Effect Of The Genetic Connectedness On Animal Ranking And Selection Response

Abstract

Lack of genetic connectedness across flocks is typical for smallholder farming system where animal mating usually takes place within flock. The genetic connectedness across flocks can be established through sire referencing scheme using both artificial insemination (AI) or natural mating. In smallholder farming system where flock of each farmer is located near by, the genetic connectedness can be established through ram rotation scheme. Genetic evaluation of across flocks animals will increase the selection intensity which in turn it will increase the selection response. To study the effect of genetic connectedness on the animal ranking and the selection response, a stochastic computer simulation study was conducted. A set of data applying simple animal model with one fixed effect of general mean and random polygenic additive effect of animal was simulated.  Three animal owners representing different flocks were assumed. A series of scenario combining two schemes: (1) genetically connected (ram rotation) or disconnected (ram static) and (2) three level of heritabilities (0.1, 0.3, 0.5 and 0.7) were simulated.  Five generations of random mating were run and the selected animals based on the BLUP EBV were then mated regardless of the animals' owner. The results showed that within the same heritability, the rank correlation of the TBV and BLUP EBV of the genetically connected population was higher than the genetically disconnected population.  Whether the population was genetically connected or disconnected, the rank correlation increased when the heritability increased. The selection response was higher on the genetically connected population.  The selection response increased when heritability increased.