Abstract #521

# 521
Methods of estimating empty body composition, energy retention, and grading characteristics of calf-fed Holstein steers.
T. J. McEvers*1, N. D. May1, J. A. Reed1, L. J. Walter1, J. P. Hutcheson2, T. E. Lawrence1, 1West Texas A&M University Beef Carcass Research Center, Canyon, TX, 2Merck Animal Health, Summit, NJ.

A serial harvest trial investigating growth characteristics of calf-fed Holstein steers (n = 115; initial BW = 449.2 ± 19.9 kg) was conducted in 28 d intervals starting at 226 d on feed (DOF) and ending at 534 DOF. Five steers were slaughtered on d 226 and utilized as a point for growth modeling. Remaining cattle (110 steers) were randomly allocated to harvest endpoint (10 cattle per slaughter day; 254, 282, 310, 338, 366, 394, 422, 450, 478, 506, and 534 DOF) with one-half of each group receiving zilpaterol hydrochloride (ZH) for 20 d followed by a 3 d withdrawal. Shrunk BW (SBW, kg) and hot carcass weight (HCW, kg) were utilized to predict empty body weight, kg (EBW). Feeding performance {dry matter intake (DMI, kg), net energy for gain, (NEG, Mcal/kg of diet dry matter), and ZH supplementation} variables were utilized to estimate EBW and empty body fat (EBF, %). For prediction of HCW, a 2 variable equation was developed with an R2 of 0.946 (P < 0.01) and root mean square error (RMSE) of 20.13 {HCW = −41.44 + (0.6637 × SBW) + (12.974 × ZH); 1 = 20-d supplementation, 0 = 0-d supplementation}. For prediction of EBW, an equation with an R2 of 0.942 (P < 0.01) and RMSE of 29.9 was developed {EBW = 57.6232 + (1.39280 × HCW) – (11.0994 × ZH)}. Utilizing feeding performance data, a model with an R2 of 0.919 (P < 0.01) and RMSE of 35.2 was developed for prediction of EBW {EBW = −1547.34 + (1.19 × DOF) + (21.13 × DMI) + (1005.73 × NEG) + (18.87 × ZH)}. To predict EBF using feeding performance variables, a 4 variable equation was developed with an R2 of 0.621 (P < 0.01) and RMSE of 2.9 {EBF = 0.7769 + (0.0003 × DOF) + (0.0046 × DMI) – (0.4346 × NEG) – (0.0167 × ZH)}. Several variables available to calf-fed Holstein producers may be implicated for use in predictive models related to finishing performance and composition of gain for calf-fed Holstein steers.

Key Words: Holstein, body composition, carcass characteristics

Speaker Bio
I am currently an Assitant Professor of Animal Science at West Texas A&M University in Canyon.  I enjoy conducting research based on growth and development dynamics of fed cattle and how those may relate to the beef supply chain.  I live near Amarillo Texas with my wife of 9 years and my 4 year old daughter.