ESTIMATION OF (CO)VARIANCE COMPONENTS FOR MILK AND FAT YIELDS IN NAJDI CATTLE BREED USING RANDOM REGRESSION MODEL

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NAZARI MAHMOUD; BEYGI NASIRI M.T.; ROSHANFEKR H.E.

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Paper Information

Journal: THE SCIENTIFIC JOURNAL OF AGRICULTURE (SJA) Year:2008 | Volume:31 | Issue:1 Page(s): 1-10

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Information Journal Paper

Title

ESTIMATION OF (CO)VARIANCE COMPONENTS FOR MILK AND FAT YIELDS IN NAJDI CATTLE BREED USING RANDOM REGRESSION MODEL

Author(s)

NAZARI MAHMOUD | BEYGI NASIRI M.T. | ROSHANFEKR H.E. | Issue Writer Certificate

Keywords

RANDOM REGRESSIONQ3

TEST-DAY RECORDQ3

MILK AND FAT YIELDSQ4

NAJDI CATTLEQ3

(CO)VARIANCE COMPONENTSQ3

Abstract

In order to estimate variance components, 8843 test day MILK AND FAT YIELDS records: from first lactation NAJDI CATTLE were used. Data were obtained between years 1989-2005 by Animal Breeding Station of NAJDI CATTLE located in Shooshtar. RANDOM REGRESSION models were studied in respect with different orders of fitting for fixed and RANDOM REGRESSION. Also, different methods of residual variance in the analysis including assumption of constant residual variance and different assumption about variable residual variance during lactation were assumed. According to the results, the assumption of heterogeneous residual variance during lactation improved characteristics of the statistical model. A suitable model with (3, 3) orders of fit for additive genetic and permanent environmental covariance functions to analyze TD fat and milk yield records were recognized. Minimum of heritability for fat and milk yield was estimated at the beginning of lactation, (0.1, 0.15), respectively. The amount of this parameter increased to mid lactation and almost in the 5thmonth of lactation reached the maximum level (0.34 for milk yield and 0.44 for fat yield), then decreased to the end of lactation. Minimum and maximum of genetic and permanent environmental correlation were estimated between 5 and 270 days of lactation.

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