Relationships between body condition score and ultrasound skin-associated subcutaneous fat depth in equine

Abstract

Background: In equids, health and welfare depend on body composition. A growing number of equids are now used as leisure and companion animals, and often found overfeed. The need for a close monitoring of body fatness led to the search for tools allowing a rapid and non‑invasive estimation of fatness. This study intends to assess real‑ time ultrasonography (RTU) usefulness in establishing a relationship between ultrasound measures of subcutaneous fat–plus–skin thickness (SF‑Skin) and body condition score (BCS) in horses and donkeys. Forty‑three healthy animals (16 donkeys and 27 horses) were used in this study to generate 95 records (RTU and BCS pairs), in multiple RTU ses‑ sions for 2 years. Using visual appraisal and palpation, BCS was graded in a 1–9 points scale. Real‑time ultrasonogra‑ phy images were taken using a 7.5 MHz linear transducer, placed perpendicular to the backbone, over the 3rd lumbar vertebra. ImageJ was used to measure the SF‑Skin on RTU images. The relation between BCS and SF‑Skin measure‑ ments was tested by linear and polynomial regression analysis. Results: The BCS values were similar in horses (5.50; from 3 to 8 points) and donkeys (5.14; from 3 to 7 points). The SF‑Skin measures show a similar trend (a mean of 7.1 and 7.7 mm in horses and donkeys, respectively). A polynomial regression among BCS and SF‑Skin explained 92 and 77 % of the variation in donkeys and horses respectively. The coefficient of determination was considerably higher for the regression developed for donkeys compared with that of horses (R2 = 0.92 vs. 0.77, respectively), which reduced the accuracy of the method in horses. Both the linear and polynomial models tested show a strong relationship among BCS and SF‑Skin for donkeys (R2 > 0.91; P < 0.01) and horses (R2 > 0.74; P < 0.01), despite that the extremes for BCS did not existed in our sample. Conclusions: Our results showed the potential RTU usefulness to monitor body fat in equids. Using a high‑frequency transducer and RTU together with image analysis allowed the identification of small SF‑skin variations. This report will support further studies on the relationships between SF‑Skin and BCS, particularly in extreme BCS scores.