Cattle breed type and anabolic implants impact calpastatin expression and abundance of mRNA associated with protein turnover in the longissimus thoracis of feedlot steers.

Two methods that the beef cattle industry can use to improve efficiency, sustainability, and economic viability are growth promotants and crossbreeding cattle of different breed types. In the United States, over 90% of cattle receive an anabolic implant at some point during production resulting in an overall increase in skeletal muscle growth. Recent research suggests that the two main cattle breed types, Bos indicus and Bos taurus, respond differently to anabolic implants. The objective of this study was to characterize changes that occur in skeletal muscle following implanting in Bos indicus influenced steers or Bos taurus steers. Twenty steers were stratified by initial weight in a 2 × 2 factorial design examining two different breeds: Angus (AN; n = 10) or Santa Gertrudis influenced (SG; n = 10), and two implant strategies: no implant (CON; n = 10) or a combined implant containing 120 mg TBA and 24 mg E2 (IMP; n = 10; Revalor-S, Merck Animal Health). Skeletal muscle biopsies were taken from the longissimus thoracis (LT) 2 and 10 d post-implantation. The mRNA abundance of 24 genes associated with skeletal muscle growth were examined, as well as the protein expression of µ-calpain and calpastatin. Succinate dehydrogenase mRNA abundance was impacted (P = 0.05) by a breed × treatment interaction 2 d post-implanting, with SG-CON having a greater increased abundance than all other steers. A tendency for a breed × treatment interaction was observed for calpain-6 mRNA (P = 0.07), with SG-CON having greater abundance than AN-CON and SG-IMP. Additionally, calpastatin protein expression was altered (P = 0.01) by a breed × treatment interaction, with SG-CON and SG-IMP steers having increased expression (P = 0.01) compared with AN-CON steers. At 2 d post-implanting, a breed × treatment interaction was observed with SG-CON steers having greater (P = 0.05) mRNA abundance of mitogen-activated protein kinase compared with AN-CON steers. Furthermore, breed affected (P = 0.05) calpastatin abundance with AN steers having increased (P = 0.05) abundance 2 d post-implanting compared with SG steers. Meanwhile, implants tended to affect (P = 0.09) muscle RING finger protein-1 mRNA abundance, with CON steers having increased (P = 0.09) abundance compared with that of IMP steers. These findings suggest that cattle breed type and anabolic implants impact calpastatin expression and mRNA abundance associated with protein turnover in the LT of feedlot steers 2 and 10 d post-implantation.