Location: Meats Safety & Quality ResearchTitle: Association of genetic markers in cattle receiving differing implant protocols Author
|King, David - Andy|
|Smith, Timothy - Tim|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2012
Publication Date: 7/1/2012
Citation: King, D.A., Shackelford, S.D., McDaneld, T.G., Kuehn, L.A., Kemp, C.M., Smith, T.P., Wheeler, T.L., Koohmaraie, M. 2012. Association of genetic markers in cattle receiving differing implant protocols. Journal of Animal Science. 90:2410-2423. Interpretive Summary: Genetic markers for growth and meat quality traits have been identified to aid in improving growth and meat quality traits through genetic selection. However, little is known regarding their effectiveness under differing management programs. Growth promotants are widely used in the U.S. beef industry to increase rate and efficiency of growth in cattle, despite detrimental effects on carcass quality and meat palatability with some implant protocols. The present study evaluated the effectiveness of genetic markers in improving growth and meat quality traits of cattle receiving differing implant protocols, the effects of genetic markers for a given trait on other important traits, and the use of genetic markers to minimize the detrimental effects of aggressive implant protocols. Implant protocol had no impact on final live weight, carcass weight, or rate of gain during the entire feeding period. The aggressive implant protocol increased carcass muscling and leanness, but decreased marbling scores and tenderness when compared to the mild implant protocol. Some of the genetic markers improved their target trait, but had negative effects on other traits of importance. Such antagonisms must be addressed when using marker assisted genetic selection. Generally, genetic marker effects were independent of implant effects, indicating that genetic markers could be used to manage, but likely not eliminate negative impacts of aggressive implant protocols.
Technical Abstract: The potential interaction of growth-promoting implants and genetic markers previously reported to be associated with growth, carcass traits, and tenderness was evaluated. Two implant protocols were applied to subsets of steers (n=383) and heifers (n=65) that were also genotyped for 47 SNP reported to be associated with variation in growth, fat thickness, LM area, marbling, or tenderness. One protocol consisted of a single terminal implant [16 mg estradiol benzoate (EB), 80 mg trenbalone acetate (TBA) or 8 mg EB, 80 mg TBA given to steers and heifers, respectively], designated the “mild” protocol. The “aggressive” protocol consisted of both a growing implant (8 mg EB, 40 mg TBA) for the lightest half of the animals on the aggressive protocol and 2 successive implants (28 mg EB, 200 mg TBA) given to all animals assigned to the aggressive treatment. Implant protocol had measurable impact on BW and ADG (P<0.05), with the aggressive protocol increasing these traits before the terminal implant (relative to the mild protocol), while the mild protocol increased ADG after the terminal implant so that the final BW and ADG over the experimental period were similar between protocols. Animals on the aggressive protocol had significantly increased (P<0.05) LM area (1.9 cm2), slice shear force (1.4 kg), and intact desmin (0.05 units), but decreased (P<0.05) marbling score (49 units) and adjusted fat thickness (0.1 cm). Among both treatments, eight of nine growth-related SNP were associated with BW or ADG, and six of 17 tenderness-related SNP were associated with slice shear force or intact desmin. Favorable growth alleles generally increased carcass yield traits but decreased tenderness. Similarly, favorable tenderness genotypes for some markers were associated with decreased BW and ADG. Some interactions of implant protocol and genotype were noted, with some growth SNP alleles increasing the effect of the aggressive protocol. In contrast, putative beneficial effects of favorable tenderness SNP alleles were mitigated by the effects of aggressive implant. These types of antagonisms of management variables and genotypes must be accounted for in marker assisted selection (MAS) programs, and our results suggest that MAS could be used to manage, but likely will not eliminate negative impact of implants on quality.