| Summary: | Altogether 540 alternatives for the Icelandic sheep breeding scheme were evaluated by stochastic simulation of a breeding population with about 120.000 ewes, considering the genetic gain for an aggregate genotype including eight traits as well as the rate of inbreeding. Selection was made according to three selection indexes, with different weights on investigated traits. Two breeding schemes were simulated: a scheme with test rams in natural mating in local flocks and elite rams (from one and a half years of age) in AI across all flocks in the country (NMAI2 scheme) and a scheme where, in addition to test rams, the youngest elite rams were used in natural mating in local flocks (from one and a half years of age), (NMAI1 scheme). One alternative within the NMAI1 scheme was used as a control representing the current breeding scheme for each selection index. Both schemes included different proportions of ewes inseminated/mated to elite rams vs. test rams (EM%) and varying numbers of ewes inseminated per elite ram in AI (EAIn), and numbers of ewes mated per test ram in natural mating (TNMn). Within the NMAI1 scheme the number of ewes mated to each elite ram in natural mating (ENMn) also varied. With a restriction on the rate of inbreeding ( ≤ 0.8% per generation), the NMAI2 scheme resulted in more annual genetic gain than the NMAI1 scheme for all selection indexes. Improvement was found to be possible also under the NMAI1 scheme by changing the annual ram usage (EM%) from the current control breeding scheme. For both scheme the lowest EM% should be chosen (30%), TNMn equals 50, combined with average EAIn (NMAI2: 900 ewes, NMAI1: 700 ewes), and 60 ENMn within NMAI1.
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