A total of 1293 normal first lactation records 01 Holstein Friesian cows were
collected from two commercial dairy herds during the period from 2000 to 2003.
Genetic parameters and breeding values for productive. reproductive traits and
persistency of lactation were analyzed by using single·trait and two-trait animal model
analyses of each reproduction, persistency and age at first calving traits jointly with
milk yield. Traits studied were total milk yield (TMY. kg). 305·day milk yield (305-d MY,
kg). 70-day milk yield (70-d MY, kg). days in milk (DIM, days), calving interval (CI,
day). the days open (DO, day), age at first calving (AFC, month) and persistency of
milk yield (Per MY). Spearman rank correlations between EBVs for traits studied from
single-trait and two-trait analysis with milk yield were estimated. Unadjusted means of
AFC. DO, CI. Per MY, DIM, 70-d MY. 305-d MY and TMY were 27.7 month. 162.7.
430.2 days. 0.822 unit. 353.9 days, 1870. 5546 and 6733 kg. respectively. Therefore.
the Holstein dairy farming system can show high production performances under
adequate management with lower reproductive efficiency under production system of
commercial herds in Egypt. Estimates of heritability of AFC, DO. Ct. Per MY, DIM, 70-d MY. 305-d MY
and TMY were 0.19tO.07S. 0.11 ±0.064, O.12±O.066, O.08±0.OS2. 0.27±O.091
O.32±0.105, 0.34±0.107 and 0.28±0.139, respectively. using single-trait analysis.
Some minor differences were observed in heritabilities obtained from single versus
two-trait genetic. The genetic and phenotypic correlations between mitk yield traits (TMY, 305-
d MY and 70-d My) and fertility traits (CI and DO) showed to be medium to high
positive (undesirable) of Holstein Friesian cows under the commercial herds in Egypt.
The phenotypic correlations between age at first calving and each of DO and Ct were
negative (-0.19 and -0.35, respectively), however, the genetic correlations between
the same traits were positive (0. 74±0.1 9 and 0.85±0.18, respectively). The phenotypic
correlation between age at first calving and persistency of lactation was negative and
close to z.ero (-0.07), however, the genetic correlation between the same traits was
positive (0.12tO.20). The range of breeding values obtained from single-trait analysis of all
pedigree animals for AFC. DO and CI were 5.02 month, 99.71 and 105.38 days,
respectively. White, the range of sire breeding values were 4.86 month. 61.59 and
106.46 days, respectively. The percentage of number of sires (animals) which had
negative breeding value estimates (EBVs %) for reproductive traits and persistency of
lactation ranked differently between the two analyses. Higher standard deviations of
breeding values were obtained for two-trait than singte-trait analyses. indicated the
existence of more genetic variation among sires (animals) and hence increase the
possibility of sire selection for daughter fertility. Lower correlations (diHered from unity)
between breeding values estimated by singte-trait and the others by two-trait analysis