Multiphasic Analysis of Milk and Fat Yield Curves of Israeli Holsteins

A multiphasic function was fitted to first through third-parity curves for milk and fat yields of Israeli Holsteins, grouped by yield and by days open classes. A triphasic function, the sum of three logistic functions, was fitted to milk yield curves, whereas a diphasic function, the sum of two logistic functions, was fitted to fat yield curves. For first parity milk, about 5% of yield occurred in first phase, about 25% in second phase, and about 70% in third phase. For first parity fat, about 14% of yield occurred in first phase and about 86% in second phase. Effect of yield was significant for initial, peak, and 305-d yields generally. Effect of days open generally was significant for time of peak yield and duration of each phase.