233 - Comparison of Intramuscular Fat Deposition in Different Muscles of Beef Cattle

Abstract: Two groups (light = 740 lbs and heavy = 942 lbs) of Akaushi cross steers (n = 20), were ultrasounded for carcass traits by an Ultrasound Guidelines Council Certified Technician every 28 days to quantify differences in intramuscular fat deposition occurring in three distinct muscles (longissimus dorsi, biceps femoris and semitendinosus). Cattle were fed at the West Texas A&M University Research Feedlot and scanned with an Aloka 500 ultrasound unit using Beef Image Analysis (BIA) Feedlot software from Designer Genes Technologies, Inc. (Harrison, AR). Carcass ultrasound measurements included 12-13^th rib ribeye area (REAU), subcutaneous fat thickness (FTU), intramuscular fat percentage along the longissimus dorsi (IMFULD), rump fat thickness (RFU) as well as intramuscular fat percentage of the biceps femoris (IMFUBF) and semitendinosus (IMFUST). A difference was detected in IMFULD for the duration of the study (P < 0.05). However, no differences occurred from day 0 to day 56 (P = 0.34), or from day 84 to day 140 (P = 0.17) for IMFULD. There was a slight numerical decrease (0.1505%) in IMFUBF from day 0 to day 56, with an increased difference from day 56 to day 84 (P < 0.05). There was a positive change from 4.113% to 5.728% in the heavy group (P = 0.08) and a change from 4.113% to 4.456% in the light group (P = 0.42) for IMFUBF. There was a significant change in IMFUST from day 56 to 84 (P < 0.05). Of note, there was a decrease in IMFULD, IMFUBF and IMFST from day 140 to day 168 which could be associated with adverse winter weather events. The data present a positive increase throughout all muscles studied for beef cattle while on feed, though weather events have the possibility to negatively affect gains more rapidly than progressive effects associated with feed and growth.