|ZIMMERMAN, MADELINE - UNIVERSITY OF NEBRASKA|
|SPANGLER, MATTHEW - UNIVERSITY OF NEBRASKA|
|Thallman, Richard - Mark|
|LEWIS, RONALD - UNIVERSITY OF NEBRASKA|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2019
Publication Date: 3/10/2019
Citation: Zimmerman, M.J., Kuehn, L.A., Spangler, M.L., Thallman, R.M., Snelling, W.M., Lewis, R.M. 2019. Comparison of different functions to describe growth from weaning to maturity in crossbred beef cattle. Journal of Animal Science. 97(4):1523-1533. https://doi.org/10.1093/jas/skz045.
Interpretive Summary: Selection for high growth rates in beef cattle over the past 40 years has resulted in a correlated increase in cow mature weights. Larger cows require more feed to maintain which can reduce profitability. Obtaining an accurate mature weight can be difficult and measurement at opportune times can be difficult. This study evaluated several functions to model growth from weaning through 6 years of age to determine which could accurately estimate mature weight at 6 years of age using cattle from the USDA, ARS, U. S. Meat Animal Research Center. The Brody function, an exponential curve with an asymptotic maximum weight over time, was found to produce the most consistent estimates of mature weight. This function could be applied to cow weights in industry cow herds to develop a consistent mature weight estimate.
Technical Abstract: Cow mature weight (MWT) has increased in the past 30 yr. Larger cows cost more to maintain, but their efficiency—and thus profitability—depends on the production environment. Incorporating MWT effectively into selection and mating decisions requires understanding of growth to maturity. The objective of this study was to describe growth to maturity in crossbred beef cattle using Brody, spline, and quadratic functions. Parameter estimates utilized data on crossbred cows from cycle VII and continuous sampling phases of the Germplasm Evaluation Program at the U.S. Meat Animal Research Center. The MWT were estimated at 6 yr from the fitted parameters obtained from the Brody (BMWT), spline (SMWT), and quadratic (QMWT) functions. These were defined as BMWT, SMWT, and QMWT for the Brody, spline, and quadratic functions, respectively. Key parameters from the Brody function were BMWT and maturing constant. The spline was fitted as piecewise linear where the two linear functions joined at a knot. Key parameters were knot position and SMWT. For the quadratic model, the main parameter considered was QMWT. Data were scaled for fitting such that 180 d was the y-intercept with the average weight at 180 d (214.3 kg) subtracted from all weights. Weights were re-expressed by adding 214.3 kg after analysis. Once data were edited, with outliers removed, there were parameter estimates for 5,156, 5,041, and 4,905 cows for the Brody, spline, and quadratic functions, respectively. The average maturing constant (SD) was 0.0023 d-1 (0.0008 d-1). The mean MWT estimates (SD) from the Brody, spline, and quadratic functions were 650.0 kg (64.0 kg), 707.3 kg (79.8 kg), and 597.8 kg (116.7 kg), respectively. The spline function had the highest average R2 value when fit to individual cows’ data. However, the Brody function produced more consistent MWT estimates regardless of the timeframe of data available and produced the fewest extreme MWT. For the spline and quadratic functions, weights through 4 and 5 yr of age, respectively, were needed before consistent estimates of MWT were obtained. Of the three functions fitted, the Brody was best suited for estimating MWT at a later age in crossbred beef cattle.