Estimation of genetic parameters for Holstein cows milk production by random regression
A total of 21,702 records of milk production from 2,429 first-lactation Holstein cows, sired by 233 bulls, collected in 33 herds in the State of Rio Grande do Sul from 1991 to 2003, were used to estimate genetic parameters for that characteristic. The random regression model adjusted to test day fro...
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| Published in: | Arquivo brasileiro de medicina veterinária e zootecnia Vol. 61; no. 2; pp. 407 - 412 |
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| Main Author: | |
| Format: | Journal Article |
| Language: | English Portuguese |
| Published: |
01-04-2009
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| Online Access: | Get full text |
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| Summary: | A total of 21,702 records of milk production from 2,429 first-lactation Holstein cows, sired by 233 bulls, collected in 33 herds in the State of Rio Grande do Sul from 1991 to 2003, were used to estimate genetic parameters for that characteristic. The random regression model adjusted to test day from the 6 super(th) and the 305 super(th) lactation day included the effect of herd-year-month of the test day, the age of the cow at parturition, and the order fourth Legendre polynomial parameters, in order to obtain the average curve for the milk production of the population and parameters from the same polynomial to estimate the additive genetic and permanent environmental random effects. The genetic and permanent environmental variances for test day milk yield ranged from 2.38 to 3.14 and from 7.55 to 10.35, respectively. The estimated heritabilities gradually increased from the beginning (0.14) to the end (0.20) of the lactation period, indicating that test day milk yield is a characteristic with moderate heritability. The genetic correlation between milk yield in different phases of lactation ranged from 0.33 to 0.99 and was higher between the adjacent test days. The permanent environmental correlations followed the same tendency of the genetic ones. The random regression animal model using Legendre polynomials of order four can be considered as a good tool to estimate genetic parameters for milk production throughout the lactation. |
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| Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 0102-0935 |
| DOI: | 10.1590/S0102-09352009000200018 |