Abstract

GARCIA-MUNIZ, José Guadalupe et al. Comparison of Equations to Fit Lactation Curves of Cattle.. Rev. Cient. (Maracaibo) [online]. 2008, vol.18, n.2, pp.160-169. ISSN 0798-2259.

The objective was to evaluate the goodness of fit of 16 equations to estimate lactation curves of six cattle genotypes. Monthly or weekly milk production records of Brown Swiss (n=826 lactations), Bos indicus (BI, n=52), ¾BI¼Bos taurus (BT, n=507), ½BI½BT (n=462), BIBT (n=167) and ¼BI¾BT (n=62) cows were analyzed. Fitting of equations to individual lactations was performed by linear or non-linear regression. The residual mean squares obtained after fitting of the equations were ranked within genotype and compared by Friedman’s test. Additional criteria to compare the equations were the proportion of cases of abnormal daily milk production, and cases with positive autocorrelation. Equations differed (P<0.05) on their suitability to properly describe lactation curves across genotypes. However, for all genotypes the equation of best fit (P<0.05) was a reparameterization of Wood’s equation in which the first test date is considered as time zero. The use of this equation is recommended to fit lactation curves of cattle genotypes such as the ones evaluated in this study.

Keywords : Lactation curves; milk production; brown swiss; Bos taurus; Bos indicus.