Dual energy X-ray absorptiometry (DXA) can be used to predict live animal and whole carcass composition of sheep

Synthetic phantoms enable calibration between abattoir based dual energy X-ray absorptiometers used for prediction of lamb carcass composition

Dual energy x-ray absorptiometry (DXA) devices were installed at two Australian abattoirs to predict computed tomography (CT) determined fat % and lean % of lamb carcasses. This study tested three algorithms developed for these devices, termed β1, β2 and β3, and assessed their accuracy and precision in predicting CT composition. Algorithm β3 included the use of a plastic phantom calibration block scanned by both DXA devices to adjust prediction equations, resulting in superior accuracy to the algorithms without phantom calibration (β1 and β2). When compared to the gold-standard CT composition, the bias of the DXA predictions was lowest when using algorithm β3 at the two sites (-1.17%, -0.49% for fat %, 0.11%, -0.37% for lean %). The difference of DXA composition predictions between sites was lowest when using algorithm β3, which demonstrated between site differences of 0.59 CT fat %, and 0.46 CT lean%. In contrast, algorithm β1 and β2 produced differences of 23.7% and 30.8% for CT fat, and 17.3% and 21.9% for CT lean between the two DXA devices. There was a small difference of 0.78% between the fat predictions of the first DXA image compared to the second DXA image for each carcass. The precision of predictions improved slightly using algorithm β3. This work demonstrates that the in-line DXA systems can produce comparable results across sites.

Effects of Dam and Sire Breeds on Lamb Carcass Quality and Composition in Pasture-Based Systems

This study explored the impacts of sire and dam breed on carcass quality and composition in a pasture-based system and the use of DXA to rapidly rank carcasses for leanness. Southdown (SD) and Suffolk (SF) ewes were mated to Texel (TX) or SD rams to produce seventy-nine lambs. Lambs were raised on pasture-based systems with limited grain supplementation. Lamb birth weight was greater (p < 0.01) for TX, regardless of dam breed. Lambing rate was lower (p < 0.01) for SD than SF ewes. Circulating myostatin concentrations were greater (p < 0.05) on d 42 than d 75 or d 110 but did not differ by sire breed. Texel-sired lambs had greater (p < 0.01) carcass weight, ribeye area and quality grade compared to SD-sired. Total and primal fat mass as predicted from DXA was higher (p < 0.05) in carcasses from SD than TX sires. Muscles from TX lambs had greater (p < 0.05) polyunsaturated fatty acid (PUFA) composition than SD-sired. Shear force values were influenced (p < 0.01) by dam breed, muscle cut and postmortem age but not by sire breed. The use of TX sires in pasture-based systems improved carcass leanness and muscle PUFA concentrations without altering tenderness.

Estimation of carcass chemical composition in beef-on-dairy cattle using dual-energy X-ray absorptiometry (DXA) scans of cold half-carcass or 11th rib cut

The aim of the present study was to estimate the chemical composition (water, lipid, protein, mineral, and energy contents) of carcasses measured postmortem using dual-energy X-ray absorptiometry (DXA) scans of cold half-carcass or 11th rib cut. One hundred and twenty beef-on-dairy (dam: Swiss Brown, sire: Angus, Limousin, or Simmental) bulls (n = 66), heifers (n = 42), and steers (n = 12) were included in the study. The reference carcass composition measured after grinding, homogenization, and chemical analyses was estimated from DXA variables using simple or multiple linear regressions with model training on 70% (n = 84) and validation on 30% (n = 36) of the observations. In the validation step, the estimates of water and protein masses from the half-carcass (R2 = 0.998 and 0.997; root mean square error of prediction [RMSEP], 1.0 and 0.5 kg, respectively) and 11th rib DXA scans (R2 = 0.997 and 0.996; RMSEP, 1.5 and 0.5 kg, respectively) were precise. Lipid mass was estimated precisely from the half-carcass DXA scan (R2 = 0.990; RMSEP = 1.0 kg) with a slightly lower precision from the 11th rib DXA scan (R2 = 0.968; RMSEP = 1.7 kg). Mineral mass was estimated from half-carcass (R² = 0.975 and RMSEP = 0.3 kg) and 11th rib DXA scans (R2 = 0.947 and RMSEP = 0.4 kg). For the energy content, the R2 values ranged from 0.989 (11th rib DXA scan) to 0.996 (half-carcass DXA scan), and the RMSEP ranged from 36 (half-carcass) to 55 MJ (11th rib). The proportions of water, lipids, and energy in the carcasses were also precisely estimated (R2 ≥ 0.882) using either the half-carcass (RMSEP ≤ 1.0%) or 11th rib-cut DXA scans (RMSEP ≤ 1.3%). Precision was lower for the protein and mineral proportions (R2 ≤ 0.794, RMSEP ≤ 0.5%). The cattle category (sex and breed of sire) effect was observed only in some estimative models for proportions from the 11th rib cut. In conclusion, DXA imaging of either a cold half-carcass or 11th rib cut is a precise method for estimating the chemical composition of carcasses from beef-on-dairy cattle.

