fat increased by approximately 7% within each step increase in BCS. The veterinarian had the strongest correlation coefficient between BCS and percent fat (r = 0.80). Mean body fat in cats classified as being in ideal body condition was 12 and 19%, for 3.0 and 3.5 BCS, respectively. Within BCS category, male cats were significantly heavier in body weight than females within the same assigned BCS category. However, DXA-measured percent body fat did not differ significantly between male and female cats within BCS category, as assigned by the veterinarian (P >0.13). Conversely, when assessed by others, mean percent body fat within BCS category was lower in males than females for cats classified as being overweight (BCS >4.0). The results of this study show that using a BCS system that has been validated within a range of normal weight to moderately overweight cats can help to differentiate between lean cats and cats that may not be excessively overweight, but that still carry a higher proportion of body fat.

Introduction

Excessive weight gain and overweight conditions are the most prevalent nutritional disorders diagnosed in pet cats today.^1,2 Diagnostically, cats are generally considered to be overweight when they are >10% above ideal body weight (BW), and obese when they are ≥20% above ideal BW. ¹ Although estimates vary somewhat, published studies report prevalence rates of feline obesity, including both overweight and grossly obese, to be at least 30% in pet cats. The most recent large study of cats living in the USA found that of 8159 cats, 29% were considered to be overweight, and an additional 6.4% were grossly obese. ² The incidence of overweight conditions in owned cat populations also appears to be increasing and may be related to a higher proportion of cats living relatively sedentary lives as indoor pets.^3,4 However, the causative data are equivocal and highly debated. Obesity in cats has a negative impact on quality of life, and increases an animal’s risk of developing health disorders, such as impaired glucose tolerance, diabetes, hepatic lipidosis, skin disease and osteoarthritis.^5,6 Although underweight conditions are less common in pet cats, less than ideal BW is also undesirable and associated with health risks. ⁷ Therefore, it is important to direct efforts toward the maintenance of ideal BW and prevention of weight gain or weight loss in cats to maximize the health and well-being of cats. Furthermore, in overweight and underweight cats, appropriate weight optimization programs need to be implemented, and body condition tracked closely to maximize the successful attainment of a healthy BW.

Maintaining a healthy weight requires a tool to accurately measure body fat. Accurate measurement of body fat will allow correct differentiation between cats in ideal body condition, cats that are overweight or gaining weight, and cats at risk of becoming obese. Both veterinarians and owners have important roles in monitoring body composition changes. For example, while most veterinarians are aware of the problem of overweight pets, some may not see it as a disorder worthy of formal diagnosis and discussion with owners. A review of computerized medical records from 52 veterinary practices found that while almost a third of hospitals’ feline patients were classified as being overweight, <2% of the cats’ records included their weight status as either a diagnosis or a notation. ² Similarly, many owners are unable to accurately assess overweight conditions in their own pets. Compared with trained evaluators, owners of overweight cats were found to consistently underestimate their cat’s body condition, considering a cat that was overweight to be in optimal condition. ⁸ Similar results have also been reported for dog owners. ⁹ Taken together, these data suggests an unmet need during regular veterinary evaluations that can be addressed to improve the health and well-being of cats.

Veterinarians routinely weigh cats during regular clinic visits. BW is an objective and repeatable measure that is useful for identifying weight changes over time and for monitoring response to a weight management program. However, BW does not reflect body composition and cannot specifically reveal the proportion of body fat or the lean-to-fat ratio. Body composition, in particular the degree of adiposity, is an important component of feline health, given the high number of indoor cats that lead sedentary lives and the increased proportion of neutered cats that may be predisposed to weight gain.^2,10 Over the last decade, understanding of the role of adipose tissue in metabolic dysregulation has increased dramatically, and it is generally accepted that adipose tissue plays an integral role in the health and well-being of mammals. Controlling body fat and BW is central to maintaining optimal health throughout the life time of cats.

