Ultrasonic Evaluation of Pigs Exhibited at Youth Shows in Virginia During the 2000 Show Season
Livestock Update, November 2000
C. M. Wood, Extension Animal Scientist, Virginia Tech, and
C. Childs, Extension ANR agent, Warren County
The most complete and comprehensive evaluation of market hogs includes both live-hog production and carcass merit. Ideally, that means weighing pigs at the beginning of the feeding period, and at market weight. It also means measuring the carcasses for composition (how much) and quality (how good) of lean pork to assess carcass merit. In many cases, however, actual carcass measurements cannot be obtained. Under those conditions, ultrasound can be used to predict carcass composition by estimating backfat and depth of the loin muscle. Although muscle quality is ignored, ultrasound estimates are reasonably accurate predictors of carcass merit. Combining live performance (daily gain), show placings, and estimated carcass merit gives the most complete evaluation of show pigs. Thanks to funding by the Virginia Pork Industry Board, support from Virginia Tech, and cooperation by Extension agents and volunteers, we were able to collect ultrasonic data on carcass characteristics of 372 market hogs exhibited in seven shows held during 2000. Of that total, 105 pigs at two shows were measured using an A-mode (single dimension) machine and the remaining pigs were measured with a B-mode (imaging) machine.
Results are tabulated in Table 1. In general, pigs were required to weigh between 220 and 270 lb to show, although different fairs vary some in their particular requirements. The wide range of starting weights (where available) and show weights probably reflect a mix of factors -- genetics, nutrition, and environment -- coupled with the need to aim for a particular weight range at a particular date with a small number of animals. In a sense, it reflects the difficulty producers sometimes have in "hitting the box" on weights desired by packers, on a schedule that works for delivery of pigs to the packing plant.
In recent years, average daily gain (ADG) has been added as an evaluation criterion in several shows. Knowing something about how fast their pigs grow can be very helpful to exhibitors and their families when planning for the next show. In addition, ADG often reflects the way pigs are managed during the growing period. As indicated in Table 1, a number of pigs gained very little weight during the growing period designated for their shows. This may be due to a number of factors such as set backs because of weather or illness, but is often reflective of the need to hold pigs back so they are not too heavy on show day. With boars often gaining close to 3 lb/day in growing trials, ADG figures of less than 1.5 lb/day are seldom due to genetics. On a commercial industry level, there is no percentage in holding pigs; it costs too much for producers to do so. Including ADG and requiring exhibitors to calculate cost of gain brings that message home very quickly.
Lean Gain takes the concept of efficient production one step further. Lean Gain is an estimate of how much of the weight gain (ADG) is strictly lean tissue. It combines on-farm production efficiency with traits packers pay for. To get an estimate of lean gain, it is necessary to have starting weights on pigs as well as estimates of backfat at market weight. Ultrasound scans work very well for this purpose. Pigs with the genetic potential for high lean gain (> .75 lb/day) should be fed accordingly. They can efficiently utilize feeds with higher protein levels. In the shows that calculated Lean Gain, the averages are similar to what is found in the commercial industry today.
Backfat was measured on all pigs at the tenth rib, off the midline. Both machines are reasonably accurate for backfat measurements, which makes ultrasound an excellent substitute when access to a packing plant and direct measurement of carcasses is not feasible. In 2000, the average of all backfat measurements taken at four shows was well under an inch, and the other two were right around an inch. This reflects much of the change occurring in the industry with the implementation of carcass merit buying systems. In all six shows, there were a number of pigs that were extremely lean, and there were only a few pigs that "got away" during the growing period, scanning more than 1.5 inches of fat. Interestingly enough, the heaviest pigs often were not the fattest pigs on show day.
Percent lean was estimated on these show pigs by using a combination of backfat depth, loin depth, and projected carcass weights. Backfat is the major component of that estimate, and in general the averages correlate fairly well. But since muscling and weight are also a part of the Lean Gain estimate, the correlation is not perfect.
Table 1. Summary of ultrasound measurements, predicted carcass merit, and estimated lean gain of pigs exhibited at youth shows in Virginia during 2000a.