Estimation of Empty Body and Carcass Chemical Composition of Lactating and Growing Cattle: Comparison of Imaging, Adipose Cellularity, and Rib Dissection Methods

The aim of present study was to compare in vivo and post mortem methods for estimating the empty body (EB) and carcass chemical compositions of Simmental lactating and growing cattle. Indirect methods were calibrated against the direct post mortem reference determination of chemical compositions of EB and carcass, determined after grinding and analyzing the water, lipid, protein, mineral masses, and energy content. The indirect methods applied to 12 lactating cows and 10 of their offspring were ultrasound (US), half-carcass and 11th rib dual-energy X-ray absorptiometry (DXA) scans, subcutaneous and perirenal adipose cell size (ACS), and dissection of the 11th rib. Additionally, three-dimensional (3D) images were captured for 8 cows. Multiple linear regressions with leave-one-out-cross-validations were tested between predictive variables derived from the methods tested, and the EB and carcass chemical compositions. Partial least square regressions were used to estimate body composition with morphological traits measured on 3D images. Body weight (BW) alone estimated the EB and carcass composition masses with a root mean squared error of prediction (RMSEP) for the EB from 1 kg for minerals to 12.4 kg for lipids, and for carcass from 0.9 kg for minerals to 7.8 kg for water. Subcutaneous adipose tissue thickness measured by US was the most accurate in vivo predictor when associated with BW to estimate chemical composition, with the EB lipid mass RMSEP = 11 kg and R² = 0.75; carcass water mass RMSEP = 6 kg and R² = 0.98; and carcass energy content RMSEP = 236 MJ and R² = 0.91. Post mortem, carcass lipid mass was best estimated by half-carcass DXA scan (RMSEP = 2 kg, R² = 0.98), 11th rib DXA scan (RMSEP = 3 kg, R² = 0.96), 11th rib dissection (RMSEP = 4 kg, R² = 0.92), and perirenal ACS (RMSEP = 6 kg, R² = 0.79) in this respective order. The results obtained by 11th rib DXA scan were accurate and close to the half-carcass DXA scan with a reduction in scan time. Morphological traits from 3D images delivered promising estimations of the cow EB and carcass chemical component masses with an error less than 13 kg for the EB lipid mass and than 740 MJ for the EB energy. Future research is required to test the 3D imaging method on a larger number of animals to confirm and quantify its interest in estimating body composition in living animals.

Accuracy of predicting chemical body composition of growing pigs using dual-energy X-ray absorptiometry

Studies in animal science assessing nutrient and energy efficiency or determining nutrient requirements benefit from gathering exact measurements of body composition or body nutrient contents. Those are acquired by standardized dissection or by grinding the body followed by wet chemical analysis, respectively. The two methods do not result in the same type of information, but both are destructive. Harnessing human medical imaging techniques for animal science can enable repeated measurements of individuals over time and reduce the number of individuals required for research. Among imaging techniques, dual-energy X-ray absorptiometry (DXA) is particularly promising. However, the measurements obtained with DXA do not perfectly match dissections or chemical analyses, requiring the adjustment of the DXA via calibration equations. Several calibration regressions have been published, but comparative studies of those regression equations and whether they are applicable to different data sets are pending. Thus, it is currently not clear whether existing regression equations can be directly used to convert DXA measurements into chemical values or whether each individual DXA device will require its own calibration. Our study builds prediction equations that relate body composition to the content of single nutrients in growing entire male pigs (BW range 20-100 kg) as determined by both DXA and chemical analyses, with R² ranging between 0.89 for ash and 0.99 for water and CP. Moreover, we show that the chemical composition of the empty body can be satisfactorily determined by DXA scans of carcasses, with the prediction error ranging between 4.3% for CP and 12.6% for ash. Finally, we compare existing prediction equations for pigs of a similar range of BWs with the equations derived from our DXA measurements and evaluate their fit with our chemical analysis data. We found that existing equations for absolute contents that were built using the same DXA beam technology predicted our data more precisely than equations based on different technologies and percentages of fat and lean mass. This indicates that the creation of generic regression equations that yield reliable estimates of body composition in pigs of different growth stages, sexes and genetic breeds could be achievable in the near future. DXA may be a promising tool for high-throughput phenotyping for genetic studies, because it efficiently measures body composition in a large number and wide array of animals.

