LACTATION CURVES OF MILK, FAT AND PROTEIN IN EGYPTIAN BUFFALO USING TEST-DAY MODEL

Data on 4971 test-day milk yield traits [milk (TDMY), fat (TDFY) and protein (TDPY)] for 691 Egyptian buffalo cows, daughters of 120 sires and 532 dams were used for fitting the lactation curve parameters of milk, fat and protein yields using multiple-trait animal model. The random effects included in the model were direct additive genetic, permanent environment and error, while the fixed effects were herd test-day, year and season of calving and parity as well as days in milk as a covariable. The means for TDMY, TDFY, TDPY and lactation curve parameters [initial (a), ascending slope (b), descending slope (c), persistency (P), and maximum milk production during lactation (Ymax) and the peak test-day (PY)] were estimated. Heritabilities of TDMY, a, b, c, P, PY and Ymax were 0.22, 0.37, 0.38, 0.39, 0.37, 0.37 and 0.38, respectively. The corresponding heritabilities for TDFY and fat curve parameters were 0.21, 0.41, 0.40, 0.39, 0.38, 0.36 and 0.42, while the estimates for TDPY and protein curve parameters were 0.22, 0.38, 0.40, 0.40, 0.38, 0.40 and 0.43, respectively. Genetic correlations among TDMY and curve parameters of a, b, c, P, PY and Ymax were 0.31, -0.23, -0.34, 0.52, 0.48 and 0.87, respectively. Genetic and phenotypic correlations between milk yield traits were high (mostly of 0.83 and 0.99), like the correlations between curve parameter in milk, fat and protein (from 0.71 to 0.96). In practice, genetic selection for lactation curve parameters (a, P and Ymax) in the Egyptian buffalo would improve total milk yield traits.