J. Anim Sci. 2008. 86:763-767. doi:10.2527/jas.2007-0560
© 2008 American Society of Animal Science
Technical note: A novel technique to assess internal body fat of cattle by using real-time ultrasound1
F. R. B. Ribeiro*,
L. O. Tedeschi*,2,
J. R. Stouffer
and
G. E. Carstens*
* Texas A&M University, College Station 77843; and
Cornell University, Ithaca, NY 14853
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Abstract
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The objectives of this study were to describe a system to assess KPH fat by using real-time ultrasound (RTU) and to develop equations to predict total physical separable internal fat (IFAT) based on ultrasound measurements. Data for this study were obtained from 24 Angus steers fed either hay- or corn-based diets during the backgrounding phase. Steers were serially slaughtered in 3 groups: at weaning (baseline), then at 4 and 8 mo after weaning. A fourth group was composed of 4 steers from the hay-fed group that were slaughtered at approximately 10 mo after weaning. The RTU measurements were collected every 2 mo, with a preslaughter scan approximately 7 d before the slaughter time. The RTU measurements consisted of 12th- to 13th-rib backfat thickness, 12th to 13th ribeye area, percentage of intramuscular fat, and kidney fat depth, which was measured in a cross-sectional image collected between the first lumbar vertebra and the 13th rib. For kidney fat, the ultrasound probe was placed on the flank region approximately 15 cm from the midline of the animal. Images were stored in the ultrasound console, and measurements were taken between the ventral part of the iliocostalis muscle and the end of the KPH fat at the chute side. The relationship between carcass and ultrasound measurements in the depths of kidney fat (cKFd and uKFd, respectively) had an r2 of 0.93, with a root mean square error (RMSE) of 1.14 cm. An allometric regression between carcass KPH weight (cKPHwt) and cKFd was identified, and the untransformed regression had an r2 of 0.96. The linear regression between total IFAT and cKPHwt had an r2 of 0.97, with an RMSE of 2.67 kg. Therefore, a system was developed to predict IFAT from uKFd measurements by combining these equations. Additionally, a single linear regression between IFAT and uKFd measurements was developed (r2 = 0.89, RMSE = 5.32 kg). Even though the system of equations had a lower RMSE of prediction and greater r2 compared with the single linear regression (4.80 vs. 5.10 kg and 0.91 vs. 0.89, respectively), there was no difference between these methods in predicting IFAT (P = 0.4936) by using a pairwise mean square error of prediction analysis. Our results indicated that uKFd measurements can accurately and precisely predict the cKFd of steers consuming either high concentrate or forage rations. The results also showed that cKFd is highly correlated with cKPHwt, which can be used to estimate total IFAT. More research is needed to further evaluate this technique with different feeding strategies, breeds, and sexes.
Key Words: carcass • internal fat • ultrasound
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INTRODUCTION
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A persistent positive energy balance leads to deposition of fat in the animal body. Fat deposition can be chemically characterized by a continued accretion of lipids, primarily in the form of triacylglycerides, and morphologically characterized by hyperplasia and hypertrophy (Nürnberg et al., 1998
). In beef cattle, body fat is accumulated in different parts of the body so that KPH and gastrointestinal tract fat is the first to be deposited, followed by intermuscular, subcutaneous, and intramuscular fat depots (Gerrard and Grant, 2003; Jones, 2004). Several factors affect the onset and amount of fat that is deposited, such as breed, sex, and level of nutrition. Body fat has an important role in determining the body composition and energy requirements of growth in beef cattle (Geay, 1984). Body fat is classified into carcass and internal organ fat. Ribeiro et al. (2006) indicated that carcass fat can be assessed by using real-time ultrasound (RTU), which is a noninvasive technique that requires immobilization of the animal for a short period of time. On the other hand, total physical separable internal fat (IFAT) assessment is difficult and expensive, and usually requires slaughter of the animal. The A-mode ultrasound has been used to measure fat and muscle depths (Temple et al., 1956) and LM area (Stouffer et al., 1961) in beef cattle. Since the 1990s, numerous studies (Wilson, 1992; Greiner et al., 2003b; Ribeiro et al., 2006), have been conducted to examine the efficacy of RTU to quantify LM area, back and rump fat thicknesses (Realini et al., 2001; Tait et al., 2005), and percentage of intramuscular fat (Hassen et al., 1999, 2001). However, similar noninvasive techniques have not been developed to quantify IFAT with RTU. The objective of this study was to develop a technique that could be used to assess total separable IFAT based on the measurement of KPH and IFAT with RTU.
