Estimation of Genetic Parameters for Milk Urea Nitrogen in Iranian Holstein Cattle Using Random Regression Models

Mehridokht Mortazavi, Mohammad Bagher Zandi (), Rostam Pahlavan, Moradpasha Eskandari Nasab and Hinayah Rojas de Oliveira ()
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Mehridokht Mortazavi: Department of Animal Science, University of Zanjan, Zanjan 45371-38111, Iran
Mohammad Bagher Zandi: Department of Animal Science, University of Zanjan, Zanjan 45371-38111, Iran
Rostam Pahlavan: Animal Breeding Centre and Promotion of Animal Products, Karaj 3158-5963, Iran
Moradpasha Eskandari Nasab: Department of Animal Science, University of Zanjan, Zanjan 45371-38111, Iran
Hinayah Rojas de Oliveira: Department of Animal Sciences, Purdue University, 270 S. Russell St., Room 3034, West Lafayette, IN 47907-2041, USA

Agriculture, 2025, vol. 15, issue 4, 1-16

Abstract: Reducing nitrogen excretion in dairy cattle is a critical factor for improving the environmental sustainability of the livestock industry. This research aimed to estimate the genetic parameters over time for the milk urea nitrogen (MUN) trait in Iranian Holstein dairy cattle. Data from 347,639 test-day records of 52,219 first-parity Iranian Holstein dairy cows (spanning 2018 to 2023), were sourced from the Iranian National Animal Breeding Center. A single-trait random regression test-day animal model was used for the genetic evaluation of MUN. Three orders of Legendre orthogonal polynomials (ranging from 1 to 3) were tested to fit the fixed curve, additive genetic effects, and permanent environmental effects. Based on the AIC, BIC, and residual variances to compare the models, the third order was considered as the appropriate order for this dataset. The average heritability and repeatability of the MUN trait were estimated to be 0.027 and 0.081, respectively. The average estimates for additive genetic variance, permanent environmental variance, and phenotypic variance were 0.14, 0.28, and 5.17, respectively. The genetic trend analysis revealed that the MUN trait exhibited fluctuations across birth years (2016–2021), with an overall negative trend. Importantly, the average MUN levels remained within the desirable range of 13–16 mg/dL for Iranian Holstein cows across calving years from 2019 to 2023. Despite the low heritability estimates, the genetic parameters obtained in this study are valuable for improving MUN in Iranian dairy cattle. These findings provide critical insights for designing effective breeding programs aimed at reducing nitrogen excretion and promoting environmental sustainability in the dairy industry.

Keywords: heritability; random regression; Legendre polynomial; milk urea nitrogen (search for similar items in EconPapers)
JEL-codes: Q1 Q10 Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 (search for similar items in EconPapers)
Date: 2025
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