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Title: The Effects of Piedmontese Inheritance and Myostatin Genotype on the Tenderness of Longissimus Thoracis, Gluteus Medius, Semimembranosus, and Biceps Femoris

Authors

Submitted to: Journal Of Animal Science
Publication Acceptance Date: July 23, 2001
Publication Date: N/A

Interpretive Summary: It was recently shown that an inactivated myostatin gene is responsible for double muscling in cattle. Most studies of double muscling in cattle indicate that meat tenderness is improved, although many studies have involved only the ribeye muscle. We have reported that Piedmontese with one copy of the double muscling gene have more tender ribeye muscle. However, the magnitude of the effect on tenderness of one (heterozygous) and two (homozygous) copies of the gene was not clear. Furthermore, it was not known how much of the effect of improved tenderness in the Piedmontese breed was due to the double muscling gene and how much was due to other genes. Thus, the objective of this study was to determine the relative contributions of percentage Piedmontese inheritance and double muscling to tenderness of ribeye, top sirloin, top round, and bottom round cuts. The results indicate that the effects of Piedmontese inheritance on meat tenderness were due entirely to the double muscling gene. All four cuts from heterozygous animals with one copy of the double muscling gene were more tender and had less connective tissue than normal animals. Only the bottom round cut was further increased in tenderness with two copies of the double muscling gene relative to one copy. Piedmontese bulls homozygous for double muscling could be used as terminal sires to produce heterozygous progeny with improved tenderness in the four muscles studied.

Technical Abstract: The objective of this study was to determine the relative contributions of Piedmontese inheritance (0, 25, 50, or 75%) and myostatin genotype (+/+, mh/+, and mh/mh) to tenderness of four major muscles. Over 4 years, matings were made to produce 396 animals with 0 (+/+), 1 (mh/+), or 2 (mh/mh) inactive myostatin alleles which were known to result in normal muscling, heavy muscling, and extremely heavy muscling, respectively. Data from four muscles at 14 d postmortem were analyzed for the main effects of group (eight combinations of myostatin genotype and percentage Piedmontese; [+/+]/0%, [+/+]/25%, [+/+]/50%, [mh/+]/25%, [mh/+]/50%, [mh/+]/75%, [mh/mh]/50%, [mh/mh]/75%) and muscle. Within myostatin genotypes, contrasts to test the effect of percentage Piedmontese were not significant (P > 0.05). Data were reanalyzed for the main effects of myostatin genotype and muscle. Tenderness, ease of fragmentation, and amount of connective tissue ratings were higher (P < 0.05) for the mh/+ and mh/mh genotypes relative to +/+ in all muscles. In biceps femoris, mh/mh had higher (P < 0.05) tenderness, ease of fragmentation, and amount of connective tissue ratings than mh/+. Juiciness ratings were lower (P < 0.05) for mh/mh than for mh/+ in all muscles and were lower for +/+ in all muscles except gluteus medius. Beef flavor intensity ratings were lower (P < 0.05) for mh/mh than for +/+ in all muscles. The effects of Piedmontese inheritance on meat tenderness were all due to myostatin genotype. Piedmontese mh/mh bulls could be used as terminal sires to produce mh/+ progeny with improved carcass value due to improved tenderness in the four muscles studied.