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MATERIALS AND METHODS
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Animal and Diet Description
Steers were fed and managed under the guidelines of the Texas A&M University Institutional Animal Care and Use Committee.
Data for this study were obtained from Angus steers (n = 24) fed either hay- or corn-based diets during the backgrounding phase at the Texas A&M University Agricultural Research Center at McGregor. Steers were serially slaughtered based on predetermined ages. Steers were weighed and sorted into 3 groups: baseline, hay-fed, or corn-fed steer treatment. Baseline steers (n = 4) were slaughtered 1 wk after being weaned (8 mo of age). Of the remaining 20 steers, 12 were assigned to a hay-based diet (Table 1) and 8 to a corn-based diet. Four months after weaning, 8 steers were slaughtered (4 hay-based diet and 4 corn-based diet) and the remaining steers from the hay- (n = 8) and corn-based (n = 4) diet groups were placed on the same diet and fed on an ad libitum basis. Eight months after weaning, 8 steers were slaughtered (4 from each group). The remaining 4 steers from the hay-based diet group were slaughtered 40 d after the third slaughter group.
Ultrasound Data
The RTU measurements were collected every 2 mo, with a preslaughter scan approximately 7 d before slaughter. Real-time ultrasound measurements consisted of 12th- to 13th-rib backfat thickness (uBF), 12th- to 13th-ribeye area, percentage of i.m. fat, and kidney fat depth (uKFd) by an Ultrasound Guidelines Council field-certified technician.
Hassen et al. (2001) used 2 ultrasound machines (Aloka 500V and Classic Scanner 200) to predict i.m. fat from 500 steers. Both machines had similar accuracies, with r2 for the model without transformation of 0.72 and 0.68, and with logarithmic transformation of 0.84 and 0.87 for the Aloka 500V and Classic Scanner 200, respectively. Therefore, an Aloka 500V instrument with a 17-cm, 3.5-MHz transducer (Aloka Co. Ltd., Wallingford, CT) was used in this study. Images were collected and interpreted on site at the ultrasound console, and the percentage of i.m. fat images were analyzed by Beef Image Analysis Pro software (Designer Genes Inc., Harrison, AR).
RTU of Kidney Fat
The RTU kidney fat image was collected between the first lumbar vertebra and the 13th rib as shown in Figure 1, as a cross-sectional image. The ultrasound probe was placed on the flank region approximately 15 cm from the midline of the animal. Hair was clipped (if longer than 0.64 cm) to increase image quality, and vegetable oil was used as a coupling agent. Images were stored in the ultrasound console and interpreted chute side by the same technician. The uKFd measurement was taken between the ventral part of the abdominal muscles (iliocostalis, obliquus abdominis interni, and obliquus abdominis externi) and the end of the kidney fat as shown in Figure 2.
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Figure 1. (A) Photograph and (B) schematic of scanning locations for real-time ultrasound image collection of kidney fat depth.
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Figure 2. Detailed images of 2 steers showing (A) the point of measurement of the kidney (between the first lumbar vertebra and the 13th rib) and (B) backfat and kidney fat depths by using real-time ultrasound with landmarks.
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Slaughter Data Collection
Feed was withheld overnight with free access to water, and steers were slaughtered at the Rosenthal Meat Science and Technology Center, Texas A&M University, College Station. Live BW and HCW were recorded. Whole gastrointestinal tracts were removed and dissected to obtain total physical separable IFAT weights. Measurements of carcass kidney fat depth (cKFd) were taken from the hot carcass by using a tape measure. The measurement was taken from the midline (vertebrae) to the end of the kidney fat. The KPH depot was removed from the carcass before splitting.
Statistical Analyses
All statistical analyses were performed by using PROC GLM and PROC REG (SAS Inst. Inc., Cary, NC). The statistical model was a complete randomized design in which each animal was the experimental unit. Steers were assigned to 2 treatments: corn-corn or hay-corn. In the corn-corn treatment, steers were fed the corn-based diets during the backgrounding and finishing phases, whereas those steers in the hay-corn treatment were fed the hay-based diet during the backgrounding phase and the corn-based diet during the finishing phase. The STEPWISE statement was used to identify the best predictors of IFAT. Outliers were tested by plotting the Studentized residual vs. the predicted values and were removed if the Studentized residual was outside the range of –.5 to 2.5. Adequacy of the models developed to predict IFAT was determined by using several measurements as discussed by Tedeschi (2006), including the root mean square error of prediction and concordance correlation coefficient.
