Factors influencing the shape components of the lactation curves of Jersey crossbred cows

Abstract

Data on 33906 fortnightly test day milk of 1718 lactation records of Jersey crossbred cows maintained at the ICAR-National Dairy Research Institute, Kalyani, West Bengal were used to elucidate the effect of important environmental factors on lactation curve parameters and traits of Wood’s function. Lactation curve parameters viz. initial milk yield after calving (a); ascending slope up to peak yield (b); and descending slope after peak yield (c) and lactation curve traits viz. peak milk yield (Y_max), time of peak yield (N_max) and persistency (P) of Wood’s function were included for this study. The lactation curve parameters and traits of individual cow for each lactation were estimated using Incomplete gamma function by fitting Gauss–Newton algorithm as an iteration method. The overall least squares means for a, b, c, Y_max, N_max, and P were 9.07±0.21 kg, 0.340±0.017, 0.108±0.004, 11.22±0.18 kg, 39.45±1.58 days and 3.13±0.03, respectively. Periods of calving had significant (P<0.05) effect on all the lactation curve parameters and traits of animals. Seasons of calving significantly (P<0.01) affected the curve parameter ‘a’ and curve traits like Y_max, N_max and P of animals. Cows calved in summer seasons were poor persistent and peaked earlier than cows calved in winter and rainy seasons. Parity of cows had significant influence (P<0.01) on all lactation curve parameters and traits except the curve parameter ‘b’. Significant effects of different environmental factors on lactation curve parameters/traits indicate that these factors must be taken into consideration for improving the shape of lactation curve of Jersey crossbred population.