Body composition can be measured objectively and accurately using dual-energy x-ray absorptiometry (DXA), a method that has been used in dogs and cats, and which has been validated to provide an accurate estimate of fat and lean tissue proportions.^11–13 However, DXA is a research tool that is not available to most practising veterinarians. It may also be cost-prohibitive to owners, and requires general anesthesia or sedation. An alternative method for assessing body fat in cats is body condition scoring (BCS). This is a semi-quantitative method that uses palpation and visual assessments to classify an animal into categories of underweight, optimal or overweight conditions. ¹⁴ Several BCS systems have been developed for companion animals, with each using between 5 and 9 integer or alphabetic categories. Advantages of a validated BCS system include ease of use, repeatability and provision of a visual image of the appearance of a normal vs an overweight or underweight animal. BCS is especially useful in pet cats and dogs because it can be performed by both veterinarians and owners. While most owners do not have access to a pet scale, they can regularly conduct a BCS procedure at home with their cats. Veterinarians can instruct clients on the proper use of BCS during routine appointments, and reduce the inclination of cat owners to underestimate their cat’s body condition and weight during home assessments.

The objectives of this study were to assess a five-point BCS system that was scored using half-points and that included a set of five descriptors for use with healthy adult cats by comparing assigned BCS scores with body composition as determined by DXA. Because systemic differences in scoring may exist among veterinary personnel and trained and untrained pet owners, the second objective was to examine differences in BCS scoring performed by a trained veterinary professional and an untrained or trained scorer.

Materials and methods

Animals

One hundred and thirty-three neutered adult cats (70 females and 63 males) were included in this study. Cats were excluded from this study if they had experienced weight loss or gain within 3 months, or had any health conditions. All cats were residents of a specific pathogen-free colony (Pet Health and Nutrition Center, Procter and Gamble Pet Care, Lewisburg, OH, USA). The age of the cats ranged from 1 to 14 years (mean age 4.6 ± 0.30 years). Sixty-eight cats (51.1%) were group-housed in rooms that provided regular outdoor access, and 65 cats (48.9%) were group-housed in indoor rooms with no outside access, but ample window space. Communally housed groups contained between eight and 20 cats, and were generally segregated by age when introduced to the colony. Group composition was maintained throughout the study. Data were collected between March 2010 and July 2010, and all experimental procedures were approved by the Institutional Animal Care and Use Committee at P&G Pet Care (Lewisburg, OH, USA).

BCS and BW

BW and BCS were measured in each cat after a 10 h fast on the same day on which DXA was performed. BCS was performed by four evaluators: a veterinarian, a veterinary technician, a BCS-trained researcher (trained and validated scorer) and an untrained researcher (untrained scorer). Evaluators assessed each cat independently, but on the same morning and were blinded to the scores of the other evaluators. The BCS method that was used consisted of a five-point (five descriptors allowing for half-point responses) scale (Figure 1). The system included palpation and visual assessment with comparison to the standard silhouette diagram.

Figure 1.

Body condition score diagram and explanation

DXA

Cats were anesthetized by intramuscular (IM) injection of dexmedetomidine hydrochloride at a dose of 0.013 mg/kg (Dexdomitor; Orion Pharma, distributed by Pfizer) in combination with hydromorphone at a dose of 0.1 mg/kg (Baxter Healthcare) to prevent movement and ensure consistency between scans. When an adequate plane of anesthesia was attained, cats were placed in a sternal position, with a cranial aspect of antebrachium on the table, with the phalanges facing caudally. Hind limbs were bent slightly upward towards the abdomen. Three DXA scans were performed, using infant software provided by Hologic (Model Delphi A with QDR for Windows). Scans were reviewed while the cat was anesthetized and on the DXA scanner to ensure that three satisfactory readings were obtained. Following completion of the scan, cats were removed from the unit and placed in a recovery area. An intramuscular injection of atipamezole (Antisedan) at a dose of 0.13 mg/kg was administered to reverse the effects of Dexdomitor (Orion Pharma, distributed by Pfizer). Body composition was recorded as bone mineral content (g), fat (g), lean (g), lean + bone mineral content (g), total mass (g) and fat (%). Whole body composition was calculated as the sum of fat (g), lean (g) and bone mineral content (g). Mean values were calculated using the readings from the three scans and used as raw data.

