الفهرس 
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Abstract
SUMMARY
Evaluation of milk production and some reproduction traits for cows
of Egyptian commercial dairy herds was done once under a crossbreeding
system using Holstein and Friesian cattle in three herds raised in Upper-,
Mid- and Lower-Egypt (Fayoum, Giza and Gharbia Governorates,
respectively) and another time under purebreeding system in a Holstein
herd raised in EI-Salhia, East of Delta. The first 90 day-, 305 day- and
total milk yield (M90, M305 and TMY, respectively) along with
M305/day of calving interval and TMY/day of calving interval (MCIl and
MCI2) were taken as milk yield traits (MYT) and when adding lactation
period (LP) and dry period (DP) all were refered to as lactation traits (LT).
Age at first calving (Ae l),age at second calving (AC2) and calving
interval (CI) were considered as reproductive traits (RT). Data of 5460,
1750 and 829 normal lactations from Fayoum, Gharbia and Giza crossing
trials, respectively were analysed separately by adopting the least squares
analysis of variance procedures. The models adopted penni ted to derive a
selected set of linear contrasts to obtain estimates of GI, aM ~aP, HI, HM~
HP and R1 for the traits of the study. Records of 5662 normal lactations
produced by 1029 cows were analysed by a single trait Animal Model to
estimate transmitting ability of cows, their dams and their sires for some
lactation traits (M90, M305, TMY and LP). The important results could be
summarized as follow:
5.1 Evaluation under crossbreeding system
Genetic group effect formed an important (P<O.05 or P<O.Ol or
P<O.OOI) source of variation in lactation traits (LT) in the three trials of
this study.
Individual, maternal and paternal additive effects (G’, GM and GP,
respectively) were generally positive, large and in favour of Holstein (H)
cattle, dams and sires for lactation traits (LT) except DP. Friesian (F)
cows, dams and sires were superior to H ones in their a’, GM and GP for
calving interval (they expressed shorter CI). Estimates of a1 and GP for
AC 1 and AC2 were in favour of F cows and sires in Upper-Egypt, while in
favour of Hcows and sires in Mid-Egypt and Lower-Egypt trials. Additive
maternity of H dams expressed earlier AC 1 and AC2 than that Fones.
Estimates of individual heterosis (H’) reveal that crossing F cows with
H bulls showed that crossbred cows relative to the average of purebred
parents, recorded lower milk yield traits (MYT) in the three trials, longer
LP and shorter DP in Upper-Egypt and Mid-Egypt trials, shorter Cl in
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Upper-Egypt trial and earlier AC I and AC2 in Lower-Egypt and Mid-
Egypt trials. Estimates of maternal heterosis (HM) reveal that crossbred
dams, relative to purebred dams improved the performance of their
daughters for milk yield traits (MYT) in Lower-Egypt trial, for LP and DP
in Lower-Egypt and Mid-Egypt trials, for CI in Upper-Egypt and Lower-
Egypt trials and for both AC J and AC2 in Upper-Egypt trial. Estimates of
paternal heterosis (HP
) indicate that crossbred sires relative to purebred
ones, have generally deteriorated the performance of their daughters
through reducing milk yield traits (MYT) in the three trials, reducing LP
and increasing DP in Mid-Egypt and Lower-Egypt trials and increasing CI
in the three trials.
Recombination effects were negative (P<0.05 or P<O.OOl) on milk
yield traits (MYT) in the three trials, positive (P<0.05) on LP in Mid-
Egypt and Lower Egypt-trials, negative (P<0.05) on DP in the previous
two trials and negative on AC I, AC2 and CI in Upper-Egypt and Mid-
Egypt trials.
5.2 Evaluation under purebreeding system using Holstein cattle
M90, M305, TMY and LP were significantly (P<O.OOl) affected by
the sire which contributed 4.7, 4.7, 5.0 and 2.1 % of the variance of these
traits, respectively. Sire heritability estimates were moderate (0.186 -
0.2000) for milk yield traits (MYT) and low (0.086) for LP.
The cow was found to have a significant (P<O.OOl) on all these traits
and contributed 38.8, 40.2, 41.2 and 14.6 % of the variance of these traits,
in the same order. Repeatability estimates were moderate or slightly high
(0.388 - 0.417) for milk yield traits (MYT) and low (0.146) for LP.
Transmitting ability values (TA) were estimated for cows (CTA)
using their own records, in addition to estimating those of their dams
COTA) and sires CSTA) without using their own records. Ranges of CTA
estimates for M90, M305, TMY and LP were 321 kg, 1087 kg, 1388 kg
and 14.1 days, respectively. The corresponding ranges were 182 kg, 600
kg, 801 kg and 6.7 days for DTA and 208 kg, 702 kg, 851 kg and 8.5 days
for STA. The ranges of CTA were 143 kg, 493 kg, 673 kg and 4.5 days
for the top 30 % cows; 80 kg; 263 kg, 805 kg and 2.6 days for 30% of the
top dams and 63 kg, 200 kg, 216 kg and 1.8 days for the top 10 % sires.
The percentages of cows, their dams and their sires that had positive TA
for lactation traits in the same order were 47.9,47.3,47.5 and 54.3 % for
eTA, 46.3, 46.4,45.7 and 53.3 % for DTA and 50.4, 52.5, 50.4 and 51.8
% forSTA.