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The use of Bioelectrical Impedance Analysis to predict carcass composition in calf-fed Holstein steers
The beef industry relies heavily upon subjective evaluation of beef carcasses to quantify carcass composition. Bioelectrical Impedance Analysis may offer the ability to objectively quantify carcass composition in a rapid, repeatable manner and more accurately determine composition of cattle fed growth promotants. Thus, bioelectrical impedance analysis was utilized to estimate the percentage of salable red meat yield (SRMY), fat trim (FT), and bone (BONE) within Holstein (n = 110) carcasses supplemented zilpaterol hydrochloride (ZH) or not supplemented (CON). Following a 36-h chilling period, bioelectrical impedance analysis was conducted by placing source and detector electrodes in the semimembranosus muscle posterior to the aitch bone and in the intercostal muscles between the 1st and 3rd ribs to attain measures of electrical resistance (Rs) and electrical reactance (Xc). Additional measurements of hot carcass weight (HCW), carcass temperature (TEMP), electrode gap (EGAP) were collected to calculate measurements of impedance (I), resistive density (RsD), reactive density (XcD), resistive volume (RsVOL) and reactive volume (XcVOL). Upon completion of measurements, carcasses were subsequently fabricated into subprimal yield components reflective of industry standards (max. fat depth ≤ 6mm). Dependent variables of SRMY (52.26 to 67.72 %), FAT (10.39 to 29.35%) and BONE (12.03 to 23.11%) were used in multiple linear regression equations. Estimates were calculated via STEPWISE regression methods in SAS (SAS 9.3, SAS Institute, Cary, NC). Predictive models for FT included variables of XcD, TEMP, RsD and EGAP accounted for 72 and 81 percent (R² = 0.72 and 0.81) of the variation in CON and ZH cattle, respectively. Moreover, predictive models for BONE included variables of Xc and HCW accounted for 43 and 58 percent (R² = 0.43 and 0.58) of the variation in CON and ZH cattle. Percentage of SRMY used variables RsD and XcD and accounted for 54 and 70 percent (R² = 0.54 and 0.70) of the variation in CON and ZH cattle respectively. These results suggest that bioelectrical impedance analysis may serve as a reliable objective measure of carcass composition for concentrate fed Holstein steers.
Keywords: Holstein, impedance, composition