|Hamlin Keith E, - TEXAS TECH UNIVERSITY|
|Green Ronnie D, - TEXAS TECH UNIVERSITY|
|Perkins T L, - TEXAS TECH UNIVERSITY|
|Miller M F, - TEXAS TECH UNIVERSITY|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 28, 1994
Publication Date: N/A
Interpretive Summary: Ultrasonic research has been an area of much interest in recent years. Almost all of the studies have had the objective of trying to determine the accuracy of various equipment and techniques for measurement of fat thick- ness and longissimus muscle area. These data indicate standardization equations needs to be developed separately for breeds or biological types for the effects of age and weight on ultrasound estimates of fat thickness and longissimus area. Additionally, regression models and exponential function models appear to equally describe relative growth of these measures. However, these same questions still need to be addressed in the area of standardization of measures obtained from immature breeding cattle (e.g., optimal measurement time and range). To allow implementation of ultrasound as a tool in national cattle evaluation programs, further research is needed in several areas. These include: (1) continued emphasis on enhancement and convenience of ultrasonic measurement of lean- ness and intramuscular fatness, (2) determining genetic components of ultrasonic measures in young breeding cattle, and (3) describing genotype by sex environment interactions for measures taken in breeding animals and their resulting slaughter progeny.
Technical Abstract: Serial ultrasonic measures of fat thickness (FTU) and longissimus muscle area (LMU) were taken on 180 feedlot steers representing 11 sire-breed groups at two 60-d intervals. Cattle then were slaughtered in four groups of 45 at 21-d intervals with ultrasonic measures taken at each interval. Analyses of variance indicated weight (WT) effects (P<.001) for all FTU measures and many of the LMU measures. Age was a source of variation (P< .05) for FTU and LMU over the first five measurement dates. Sire-breed (SLINE) effects (P<.001) were prevalent for all FTU estimates and early LMU predictions. Some DAM line and SLINE*DAM line interactions were detected (P<.1) for the FTU and LMU estimates. Age effects were de- scribed quadratically (P<.001) when FTU and LMU were regressed on age (R- squared = 47 and 68%, respectively). When FTU and LMU were regressed on WT, effects were described quadratically (P<.001) with R-squared values of 46 and 72%, respectively. Animals then were assigned to one of four bio- logical types (BT) based on percentage retail product (0 mm fat trim) us- ing discriminant cluster analysis. Within BT, ultrasonic variables were regressed on age. Quadratic effect (P<.01) were detected for both FTU and LMU. Ultrasonic measures were also affected (P < .001) by weight for all BT. These data indicate that WT, AGE and BT have an effect on ultrasonic estimates and illustrate the need for development of adjustment equations for between animal comparisons on a standard basis by biological type.