Carcass and Primal Composition Predictions Using Camera Vision Systems (CVS) and Dual-Energy X-ray Absorptiometry (DXA) Technologies on Mature Cows

This study determined the potential of computer vision systems, namely the whole-side carcass camera (HCC) compared to the rib-eye camera (CCC) and dual energy X-ray absorptiometry (DXA) technology to predict primal and carcass composition of cull cows. The predictability (R²) of the HCC was similar to the CCC for total fat, but higher for lean (24.0%) and bone (61.6%). Subcutaneous fat (SQ), body cavity fat, and retail cut yield (RCY) estimations showed a difference of 6.2% between both CVS. The total lean meat yield (LMY) estimate was 22.4% better for CCC than for HCC. The combination of HCC and CCC resulted in a similar prediction of total fat, SQ, and intermuscular fat, and improved predictions of total lean and bone compared to HCC/CCC. Furthermore, a 25.3% improvement was observed for LMY and RCY estimations. DXA predictions showed improvements in R² values of 26.0% and 25.6% compared to the HCC alone or the HCC + CCC combined, respectively. These results suggest the feasibility of using HCC for predicting primal and carcass composition. This is an important finding for slaughter systems, such as those used for mature cattle in North America that do not routinely knife rib carcasses, which prevents the use of CCC.

Dietary nano chromium picolinate can ameliorate some of the impacts of heat stress in cross-bred sheep

Two studies were conducted to evaluate the effect of nano chromium picolinate (nCrPic) during heat stress (HS) in sheep. In the initial study, 36 Merino × Poll cross-bred sheep were individually penned and allocated to 3 dietary treatments (0, 400 and 800 μg/kg nCrPic) for 8 wk. Body composition was determined at the beginning and end of the experiment using dual energy X-ray absorptiometry. The sheep remained in their dietary groups but were then placed in metabolic cages and randomly allocated within the dietary group to differing ambient temperature regimes, i.e., thermo-neutral (TN) (n = 18) and HS (n = 18), for 3 wk. Dietary nCrPic had no effect on growth performance and body composition during the initial study conducted under TN conditions. Heat stress decreased average daily feed intake (ADFI) (P = 0.002) whereas sheep under HS had reduced average daily gain (ADG) and indeed lost weight (P < 0.001). Dietary nCrPic increased both ADFI (P = 0.041) and ADG (P = 0.049) under both TH and HS conditions such that the performance of sheep receiving supplemental nCrPic and exposed to HS was similar to that of control sheep maintained under TN conditions. Heat stress increased rectal temperature (P < 0.001) and respiration rate (P < 0.001), particularly during the hottest parts of the day as indicated by interactions (P < 0.001) between time of day and thermal treatment. Rectal temperature was lower in sheep fed nCrPic (P = 0.050), particularly under peak HS conditions during the afternoon as indicated by the interactions between dietary nCrPic and time of day (P < 0.001) and dietary nCrPic, thermal treatment and time of day (P = 0.010). Similarly, respiration rate was lower in sheep fed nCrPic under peak HS conditions during the afternoon as indicated by the interactions between dietary nCrPic and thermal treatment (P < 0.001) and dietary nCrPic and time of day (P = 0.030). In conclusion, dietary nCrPic can partially ameliorate the negative effects of HS as indicated by the maintenance of ADFI and decreased physiological responses, such as elevations in rectal temperature and respiration rate.

