208 MicroRNA Expression in Longissimus Muscle Biopsies During Feedlot Finishing of Angus Steers

Intramuscular fat or marbling (IMF) is highly desired in beef products due to its ability to improve carcass value. Studies indicate that finishing cattle on high concentrate diets increase marbling deposition over time-on-feed (TOF). Angus-cross steers (n = 7; 433 + 17 kg) were individually fed a high concentrate diet for a period of 124 d. Steers were weighed and ultrasounded every 30 d on feed. Longissimus muscle biopsies were taken between the 11th and 13th rib on alternating sides at d 0, 90, and 124. RNA was extracted from the biopsy samples and subjected to microRNA (miRNA) sequencing and qPCR for mRNA expression of key lipogenic genes. Data were analyzed with time-on-feed in the model. ADG was increased between d30 and d90 (P < 0.05). The feed conversion ratio was lowest during d0 to d60 and increased from d90 to d124 (P < 0.05). Fat thickness increased (P < 0.05) between 90 to 124 d. Ultrasound intramuscular fat percentage increased (P < 0.05) between 60 and 90 d. miRNA sequencing results showed that mir-122 was differentially expressed from d0 to d90 (6.72 log fold change; P = 0.0048) and from d0 to 124 (3.83 log fold change; P = 0.026). Several miRNA were down regulated (> 2 log fold change; P < 0.05) during TOF, which included miR-2411, -449a, -1197, -323, and -485. Relative expression of key lipogenic genes, stearoyl Co-A desaturase (SCD-1) and fatty acid synthase, were up-regulated (P < 0.05) between d90 and 124 d. These results show that miR-122 appears to be a novel miRNA associated with marbling deposition and lipid metabolism.

Gene Expression and Carcass Traits Are Different between Different Quality Grade Groups in Red-Faced Hereford Steers

Fat deposition is important to carcass value and some palatability characteristics. Carcasses with higher USDA quality grades produce more value for producers and processors in the US system and are more likely to have greater eating satisfaction. Using genomics to identify genes impacting marbling deposition provides insight into muscle biochemistry that may lead to ways to better predict fat deposition, especially marbling and thus quality grade. Hereford steers (16) were managed the same from birth through harvest after 270 days on feed. Samples were obtained for tenderness and transcriptome profiling. As expected, steaks from Choice carcasses had a lower shear force value than steaks from Select carcasses; however, steaks from Standard carcasses were not different from steaks from Choice carcasses. A significant number of differentially expressed (DE) genes was observed in the longissimus lumborum between Choice and Standard carcass RNA pools (1257 genes, p < 0.05), but not many DE genes were observed between Choice and Select RNA pools. Exploratory analysis of global muscle tissue transcriptome from Standard and Choice carcasses provided insight into muscle biochemistry, specifically the upregulation of extracellular matrix development and focal adhesion pathways and the downregulation of RNA processing and metabolism in Choice versus Standard. Additional research is needed to explore the function and timing of gene expression changes.

217 Young Scholar Presentation: The use of diverse cattle breeds to understand marbling development and growth

Wagyu cattle have been genetically selected to have superior marbling deposition compared with many other cattle breeds, including Angus. It was hypothesized that greater marbling deposition by Wagyu influenced cattle may be due to an additional wave of adipogenic gene expression compared with Angus cattle. The present study compared the expression of lipid metabolism genes within the longissimus muscle (LM) of Wagyu and Angus sired cattle at similar harvest endpoints: days on feed and age, or body weight (613 kg). Angus sired steers were sired by an Angus bull selected for marbling (T1), while Wagyu sired steers were sired by either a Wagyu bull selected for growth (T2 & T4) or marbling (T3 & T5), at the respective age or body weight endpoints. Cattle were weaned at 7 months of age, entered the feedlot 54 d later, and consumed the same growing (119 d) and finishing ration. Muscle biopsies were collected from the LM posterior to the 13th rib at approximately 7, 9, 11, 14, and 17 months of age (harvest) for T1, T2, and T3 cattle. Muscle biopsies for T4 and T5 cattle were collected when their body weight was similar to T1 cattle at the time of biopsy, approximately 241, 276, 400, 531, and 613 kg (harvest). The high marbling sired Wagyu steers (T3 &T5) had greater marbling scores and percent LM lipid compared with high growth Wagyu (T2 & T4) and Angus sired steers. Gene expression results from high marbling sired Wagyu steers (T3 &T5) demonstrated additional peaks of PPARδ mRNA expression, greater and earlier PPARγ mRNA expression, and greater or additional peaks of GPAM1, LPIN1, and HSL mRNA expression compared with high growth Wagyu (T2 & T4) and Angus sired steers.

The Effects of Age at Weaning and Length of Lipid Supplementation on Growth, Metabolites, and Marbling of Young Steers

The objective of this study was to determine how weaning age, days on supplements, and lipid supplementation affected the growth and marbling deposition of steers. Steers from a single sire were early weaned (n = 24) at 150 ± 11 days of age or traditionally weaned (n = 24) at 210 ± 11 days of age. Steers were assigned to control (n = 12/weaning group) or an isocaloric, isonitrogenous rumen by-pass lipid (RBL, n = 12/weaning group) for either 45 (n = 6/treatment) or 90 (n=6/treatment) days then harvested. Steer body weight (BW) was recorded on days −14 and −7, then BW and blood samples were collected on days 0, 22, 45, 66, and 90. The right rib section of each animal was collected for proximate analysis. Longissimus dorsi from RBL steers had increased lipids compared with control steers (3.6 ± 0.2 vs. 2.4 ± 0.2% on a wet basis; p < 0.0001). Steers fed for 90 days had greater (p = 0.02) concentrations of Longissimus dorsi lipid (3.3 ± 0.2%) than those fed for 45 days (2.7 ± 0.2%). There was a weaning age by treatment by days on feed interaction for intramuscular adipocyte diameter (p = 0.02) in which early weaned RBL fed for 90 days steers had an increased adipocyte diameter compared to the early weaned control fed for 90 and early weaned fed for 45 days steers with all other treatment groups as intermediates. Supplementation of RBL increased concentrations of C18:2, C20:4, and total fatty acids on days 45 and 90 (p ≤ 0.05). Data show that RBL supplementation increased the marbling content of the Longissimus dorsi. Furthermore, a longer period of supplementation resulted in increased adipose diameter.