Aparato Reproducror Del Toro

Technical Bulletin — Myostatin Analysis

DNA profiling makes it practical to select for or against increased muscling.
The myostatin gene (GDF-8) was one of the first identified genes proven to have a large effect on an economically important trait.1 Myostatin normally prevents excessive muscular development. Therefore, changes (mutations) in the gene lead to reduction or loss of function.Forms of these genetic mutations have a large effect on muscle mass and been associated with the phenotype described as “doublemuscling.” They also have been associated with heavier birth weights, heavier weaning weights and higher yield of lean.2 Some breed associations treat the calving difficulties associated with double-muscling as a genetic defect that needs to be eliminated3 while another(Piedmontese) makes myostatin genotype status a mandatory registration requirement and proudly calls themselves “the Myostatin Beef Breed.”4 Whether a producer considers the effects of the myostatin gene desirable or not, it is now practical for producers to identify the presence of a range of myostatin mutations by using the myostatin analysis as part of the IGENITY® profile. BAckgrouND Discovered byJohns Hopkins University scientists in 1997, myostatin is a member of the family of secreted growth and differentiation factors that are essential for proper regulation of muscle mass.5 Following the initial findings in mice, the gene also was localized in other species and numerous distinct mutations were identified.2 Considerable research has been conducted in the last few years to characterizethe various myostatin mutations present in cattle. A study involving 678 animals from 28 European beef breeds genotyped at the myostatin locus revealed a total of 20 different genotype combinations.6 Additional research at the U.S. Meat Animal Research Center has further characterized two of the most common myostatin mutations in Piedmontese (C313Y) and Belgian Blue (nt821 del11).2,7,8 See insidefor a summary of research conducted on the effects of myostatin mutations and tools available for analysis. ExAmplEs of thE ImpAct of myostAtIN mutAtIoNs In cattle, myostatin affects traits of economic importance, including weight, muscling and calving difficulty.1 • It has been suggested that calving difficulty may be a function of the dam’s genotype as well as that of the calf.1 • A myostatinmutation has been associated with early life mortality, and calves with two copies of this mutation are especially susceptible to harsh conditions at birth.2 • In one study, animals with two copies of a myostatin mutation were heaviest at birth, were leaner and had a higher proportion of muscle mass; heterozygous animals were heaviest at weaning and had the highest live weight; and animals with zerocopies had the highest fat content.2 • Production systems that can select for calves with one copy of certain myostatin mutations will benefit from heavier weaning weights and higher yield of lean, compared with cattle with zero copies.2

1

myostAtIN ANAlysIs commoN mutAtIoNs

AND

ImpAct

of
Mutation

Table 1. Myostatin gene mutations and birth weight
BIRTH WEIGHT
Trait Numberof Mutated Alleles Population/Animals Reference

The myostatin analysis, as part of the IGENITY profile, detects nine different mutations of the myostatin gene. Research suggests that these changes are breed-specific.6 Of the nine mutations, six cause double-muscling and are referred to as “disruptive.” Animals that are homozygous (two copies) for any one of these six variations tend to havelarger birth weights, increased dystocia, reduced fat cover, larger longissimus muscle (ribeye) area and enhanced meat tenderness.1-11 The other three mutations are referred to as “missense.” They yield increased muscularity and a reduction in external and intramuscular fat with no effect on birth weight or dystocia. Animals that are heterozygous for this mutation are typically intermediate for...