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 11^th and 13^th 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.