Non-Destructive Imaging and Spectroscopic Techniques for Assessment of Carcass and Meat Quality in Sheep and Goats: A Review

In the last decade, there has been a significant development in rapid, non-destructive and non-invasive techniques to evaluate carcass composition and meat quality of meat species. This article aims to review the recent technological advances of non-destructive and non-invasive techniques to provide objective data to evaluate carcass composition and quality traits of sheep and goat meat. We highlight imaging and spectroscopy techniques and practical aspects, such as accuracy, reliability, cost, portability, speed and ease of use. For the imaging techniques, recent improvements in the use of dual-energy X-ray absorptiometry, computed tomography and magnetic resonance imaging to assess sheep and goat carcass and meat quality will be addressed. Optical technologies are gaining importance for monitoring and evaluating the quality and safety of carcasses and meat and, among them, those that deserve more attention are visible and infrared reflectance spectroscopy, hyperspectral imagery and Raman spectroscopy. In this work, advances in research involving these techniques in their application to sheep and goats are presented and discussed. In recent years, there has been substantial investment and research in fast, non-destructive and easy-to-use technology to raise the standards of quality and food safety in all stages of sheep and goat meat production.

Understanding the impact of sire lean meat yield breeding value on carcass composition, meat quality, nutrient and mineral content of Australian lamb

Advances in genomics and technology measuring body composition are now allowing sheep producers to select directly for increased lean meat yield (LMY) using Australian Sheep Breeding Values (ASBV). This experiment evaluated the impact of sire LMY ASBV on carcass composition, meat quality, nutrient and mineral content for lambs reared at pasture and finished in a feedlot. A 1% unit increase in sire LMY ASBV resulted in progeny that were leaner (0.8%) and had less fat (1.0%) on carcass. There was also a 0.2% reduction in the intramuscular fat content, a 3.2 N increase in meat toughness determined by shear force at day 5 ageing, a reduction in the redness of the fresh meat and a lower iron content. It is concluded that Australian sheep producers will need to incorporate ASBVs for other aspects of meat quality when selecting sires with increased LMY to avoid deterioration in meat quality, nutritional content of lamb and fresh meat colour.

Dual energy X-ray absorptiometry precisely and accurately predicts lamb carcass composition at abattoir chain speed across a range of phenotypic and genotypic variables

Dual energy X-ray absorptiometry (DEXA) is an imaging modality that has been used to predict the computed tomography (CT)-determined carcass composition of multiple species, including sheep and pigs, with minimal inaccuracies, using medical grade DEXA scanners. An online DEXA scanner in an Australian abattoir has shown that a high level of precision can be achieved when predicting lamb carcass composition in real time. This study investigated the accuracy of that same online DEXA when predicting fat and lean percentages as determined by CT over a wide range of phenotypic and genotypic variables across 454 lambs over 6 kill groups and contrasted these results against the current Australian industry standard of grade-rule (GR) measurements to grade carcasses. Lamb carcasses were DEXA scanned and then CT scanned to determine CT Fat % and CT Lean %. All phenotypic traits and genotypic information, including Australian Sheep Breeding Values, were recorded for each carcass. Residuals of the DEXA predicted CT Fat % and Lean %, and the actual CT Fat % and Lean % were calculated and tested against all phenotypic and genotypic variables. Excellent overall precision was recorded when predicting CT Fat % (R2 = 0.91, RMSE = 1.19%). Small biases present for sire breed, sire type, dam breed, hot carcass weight and c-site eye muscle area could be explained by a regression paradox; however, biases among kill group (-0.73% to 1.01% for CT Fat %, -1.48% to 0.76% for CT Lean %) and the Merino sire type (0.36% for CT Fat %, -0.73% for CT Lean %) could not be explained by this effect. Over the large range of phenotypic and genotypic variation, there was excellent precision when predicting CT Fat % and CT Lean % by an online DEXA, with only minor biases, showing superiority to the existing Australian standard of GR measurements.