The newer generation of fan beam DXA scanners is considered the gold standard for body composition measurements in infants and young children, and is widely accepted as a precise and accurate, non-invasive method to assess the body composition of small subjects. ¹⁵ A study conducted in 2003 validated fan beam body composition measurements against chemicalanalysis of a piglet carcass. ¹⁶ In our study, we utilized a Hologic scanner (Delphi A system software 12.5 upgraded to Discovery QDR APEX OS) with an infant software package. The global region of interest was used for scan analysis. Preventive maintenance is performed routinely on the scanner by Hologic service personnel. Instrument quality control procedures were performed each day prior to scanning any cats. Daily quality control graphs were examined for any shifts or drifts in the system.

Statistics

A linear regression model was used to predict the percentage of body fat from the BCS for each of the four evaluators. Scatter plots were constructed to compare BCS scores between pairs of evaluators. A small random number was added to each BCS score to prevent data from overlapping on scatter plots. Because BCS data are ordered categories, a weighted Kappa statistic was calculated to test for inter-rater reliability between pairs of evaluators. Kappa statistics were interpreted as slight (≤0.20), fair (0.20–0.40), moderate (0.41–0.60), substantial (0.61–0.80) or almost perfect (>0.80). ¹⁷

Results

All of the cats were healthy at the time of assessments, and had no health-related diet or housing restrictions. None of the cats had prior excluding health conditions, or was receiving medication or veterinary care for acute or chronic health conditions at the time of assessment. Mean BW (kg) for the group of 133 cats was 4.56 kg ± 0.085 (SE). Mean BCS score for the entire group of cats (veterinarian assessor) was 3.51 ± 0.04 (SE), with a range of 3.0 to 5.0. This range shows that none of the cats in the study was assessed as being underweight (BCS <3) and a very small number (3/133, 2%) was assessed as obese (BCS = 5). Table 1 reports mean BW and DXA-measured percent body fat within each BCS category (veterinarian assessed) for male and female cats. When evaluated by the veterinarian, 75% of the cats (100/133) were classified as being in ideal body condition, with a BCS score of 3.0 or 3.5. Mean percent body fat of male and female cats that were classified as being in ideal body condition (BCS = 3.0 or 3.5) was 12% and 19%, respectively.

Table 1.

Mean body weight (BW) and dual-energy x-ray absorptiometry-measured percent fat (±SD) in male and female cats assigned body condition scores (BCS) by a veterinarian using a five-point BCS system

BCS (veterinarian)	Males			Females
	n	BW*	% Fat †	n	BW	% Fat
3.0	17	4.72 ± 0.65	11.74 ± 4.04	29	3.51 ± 0.45	11.74 ± 4.51
3.5	23	4.99 ± 0.87	18.66 ± 4.77	31	4.23 ± 0.66	19.44 ± 5.75
4.0	4	5.96 ± 0.69	22.30 ± 1.89	17	4.97 ± 0.68	26.25 ± 4.88
4.5	5	6.27 ± 0.57	29.02 ± 6.17	4	5.35 ± 0.80	31.23 ± 3.39
5.0	–	–	–	3	5.73 ± 0.52	38.97 ± 5.88

^*Male cats were significantly heavier (kg) than female cats within BCS category (P <0.05 for BCS ≤4.0; P = 0.08 for BCS = 4.5)

^†Percent body fat did not differ significantly between males and females within BCS category (P >0.13 for all comparisons).

Mean percent body fat increased with each level of BCS, although there was an overlap in weight ranges among categories. Within BCS category, male cats were significantly heavier in BW than females within the same assigned BCS category (P <0.05 for BCS <4.0; P = 0.08 for BCS = 4.5). However, DXA-measured percent body fat did not differ significantly between male and female cats within BCS category, as assigned by the veterinarian (P >0.13 for all comparisons). Table 2 reports these data for the other three scorers (veterinary technician, trained scorer, untrained scorer). While, again, male cats were heavier than females within each assigned BCS category, mean percent body fat within BCS category was numerically lower in males when compared with females for cats that were classified as being overweight (BCS >4.0). These differences were statistically significant for the veterinary technician and the trained scorer.

