The estimation of genetic parameters for milk somatic cell scores in Murciano-Granadina goats by B-Spline random regression models

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Authors

1 Department of Animal Science, Faculty of Agriculture, University of Jiroft

2 Department of Animal Science, Faculty of Agriculture, Shahid Bahonar University of Kerman

3 Ghale-Ganj dairy farm, Fajr Isfahan Agricultural and Livestock Company

10.22069/ejrr.2026.24458.2039

Abstract

Background and objectives: In domestic livestock such as dairy goats, the trait of somatic cell count (SCC) in milk is collected as test day records and serves as a reliable indicator for the early detection of udder diseases and the health status of mammary glands. Improving the genetic potential of dairy goats requires selecting an appropriate model and an efficient method for genetic evaluation of milk production traits and their components. Random regression models, due to their numerous advantages, including the ability to account for environmental effects influencing test day records, the capacity to incorporate large volumes of data, and the provision of more accurate estimates of genetic values in the analysis of repeatable traits over time, such as milk SCC, are superior to other models, such as repeatability and multi-trait models. Therefore, the present study was conducted to estimate genetic and phenotypic parameters of milk somatic cell count during the first lactation of Murciano Granadina goats in Iran using random regression models under B-Spline functions.
Materials and methods: In the present study, a total of 7,089 test day records of somatic cell count (SCC) from the first lactation of 2,432 Murciano Granadina goats were used. These records were collected between 2017 and 2024 at the Murcia Dairy Goat Breeding Complex in Qaleh Ganj County, Iran. For genetic analysis, random regression models based on B-Spline functions were applied. The models were fitted in three forms, linear, quadratic, and cubic, and with 3 to 6 equally spaced knots, for both additive genetic and permanent environmental effects. Residual variance was considered in two ways: homogeneous and heterogeneous. The fitted random regression models were compared using the Akaike Information Criterion and the Bayesian Information Criterion.
Results: Heritability estimates for somatic cell score started at 0.11 on day 5 of lactation, decreased with fluctuations to 0.03 on day 175, and then increased again with some variation to reach 0.12 by day 265 of lactation. The estimated ratios of permanent environmental variance to phenotypic variance were relatively low but showed greater fluctuations throughout lactation, rising from 0.09 on day 5 to 0.14 on day 265. Genetic correlations between different test day records were generally higher than phenotypic correlations, with stronger correlations observed between adjacent test days and weaker correlations between more distant test days.
Conclusion: Based on the results of this study, direct selection for the genetic improvement of somatic cell score in Murciano Granadina goats is not effective. Improvement in the performance of these goats with respect to milk somatic cell score requires enhanced environmental and management conditions, particularly improved hygiene practices during different stages of lactation.

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Journal of Ruminant Research

Articles in Press, Corrected Proof
Available Online from 12 September 2026

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