Comparative assessment of the effective population size and linkage disequilibrium of Karan Fries cattle revealed viable population dynamics

Abstract

Objective: Karan Fries (KF), a high-producing composite cattle was developed through crossing indicine Tharparkar cows with taurine bulls (Holstein Friesian, Brown Swiss, and Jersey), to increase the milk yield across India. This composite cattle population must maintain sufficient genetic diversity for long-term development and breed improvement in the coming years. The level of linkage disequilibrium (LD) measures the influence of population genetic forces on the genomic structure and provides insights into the evolutionary history of populations, while the decay of LD is important in understanding the limits of genome-wide association studies for a population. Effective population size (N<sub>e</sub>) which is genomically based on LD accumulated over the course of previous generations, is a valuable tool for e valuation of the genetic diversity and level of inbreeding. The present study was undertaken to understand KF population dynamics through the estimation of N<sub>e</sub> and LD for the longterm sustainability of these breeds.Methods: The present study included 96 KF samples genotyped using Illumina HDBovine array to estimate the effective population and examine the LD pattern. The genotype data were also obtained for other crossbreds (Santa Gertrudis, Brangus, and Beefmaster) and Holstein Friesian cattle for comparison purposes.Results: The average LD between single nucleotide polymorphisms (SNPs) was r<sup>2</sup> = 0.13 in the present study. LD decay (r<sup>2</sup> = 0.2) was observed at 40 kb inter-marker distance, indicating a panel with 62,765 SNPs was sufficient for genomic breeding value estimation in KF cattle. The pedigree-based N<sub>e</sub> of KF was determined to be 78, while the N<sub>e</sub> estimates obtained using LD-based methods were 52 (SNeP) and 219 (genetic optimization for N<sub>e</sub> estimation), respectively.Conclusion: KF cattle have an N<sub>e</sub> exceeding the FAO's minimum recommended level of 50, which was desirable. The study also revealed significant population dynamics of KF cattle and increased our understanding of devising suitable breeding strategies for longterm sustainable development.