The aim of this study was to detect genetic and phenotypic trends for test-day (TD) milk, fat and protein
yields and age at first calving (AFC) in Frisian cattle in Egypt applying the random regression model (RRM).
Data of 5237 TD milk yield traits were recorded for 953 Friesian cows, daughters of 208 sires and 944 dams
from two herds in the Animal Production Institute (APRI), Egypt. Ten-month classes of lactation days were
considered for the TD yields. The model included the random effects of direct additi ve genetic, permanent
environment and error, while the fixed effects were herd-year-season of calving and parity, which was modeled
by Orthogonal Legendre Polynomials. The additive genetic variance at first TD for milk, fat, protein yields and
AFCwere4.7 kg, 13.3 g, 5.3 g and 2.8 monthrespectivelyand increased until the fourth, decreased until the
lowest value at the tenth TD for milk but fat and protein yields the lowest value at the ninth TD.The lowest value
of AFC was at the sixth TD then increased until the tenth TD. Heritability estimates at first TD were 0.12, 0.25,
0.25 and 0.05 for TDMY, TDFY, TDPY and AFC, respectively, and increased until the third for TDFY, TDPY
and AFC but TDMY trait reached the highest value at the fourth TD, then decreased at the tenth TD.But
reached the lowest value at sixth TD, and increased until the tenth TD. The phenotypic trendfor TDMY
decreased by 26 to 18 kg from the first to the fifth TD, then it increased until the tenth TD. The phenotypic trend
was started by 44 g and 18 g for fat and protein, respectively until the fourth TD then decreased until the ninth
TD. The genetic trends were slightly positive for all traits, indicating that the selection program p erforms
correctly. |