Reducing the level of nutrition of twin-bearing ewes during mid to late pregnancy produces leaner prime lambs at slaughter

The Australian prime lamb industry is seeking to improve lean meat yield (LMY) as a means to increasing efficiency and profitability across the whole value chain. The LMY of prime lambs is affected by genetics and on-farm nutrition from birth to slaughter and is the total muscle weight relative to the total carcass weight. Under the production conditions of south eastern Australia, many ewe flocks experience a moderate reduction in nutrition in mid to late pregnancy due to a decrease in pasture availability and quality. Correcting nutritional deficits throughout gestation requires the feeding of supplements. This enables the pregnant ewe to meet condition score (CS) targets at lambing. However, limited resources on farm often mean it is difficult to effectively manage nutritional supplementation of the pregnant ewe flock. The impact of reduced ewe nutrition in mid to late pregnancy on the body composition of finishing lambs and subsequent carcass composition remains unknown. This study investigated the effect of moderately reducing ewe nutrition in mid to late gestation on the body composition of finishing lambs and carcass composition at slaughter on a commercial scale. Multiple born lambs to CS2.5 target ewes were lighter at birth and weaning, had lower feedlot entry and exit weights with lower pre-slaughter and carcass weights compared with CS3.0 and CS3.5 target ewes. These lambs also had significantly lower eye muscle and fat depth when measured by ultrasound prior to slaughter and carcass subcutaneous fat depth measured 110 mm from the spine along the 12th rib (GR 12th) and at the C-site (C-fat). Although carcasses were ~5% lighter, results showed that male progeny born to ewes with reduced nutrition from day 50 gestation to a target CS2.5 at lambing had a higher percentage of lean tissue mass as measured by dual energy X-ray absorptiometry and a lower percentage of fat during finishing and at slaughter, with the multiple born progeny from CS3.0 and CS3.5 target ewes being similar. These data suggest lambs produced from multiple bearing ewes that have had a moderate reduction in nutrition during pregnancy are less mature. This effect was also independent of lamb finishing system. The 5% reduction in carcass weight observed in this study would have commercially relevant consequences for prime lamb producers, despite a small gain in LMY.

Dual-energy X-ray absorptiometry (DXA) and chemical composition as measures of body composition of the short-beaked echidna (Tachyglossus aculeatus aculeatus)

Dual-energy X-ray absorptiometry (DXA) is a non-invasive technology for measurement of body composition that requires validation against reference methods when applied to a new species. The aim of this work was to validate DXA for the assessment of body composition of the echidna. Body composition was determined in the short-beaked echidna (Tachyglossus aculeatus aculeatus) using a Norland XR36 DXA scanner and validated by proximate chemical analysis for dry matter, ash, crude fat (FM) and protein (as 6.25 × N) and bone mineral content (BMC). Echidnas were opportunistically obtained as ‘road kill’. Body composition data were compared between techniques by correlation and limits of agreement (LOA) analyses. Twenty-eight echidnas (11 males, 13 females, 4 not determined), weighing 520–5517 g, underwent analyses. Mean FM was 489.9 ± 439.5 g and 448.5 ± 337.5 g, lean mass was 2276.0 ± 1021.4 g and 2256.0 ± 1026.0 g, fat-free mass was 2356.3 ± 1055.1 g and 2389.5 ± 1081.1 g and BMC was 80.3 ± 39.5 g and 79.9 ± 42.4 g by DXA and chemical analysis, respectively. The two methods were highly correlated (0.84 to 0.99) and not significantly different, although LOA were large. DXA has the potential to be used to assess body composition of echidnas although further work is required to improve accuracy of measurement.

Exploration of methods for lamb carcass yield estimation in Canada

Different approaches were evaluated to improve the accuracy of carcass yield predictions of Canadian lamb carcasses using manually obtained measurements and dual-energy X-ray absorptiometry (DEXA). Several linear carcass measurements were obtained from a population of commercial lamb carcasses representative of the variability in Canadian slaughter plants (n = 155). Carcass measures were categorized into four sets according to when each measure could be obtained in the slaughter process. Each set of carcass measurements were subjected to stepwise regression and used to develop models for the estimation of lean meat and saleable yield percentages. Tissue depth measures (at the GR site) explained 44% of variation in lean meat yield in hot carcasses and 53% in cold carcasses. When additional parameters were included with cold GR, the regression model explained 61.9% of the variability in lean meat yield. Saleable yield predictions were less accurate (R2 < 0.40); the greatest degree of variability was predicted when the model included ribeye area (R2 = 0.39). The DEXA scans obtained on carcass sides were able to predict about 78% of variability in carcass lean meat yield and 91% of fat content. This information could be used by the lamb meat industry to establish new carcass classification systems based on more accurate lean meat yield values.

