Adjustment of the lactation curve of Holstein cows according to Wood's model

Abstract

The two objectives of this study were to adjust the lactation curves of Holstein cows in Tunisia and to study the factors of variation of the parameters of the latter. The adjustment was made according to the Wood model for the first 9 lactations. The data comes from 190,905 daily checks of the quantity of milk, fat (MG) and protein (MP), collected between 1995 and 2011 and distributed over 10 herds from 4 different production sectors. Wood's function was used to model the lactation curves by nonlinear regression. The highest “a”, MG and MP lactation curve parameters were recorded at the 3_rd, 4^th and 5^th lactation, unlike the “b” parameter. The “c” parameter and the highest persistence of the lactation curve were recorded in the 1^st lactation. For the parameters of the lactation curves and its traits (milk, fat and protein), they were all affected by the factors included in the analysis model, namely the sector, the herd, the interaction year of calving - calving season and lactation number.

Keywords: Daily checks, adjustment, Wood, lactation curve