Relationship among BCS and Fat Thickness in Horses of Different Breed, Gender and Age

Aims: The aims of the study were to investigate i) the kind of the relationship among BCS and subcutaneous fat thickness (FT) in horses, as affected by breed, gender and age, and ii) the effectiveness of a combination of the two variables in order to better estimate adiposity.
Study Design: Body weight (BW), FT (at croup level, by means of an ultrasound device) and BCS (5 point scale) were recorded in 124 horses (55 Standardbred; 25 Italian Saddler; 44 Thoroughbred) of different gender (95 mares; 14 stallions; 15 geldings) and age (26 ≤4 years of age; 98 >4 years of age) at five commercial herds.
Methodology: After at least one hour from the morning meal, BW, by means of an electronic balance, and FT on the croup, at approximately 11 cm cranial to the tail head and 10 cm lateral to the midline, by means of an ultrasound device (Lean-Meater, Renco Corporation) were recorded. BCS was evaluated at the same moment on a scale of 1 to 5 (1 = emaciated and 5 = extremely obese).
Results: BCS was affected by breed (P<.05), while FT was independent of breed, gender and age (P>.05). Overall FT and BCS were moderately correlated (r=0.335; P<.01); correlation coefficients were higher in Italian Saddler (r=0.549; P<.01), stallions (r=0.631; P<.05), and young horses (r=0.539; P<.01). A new variable (FT_BCS), calculated as (FT*BCS)/(FT+BCS), is proposed. It resulted correlated both to FT (r=0.754; P<.01) and BCS (r=0.824; P<.01). Allometric coefficients of FT and BCS on BW were of the same sign, regardless of sex and breed, as mature horses tended to decrease FT and increase BCS with the increase of BW; coefficients for FT_BCS on BW gave a better fit than FT or BCS alone, as in Thoroughbred and in young horses they gave a better fit than both FT and BCS.
Conclusion: The study showed that, due to their correlation, BCS or FT alone could be not sufficient to describe horse body adiposity, but their association could be more useful; in the weight range between 470 and 500 kg, their combination is able to appreciate a deviation from linearity of the allometric equation with BW in geldings and Italian Saddler horses.