Dual-energy X-ray absorptiometry scans accurately predict differing body fat content in live sheep

Background

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.

Results

In 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).

Conclusions

Overall, 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.

Repeatability and reproducibility of measurements obtained by dual-energy X-ray absorptiometry on pig carcasses

The precision of a dual-energy X-ray absorptiometry (DXA) device in terms of repeatability and reproducibility was evaluated on nine left half-carcasses from pigs with large variability in body weight and fat content. Repeatability was assessed by scanning each carcass 10 times sequentially in the same position. Reproducibility was assessed by scanning each carcass in 10 different positions. Images were analyzed with DXA software using a custom region of interest (ROI) and the standard head, trunk, arm, and leg ROI. Predicted values from the DEXA for bone mineral content (BMC), bone area, bone mineral density (BMD), total weight, soft-tissue weight, fat-tissue weight, and lean-tissue weight were considered. Repeatability was associated with the variance between measurements on the same carcass in the same position (repeatability conditions). An average variance value was obtained with all the carcasses combined, and the SD was calculated as the square root of this combined variance. The CV was the ratio between the SD of the measurements and its average value. Reproducibility was calculated for each carcass as the difference between the variance obtained under the reproducibility conditions and that obtained under the repeatability conditions. The effects of the ROI and conditions were evaluated by ANOVA and Tukey's test. Means of BMC, bone area, BMD, fat tissue, and lean tissue differed among the ROI (P < 0.05) in both the repeatability and reproducibility conditions. The CV of DXA measurements under repeatability condition obtained in the head, arm, and leg ROI was lesser than 1%. Only the repeatability errors of fat tissue differed (P < 0.05) among the ROI, with the lowest precision found for the trunk ROI. The reproducibility errors of BMC, bone area, fat tissue, and lean tissue differed (P < 0.05) among the ROI. The custom ROI had reproducibility errors greater than 2% for fat tissue and greater than 3.5% for BMC and bone area. In addition, the trunk ROI had the highest reproducibility errors for fat tissue (20.7%) and lean tissue (6.2%) when compared to the other ROI. In conclusion, repeatability and reproducibility results obtained for most of the studied ROI indicate that DXA is a valuable tool for carcass evaluation. From a methodological viewpoint and considering the variations observed in this study, the ROI should be chosen based on the item to be evaluated or on the conditions in which the DXA measurements are to be taken.

Rosiglitazone maleate increases weight gain and body fat content in growing lambs

Thiazolidinediones (TZD) are synthetic orally active peroxisome proliferator-activated receptor γ ligands used in the treatment of diabetes mellitus. The peroxisome proliferator-activated receptor γ gene plays an important role in regulating fat cell development, energy balance, and lipid metabolism in adipose and skeletal muscle tissue. There is interest in pharmacologic or nutritional means that may complement genetic techniques to improve growth and carcass composition of lambs and the major aim of the present study was to determine whether TZD impact on growth performance and meat quality of growing lambs. An initial study with four cross-bred lambs confirmed that rosiglitazone maleate is absorbed after oral dosing for 7 days. A second study was conducted with 30 cross-bred lambs to investigate the effects of sex (ewe vs wether) and dose of orally administered rosiglitazone maleate (0, 8 and 24 mg/day) for 55 days on growth performance, body composition, plasma metabolites and insulin and meat quality. Feed intake tended to increase linearly with dose of TZD (1521, 1816 and 1878 g/day for 0, 8 and 24 mg/day, P = 0.07) over the entire study, and particularly during the second half of the study (P < 0.05). There were both linear (P = 0.05) and quadratic (P = 0.04) responses in average daily gain to TZD (215, 270 and 261 g/day) with the quadratic response being most pronounced over the second half of the study (P = 0.004). As a result of the increased feed intake back fat (9.4, 11.1 and 13.5 mm, P < 0.001) and carcass fat (27.5%, 29.2% and 30.1%, P = 0.05) increased linearly with dose of TZD. However, there was no effect of TZD on internal fat depots. Plasma non-esterified acid concentrations increased linearly (0.37, 0.39 and 0.41 mM, P = 0.01) whereas plasma insulin concentrations (23.2, 26.9 and 20.9 mU/L, P = 0.05) and the homeostatic model assessment (6.82, 7.73 and 5.98, P = 0.05) exhibited quadratic responses to TZD. There were no significant effects of TZD on muscle pH, temperature or colour although muscle pH was higher at any temperature in ewes (+ 0.05 of a pH unit, P = 0.036) than in wethers. In conclusion, these data confirm that rosiglitazone maleate was rapidly absorbed from the digestive tract of growing ruminant lambs and was metabolically active. Oral TZD treatment appeared to mitigate against the inhibitory effect of carcass fatness on feed intake but the additional energy consumed was in turn deposited as fat.

