پديد آورندگان :
محمدي پور سعادت آبادي، ليلا دانشگاه شهيد باهنر كرمان - دانشكده كشاورزي - بخش مهندسي علوم دامي , اسدي فوزي، مسعود دانشگاه شهيد باهنر كرمان - دانشكده كشاورزي - بخش مهندسي علوم دامي , آيت الهي مهرجردي، احمد دانشگاه شهيد باهنر كرمان - دانشكده كشاورزي - بخش مهندسي علوم دامي
كليدواژه :
آناليز ژنتيكي , گاوهاي هلشتاين , ميزان توليد شير , اثر متقابل ژنوتيپ و محيط
چكيده فارسي :
زمينه مطالعاتي: براي افزايش دقت برآورد پارامتر‌هاي ژنتيكي صفات، انتخاب مدل مناسب براي آناليز ژنتيكي آنها مهم مي‌با‌‌‌شد. هدف: اين تحقيق به منظور بررسي اهميت اثر متقابل ژنوتيپ و محيط بر تجزيه ژنتيكي ميزان توليد شير گاوهاي هلشتاين انجام گرديد. روش كار: در اين مطالعه از 90315 ركورد توليد شير اولين دوره شيردهي اين گاوهاي شيري استفاده شد. اين داده ها طي سالهاي ۱۳۷5تا ۱۳87 توسط مركز اصلاح نژاد دام و بهبود توليدات دامي كشور جمع آوري شده اند كه مربوط به 19 استان مختلف، 188 گله، 145 پدر و 72857 مادر مي‌باشند. داده هاي اين تحقيق با استفاده از روش اثر متقابل و در قالب مدل حيواني آناليز شدند. نتايج: در اين تحقيق اثرات متقابل پدر و استان، پدر و گله، پدر و سال تولد و پدر و سال زايش بر آناليز ژنتيكي صفت توليد شير معني دار بود (P<0.05). البته در مقايسه با ساير اثرات متقابل، اثرمتقابل پدر و گله بر آناليز ژنتيكي ميزان توليد شير بيشتر بود. همچنين مقادير يكساني براي وراثت پذيري توليد شير دو بار دوشش (۲۸/۰۱±۰/۰) و وزن معادل بلوغ (۲۷/۰۱±۰/۰) در زمان لحاظ و عدم لحاظ اثر متقابل پدر و گله در مدل برآورد شد چون لحاظ كردن اثر متقابل ژنوتيپ و محيط در مدل موجب كاهش هر دو واريانس ژنتيكي افزايشي و خطاي آزمايش بطور مشابه گرديد. همبستگي بين ارزش اصلاحي گاوهاي نر برآورد شده توسط مدل داري اثر متقابل ژنوتيپ و محيط و مدل فاقد اثر متقابل ژنوتيپ و محيط ۰/۹۹ محاسبه گرديد. نتيجه گيري نهايي: نتايج حاصل از اين تحقيق نشان مي‌دهد لحاظ كردن اثر متقابل ژنوتيپ و محيط در زماني كه گله، استان، سال تولد و يا سال زايش براي تعريف محيط استفاده مي‌شوند در ارزيابي ژنتيكي گاوهاي نر براي ميزان توليد شير اثر مهمي ندارد.
چكيده لاتين :
Introduction:
Efficiency of a breeding program affected by accuracy of genetic parameters and
appropriate genetic model analysis is important to increase the accuracy of estimated genetic
parameters.
In an appropriate model all significant fixed and random effects are
included. Previous
studies show that genotype by environment interaction is an important random effect for genetic
analysis of milk production in dairy cattle. Changes in the relative performance of genotypes (sires)
across different environments play an i
mportant role in dairy production systems, especially in
countries relay on imported genetic material (sperms). Genotype by environment interaction arises
when the performance of the different genotypes is not equally influenced by the different
environmen
ts. Then, ignoring the interaction, can led to biased estimates of genetic parameters and
reduce the accuracy of selection by changing the ranking of the animals. Therefore, considering this
interaction in a model may improve genetic gain and selection acc
uracy.
This study was carried out
to investigate the effect of genotype by environment interaction in genetic analysis of milk yield of
Holstein dairy cows.
Materials and methods
:
In this research, 90315 records of first lactation
of the dairy cattle
we
re
used. The data were collected
from 1996 to 2008
by the Iranian center of Animal Breeding and
Animal Production Improvement
which are from
19 different provinces, 188 herds and originated
from 145 sires and 72857 dams.
The milk yield records were correct
ed for 2 times milking frequency
and mature body weight.
Genotype by environment interaction can only be identified, if at least two
different environments are considered. Environment can be defined as a unit, but also as a continuous
value of the environm
ent.
In this study, t
he sires were defined as different genotypes. Province, herd,
birth year and calving year were used as the criteria to define different environments.
Then sire by
province, sire by herd, sire by birth year and sire by calving year were considered as the genotype by
environment interaction effects. To investigate the importance of these effects on genetic analysis of
the milk yield, they were added to a
base model where only additive genetic effect was fitted as the
random effect. Log likelihood ratio test was used for the model comparison. Univariate animal model
was used for analyzing the
both dataset including t
he milk yield records corrected for 2 tim
es milking
frequency and for mature body weight. R
esults and discussion
:
In this research,
log likelihood
value
of the base model
for genetic analysis
of the milk yield corrected for 2 times milking frequency and for mature body weight
was
significantly
improved
when
t
he
effects of
sire by province, sire by herd, sire by birth year
or
sire by
calving year
were added.
Accordingly,
in both dataset,
0.001, 0.014, 0.001 and 0.002 percent of the
phenotypic variance was due to the effects of
sire by province, s
ire by herd, sire by birth year and sire
by calving year, respectively.
Then these effects
were important for genetic analysis of milk yield
(P<0.05)
but the
effect of sire by herd on the genetic analysis of milk yield was more than the other
interaction
e
ffects. The
same heritabilities were estimated for the milk yield corrected for 2 times
milking frequency (0.28
±
0.01
) and mature body weight (
0.27
±
0.01
)
when the sire by herd was included or ignored from the model
because both the additive genetic variance and the error variance
were decreased similarly when the
sire by herd
was added to the model. Correlation between the
breeding values of the sires estimated by the model including
and ignoring
the
sire by herd int
eraction
was
calculated to be
0.99.
Genotype by environment interaction arises when the performance of the
different genotypes is not equally influenced by the different environments. Then, ignoring the
interaction, can led to biased estimates of genetic p
arameters and reduce the accuracy of selection by
changing the ranking of the animals. Therefore, considering this interaction in a model may improve
genetic gain and selection accuracy.
Conclusion:
This research highlights the importance of genotype by e
nvironment interaction in
Iranian dairy cattle. Our results indicated that genotype by environment interaction is not important
for genetic evaluation of the sires when herd, province, birth year or calving year are used to define
the environment. Therefor
e, the genotype by environment interaction does not change the bulls
ranking in the different environments.
