The effects of genotype by environment interactions in dairy cattle open nucleus breeding schemes

1993 ◽  
Vol 110 (1-6) ◽  
pp. 186-193 ◽  
Author(s):  
O. L. Bondoc ◽  
Ch. Smith
Keyword(s):  
Dairy Cattle ◽  
Genotype By Environment Interactions ◽  
Genotype By Environment ◽  
Breeding Schemes ◽  
Nucleus Breeding ◽  
Open Nucleus

The value of cloning in MOET nucleus breeding schemes for dairy cattle

1989 ◽  
Vol 48 (1) ◽  
pp. 31-35 ◽  
Author(s):  
J. A. Woolliams
Keyword(s):  
Dairy Cattle ◽  
Selection Intensity ◽  
Genetic Progress ◽  
Selection Accuracy ◽  
Potential Problems ◽  
Breeding Schemes ◽  
Nucleus Breeding

ABSTRACTThe value of cloning in MOET nucleus breeding schemes has to be considered within the constraint of fixed resources. Under this constraint cloning was found to add to genetic progress only when (i) the heritability is low and (ii) it is used at the expense of a reduction in the number of bull families. This course would exacerbate inbreeding and other potential problems with MOET. All other options for using clones lead to a reduction in genetic progress due to a loss of selection intensity that is not made up for by gains in selection accuracy.

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.

The importance of family sizes in adult multiple ovulation and embryo transfer (MOET) nucleus breeding schemes in dairy cattle

1991 ◽  
Vol 52 (1) ◽  
pp. 33-47 ◽  
Author(s):  
J. Ruane
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Dairy Cattle ◽  
Embryo Transfer ◽  
Sex Ratios ◽  
Survival Rates ◽  
Biological Factors ◽  
Multiple Ovulation ◽  
Breeding Schemes ◽  
Nucleus Breeding

ABSTRACTThe importance of family sizes in adult multiple ovulation and embryo transfer (MOET) nucleus schemes with discrete generations of single trait selection was examined using Monte Carlo simulation. Two areas were investigated. Firstly, the number of sons and daughters per dam was varied in schemes using hierarchical mating designs. With four or eight sires and 32 dams selected, increasing the number of sons per dam from one up to four achieved 1 to 8% higher rates of response but at the expense of increased variation in response and 10 to 56% higher rates of inbreeding. With four or eight sires and 16, 32 or 64 dams selected, the number of daughters was set to two, four or eight (with one son per dam in each case). For schemes transferring equal numbers of embryos, responses were lower with two daughters per dam but were fairly similar with four or eight daughters per dam while inbreeding rates increased as fewer sires and dams were selected. Secondly, the effects of variation in family sizes due to biological factors and chance were investigated with eight sires and 32 dams selected and with hierarchical or factorial (two or four sires per dam) mating designs. When all selected cows yielded embryos, changes in family sizes due to differences in sex ratios, in survival rates of embryos to selection and to variation in the number of embryos per donor reduced response by 1 to 4%. However, when 20% or 33% of the superovulated females yielded no embryos, thus requiring the use of genetically inferior replacements, response was reduced by a further 9 to 13%

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.

Modifications to MOET nucleus breeding schemes to improve rates of genetic progress and decrease rates of inbreeding in dairy cattle

1989 ◽  
Vol 49 (1) ◽  
pp. 1-14 ◽  
Author(s):  
J. A. Woolliams
Keyword(s):  
Dairy Cattle ◽  
Mating System ◽  
Mating Systems ◽  
Breeding Value ◽  
Selection Intensity ◽  
Genetic Progress ◽  
Factorial Mating ◽  
Breeding Schemes ◽  
Best Linear Unbiased ◽  
Nucleus Breeding

ABSTRACTThe effect of changes in the mating system on the rates of genetic progress and rates of inbreeding are considered for MOET nucleus breeding schemes. Methods are derived to calculate best linear unbiased predictors of breeding value in MOET schemes and the rate of inbreeding under selection. These are applied to different mating systems in which the numbers of sires and dams, and the number of offspring per sire and offspring per dam, remain constant.Results showed that compared with nested mating systems, factorial mating systems in which the maternal half-sibs are produced instead of full-sibs, could increase genetic progress by 1·12-fold with no additional inbreeding. The increased progress arose through an increase in the selection intensity applied. The rates of inbreeding derived were found to be approximately double those estimated by the formula of Wright (1931) in the absence of selection.In practice, even if a complete factorial system were to increase the generation interval and consequently reduce progress below that predicted, changes in the mating system avoiding this problem could be implemented that would be of immediate benefit.

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