TITLE:
Use of Random Regression Test-Day Model to Estimate Genetic Parameters of Milk Yield in Holstein Cows
AUTHORS:
Yaser Fazel, Masoud Asadi Fozi, Ali Esmailizadeh, Fatemeh Fazel, Ahmad Massoud Niazi, Shahpoor Rahmati, Mohammad Ibrahim Qasimi
KEYWORDS:
Genetic Parameters, Random Regression Model, Test-Day Records, Milk Yield, Holstein Cows
JOURNAL NAME:
Open Journal of Animal Sciences,
Vol.8 No.1,
December
19,
2017
ABSTRACT: (Co) variance components and genetic parameters were
estimated for milk yield of Iranian Holstein cows. A total number of 68,945
milk test-day records of first, second and third lactations of 8515 animals
from 100 sires and 7743 dams originated from 34 herds collected during 2007 to
2009 by Iranian animal breeding center were used. The ASReml computer program
was used to analyze the milk test-day records using the random regression
procedure. Herd test date (HTD), milking times per day (milking frequency),
number of lactations, year of birth, year of calving, age of animal at calving
and days in milk (DIM) considered as fixed effects and additive genetic effects
and animal permanent environmental effects were considered as the random
effects. Additive genetic variance, animal permanent environment variance,
residual variance, phenotypic variance, heritability and repeatability were
estimated during different months of lactation between 5.7 - 19.6, 15.3 - 27.1,
31.4 - 17.2, 45.8 - 64.83, 0.1 - 0.32 and 0.4 - 0.6, respectively. Genetic
correlation and phenotypic correlation were also estimated between months of
lactation in range of -0.35 - 0.98 and 0.03 - 0.67, respectively. Genetic
correlation and phenotypic correlation both showed the same changing pattern
and they decreased as the interval between months of lactation increased.