deterministic simulation

The objectives of this research were to simulate and optimize three open nucleus breeding schemes for improvement of growth traits and carcass composition in Lori-Bakhtiari lambs with 500 ewes in nucleus using a deterministic approach. These schemes were: scheme 1 with natural mating and mating ratio (M) of 50 ewes per ram in nucleus and member flocks (base), scheme 2 with artificial insemination in nucleus (M=250) and natural mating in base (M=50) and scheme 3 with artificial insemination in nucleus (M=250) and base (M=500). An economic selection index with accuracy of 0.42 was envisaged for base and one with accuracy of 0.67 for nucleus. Advantage of open nucleus over closed nucleus for schemes 1, 2 and 3 was different but optimal relative sizes and monetary genetic lags were 7.5, 5.7 and 8 percent, respectively. With equalization of the monetary genetic lags )sub-optimal( for schemes 1 and 2 being equal to the lag of optimum scheme 1, their base population sizes were 1.035 and 3.1 times the base size of optimum scheme 1 and their monetary genetic gains were 18.9 and 21.1 percent greater than the gain of the latter scheme, respectively. In the above sub-optimal situation, the base population size of scheme 3 was 3 times that of scheme 2, its monetary genetic gain being 1.91% greater. Shifting from traditional system with selection based on body weight at 6 months of age to schemes 1, 2 and 3 with same monetary genetic lags, the monetary genetic gain increased 84.3, 119.12 and 123.3 percent, respectively. However, due to the similarity of the monetary genetic gains of schemes 2 and 3 at the same monetary genetic lags and the higher practicability of scheme 2, implementation of this scheme for ease of initiation and promotion of the open nucleus breeding system was recommended.

The objective of this research was to study the factors affecting the annual genetic gain resulting from an open nucleus breeding system with selection of base-born nucleus replacement ewes in two stages using base and nucleus indices, respectively. For this purpose, an open nucleus breeding system was simulated using a deterministic approach with information from Lori-Bakhtiary sheep population. First, the genetic gain from two-stage selection in basic conditions was estimated. Then, different levels of accuracies in base and nucleus and two different levels of fertility were envisaged. In basic conditions, advantage of two-stage selection over single stage selection using base index was 7.65 %. Correlation between base and nucleus indices in this situation was 0.627. Advantage of two-stage selection depended on the accuracies of selection in the two stages and varied from 4.6% (with accuracies of base and nucleus of 0.5 and 0.65, respectively) to 15.45% (with accuracies of base and nucleus of 0.2 and 0.95, respectively). Maximum advantage of two-stage selection (15.45%) resulted from low fertiliry rate (0.7) and low correlation (0.211) between indices of the two stages. In general, results showed that with lower correlations of base and nucleus indices and low fertility rates, advantage of two-stage selection is greater.