Non-invasive methods for the determination of body and carcass composition in livestock: dual-energy X-ray absorptiometry, computed tomography, magnetic resonance imaging and ultrasound: invited review

The ability to accurately measure body or carcass composition is important for performance testing, grading and finally selection or payment of meat-producing animals. Advances especially in non-invasive techniques are mainly based on the development of electronic and computer-driven methods in order to provide objective phenotypic data. The preference for a specific technique depends on the target animal species or carcass, combined with technical and practical aspects such as accuracy, reliability, cost, portability, speed, ease of use, safety and for in vivo measurements the need for fixation or sedation. The techniques rely on specific device-driven signals, which interact with tissues in the body or carcass at the atomic or molecular level, resulting in secondary or attenuated signals detected by the instruments and analyzed quantitatively. The electromagnetic signal produced by the instrument may originate from mechanical energy such as sound waves (ultrasound - US), 'photon' radiation (X-ray-computed tomography - CT, dual-energy X-ray absorptiometry - DXA) or radio frequency waves (magnetic resonance imaging - MRI). The signals detected by the corresponding instruments are processed to measure, for example, tissue depths, areas, volumes or distributions of fat, muscle (water, protein) and partly bone or bone mineral. Among the above techniques, CT is the most accurate one followed by MRI and DXA, whereas US can be used for all sizes of farm animal species even under field conditions. CT, MRI and US can provide volume data, whereas only DXA delivers immediate whole-body composition results without (2D) image manipulation. A combination of simple US and more expensive CT, MRI or DXA might be applied for farm animal selection programs in a stepwise approach.

The accuracy and precision of DXA for assessing body composition in team sport athletes

This study determined the precision of pencil and fan beam dual-energy X-ray absorptiometry (DXA) devices for assessing body composition in professional Australian Football players. Thirty-six professional Australian Football players, in two groups (fan DXA, N = 22; pencil DXA, N = 25), underwent two consecutive DXA scans. A whole body phantom with known values for fat mass, bone mineral content and fat-free soft tissue mass was also used to validate each DXA device. Additionally, the criterion phantom was scanned 20 times by each DXA to assess reliability. Test-retest reliability of DXA anthropometric measures were derived from repeated fan and pencil DXA scans. Fat-free soft tissue mass and bone mineral content from both DXA units showed strong correlations with, and trivial differences to, the criterion phantom values. Fat mass from both DXA showed moderate correlations with criterion measures (pencil: r = 0.64; fan: r = 0.67) and moderate differences with the criterion value. The limits of agreement were similar for both fan beam DXA and pencil beam DXA (fan: fat-free soft tissue mass = -1650 ± 179 g, fat mass = -357 ± 316 g, bone mineral content = 289 ± 122 g; pencil: fat-free soft tissue mass = -1701 ± 257 g, fat mass = -359 ± 326 g, bone mineral content = 177 ± 117 g). DXA also showed excellent precision for bone mineral content (coefficient of variation (%CV) fan = 0.6%; pencil = 1.5%) and fat-free soft tissue mass (%CV fan = 0.3%; pencil = 0.5%) and acceptable reliability for fat measures (%CV fan: fat mass = 2.5%, percent body fat = 2.5%; pencil: fat mass = 5.9%, percent body fat = 5.7%). Both DXA provide precise measures of fat-free soft tissue mass and bone mineral content in lean Australian Football players. DXA-derived fat-free soft tissue mass and bone mineral content are suitable for assessing body composition in lean team sport athletes.