Effects of Days Open and Days Dry on Lactation Milk and Fat Yields of Friesian Cows in Egypt

Abstract

A total of 2352 complete lactation records of Friesian cows, raised at Dalla farm which is 130 km from Cairo, Egypt, during the period from 1987 to 1992, were used to determine the effect of days open and days dry on milk and fat yields. A least squares analysis of variance was done for each trait using a model which included season and year of calving, parity, days open and days dry with possible interactions between year by season, year by parity and season by parity. The least squares analysis of variance showed the significant effects of all factors and probable interactions on 305-dMY and fat yield. Partial linear and quadratic regression coefficients showed an average increase of 4.05 and 0.158 kg of 305-dMY and fat yield. respectively, for each additional day open, and average decrease of 3.58 and 0.017 kg of 305-dMY and fat yield, respectively, for each additional day dry. Mixed model procedures were used to estimate variances and covariance. Heritabilities for 305-dMY, fat, days open and days dry were 0.223, 0.220, 0.018 and 0.067, respectively. Genetic correlations between different traits ranged from -0.129 to 0.958. Phenotypic correlations between different traits ranged from -0.122 to 0.660. A days' open length of 60-90 and dry period length of 60 days were suggested as optimal for attaining maximum lactation milk and fat yields for Friesian cows in Egypt.