The growth of replacement heifers in dairy farms in Costa Rica. 1. Growth typing of Holstein and Jersey heifers.
The growth standard for replacement dairies from Costa Rica was calculated by fitting the average growth curves of the Holstein and Jersey breeds to six mathematical models, five of which were of the exponential type: Brody (Br) , Richards (Ri), Bertanlaffy (Be), Gompertz (Go), and Logistic (Log) and one intrinsically linear (Men), using least squares with the Marquart method. The real curves were obtained through the calculation of the mean weight for each week of age from 1 to 104, using 20,310 weight observations of 4,264 Holstein breed animals in 80 farms and 9,520 observations of 1,689 Jersey animals. in 51 farms, collected between 1988 and 1995 in three geographic zones of Costa Rica, corresponding to four life zones: humid forest (Bh), dry forest (Bs), very humid forest (Bmh), and rain forest (Bp). The selection of the model with the greatest potential was carried out by comparing five goodness-of-fit statistics. The mean prediction error (EMP), the standard deviation of the residuals (SD), the range of residuals (RA), the Dubin-Watson statistic (DW) and the coefficient of determination (R2). Once the best fit model was selected, the parameters of the growth curves were calculated for each life zone and year of birth group (1988-1991 and 1992-1995). The results of the adjustment of the models to the average curves showed that the six models have a high goodness of fit, with R2 values greater than 0.98, EMP values less than 6.7% and a maximum SD of 4.5 kg. showed great variation, ranging between 12 and 22 kg and between 0.38 and 2.32, respectively. The Br and Ri models proved to be the most efficient in describing the growth of both races. Satisfactory statistics were obtained in the calculation of the parameters of the curves by life zones and years of birth.
Copyright (c) 1997 Cesar Solano Patino, Bernardo Vargas-Leitón
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