Theory of nucleus breeding schemes with overlapping generations

1978 ◽  
Vol 53 (1) ◽  
pp. 17-24 ◽  
Author(s):  
I. R. Hopkins ◽  
J. W. James
Keyword(s):  
Overlapping Generations ◽  
Breeding Schemes ◽  
Nucleus Breeding

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.

Bull Selection in MOET Nucleus Breeding Schemes with Limited Testing Capacity

2001 ◽  
Vol 51 (4) ◽  
pp. 235-245
Author(s):  
I. Strandén ◽  
P. Korpiaho ◽  
M. Pakula ◽  
E. A. Mäntysaari
Keyword(s):  
Breeding Schemes ◽  
Nucleus Breeding ◽  
Limited Testing

Genetic progress and inbreeding for alternative nucleus breeding schemes for beef cattle

1995 ◽  
Vol 61 (2) ◽  
pp. 231-239 ◽  
Author(s):  
B. Villanueva ◽  
G. Simm ◽  
J. A. Woolliams
Keyword(s):  
Beef Cattle ◽  
Mating Strategies ◽  
Percentage Increase ◽  
Expected Number ◽  
Genetic Progress ◽  
Multiple Ovulation ◽  
Population Sizes ◽  
Breeding Schemes ◽  
Nucleus Breeding ◽  
Selection Intensities

AbstractAlternative closed breeding schemes for beef cattle are analysed using stochastic computer simulation. Multiple ovulation and embryo transfer (MOET) schemes are compared with conventional schemes (schemes without MOET) with an equal expected number of progeny born per year. Schemes are compared for genetic gain and inbreeding obtained after 25 years of selection. The trait considered, evaluated in both sexes, has an initial heritability of 0·35. Different population sizes and numbers of sires selected are evaluated. Current realistic parameters for embryo production are assumed in MOET schemes.After 25 years of selection, and with no control on inbreeding, cumulative genetic gains are about 50% higher in MOET schemes compared with conventional schemes. The benefit from MOET is mostly due to increased selection intensities in females. The rate of inbreeding increases by up to nearly 300% when MOET is used. This maximum percentage increase in inbreeding following the use of MOET can be reduced to about 100% when selection and mating strategies for controlling inbreeding are used. The effect of the number of sires used on the inbreeding obtained is more important than the effect of the size of the herd. In MOET schemes, increasing the number of sires selected by a factor of three, leads to reductions in inbreeding rates of 40%. When schemes of the same size are compared at similar acceptable inbreeding levels, MOET schemes give around 30% higher genetic progress than conventional schemes.

Selection with control of inbreeding in populations with overlapping generations: a comparison of methods

2000 ◽  
Vol 70 (1) ◽  
pp. 1-8 ◽  
Author(s):  
A. K. Sonesson ◽  
B. Grundy ◽  
J. A. Woolliams ◽  
T. H. E. Meuwissen
Keyword(s):  
Computer Simulations ◽  
Optimization Algorithm ◽  
Genetic Gain ◽  
Overlapping Generations ◽  
Current Level ◽  
Comparison Of Methods ◽  
Genetic Response ◽  
Age Classes ◽  
Feasible Method ◽  
Breeding Schemes

AbstractMethods that maximize genetic response in populations with overlapping generations while controlling rate of inbreeding by constraining the average relationship among selection candidates were compared. Firstly, computer simulations of closed nucleus selection schemes showed that a two-stage optimization algorithm approach, where the distribution of parents within and thereafter over age classes was optimized resulted in different breeding schemes than an approach that performed an iteration on this distribution. It yielded significantly lower annual genetic gain (0·194 v. 0·223 σp units), fewer animals selected (21·9 v. 26·4) and longer generation intervals (2·38 v. 1·68 years) but maintained the rate of inbreeding closer to its constraint. In large schemes, iteration may be computationally the only feasible method for the optimization of parents across age classes. Secondly, the use of conventional relationships for constraining inbreeding was compared with that of augmented relationships, which do not depend on the level of inbreeding. Both relationships resulted in very similar breeding schemes, but the use of augmented relationships avoids correction of the current level of inbreeding. Thirdly, a constraint of the rate of inbreeding on a per year basis was compared with a constraint on a per generation basis. When optimizing per generation, the generation interval was shorter compared with a scheme where an analogous annual restriction was in place (2·01 v. 2·38 years) and the annual rate of genetic gain was higher (0·214 v. 0·194 σp units).

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%

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