Effects of reduced variance due to selection in open nucleus breeding systems

1983 ◽  
Vol 34 (1) ◽  
pp. 53 ◽  
Author(s):  
JP Mueller ◽  
JW James
Keyword(s):  
Genetic Variance ◽  
Breeding Systems ◽  
Breeding Programs ◽  
Transfer Rates ◽  
Constant Variance ◽  
High Heritability ◽  
Breeding Schemes ◽  
Nucleus Breeding ◽  
Open Nucleus ◽  
Parameter Theory

In the design of breeding programs the consideration of open nucleus breeding systems may result in a useful alternative. The available theory dealing with these systems assumes constant parameters, but a more exact approach would take into account the possible changes in genetic variance. Numerical evaluation of formulae allowing for loss of genetic variance due to linkage disequilibrium and increase of variance due to mixing groups with different breeding values, suggests that optimum transfer rates, as predicted from the constant parameter theory, are in close agreement with the actual values; however, genetic gain is overestimated by about 20 % in common cattle and sheep nucleus breeding schemes for traits with high heritability, but less for traits with low heritability. The advantage of opening the nucleus is approximated well by constant variance theory.

Some optimum age structures and selection methods in open nucleus breeding schemes with overlapping generations

1978 ◽  
Vol 26 (3) ◽  
pp. 267-276 ◽  
Author(s):  
I. R. Hopkins
Keyword(s):  
Survival Rates ◽  
Age Groups ◽  
Selection Methods ◽  
Selection Procedures ◽  
Transfer Rates ◽  
Breeding Schemes ◽  
Nucleus Breeding ◽  
Genetic Responses ◽  
Open Nucleus ◽  
Age Structures

ABSTRACTDesigns of open nucleus breeding schemes, which comprise a nucleus having the best males and females and a base comprising the remainder, with some base-born individuals used in the nucleus and vice versa, are studied.Steady-state genetic responses, optimum transfer rates between nucleus and base in both sexes, and genetic differences between nucleus and base are estimated for a range of age structures, selection either within or among age groups (selection methods), nucleus sizes, mating ratios, fertility rates and survival rates appropriate to sheep and cattle populations. With optimum transfer rates between layers maximum or near maximum genetic responses are obtained with nucleus sizes varying from 2 to 15% of the population. Optimum transfer rates are fairly stable for nucleus sizes larger than about 5% and where the same selection procedures are used in both layers. However, a small nucleus with more efficient age structures and selection procedures and more accurate selection than in the base is economically desirable, and then almost no base-born females should be selected as nucleus replacements and up to 70% of male replacements for the base should come from the base. Optimum age structures differed markedly between selection methods.Although few ‘rules of thumb’ about optimum age structures and transfer rates are sufficiently robust to be widely recommended in commercial situations, the nucleus breeding system behaves according to a few basic principles that can be used to predict the direction if not the magnitude of effects of changes in structure.

A simulation study of open nucleus and closed nucleus breeding systems in a sheep population

1995 ◽  
Vol 60 (1) ◽  
pp. 117-124 ◽  
Author(s):  
J. A. Roden
Keyword(s):  
Genetic Gain ◽  
Live Weight ◽  
Breeding Systems ◽  
Breeding Value ◽  
Linear Unbiased Prediction ◽  
Sheep Population ◽  
Best Linear Unbiased ◽  
Nucleus Breeding ◽  
Open Nucleus ◽  
Selection Of

AbstractStochastic simulation was used to compare the results of alternative breeding systems in a sheep population divided into 10 flocks of 120 ewes. The breeding systems compared were selection within closed flocks (CF), a closed nucleus system (CNS), an open nucleus system (ONS) and open nucleus systems with the selection of nucleus replacements being restricted to either nucleus born males (ONSRm) or nucleus born females (ONSRf). Selection was for a best linear unbiased prediction of breeding value for lamb live weight which had a heritability of 0·17. The open nucleus breeding systems (ONS, ONSRm, ONSRf) resulted in higher rates of genetic gain, more predictable selection responses and lower rates of inbreeding than either the closed nucleus system (CNS) or selection within closed flocks (CF). Initial genetic differences between flocks resulted in higher rates of genetic gain in the nucleus breeding systems due to the use of between flock genetic variance. In the ONS system up to 25% of nucleus sires and approximately 50% of nucleus dams were born in base flocks. Nevertheless if selection of either nucleus sires or dams was restricted to nucleus born animals there was very little change in genetic gain or rate of inbreeding.

