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Genetic parameters for tunisian holsteins using a test-day random regression model.

H Hammami1, B Rekik, H Soyeurt

  • 1Animal Science Unit, Gembloux Agricultural University, B-5030 Gembloux, Belgium.

Journal of Dairy Science
|April 19, 2008
PubMed
Summary

Genetic parameters for Tunisian Holsteins show moderate heritability for milk, fat, and protein yields. Results suggest limited adaptation to local conditions, highlighting the need for improved data quality in breeding programs.

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Area of Science:

  • Animal Genetics
  • Dairy Science
  • Quantitative Genetics

Background:

  • Estimating genetic parameters is crucial for effective dairy cattle breeding programs.
  • Understanding genetic variation in milk, fat, and protein yields across lactations informs selection strategies.
  • Previous studies have focused on different breeds and management systems, necessitating breed-specific analyses for Tunisian Holsteins.

Purpose of the Study:

  • To estimate genetic parameters for milk, fat, and protein yields in Tunisian Holsteins across their first three lactations.
  • To assess the heritability and genetic correlations of yield traits at different stages of lactation.
  • To provide insights for implementing a Best Linear Unbiased Prediction (BLUP) evaluation system for Tunisian dairy cattle.

Main Methods:

  • Utilized a large dataset of test-day production records from 22,538 first-parity, 15,257 second-parity, and 9,722 third-parity Tunisian Holstein cows.
  • Employed Bayesian methods with Gibbs sampling to estimate (co)variance components using a 3-trait-3-lactation random regression model.
  • Incorporated fixed effects including herd-test date, calving season/age, and stage of lactation, alongside random effects for additive genetics, permanent environment, and herd-year.

Main Results:

  • Heritability estimates for 305-day milk, fat, and protein yields were moderate (0.12-0.18), consistent with low-to-medium production systems.
  • Heritability patterns varied by trait and lactation stage: milk and protein yields were higher mid-lactation, while fat yield was higher at lactation extremes.
  • Genetic correlations between 305-day yield traits ranged from 0.50 to 0.86, with the highest correlation observed between the first and second lactations.

Conclusions:

  • The estimated genetic parameters suggest a potential lack of adaptation to local Tunisian management and climatic conditions.
  • Results support the implementation of BLUP evaluations for Tunisian dairy populations.
  • Further research focusing on data quality is recommended to refine genetic evaluations and breeding strategies.