Table 2.

Mean body weight (BW) and dual-energy x-ray absorptiometry-measured percent fat (±SD) in male and female cats assigned body condition scores (BCS) between 2.0 and 5.0 on the basis of palpation and visual assessment using a five-point BCS system scale assessed by a veterinary technician, trained scorer and untrained scorer

BCS (veterinary technician)	Males			Females
	n	BW	% Fat	n	BW	% Fat
3.0	24	4.63 ± 0.77	14.05 ± 5.03	37	3.70 ± 0.56	13.42 ± 5.45
3.5	12	5.23 ± 0.75	18.98 ± 6.17	24	4.17 ± 0.70	19.40 ± 6.17
4.0	5	5.27 ± 0.30	17.54 ± 4.56*	17	5.13 ± 0.76	27.48 ± 4.91
4.5	7	6.18 ± 0.49	24.74 ± 4.65*	6	5.29 ± 0.60	33.63 ± 7.45
5.0	1	6.82 ± _	37.10 ± _	_	_	_
BCS (trained scorer)	n	BW	% Fat	n	BW	% Fat
3.0	3	3.82 ± 0.32	11.30 ± 0.69	15	3.25 ± 0.30	10.84 ± 3.44
3.5	26	4.78 ± 0.73	14.05 ± 5.04	32	3.88 ± 0.55	15.62 ± 6.25
4.0	15	5.59 ± 0.70	22.68 ± 5.43	29	4.88 ± 0.68	24.01 ± 5.28
4.5	5	6.16 ± 0.54	24.72 ± 5.90*	5	5.01 ± 0.65	34.48 ± 6.65
BCS (untrained scorer)	n	BW	% Fat	n	BW	% Fat
2.0		_	_	1	3.31 ± _	7.90 ± _
2.5	3	4.41 ± 0.46	9.37 ± 3.65	8	3.18 ± 0.25	9.35 ± 4.99
3.0	20	4.64 ± 0.73	13.44 ± 4.43*	37	3.95 ± 0.63	16.55 ± 5.73
3.5	12	5.14 ± 0.74	19.21 ± 4.16	11	4.13 ±0.94	16.47 ± 6.36
4.0	12	5.77 ± 0.71	23.22 ± 5.56	21	4.80 ± 0.41	26.46 ± 5.78
4.5	1	6.54 ± _	19.90 ± _	5	5.72 ± 1.04	30.74 ± 5.47
5.0	1	6.82 ± _	37.10 ± _	1	6.01 ± _	45.50 ± _

^*Denotes significant difference in percent body fat between male and female cats within BCS category (P <0.05).

Table 3 reports correlation statistics between BCS category and DXA-measured percent body fat and BW for each of the four assessors. BCS scores were more strongly correlated with DXA-measured percent body fat than with BW for all four scorers. The veterinarian had the strongest correlation coefficient between BCS and percent fat (r = 0.80), followed by the untrained scorer (r = 0.73). The BCS scores recorded by the veterinary technician had the lowest correlation with percent body fat (r = 0.69). Weighted Kappa statistics for each pair of scorers showed that scores assigned by all pairs of evaluators were significantly correlated, and fell within the substantial and moderate Kappa statistic categories. The veterinarian and veterinary technician had the highest inter-rater agreement (Kappa = 0.752), while the lowest BCS scoring agreement occurred between the untrained scorer and the trained scorer (Kappa = 0.499). Because the veterinarian and the veterinary technician had the highest agreement in BCS scoring (highest Kappa statistic), their assigned BCS scores were averaged for each cat, and the mean value was tested for correlation with BW and percent body fat. The combined correlation was as high as the veterinarian’s correlation, and is reported in Table 3 (r = 0.80). The relationship between percent body fat as measured by DXA and BCS measured by the veterinarian is shown in Figure 2.

Table 3.

