Gene mapping is an ideal tool to advance long-term goals like pork quality and disease resistance, but it can also be used to improve economics on your farm by improving growth traits.

In the case of gene mapping for growth traits, it is a tale of two markers, since they are the only major ones identified to date.

One marker was recently discovered by Gentec, the Belgian sister company of Newsham Genetics.

“The positive allele of this gene is associated with an increase in average daily gain by 30 grams per day, or about 0.05 pounds per day calculated from birth to slaughter,” says Nadine Buys, molecular geneticists for Gentec.

The faster growth rate would allow hogs to put on an extra 9 pounds by the time they go to market, or would allow you to empty your barns a few days earlier, notes Buys. The added benefits, minus the additional feed costs add up to an additional $1.50 per pig profit – depending on feed and hog prices.

“The new marker has no negative influence on backfat thickness, lean-meat percentage or meat quality characteristics,” says Buys. “This means the new marker will improve facility turnover in finishing units and have a significant influence on feed conversion.”

That is surprising, since from a quantitative genetics standpoint, when you select for faster growth you inadvertently select for a fatter animal, says Fields Gunsett, Newsham Genetics’ vice president of genetics and product development.

The other important growth-based gene is the MC4R. This gene is unique because both forms of the allele can offer different benefits, says Max Rothschild, U.S. pig genome coordinator.

“One allele provides slower-growing pigs that are leaner and more heavily muscled,” says Rothschild. “The other allele provides much faster growth, but a slightly fatter hog. Producers will need to do calculations based on their packer’s buying matrix to determine which allele is right for them.”

PIC has commercial boars with either of the MC4R alleles available. The 337G boar features the growth allele, while the 337E boar features the more efficient, leaner growth allele.

The lean allele has an effect of adding more than 1 percent lean, and reducing backfat by about 0.04 inch on market-weight hogs. Such gains would cost you in terms of a hog taking about two days longer to market. It’s usefullness in the United States will depend on the packer’s buying program. Estimates of its value exceed $1 per market hog.

The lean allele also could be considered the environmental allele, says Rothschild. If a sire is homozygous for the lean allele, and produces 6,000 progeny, it will result in 28 tons less feed consumed, which leads to about 33,000 gallons less manure. If you have 10,000 sows that are homozygous for the lean allele, there will be 930 tons less feed and 1.1 million gallons less manure per 10,000 sows than with the growth allele.

“The growth allele is still useful because to some producers the most important factor in their profitability is how fast they can get pigs to market,” says Rothschild.

The MC4R gene is found in intermediate frequency in today’s commercial herds. This means a gene marker will be more valuable because it will respond easily to selection.

Growth traits are about 35 percent to 40 percent heritable, so scientists expect to find more growth and carcass composition related gene markers. Specifically, scientists are always looking for markers that decrease backfat and increase intra-muscular fat.

The quantitative trait loci affecting growth traits have been identified on all porcine chromosomes. Genome-wide significant results have been obtained for 11 of the 19 porcine chromosomes. The most clearly established QTL results have been obtained for chromosomes 1, 4 and 7. The QTL located on chromosome 4 explains 4 percent to 10 percent of the phenotypic variance in growth traits. The QTL located on chromosome 7 explains 10 percent to 15 percent of the variance.

But developing gene markers takes time. The first matings from the Newsham trials occurred in 2000. Since then they have bred three generations, done the original gene scan and matched it up with the marker. The company is looking to do another study with boars, which means it could be another 18 months before a commercial line is available in the United States, says Gunsett.

Essentially, most gene markers are at least a five-year project before a commercial line is available.

PIC started to invest heavily in molecular biology research more than a decade ago. It began working on growth markers in the mid-1990s and started selling its first boar selected on MC4R in 2000.

As gene mapping becomes a more widely used technology, the rate of genetic improvement resulting from it may also speed up.

“PIC expects to see more genes becoming available for use,” says Graham Plastow, chief technology officer for Sygen, PIC’s parent company. “With advances in gene-mapping technology we are now able to look at more genes more quickly, and validate them faster than in the past.”

So far, the story of gene markers for growth traits has revolved around the two genes. But genes with the most influence over certain traits tend to show up first, much like the Napole and Halothane genes did for pork quality. The growth genes may not hold the same significance as the Napole and Halothane genes, but they are certainly major finds.

“Both of these growth genes are well proven,” says Rothschild. “There is no doubt they work in a variety of lines and are very effective.” 

Editor’s note: This is Part III in a series on the swine genome.