Linden Olson
Linden Olson

In early June the USDA daily report (lm_hg201) showed the average market weight of pigs sold for several days was over 286 pounds, the highest average weight since reporting started. I was reflecting on how the average weight of pigs has changed since the 1950s when the average weight was in the 230-pound range. But far more than the weight has changed! 

In the early 1950s, there was a large movement to reduce the amount of fat on pigs because World War II was over and fat was no longer in high demand. In 1952, Dr. Hazel from Iowa State University developed the backfat probe to measure the fat on live pigs with the measurements used to select breeding animals that were leaner. The backfat probe was a 2-inch piece of wood that was cut in half, with a small groove cut on each side. On one side, a small sharp knife similar to a scalpel was fastened.  The groove on the other side allowed a stainless steel ruler to be inserted in the slot after the knife cut a slit in the pig’s skin. The pig to be probed would be restrained by the nose with a hog holder, the knife inserted and a stainless steel ruler pushed through the fat until it was stopped by the layer of lean tissue. Each pig was probed over the shoulder, the 10 rib and the last rib area and the measurements were averaged and corrected to 230 lbs. 

It was not uncommon for pigs to have over 2 inches of backfat in the early to mid ‘50s. The use of these backfat measurements when selecting replacement animals for the breeding herd allowed a lot of improvement to be made in a fairly short period of time. 

About the same time, a number of swine testing stations were started. These testing stations would evaluate progeny groups, often three boars and a barrow from the same sire for backfat thickness, feed efficiency, and rate of gain. The barrow would be slaughtered and the carcass evaluated for length, average backfat and loin eye area.

In addition, several of the swine breed associations started the Certified Meat Sire program. This program allowed breeders to get their herd sires designated as a Certified Meat Sire if the progeny met certain standards. The first standards required that two pigs from each of five different litters had to meet the minimum carcass standards (adjusted to 230 lbs.) of 29.5 inches in length, a minimum of 3.5 square inches of loin eye and less than 1.6 inches of backfat.

As pigs improved over the years the minimum standards rose. The National Swine Improvement Federation was formed in 1974 and developed indexes to be used in ranking boars to be used as herd sires. These indexes weighted backfat, feed efficiency, and rate of gain using economic values for each.  Over the years, new technology has enabled live-animal evaluation methods like ultrasound to replace much of the carcass evaluation of the past.

The average pig being marketed today weighs over 280 lbs., has 8.0 sq. inches of loineye and about .70 inches of backfat. That’s a far cry from the pigs in the 1950s that weighed about 230 lbs., had less than 4 sq. inches of loineye and carried over 1.6 inches of backfat. The swine industry has made huge strides in converting feed into protein over the last 60 years through various genetic selection programs that use information gained from a combination of on-farm, central testing and carcass data from packers.      

It will be interesting to see how and what technologies will be used to measure and change meat quality parameters like marbling, color, firmness, flavor and juiciness in the coming years to meet consumers’ preferences for pork.