Correlations between body condition score assigned by a veterinarian, a veterinary technician, a trained scorer and an untrained scorer, and body weight and dual-energy x-ray absorptiometry-measured percent body fat in 133 adult cats

Evaluator	Body weight	% Body fat
Veterinarian	0.58	0.80
Veterinary technician	0.60	0.69
Trained scorer	0.66	0.71
Untrained scorer	0.62	0.73
Veterinarian + veterinary technician	0.63	0.80

Figure 2.

Scatter plot showing correlation between body condition score (BCS) (veterinarian assessed) assigned using a five-point BCS system and percent body fat as measured by dual-energy x-ray absorptiometry in 133 adult cats (r = 0.80)

Discussion

There is widespread agreement among both veterinarians and nutritionists that obesity is a leading chronic health problem for pet cats and that the proportion of overweight cats has been increasing over the last decade. Additionally, there is evidence that pet owners are inclined to underestimate their cat’s body condition, and veterinarians may not always identify that a cat that is overweight or is gaining weight to be clinically important.^2,8 Having a simple and reproducible method that accurately assesses body condition, in particular the degree of body fat, can be used by both veterinary professionals and pet owners to identify cats that are overweight and in need of treatment, and cats that are gaining weight and at risk of becoming overweight. Both of these interventions would reduce the number of cats that have to be treated for obesity-related comorbidities and weight loss-associated hepatic lipidosis. Results from the present study show high reproducibility (inter-rater reliability) of the five-descriptor BCS system when applied by a veterinarian, a veterinarian technician and by two non-veterinary scorers. The data also show strong correlations between BCS category and DXA-measured percent body fat for all four scorers. These results suggest that this system can be valuable when used by both veterinary professionals and cat owners, and help to guide healthy life plans for cats.

Several other BCS systems have been developed, two of which have been validated using measures of correlation between assigned scores and percent body fat as determined by DXA. The earliest study, published in 1997, validated a nine-point scale using a group of 48 adult research colony cats (16 males and 32 females). ¹⁸ A more recent examination of the same BCS system used client-owned cats attending a veterinary clinic for weight-related problems. ¹⁹ A third study validated a seven-point algorithm system with 20 cats that were referred to a small animal teaching hospital either for weight-related problems or related disorders. ²⁰ It was not our intent to compare the validity of different scales, but to assess cats with a wide range of body conditions and BW with individuals with different amounts of experience and knowledge. Similar to the reported results of these three studies, the results from the present study demonstrate that BCS predicts body fat more accurately than it predicts BW, and that body fat consistently increases with each unit increase in BCS. When a nine-point scale is used, a single unit increase as a cat progresses from ideal weight to overweight conditions is associated with an approximately 5% increase in body fat. In this study, we showed a similar relationship, with an approximately 7% increase in body fat for each half-point increase in score above 3.0. While we cannot directly compare studies because of differences in conduct and cohorts, this agreement provides further evidence that BCS tools provide an accurate and consistent method for assessing body condition in cats, and is particularly reflective of the proportion of body fat.

The percent body fat that was associated with an ideal body condition in this study was somewhat lower than values reported by other investigators. The range of mean percent body fat in cats classified with a BCS score of either 3.0 or 3.5 among the four evaluators was approximately 11–19% for male and female cats. Laflamme ¹⁸ reported a mean of 22% body fat in male cats that were classified as being in optimal body condition. Mean body fat was not reported for females in ideal condition because, in Laflamme’s study, all of the female cats were overweight or obese. The second, and more recent, study of the same BCS system used client-owned indoor pet cats, and reported an even higher percent body fat for cats classified as being in ideal body condition. ¹⁹ Male cats in ideal body condition were reported to have a mean body fat of 30%, and female cats within this category had a mean body fat of 32%. Although German et al ²⁰ did not report mean percent fat values within BCS category, an examination of their regression plots suggests that cats within the ideal BCS category (4 or 5 on a seven- or nine-point BCS scale, respectively) had body fat percentages closer in range to the values found by us (~15–20%).

