Estimation of Genetic Parameters for Milk Fat Yield Trait in Holestein Cattle by Test Day Model

• Published in: Pajouhesh And Sazandegi no. 4
• Main Authors: Allahyarzadeh, H., MSc Graduated of Zabol University, Farhangfar, H., Associate Professor of Birjand University, Naeemipour, H., MSc Graduated of Birjand University, Shojaeian, K., Assistant Professor of Zabol University
• Format: Journal Article
• Language: Persian
• Published: 2011
• Subjects: COWS; GRASA DE LA LECHE; HOLSTEIN COWS; http://www.fao.org/aos/agrovoc#c_1939; http://www.fao.org/aos/agrovoc#c_4828; http://www.fao.org/aos/agrovoc#c_8488; MATIERE GRASSE DU LAIT; MILK FAT; RENDEMENT; RENDIMIENTO; VACA; VACHE; YIELDS
• ISSN: 1019-9632

A total of 159, 465 monthly test day fat yield records belonging to 18,808 Holstein heifers were used to estimate genetic parameters. The data were collected between 1993 and 2007 from the herds over the Khosrasan provinces. Two test day models, fixed and random regression models, were used to estimate genetic and phenotypic parameters. In both models, fixed environmental factors of herd- year- season- milking times, and the covariates of age at recording as well as Holstein gene proportion were included. To take account of additive genetic and permanent environmental variation, the cow numbers were also included in the model. Legendre polynomials were utilised in both models for accounting for fat yield variation over the course of the lactation at phenotypic and genetic levels. SAS programme was used to study the effects of environmental factors and DFREML was applied to estimate variance and covariance components in test day models. The results showed that average heritability and repeatability of monthly test day fat yield were 0.08 and 0.318 respectively for random test day model while the corresponding figures were found to be 0.059 and 0.233, respectively for fixed test day model. Average genetic, phenotypic and permanent environmental correlation of monthly test day milk fat yield were 0.728, 0.229 and 0.728, respectively for random test day model.