| dc.description.abstract | The first objective was to estimate total internal fat in beef cattle based on a technique that measures kidney fat (uKFd) using real-time ultrasound (RTU). Data were obtained from 109 cattle from four studies, and animals were scanned 7 d preslaughter for uKFd and ultrasound backfat thickness. At slaughter carcass kidney fat depth (cKFd), KPH weight, and total internal fat were measured. The second objective was to characterize residual feed intake (RFI) in finishing cattle fed high grain diets and to examine the relationships with growth, ultrasound, carcass, non-carcass, and tenderness traits in two studies involving Santa Gertrudis (n = 114) steers, and Angus bulls (n = 16) and heifers (n = 16). In both experiments, RFI was calculated as the difference between actual DMI and predicted DMI.
Results for the first objective indicated that RTU can be used to estimate cKFd, KPH weight and total internal fat (IFAT). Prediction equations developed to predict IFAT had R2 that ranged from 0.65 to 0.97 (P < 0.05). Results for the second objective indicate that RFI was not correlated with ADG, but was positively correlated with DMI and feed conversion ratio. Carcass 12th-rib fat depth was positively correlated with RFI in Santa Gertudis steers, such that steers with low RFI were leaner than steers with high RFI. Residual feed intake was not correlated with carcass or non-carcass composition traits in Angus bulls and heifers. Marbling and tenderness traits were not associated with RFI. Results from these studies indicate that we are able to measure IFAT with RTU, and that beef cattle producers can utilize RFI to identify animals that are more efficient with minimal impacts on growth, carcass composition and tenderness. | en |