These dissimilarities may reflect the different sources of cats that were included in each study. Laflamme’s early study ¹⁸ used a group of research cats that included a high proportion of overweight and obese animals. Of the 16 female cats in that study, all were classified as heavier than optimal, and 11/16 (69%) were classified as obese or grossly obese. Of the 32 male cats, more than half (56%) were overweight. Similarly, the cats used by Bjornvad et al ¹⁹ were client-owned cats that lived exclusively indoors, and the majority were classified as overweight (74%). In contrast, the cats included in our study were group-housed cats living in a kennel situation. All cats had opportunities for daily human socialization and play, daily socialization with other cats, and access to indoor play and climbing structures. Some of the cats also had regular opportunities for outdoor access and exercise. When compared with the previous two studies,^18,19 which included more overweight than ideal weight cats, the majority of cats used in our study (75%) were classified as ideal or close to ideal body condition. As a result, the evaluators in this study were assessing more cats that were close to their optimal BW as opposed to the evaluators in the previous studies who were repeatedly assessing cats that were overweight or obese. Scorers who evaluate a large proportion of overweight animals may reflexively develop a systemic bias to classify cats that are moderately overweight as ideal, thus resulting in higher percentages of body fat in the ideal body condition categories. The subjective nature of BCS scoring, coupled with the potential for systemic bias when presented with a high proportion of overweight animals, would compound a tendency to place cats with higher proportion of body fat into the ideal BCS category. These data suggest that more objective measures, such as anthropometric measurements, such as chest and abdominal circumference, and muscle condition scoring may be of greater value than BCS alone when applied to clinical practice, and should be investigated. A validated measure of lean body tissue would be especially helpful in distinguishing between cats who are at normal BW and are physically fit, and those of normal BW that may have a higher proportion of body fat and reduced proportion of muscle.

Cats that live in homes, especially those who have limited opportunities for socialization with other cats or outdoor exercise, may be less active and less physically fit than cats who are group-housed and who have daily opportunities for exercise and play with other cats. It is expected that cats that are less physically fit would have a higher proportion of body fat and lower lean mass when compared with cats of a similar weight that are more physically active. The term ‘skinny fat’ has been used in the human literature to describe an individual who may be measured as having a healthy body mass index, yet still have a relatively high percent body fat as a result of a sedentary lifestyle. ²¹ The study by Bjornvad et al ¹⁹ of indoor neutered and inactive cats reported this phenomenon, finding that the mean percent body fat in cats classified with a BCS of 5 on a nine-point scale was almost 32%. By comparison, our cohort of communally living, active adult cats classified as being in ideal body condition had a mean body fat of about 19%. Humans identified as ‘skinny fat’ have been reported to be at increased risk for chronic disorders, such as diabetes and cardiovascular disease. ²² In cats, the association between being overweight and increased risk of diabetes mellitus is well-documented. ²³ The specific health risks that may increase in normal-weight cats that have a higher proportion of body fat as a result of a sedentary lifestyle have not been studied. Our data complement the results of Bjornvad et al, ¹⁹ showing that active adult cats that are classified as having ideal BCS have percent body fat that is substantially lower than the proportion of fat found in inactive house cats classified in a similar BCS category.

Differences in size, weight and body composition between male and female cats have been reported by others.^24,25 Male cats are typically larger than females, weigh more and have a lower proportion of body fat than female cats. Although not as pronounced as in dogs, breed differences in size and mature BW also exist in cats. ²⁶ In this study, males assigned to a given BCS category weighed more than females within the same category, when assessed by a veterinarian. However, the percent body fat of male and female cats that were in ideal body condition (BCS of 3.0 or 3.5) did not differ significantly. As cats gained weight, female cats that were assessed as being overweight (BCS between 4.0 and 5.0) had higher percentages of body fat than male cats within the same overweight BCS category. The magnitude of this difference was only slight in the veterinarian assessments, but was more pronounced in the veterinary technician and trained scorer assessments. This suggests that the veterinarian may have been more accurately assessing body fat through handling and then assigning categories based upon palpation of body fat deposits, rather than upon the perceived size and weight of the cat. It is also possible that knowledge of body fat deposits allowed the veterinarian to more accurately assess the degree of adiposity in cats. Conversely, the veterinary technician and trained scorer may have been more influenced by size and weight, and may have not assessed body fat as thoroughly via palpation. Because the number of cats in the overweight categories was quite small in this study, further studies are needed to assess the importance of manual handling and palpation during BCS evaluations. An additional limitation to this study was that assessments were completed by a single veterinarian and technician. Future studies that examine BCS scoring in groups of veterinary professionals and pet owners would allow a more precise examination of the potential differences in animal body condition assessment skills between trained and untrained individuals.

