الفهرس 
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Abstract
6. SUMMARY
Cow productivity of three dairy cattle breeds (Friesian, FR, Holstein
Friesian, HF and Brown Swiss, BS) was analysed in three commercial private
farms located at Mashal (in El-Gharbia Governorate), ’Kombera (in EI-Giza Governorate)
and at El-Azizia (in El-Fayoum Governorate). These three farms
belon~ to the General Cooperative of Developing Animal Wealth and Products in
Egypt. FR were raised in the three farms, while HF and BS In EI-Azizia and
Komhera farms, respectively.
Records of ~267. 201 and 251 normal lactations of FR, HF and BS cows,
respectively were used. These records covered the period from 1982 to 1989
for FR and BS while from 1987 to 1990 for HF.
Milk production traits under study represented by initial milk yield
(IMY), 305-day milk yield (305MY), total milk yield (TMY), length of lactation
period (LP) and length of dry period (DP), while reproductive traits
represented by age at first calving (AFC), length of days open (DO) and
length of calving interval (CI). All these traits except AFC were considered
in the study for each of the first and second lactation for FR, HF and BS
cattle and across all lactations for FR cattle only because of the small size
of the data of the other two breed groups. Age at first calving was studied
for FR cattle because of the small numbers of cows available for HF and BS
cattle. Correction factors for FR cattle were derived to adjust milk yield
traits for the effects of each of age at calving, DO and preceding CT. Cow
within herd effects and repeatabilities of all traits were also estimated.
~ji~production traits of first and second lactations in FR, HF and BS cattle
Avera~es in the first lactation for IMY (kg), 305MY (kg), TMY (kg), LP
(days) and DP (days), respectively were 1335, 3789, 4185, 345 and 61 for FR
cattle; 2230, 6120, 6780, 364 and 52 for HF cattle and 1347. 3957, 4223, 339
and 68 for BS cattle. The corresponding averages of the second lactation were
1641, 4076. 4389, 334 and 64 for PH cattle; 2381. 5989. 6347. 337 and 54 for
HF cattle and 1740. 4595. 4845, 326 and 73 for BS cattle.
Ilerd effects were generally significant (P<0.05 or P<O.Ol or P<O.OOl) on
all milk production traits of FR cattle in the first and second lactations
(IMY, 305MY. TMY, LP and DP). The highest .ilk yield was generally recorded
by cows of EI-Azizia herd in the first lactation, while by those of Mashal
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herd in the second lactation. EI-Azizia herd showed the shortest DP in both
the first and second lactations. Source of cow constitutedt in generalt a
si~nificant (P<O.05 or P<O.Ol or P<O.OOl) source of variation in 305MY and
TMY of FR cattle in both the first and second lactations, but non-significant
one in LP and DP of cows of same breed. Imported FR cows produced hi~her milk
yield and longer LP than locally born ones in both lactations. All milk yield
I traits lIMY, 305MY and TMY) varied significantly (P<O.OOl) with year of calving
in each of the first and second lactations in FR cattle. The same observation
(P<O.Ol or P<O.OOl) was detected in the first lactation of HF and BS
cattle. Milk yield traits, in generalt were significantly (P<O.05 or P<O.Ol
or P<O,OOl) affected by season of calving in the first lactation of FR and HF
cattle. At least two milk yield traits in both lactations were at their maximum
level when calvings occured in spring for the same two breeds. At least
two of the milk yield traits were significantly (P<O.05 or P<O.001) influenced
by DO in FR cattle in the first and second lactations. Similarly, significant
(P<O.05 or P<O.OOl) effects for DO were observed on TMY of the first
lactation in both HF and BS. LP of either the first or the second lactation
in the three breeds of the study varied significantly (P<O.OOl) with the
change of DO. There was a curvilinear relationship between days open and
305MY in the first and second lactations. Partial linear and quadratic
regression coefficients of IMYt 305MY and TMY on age at calving were significant
(P<O.OOl) for the first lactation in FR cattle and showed curvilinear
relationships between age at calving and these traits. The interaction
effects between season of calving and each of herd of the cOWt source of cow
and year of calving on milk yield traits of the first and second lactations
of FR cattle were mostly significant (P<O.05 or P<O.Ol or P<O.OOl).
Milk production traits across all lactations in Fa cattle
The averages of IMYt 305NY and TMY were 1588, 4071 and 4398 kg, respectively
and those of LP and DP were 336 and 64 days, respectively. Herd
effects constituted a significant (P<O.05 or P<O.Ol or P<O.OOl) source of
variation in all milk production traits (IMY, 305MY, TMY”, LP and DP). Cows of
Mashal herd recorded the highest 305MY and TMY when co.pared with those of
the other two herds while EI-Azizia herd recorded the shortest DP. IMY, 305MY
and TMY were significantly (P<O.01 or P<O.OOl) affected by source of cow but
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the reverse was true when considering LP and DP. Locally-born cows were
heavier in milk production than imported ones. IMY, 305MY and TMY varied significantly
(p<0.05 or P<O.Ol or p<O.OOl) with the change of year or season of
calving. Spring calvers recorded the heaviest IMY, 305MY and TMY, the longest
LP and shortest DP when compared with those calved in other seasons of the
year. Days open affected 305MY, TMY, LP and DP significantly (P<0.001) and
presented a curvilinear relationship with each of 305MY, LP and DP. IMY,
305MY, TMY and LP increased significantly (p<0.05 or P<O.01 or P<O.001) as
parity advanced from the first to the fourth. Partial linear and Quadratic
regressions of IMY, 305MY, TMY and LP on age at calving were significant
(p<O.05 or P<O.OOl). The interaction between season of calving and each of
herd, parity and year of calving was significant (p<0.05 or p<0.01 or
p<O.OOl) on all milk yield traits. All milk production traits were significantly
(P<O.05 or p<O.01 or P<O.001) affected by preceding dry period. A curvilinear
relationship between preceding dry period (PDP) and each of IMY,
305MY and LP was detected. Preceding calving interval (PCI) constituted a
si~nificant (P<O.05 or p<O.Ol or p<O.001) source of variation in 305MY, TMY,
LP and DP since a curvilinear relationship with TMY was only detected.
Repr:oductive.intervals of_the 1st and 2nd lactations in FR, HF and BS
The average age at first calving for FR cows of the present study was
27.8 months. Herd, source of cow, year of birth, season of birth and the
interaction between herd and source of cows did not exert any significant
effect on AFC.
The averages of DO and CI~ respectively in FR cattle were 126.8 and 407.9
days for the first lactation as well as 117.5 and 398.5 days for the second
lactation. Averages of CI in the first and second lactationst respectively
were 417 and 392 days in HF and 406 and 401 in BS cattle. Shorter DO and CT
in the second lactation than in the first one was observed. Differences in DO
of FR cattle of either the first or the second lactation due to herd effects
were si~nificant (P<O.Ol or P<O.OOl) and in favour of Ko.bera herd in the
first lactation and Mashal herd in the second lactation. Source of cow
exerted significant (P<O.Ol) effect on DO of the first lactation which was in
favour of locally born cows which recorded shorter DO. Effects of year of
calving was significant on DO of the first and second lactations but non-