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RESULTS AND DISCUSSION
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Group means of animal BW and carcass measurements are listed in Table 1
. Steers from the corn-fed group deposited more IFAT than steers from the hay-fed group (P < 0.001), which was expected because the corn-based diet provided more energy than the hay-based diet. The development of KPH fat weight and cKFd (Table 1) and IFAT (Table 1) for steers fed either hay or corn followed an exponential pattern, probably because the rate of accretion of fat increases with maturity (Owens et al., 1995). Other studies have shown that RTU can also be used to predict carcass weight and the percentage of beef carcass retail product (Greiner et al., 2003a), but RTU has not previously been used to predict noncarcass components in beef cattle.
When all ultrasound measurements (Table 1) were used to predict observed IFAT, the stepwise procedure selected uBF and uKFd measurements, accounting for 92% of the variation, with an RMSE of 4.61 kg (Eq. 1 in Table 2). Because uKFd accounted for more of the variation, we removed uBF and obtained Eq. 2 in Table 2 (r2 = 0.89 and RMSE = 5.32 kg). This suggested that ultrasound measurements might be able to explain the variation in IFAT of growing and finishing steers fed either hay- or corn-based diets. Previous work using ultrasound measurements to predict carcass traits has shown that this technology is useful in measuring body composition. Perkins et al. (1992) reported simple correlations between uBF and ultrasound 12th- to 13th-ribeye area and carcass measurements of 0.60 and 0.75, respectively, in feedlot steers and heifers.
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Table 2. Regression equations to predict carcass kidney fat depth (cKFd, cm), carcass KPH weight (cKPHwt, kg), and internal fat (IFAT, kg)
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However, because of the nonlinear relationship among some of the variables of interest (Table 1), a more complicated system to predict IFAT was developed that would allow stepwise calculations of variables of interest. Equation 3 in Table 2 estimated cKFd from uKFd, with an r2 of 0.93 and RMSE of 1.14 cm. The relationship between carcass KPH weight and cKFd was nonlinear (Eq. 4 in Table 2), and the untransformed equation yielded a RMSE of 1.20 kg (Eq. 5 in Table 2). Finally, the relationship between IFAT and carcass KPH weight was close, with an r2 of 0.97 and RMSE of 2.67 kg (Eq. 6 in Table 2).
Despite the strong relationships obtained in this study, additional work is needed to study the impact of using uKFd measurements to predict IFAT at different stages of growth. Brethour (2000) reported that uBF measures taken 30 d or less before slaughter could be used to predict carcass back fat thickness more accurately. The author also reported that marbling score could be predicted more accurately by RTU measurements later in the feeding period.
When we compared the adequacy for predicting IFAT between the single linear regression (Eq. 2 in Table 2) and the stepwise model (Eq. 3 to 6 in Table 2), the stepwise model had a lower root mean square error of prediction than the single linear regression (4.80 and 5.10 kg, respectively) and a greater coefficient of determination (0.91 and 0.89, respectively). The concordance correlation coefficient for the stepwise model was 0.943, and for the single linear regression it was 0.939. The pairwise mean square error of prediction analysis (Tedeschi, 2006) indicated that the 2 approaches were not different in computing IFAT (P = 0.4936).
Our findings indicated that RTU measurements adequately predicted IFAT. This technique might improve our ability to estimate total body fat content in growing and finishing steers fed either hay- or corn-based diets. Consequently, this technique might be used in feedlot sorting systems to better allocate animals into different feeding and management strategies to improve profit-ability.
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Footnotes
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1 The authors wish to express their gratitude to Ryan D. Rhoades, David K. Lunt, and Stephen B. Smith from Texas A&M University for allowing us to take the ultrasound measurements of the steers. 
2 Corresponding author: luis.tedeschi{at}tamu.edu
Received for publication November 4, 2007.
Accepted for publication November 22, 2007.
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LITERATURE CITED
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Abstract
INTRODUCTION
