Algebraic models of the lactation curve in Sahiwal, Frieswal and other grades of Friesian cattle*

Abstract

Comparative efficiency of inverse polynomial and gamma type algebraic models of the lactation curve were studied to estimate milk production trends during a lactation on 487 records ofSahiwal, Frieswal and other grades of Friesian cattle extending over 14 years (1980-1993). Principles of least squares analysis were used to solve the equations. The slope of ascending phase was steeper than the descending phase indicating high rate of increase in milk yield in ascending phase in all the genetic groups. The inverse polynomial and gamma type models estimated an initial ascending phase followed by a peak and then a descending phase with the advancement of the lactation. The inverse polynomial was marginally superior to gamma type and considered as model of choice for individual lactation curve (R²>98%) in all the genetic groups. The gamma type function estimated the lactation curves most efficiently in Sahiwal and crossbred.