Abstract
BackgroundThere is considerable interest in implementing mobile scanning technology for on-farm body composition analysis on live animals. These experiments evaluated the use of dual energy X-ray absorptiometry (DXA) as an accurate method of total body fat measurement in live sheep.ResultsIn Exp. 1, visceral and whole body fat analysis was undertaken in sheep with body condition scores (BCS) in the range 2 to 3.25 (scale 1: thin to 5: fat). The relationship of BCS was moderately correlated with visceral fat depot mass (r = 0.59, P < 0.01, n = 24) and whole body fat (r = 0.70, P < 0.001, n = 24). In Exp. 2, sheep with BCS in the range 2.25 to 3.75 were blood sampled to analyse circulating leptin concentrations, and were DXA scanned immediately post mortem for total body fat. Plasma leptin concentrations had low correlations with BCS (r = 0.50, P < 0.05, n = 17) and DXA body fat (r = 0.42, P < 0.05, n = 17), and no correlation with chemical body fat (r = 0.17, P > 0.05, n = 9). There was a moderate correlation between DXA body fat and BCS (r = 0.70, P < 0.01, n = 17), and DXA body fat was highly correlated with chemical body fat (r = 0.81, P < 0.001, n = 9). In Exp. 3, a series of five DXA scans, at 8-week intervals, was performed on growing sheep over a 32-week period. The average BCS ranged from 2.39 ± 0.07 (S.E.M.) to 3.05 ± 0.11 and the DXA body fat (%) ranged from 16.8 ± 0.8 to 24.2 ± 1.2. There was a moderate correlation between DXA body fat and BCS over the 32 weeks (r = 0.61, P < 0.001, n = 24).ConclusionsOverall, these experiments indicated that there was good agreement between BCS, DXA and chemical analysis for measuring total body fat in sheep, and that DXA scanning is a valid method for longitudinal measurement of total body fat in live sheep.
Highlights
There is considerable interest in implementing mobile scanning technology for on-farm body composition analysis on live animals
There was a moderate correlation between dual energy X-ray absorptiometry (DXA) body fat and body condition scoring (BCS) (r = 0.70, P < 0.01), while plasma leptin concentrations had low correlations with BCS (r = 0.50, P < 0.05) and DXA body fat (r = 0.42, P < 0.05)
A previous study indicated that the circulating concentration of leptin was a moderate indicator of back-fat thickness in sheep [5], and in Exp. 1 we found DXA to be highly correlated to visceral fat mass, which is known to be a determinant of plasma leptin levels in humans [28]
Summary
There is considerable interest in implementing mobile scanning technology for on-farm body composition analysis on live animals. These experiments evaluated the use of dual energy X-ray absorptiometry (DXA) as an accurate method of total body fat measurement in live sheep. Body condition scoring (BCS) is the accepted method of estimating body fatness in live sheep. This provides an adiposity score from assessment by palpation of the prominence and degree of cover of the spinous and transverse processes of Subcutaneous backfat depth measured by ultrasound scanning is an ‘on-farm’ method of predicting carcass lean/fat content [7]. For live sheep, the high cost/limited access, to date, of some of the more precise methods for evaluation of body composition, such as X-ray computer tomography (CT) or dual energy X-ray absorptiometry (DXA), has meant that ultrasound has been preferentially used in selection indexes to improve body composition [9, 10], despite its relatively low precision
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