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Describing growth pattern of Brakmas cows using non-linear regression models

Mohd. Hafiz, A.W.¹*, Mohamad Hifzan, R.², Izuan Bahtiar, A.J.² and Ariff, O.M.³

¹Animal Science Research, MARDI Muadzam Shah, 26700 Muadzam Shah, Pahang
²Animal Science Research, MARDI Kluang, 86009, Kluang, Johor
³Faculty of Veterinary Medicine, Universiti Putra Malaysia, 43400 Serdang, Selangor

Malaysian J. Anim. Sci. 2015 18(2): 37-45

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The objective of this study was to evaluate the best fit non-linear regression model to describe the growth pattern of Brakmas cows. Estimates of asymptotic mature weight, rate of maturing and constant of integration were derived from Brody, von Bertalanffy, Gompertz and Logistic models which were fitted to cross-sectional data of body weight taken from 279 Brakmas cows raised in MARDI Muadzam Shah. Coefficient of determination (R2) and residual mean squares (MSE) were used to determine the best fit model in describing the growth pattern of Brakmas cows. Logistic model was the best model among the four growth functions evaluated to determine the mature weight of Brakmas cattle as shown by the highest R2 and lowest MSE values (0.973 and 1037.4, respectively), followed by Gompertz (0.973 and 1050.4, respectively), von Bertalanffy(0.972 and 1067.1, respectively) and Brody (0.912 and 1037.4, respectively) models. The correlation between rate of maturing and mature weight was found to be negative in the range of -0.528 to -0.874 for all models, indicating that animals of heavier mature weight had lower rate of maturing. The use of non-linear model could summarize the weight-age relationship into several biologically interpreted parameters compared to the entire lifespan weight-age data points that are difficult to interpret.