Association of real-time ultrasound fat thickness and ribeye area to carcass measurements and changes over time in feedlot cattle

Abstract

Ultrasonography technology has been applied to livestock production and can be used to estimate carcass characteristics that were once only obtainable at slaughter. To be effective, these measurements must be accurate estimates of actual carcass composition. Animals (n=643) were evaluated for ultrasonic ribeye area (UREA) and backfat thickness (LJFAT) prior to slaughter. At slaughter, carcass ribeye area (CREA) and fat thickness (CFAT) were measured. UFAT was found to be correlated to CFAT (r = .89) while UREA was related to CREA (r = .80) at a lower level. The correlations between the ultrasonic measurements and the actual carcass data suggests that ultrasonography is an acceptable means of estimating carcass composition on a live animal. Using the ultrasound technology evaluated in experiment 1, four groups of feedlot steers were ultrasonically scanned at 28d intervals for 6 periods to determine growth of ribeye area (REA), fat thickness (FT), weight (Wt) and hip height (Ht). The steers were identified by breed as Hereford (H), Brahman (B), B x H Fl's, and H x B F I's. There was a significant breed effect for Wt, Ht and FT (P< .0 1), while period effect was significant (P< .0 1) for Wt, REA and FT. However, only Wt and FT had a significant (P< .001) breed x period interaction effect. This breed x period interaction indicates that the relative ranking within the four breed types did not remain consistent across periods. Consequently, FT can not be measured early in the growth phase as an accurate estimate of final FF at slaughter. There was no significant breed x period interaction for REA, thus REA can be measured at, any period and be useful in predicting ranking at a later date. However, it would be more accurate to measure REA later in the feeding period closer to slaughter. Fat was significantly different between breeds as animals with H dams deposited more fat than B dams. Purebred H had the highest Wt gain over the treatment period while the B x H retained their position as the heaviest Wt group throughout. For Ht, the H were significantly shorter than any of the other breeds.