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Control charts to monitor growth in dairy heifers.

P. Turiello



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Control charts to monitor growth in dairy heifers.
P. Turiello*1, B. Mancilla1, C. Vissio1,2, A. Larriestra1. 1UNRC R�o Cuarto, C�rdoba, Argentina, 2IDAS UNRC-CONICET R�o Cuarto, C�rdoba, Argentina.

There is a need to monitor processes in dairy systems, and there are methods of statistical quality control, like control charts, to effectively do it. Although widely applied in manufacturing industry, control charts have not been much used in animal growth processes. The objective of this study was to build a control chart application as a management tool in a commercial dairy for monitoring and surveillance of the growing process of replacement heifers. Control charts were built from BW data of 295 9-mo old heifers born during the years 2016 to 2018 in a commercial dairy farm in C�rdoba province. During the first phase we built the control charts for X-bar and R from 30 samples of 10 heifers each, following the instructions of Montgomery (2005). The center line of the X-bar chart was the average of the sample means (260 kg), and the upper and lower control limits (UCL and LCL, respectively) were calculated with the average of the sample means, the mean range and a constant A2 (UCL = X-bar-bar + A2 x R-bar; LCL = X-bar-bar - A2 x R-bar). For the R chart, the center line was the average of the sample ranges (70 kg), and the UCL and LCL were the average of the sample ranges multiplied by a different constant for each (UCL = D4 x R-bar; LCL = D3 x R-bar). The constants A2, D4 and D3 are tabulated values for different sample sizes. Control charts were built and 5 samples out of control were removed after finding assignable causes. From the final graphs the dairy manager can add future sample results and determine that the process is under control if its average is between 238 and 281 kg and the range is between 16 and 124 kg. If the contrary happens the manager can suspect that an assignable cause has occurred, and some investigation should be made and corrective action should be taken to remove the unusual source of variability. These control charts could be used to monitor the growing process of the heifers in the evaluated farm, to detect when some changes are required to take the process back to an in-control state thus reducing the process variability, and to estimate heifer weight among other process variables.

Keywords: quality control, management, replacement program.