A comparison of alternative nucleus breeding systems and a sire referencing scheme for sheep improvement

1996 ◽  
Vol 62 (2) ◽  
pp. 265-270 ◽  
Author(s):  
J. A. Roden
Keyword(s):  
Selection Response ◽  
Best Linear Unbiased Prediction ◽  
Breeding Systems ◽  
Linear Unbiased Prediction ◽  
Sequential Selection ◽  
Best Linear Unbiased ◽  
The Mean ◽  
Nucleus Breeding ◽  
Open Nucleus ◽  
Selection Of

AbstractStochastic simulation was used to compare selection response and rate of inbreeding in four nucleus breeding systems and a sire referencing scheme for sheep: an open nucleus system (ONS), an open nucleus system with sequential selection of the nucleus (ONS-S), a sire referencing scheme (SRS) and a dispersed open nucleus system (DONS). Selection was based on best linear unbiased prediction of breeding values for a single trait measurable on all individuals prior to selection. Selection in a population of 1200 ewes equally divided into 10 flocks was simulated over a 15-year period. The mean rate of genetic gain was proportionately about 0-15 higher in ONS-S and DONS compared with ONS and SRS. The rate of inbreeding in SRS was considerably lower and in ONS-S, considerably higher, than in the other systems. The level of prolificacy in the population did not influence the relative ranking of the breeding systems but may have implications for their optimal structure.

Open nucleus breeding systems

1977 ◽  
Vol 24 (3) ◽  
pp. 287-305 ◽  
Author(s):  
J. W. James
Keyword(s):  
Numerical Analysis ◽  
Genetic Gain ◽  
Breeding Systems ◽  
Generation Model ◽  
Selection Intensity ◽  
Base Population ◽  
Cattle Breeding ◽  
Discrete Generation ◽  
Nucleus Breeding ◽  
Open Nucleus

SUMMARYA theoretical analysis of open nucleus breeding systems, in which there is some introduction of breeding females to the sire breeding nucleus, is presented. Numerical analysis of a discrete generation model shows that the rate of genetic gain may be increased by 10 to 15% by opening the nucleus when selection intensity in females is low. In sheep and beef cattle breeding the optimal structure would be to have about 10% of the population in the nucleus, to get half of the nucleus female replacements from the base population, and to use all nucleus-born females not needed as nucleus replacements for breeding in the base population. The genetic gain, however, is not very sensitive to variation in these parameters. The rate of inbreeding in such an open nucleus would be about half that in a closed nucleus of the same size.

A comparison of the rate of genetic gain and inbreeding in open nucleus and closed flock breeding systems for sheep.

1993 ◽  
Vol 1993 ◽  
pp. 34-34
Author(s):  
Janet A. Roden
Keyword(s):  
Breeding Population ◽  
Best Linear Unbiased Prediction ◽  
Breeding Systems ◽  
Optimum Structure ◽  
Linear Unbiased Prediction ◽  
Sheep Breeding ◽  
Group Breeding ◽  
Breeding Schemes ◽  
Best Linear Unbiased ◽  
Open Nucleus

Open nucleus systems (ONS) have been used in sheep breeding for a number of years, usually in group breeding schemes. In the simplest form the population is divided into two tiers, the nucleus flock composed of elite individuals, while the base, which forms the majority of the population, is usually sub-divided into a number of individual flocks. Animals born in the nucleus may be selected as replacements in the base, while superior animals born in the base may become part of the breeding population of the nucleus. The optimum structure and genetic benefits of using an ONS under Australasian conditions have been extensively studied using deterministic predictions (James, 1977; Mueller and James, 1983). However, subsequent advances in genetic evaluation (e.g. the application of Best Linear Unbiased Prediction (BLUP)) and the smaller flock sizes typical in Europe, are likely to impact on the outcome and optimum structure of such systems.

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