USING HISTORICAL POPULATION DATA TO ESTIMATE THE INBREEDING COEFFICIENT IN THE DAIRY CATTLE POPULATION USING A SIMULATION TECHNIQUE

Abstract

This study aimed to simulate the effects of genetic variation and pedigree structure on the estimation of the inbreeding coefficient (FX). Dairy cow populations of 2,000 , 5,000 and 10,000 cows were simulated with varying numbers of sires (1, 5, 10, 20 and 4), three levels of heritability (low, medium, and high) and two litter sizes (1 and 2 calves per litter). Four pedigree structures were considered: 1) constant population size, 2) increasing population size by 1% per year, 3) bottlenecked population with a 1% annual increase followed by 1% annual decrease and 4) current population representing 10% of the actual dairy cattle population. QMSim software was used for analysis. The results indicated that the constant population structure produced the lowest average FX, whereas the current population has the highest average FX, with mean values of 0.602, 0.609, 0.616, and 0.627 across the four structures, respectively. Increasing the number of sires and maintaining greater population numbers were effective ways to reduce inbreeding.  Populations with higher heritability and larger size have broader genetic bases, making it easier to manage inbreeding.  Estimating the heritability of variables linked with inbreeding, like fertility, milk production, and disease resistance, might help breeders make better educated breeding decisions to eliminate inbreeding and maintain healthy genetic pools.  Additionally, cows with single calves displayed lower average inbreeding than those with twins, suggesting that reproductive patterns may influence genetic diversity within herds.