Genetic and phenotypic trends for test day milk, fat and protin yields applying random regression model in Egyptian buffaloes

الملخص EN

The aim of this study was to detect genetic and phenotypic trends for test day milk, fat and protein yields in Egyptian buffalo applying the random regression model (RRM) and determining the genetic and phenotypic trend.

Data of 4971 test days (TD) milk yield traits were recorded for 691 Egyptian buffalo cows, daughters of 120 sires and 532 dams from four herds belonging to the Animal Production Research Institute, Egypt.

Ten-month classes of lactation days were considered for the test-day yields.

The model included the random effects of 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, which was modeled by orthogonal Legendre polynomials.

The additive genetic variance estimates at first test day for milk, fat and protein yields were respectively 0.035kg, 2.26g, 0.80g, increased until the fourth (0.807kg, 30.52g, 12.52g), decreased thereafter, reaching the lowest value at the ninth test day for milk and protein yields (0.238kg, 0.97g) and at the tenth test day for fat yield (7.28g).Heritability estimated at first test day was 0.05, increased until the fourth test day (0.30), and decreased thereafter and reached the lowest value at the tenth test day (0.06).

The highest heritabilities were found to be 0.29 and 0.31 for fourth test day in fat and protein yields, respectively.

The range in phenotypic values change decreased from 7.99 to 5.66kg, 53.37 to 35.07g and 30.86 to 21.54g, while the respective genetic values change increased from -0.22 to 0.17kg, -1.41 to 1.36g and -0.82 to 0.70g for milk, fat and protein yields, respectively.

The genetic trends were slightly positive for all traits indicating that the selection program performs correctly.

For all traits, the phenotypic trends showing deteriorating trends indicating the presence of some environmental inadequacies especially for nutritional level