Often carcass changes occur in exhibition events at a faster rate than within the industry. This is primarily due to pre-selection by exhibitors for traits currently emphasized for industry change. The guidance given to many individuals is that more is better. Consequently, extremes for highly heritable traits are often deemed more desirable. Unfortunately, selection for improvement of only one trait may cause detrimental changes in others. For example, exclusive improvement for percent lean will lead to adverse changes in growth and meat quality.

The Michigan State Fair (MIFAIR) and Oklahoma Junior Livestock Show (OKJ) have gathered carcass information over an extended period of time. The MIFAIR used ultrasound to estimate backfat, loin muscle area, and calculate percent lean for each pig entered in the youth show. To estimate percent lean based on carcass data, the OKJ slaughtered the first place pig or first and second place pig from each class. Information from these shows (see Figure 2 ) demonstrated improvement in percent lean over the last 10 years. This substantiates testimonials of most junior market pig shows around the country.

However, concern has been voiced that market pigs in youth shows may have become too extreme for percent lean. This uneasiness is supported by the fact that the percent lean of the highest-ranking animals at many major youth shows is over 60% (see Figure 3). This conflicts with industry trends and carcass merit buying programs that provide no further reward for carcasses over 57% lean. In fact, one carcass merit program reduces premium for carcasses over 59% lean, to further emphasize the need to moderate selection criteria. Over time this can be destructive if youth and those who instruct them believe the ideal animal is too extreme. Animals that are too far reaching for percent lean will exhibit poor meat quality traits. This can translate into lower quality pork products and potentially be a detriment to pork demand.

To further understand the trend for carcass merit within youth shows, all pigs with carcass data were summarized across four major shows from 1995 to 1999—MIFAIR, OKJ, San Antonio Texas Livestock Exhibition, and Houston Texas Livestock Show. Not all shows have data for each year, but short-term trends for each show can be determined. During the last five years, animals exhibited in youth shows have not significantly changed in percent lean (see Figure 4).
It is true that top ranking individuals within these contests have been far reaching for percent lean; however, percent lean of animals within the carcass evaluation portions of these exhibitions appear to be remaining constant. Since Houston, San Antonio, and OKJ slaughter only class winners, this indicates judges may have moderated their selections in regard to percent lean.

It is of further interest to understand how the components of lean percentage have changed within shows as well. Estimation of percent lean is calculated using weight (either live or carcass weight), tenth rib backfat, and loin muscle area at the tenth rib. Figure 5 shows a summary of live weight at these four shows. A trend for increased weight is evident, which also occurred within the industry. However, at San Antonio, weight has not changed significantly over the three years summarized.

The trend for backfat is illustrated in Figure 6. Three of the four shows summarized for backfat have not significantly changed over the time period evaluated. However, the MIFAIR has seen a trend for backfat to decrease over time. This was not true for loin muscle area (see Figure 7).
A significant trend for increased loin muscle area occurred with all four shows. It would be logical to conclude that with no change in backfat and an increase in loin muscle area, percent lean would increase. However, pig weight increased also.

The increased weight more than compensated for the increased loin muscle area; thus, percent lean within these shows remained virtually the same during the last three to five years.