A polymorphism in myostatin influences puberty but not fertility in beef heifers, whereas µ-calpain affects first calf birth weight

Authors: Cushman, Robert - Bob; Tait Jr, Richard; McNeel, Anthony; FORBES, E - South Dakota State University; AMUNDSON, OLIVIA - South Dakota State University; Lents, Clay; Lindholm-Perry, Amanda; PERRY, GEORGE - South Dakota State University; WOOD, J - University Of Nebraska; CUPP, ANDREA - University Of Nebraska; Smith, Timothy - Tim; Freetly, Harvey; Bennett, Gary

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2014
Publication Date: 1/9/2015
Publication URL: https://handle.nal.usda.gov/10113/60158
Citation: Cushman, R.A., Tait Jr, R.G., McNeel, A.K., Forbes, E.D., Amundson, O.L., Lents, C.A., Lindholm-Perry, A.K., Perry, G.A., Wood, J.A., Cupp, A.S., Smith, T.P., Freetly, H.C., Bennett, G.L. 2015. A polymorphism in myostatin influences puberty but not fertility in beef heifers, whereas µ-calpain affects first calf birth weight. Journal of Animal Science. 93(1):117-126.

Interpretive Summary: A study was conducted to determine if using genetic variants of the myostatin and mu-calpain genes to select for carcass traits in beef cattle, would have antagonistic influences on reproductive traits in the cow herd. Heifers with one or more copies of the genotype of myostatin associated with increased rib-eye area reached puberty at a later age, but there was no delay on calving day. This genotype tended to increase the birth weight of the heifer herself. In pubertal heifers carrying the myostatin genetic variant, there were no gross or histological differences identified in the reproductive tract or the pituitary gland, indicating that the delay in puberty did not result in permanent insults to these tissues. The mu-calpain genotype that was associated with decreased meat tenderness was also associated with a decrease in the birth weight of the first calf born to those heifers. This study demonstrates that selecting for these genotypes to improve performance in the steers could delay puberty in heifers and impact birth weights, but does not appear to negatively impact reproductive performance of the cow herd. However, care should be taken when implementing these markers because we still do not understand their interactions with other genetic markers for growth and carcass traits. Combining genetic markers for growth and production traits could still result in reaching a tipping point that eventually compromises reproductive performance in the cow herd.

Technical Abstract: The use of genetic markers to aid in selection decisions to improve carcass and growth characteristics is of great interest to the beef industry. However, it is important to examine potential antagonistic interactions with fertility in the cows before widespread application of marker-assisted selection. The objective of the current experiment was to examine the influence of 2 commercially available markers currently in use for improving carcass traits, the myostatin (MSTN) F94L and '-calpain (CAPN1) 316 and 4751 polymorphisms, on heifer development and reproductive performance. In Exp. 1, beef heifers (n = 146) were evaluated for growth and reproductive traits over a 3-yr period to determine if these polymorphisms influenced reproductive performance. In Exp. 2, heifers representing the 2 homozygous genotypes for the MSTN F94L polymorphism were slaughtered on d 4 of the estrous cycle and reproductive tracts were collected for morphological examination. In Exp. 1, there was a tendency (P = 0.06) for birth BW to be affected by MSTN with the L allele increasing birth BW in an additive fashion. Additionally, MSTN significantly affected proportion of pubertal heifers by breeding (P < 0.05) with the L allele additively decreasing proportion pubertal; however, this did not result in a delay in conception or a decrease in pregnancy rates during the first breeding season (P > 0.15). The GT haplotype of CAPN1, which was previously associated with decreased meat tenderness, was associated with an additive decrease in birth BW of the first calf born to these heifers (P < 0.05). In Exp. 2, there were no differences between the MSTN genotypes for gross or histological morphology of the anterior pituitary, uterus, or ovaries (P > 0.05). From these results, we conclude that the MSTN F94L and CAPN1 polymorphisms can be used to improve carcass traits without compromising fertility in beef heifers. The influence of these markers on cow performance and herd life remains to be determined. While the delay in puberty associated with the MSTN F94L polymorphism did not negatively impact reproductive performance in heifers, caution should be used when combining this marker with other markers for growth or carcass traits until the potential interactions are more clearly understood.