Selection of dairy goats by using lactation curve model

摘要

Changes in daily milk yields during lactation, environmental factors influencing lactation, and possibilities for fitting lactation curve with a non-linear model were investigated in 259 lactations in 120 dairy goats of local population (Saanen type), during a period of 3 years (1993-95). In the first two years (1993-94), milk controls were taken by using the A4 method for 7 months, beginning after the suckling period (60 days). In 1995, a control system began at 10 days after kidding, every 10 days during 9 months. Four non-linear models of lactation curves were fitted (Wood's model, the model of Cobby & Le Du, 4 parameters Morant and two phases function), by the quasi Newton algorithm. The best fit was obtained by the Wood equation (R~2 = 89.429), while the Morant, the Cobby & Le Du and the two phases function models achieved R~2 = 83.263 percent, 76.715 percent and 20.754 percent, respectively. The highest daily milk yield (994.18kg) was recorded 136.82 days after parturition, and the persistency index was S = 15.23. The influence of the year and parity was highly significant (p<0.01) with regard to the level of production, represented by the scalar values of parameter a in the Wood equation. The other two parameters were not significantly (p>0.05) influenced by environmental factors.