Growth curves, weight gain, and energy and protein requirements in Holstein Friesan and Hereford females

Abstract

In order to develop a mathematical model to describe and predict the growth and energy and protein requirements of Holstein Friesan (HF) and Hereford (H) breed animals, females of these two breeds were followed, under two conditions considered as typical for the central zone of Chile. The monthly body weights of 693 HF females, between 1 and 155 months of age and of 487 H females between 1 and 106 months of age were recorded. Different growth models were fitted to the data obtained, such as Brody, Von Bertalanffy, Gompertz, Richards and logistic. The best fit was that of a model of the type Y = α* (1-e^-kX) with an R² = 0.92 for HF and 0.96 for H, whose parameters are represented by the estimators for α, 620 and 415, and for k, -0.0514 and -0.077, respectively. The two curves can be estimated by a common β, but in different places within the coordinates, suggesting that animals born with a higher weight reached higher mature weights, at the respective ages of 66 and 44 months. Up to 6 months of age, the energy requirement for maintenance is more or less similar for both breeds, increasing from this age for HF, but if this requirement is expressed as a percentage of the total requirement, H cows spend a greater proportion on maintenance. The protein requirement shows a similar behavior to that of energy up to 20 months, and subsequently the maintenance protein requirement, expressed as a percentage of the total, is similar for both breeds.