Chemical body composition of 20 Thoroughbred foals at 160 days of age, and preliminary investigation of techniques used to predict body fatness

Abstract

AIMS: To determine the chemical body composition of Thoroughbred foals born in two consecutive years, and to investigate several techniques used to predict body composition in foals born in the second year, with particular reference to fat.

METHODS: The chemical composition of 20 foals at around 160 days of age, born in two years, was determined. In vivo techniques to predict body composition were assessed in 23 foals born in Year 2, before and after euthanasia; 10 of these foals were used for chemical body composition analysis. Techniques to assess body composition in vivo included liveweight (LW), overall and regional condition scores, ultrasonic fat thickness measurements over the ribs and rump, linear measurements and bioelectrical impedance analysis. Correlations were determined between ultrasonic fat thickness, and bioelectrical impedance analysis, before and after euthanasia. Stepwise regression analysis was used to determine the relationships between in vivo techniques used to assess body composition and the chemical body composition of 10 animals.

RESULTS: Foals used for analysis of chemical composition weighed between 220.5 and 260.0 kg before euthanasia. Fat content ranged from 5.5-13.0% of the partial empty body-weight (LW less head, gastrointestinal contents, distal limbs and skin). Fillies had significantly more fat mass and percentage fat than colts (p=0.031 for both measurements). The mean chemical composition of the fat-free partial empty body was 73.2% (SD 0.6) water, 22.7% (SD 0.9) protein and 4.1% (SD 0.4) ash. Most of the variation in the concentration of empty body water was associated with variation in the concentration of fat (p<0.001). The live animal overall condition scores were correlated with fat mass and concentration (p=0.006 and p=0.013, respectively; n=10). Condition score over the rib region was highly correlated with fat mass and fat concentration (p=0.004 and p<0.001; n=10). Ultrasound measurements taken 10 cm cranial to the tailhead and 4 cm from midline, used to assess the thickness of rump fat, were correlated with condition score (p=0.001), and explained 71% of the variation in body fat mass (p=0.002; n=10). Nearly 50% of the variation in fat-free mass and partial empty body water mass were associated with variation in the impedance indices calculated from length and bioelectrical impedance analysis measurements (p=0.023 and p=0.026, respectively; n=10).

CONCLUSIONS: At around 42% of expected mature weight, fillies were significantly more fat than colts. Condition scores were correlated with partial empty body fat mass, and there was a trend for higher scores in fillies compared to colts. Much of the variation in water or protein mass of the partial empty body could be explained by variations in LW.

CLINICAL RELEVANCE: Measurements of LW, rump fat and condition score are useful predictors of the chemical composition of foals at 5 months of age.

KEYWORDS:

• Horse
• Thoroughbred
• chemical composition
• fatness
• body condition