The study by Laflamme ¹⁸ also reported a higher proportion of body fat in overweight female cats compared with overweight male cats. ¹⁸ Female cats had approximately 10% more body fat than males within the four overweight BCS categories (6–9). However, that study did not include any female cats that were assessed to be at their ideal BW, so comparisons within those categories were not possible. Conversely, the study by Bjornvad et al ¹⁹ study found similar body fat proportions between males and females within BCS category throughout the scale, although the overall proportions of body fat within each category were higher than our data. All of the males in the study by Bjornvad et al ¹⁹ had been neutered before 1 year of age. Therefore, the different results between the two studies may again reflect differences in body composition that come about as a result of a sedentary lifestyle in indoor neutered cats, resulting in an increased proportion of body fat in neutered male cats that becomes equivalent to that of female cats within a given BCS, including ideal body condition.

An optimal percent body fat for adult pet cats has not been determined, but has been suggested to be between 20 and 30%. ¹⁸ In this study, the mean percent body fat for male and female cats with a BCS of 3.0 was 11.74, and with a BCS of 3.5 was 18.7 and 19.4, respectively, and fell slightly under the suggested 20–30% proposed previously. The different body fat values between cats classified as a 3.0 and cats classified as a 3.5 may reflect differences in body type, breed or activity level. While both scores may reflect cats who are assessed as being in optimal condition, the lower score category (3.0) may encompass more active and physically fit cats who have lower fat levels and higher muscle mass. The higher score category (3.5) may include more sedentary cats that are at their correct weight and body condition, but that are not as physically fit. It is also possible that for this BCS scale, a score of 3.0 reflects a highly active and lean cat, while a score of 3.5 is indicative of optimal body condition for an indoor, relatively sedentary cat. This distinction can be useful for veterinarians to recognize and address when examining cats and educating clients about proper feeding and exercise habits for their pet cats. Modifying BCS systems to allow for a distinction between these two categories of cats may be especially important as the proportion of completely indoor and more sedentary cats continues to rise.

A benefit of the evaluations presented in this study was the inclusion of a high proportion of cats that were close to or at their ideal body condition, a category that was lacking in previous studies. The high body fat values in ideal BCS categories reported in other studies that included a high proportion of overweight animals suggest that scorers may benefit from BCS practise that includes a high proportion of cats that are in ideal body condition, as well as cats that are overweight or obese. We also found that BCS assessments by the veterinarian were most predictive of percent body fat when compared with a veterinary technician or with a trained or untrained scorer. The results suggest that it may be important to emphasize palpation and estimation of fat deposits as opposed to relying upon visual assessments when training veterinary staff and pet owners to utilize a BCS tool. Finally, a limitation to this study, similar to previous studies, was the omission of cats that were considered to be underweight. Therefore, accurate predictions of percent BW within BCS category for the underweight categories are still lacking and should be pursued.

Conclusions

Prevention of weight gain and obesity is expected to be most effective if instituted while cats are just beginning to gain weight or before they have become obese. While BCS is a predictor of a cat’s proportion of body fat, it has less value as a predictor of BW. Because veterinarians can easily record weight, having both the veterinarian and the owner assess BCS regularly can supply additional body composition information that weight data alone do not provide. Using a BCS system that has been validated using a range of normal weight to moderately overweight cats is essential, especially when differentiating between active cats that are lean and sedentary cats that may not be excessively overweight, but that still carry a higher proportion of body fat (ie, ‘skinny fat’). Indeed, it is well accepted that BW itself is not a predictor of health, whereas percent body fat is a major risk factor for adverse health events in dogs, cats and humans. Adequate training in the use of a validated BCS system such as the one that was tested in this study can aid veterinary staff and owners in correctly classifying cats according to palpated body fat stores.