Correlations among production and linear type traits in Holstein cows: A meta-analysis study

Document Type : Research Paper

Authors

• Sorayya Rafiee ¹
• S Reza Miraei-Ashtiani ²
• Ali Sadeghi-Sefidmazgi ³
• Hasan Mehrabani Yeganeh ³

¹ Department of Animal Science, Faculty of Agriculture, University of Tehran.Karaj. Iran

² Department of Animal Science, Faculty of Agriculture, University of Tehran, Karaj. Iran

³ Department of Animal Science, Faculty of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

Abstract

Keywords

• Holstein Cow
• Meta-analysis
• Production Traits
• Type Traits

Main Subjects

• Animal Breeding and Genetics

Extended Abstract

Introduction

Linear type traits could be appropriate indirect indicators of production performance of dairy cows and might be used to describe milk yield and composition. Cows might reach to high productive length and milk yield based on their ideal scores of type traits. In some countries, selection indices have focused on breeding goals including production (especially protein and fat content and percent) longevity, mammary system health, linear type and reproduction traits. In dairy industry, type traits have indirect economic values due to genetic correlation with production traits. Thus, we can estimate the type traits’ economic values through reaching genetic correlation coefficients data published in conducted independent studies. Meta-analysis procedure as a statistical tool is used to combine quantitative results of the previous researches, analyze data and summarize the results. Therefore, the main object of the present study was meta-analysis of genetic correlation among production traits (milk yield, fat content and protein content) with type traits in Holstein cows.

Materials and Methods

In order to perform a systematic search of the literature across a wide variety of sources, we used key words “genetic correlation”, “type traits”, “production traits”, “Holstein cow” with Google Scholar search engine. After excluding inappropriate studies, finally we came up with 27 papers conducted in relation to estimate genetic correlation among production traits and type traits in first parity Holstein cows. Number of cows for milk yield, fat content, and protein content were 1407598, 1252515, and 1159124, respectively. Analyses were performed using “metafor” package in R environment. We used random model to estimate effect size, 95% confidence interval, and statistical significance of the effect sizes. In a meta-analysis study,  statistic (with a range of 0% to 100%) estimates how much of the total variability in the observed effect sizes can be attributed to heterogeneity among the studies (not chance).

Results and discussion

The obtained results showed that the linear type traits with higher genetic correlations with milk yield were angularity 0.36, body condition score -0.31, udder depth -0.30, and rear udder width 0.26. Furthermore, fat content was most highly genetically correlated with angularity 0.39 and body condition score -0.25. The largest genetic correlation of protein content was estimated with angularity 0.46. The next leading genetic correlations of protein content were rear udder width 0.39, udder depth -0.29, and rump angle 0.28. Test of heterogeneity (I² statistics) indicated that there was significant heterogeneity (variance among studies) at the highest level (more than 99%). Results of this study might be applicable to estimation of type traits’ economic values of Holstein cow’s selection indices.  

Conclusion

Generally, the meta-analysis on the correlations among production and linear type traits clarified that angularity, body condition score, udder depth, rear udder width and rump angle were of main importance, considering the genetic correlation among production and linear type traits. Cows can produce higher amount of milk and spend higher productive period when they have achieved the ideal scores of type traits. The findings of this study could be used in estimation of type traits’ economic values to be included in selection index in order to select relatively higher producing cows.

Author Contributions

Soraya Rafiee: Investigation, Preparation, Writing original draft of the Manuscript, Methodology Data curation, Software and Analysis.

Seyed Reza Miraei-Ashtiani Conceptualization, Validation, Review and Editing the manuscript, Project administration and Supervision.

Ali Sadeghi-Sefidmazgi: Conceptualization, Resources Methodology, Validation and Supervision.

Hasan Mehrabani – Yeganeh: Validation, Funding acquisition, Review and Editing the Manuscript,

All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.

Data Availability Statement

The data supporting reported results are collected and used from published articles, to them we have referred in the manuscript.    

Acknowledgements

The authors would like to thank Chaltasion and Talise Asil-e Jahan, Animal Husbandries for availability of their data to the project.

Ethical considerations

The study was approved by the Ethics Committee of the University of Tehran (Ethical code: IR.7108004/6/41). The authors avoided data fabrication, falsification, plagiarism, and misconduct.