Introduction

Ultrasonic measurement is routinely used for fat and muscle prediction in swine. One of the main reasons commercial producers currently have interest in the fat and lean composition of the live animal is because carcass value programs have become the predominant pricing system for marketing swine. Ultrasonic measures are also useful to determine lean gain patterns, select replacements, refine feeding programs and condition score sows.

Much of the recent research with ultrasound has been conducted using brightness (B) mode instruments, with multi-element linear probes that produce two-dimensional cross-sectional images of the body. A-mode ultrasound machines generally use a single transducer in a single point estimation of depth. Therefore, B-mode ultrasound is currently considered the industry standard for live animal evaluation. However, A-mode ultrasonic equipment is generally less expensive, more durable and more portable than B-mode equipment. The objective of this study was to examine the accuracy of various A-mode ultrasound machines, as compared to B-mode ultrasound, for measurement of last rib backfat, tenth rib backfat and tenth rib loin muscle depth and to evaluate technician by machine interactions.

Materials and Methods

Twenty-seven market pigs of a uniform genetic source were visually selected for maximum variation in fat depth. The 15 barrows and 12 gilts averaged 112 kg in live weight. Tenth rib fat depth (tenth) and loin muscle depth (loin depth) were measured at a location 18 cm in front of the last rib and 7 cm from the dorsal midline. Last rib fat depth was measured at the C and K positions. The last rib was located by palpation and C and K were measured at locations 5 cm and 7.5 cm from the dorsal midline, respectively. All pigs were measured by three different technicians using five different A-mode ultrasonic machines (machine). Measurement sites were independently determined by each technician. No technician had previously used all five machines. The five A-mode machines are described in Table 1. Three of these machines have the ability to electronically store data and transfer it to a printer or personal computer. After all measurements were completed by each technician pigs were evaluated with B-mode ultrasound by a fourth technician who was certified by the National Swine Improvement Federation. B-mode measures of C, K, tenth and loin depth were taken using an Aloka 500V ultrasound unit (distributed by Corometerics Medical Systems, Wallingford, CT). The B-mode ultrasound measures were used as the standard for comparison.

General linear model procedures were used to analyze accuracy of ultrasound measures for the 27 pigs, 3 technicians, and 5 machines. The absolute values of the difference between the A-mode ultrasound and B-mode ultrasound measurements were analyzed with fixed effects for technician, machine, and technician x machine interaction and the random effects of pig, pig x technician interaction and pig x machine interaction.

Results and Discussion

Table 2 contains least square means for absolute differences from B-mode ultrasound by machine. For all ultrasonic measures machine 3 was the least accurate. For measures of fat depth at the last rib, machine 1 was significantly (P < .001) less accurate than machine 2, machine 4 and machine 5. For the analysis of absolute difference between A-mode and B-mode ultrasonic fat depth at the last rib (C and K) the effects of machine and pig were highly significant (P < .001). However, the interaction between machine x pig was also significant (P < .01). Pig and machine x pig interactions may be explained by the overestimating of C and K for leaner pigs and underestimating C and K for fatter pigs, as shown in Figure 1. The deviation between the A-mode and B-mode measurements was plotted against the actual B-mode measurements and indicates a potentially greater underestimation of C and K fat depth with A-mode machines. A- mode ultrasonic machines have previously been found to underestimate backfat, relative to carcass measurements. For the absolute difference between A-mode and B-mode ultrasonic fat depth at the tenth rib (Tenth) only the effect of machine was significant (P < .001).

For the absolute difference between A-mode and B-mode loin depth (Loin Depth) the effect of machine was highly significant (P < .001) and the effects of technician (P < .05) and technician x machine interaction were significant (P = .08). This tendency for technician x machine interaction is in agreement with previous research and indicates that the evaluation of the loin muscle is much more dependent on the training and qualifications of the technician. All three machines were significantly different (P < .01) for accuracy of loin depth measurement with machine 5 the most accurate. The poorest level of accuracy for the measurement of loin depth was obtained with machine 3 by all technicians. When ranked on |Loin Depth| within technician all machines ranked the same for accuracy. However, across technicians there was a machine x technician interaction (P = .08). Technician 3 was the most accurate with machines 3 and 4 and technician 2 was the most accurate with machine 5. However, all technician by machine combinations tended to over estimated loin muscle depth as compared to B-mode.

Summary

Machines 2, 4, and 5 were the most accurate for the estimation of fat depth at the tenth and last rib. Machine 5 was found to be the most accurate for the estimation of loin muscle depth at the tenth rib.