Theory of nucleus breeding schemes with overlapping generations

Hopkins, I. R.; James, J. W.

doi:10.1007/bf00273131

Cited by 11 publications

(5 citation statements)

References 4 publications

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“…James (1977) concluded that migration in an open-nucleus system reduces the rate of inbreeding to approximately one half of that in a closed-nucleus system (when the size of nucleus is small). James (1978) derived a simple formula for effective population size with an open-NB system and Hopkins and James (1978) introduced a modified model for overlapping generations. All of these models assumed constant genetic variances.…”

Section: Introductionmentioning

confidence: 99%

Open-nucleus breeding strategies compared with population-wide positive assortative mating

et al. 2004

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Positive assortative mating (PAM) can enhance the additive genetic variance in a breeding population(BP). This increases the potential for gains in the production population (PP, selected subset of the BP) for recurrent selection programs in forest trees. The assortment of mates can be either: (1) by individual tree rank across the whole BP (PAM), or (2) trees of similar rank can be merged into larger hierarchical groups and then mated randomly within group ("open"-nucleus breeding,NB). The objective of this study was to compare PAM and NB in quantitative terms. The NB simulation model assumed two tiers (nucleus, main) with unrestricted migration between the tiers. Clonal tests were used to predict breeding values and test resources per mate were kept constant for all mates. Both gain and diversity were combined into a single selection criterion, "group-merit selection." Alternatives were compared over five breeding cycles by considering genetic gain and diversity in a selected PP established in a seed orchard. The assortment of mates in both alternatives enhanced additive variance and increased the additive effect in the BP, leading to additional gain in the PP. Gains generated under PAM always exceeded gains under NB. Thus, the main message from this study is that PAM in both the short- and long-term results in more gain at any target level of diversity in the PP (the breeder's target) than is achieved by the NB alternative. The optimum size of the nucleus varies with the desired level of seed orchard diversity. At lower target diversity, smaller nucleus sizes are favorable, while larger sizes result in more gain when seed orchard diversity is considered more important.

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Section: Introductionmentioning

confidence: 99%

Open-nucleus breeding strategies compared with population-wide positive assortative mating

et al. 2004

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“…As shown by H opkins and J ames (1978), genetic gain in a open nucleus breeding system is maximized when the transfer rates are chosen so that the expected breeding values at corresponding truncation points are the same in both tiers. In the system with the optimal transfer rates, the difference between the average breeding values of introduced and own‐bred parental groups will not be large.…”

Section: Discussionmentioning

confidence: 99%

Prediction of effective population size in open nucleus breeding systems

Nomura

1997

J Animal Breeding Genetics

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“…To account for this, selection of heifer replacements was based on truncation selection of the BPI using EBV across natural and AI-born calf populations. The methodology of Hopkins and James (1978) was followed to find the BPI value that resulted in the desired number of herd replacements being selected from the 2 populations. This is represented by a vertical line in Figure 1.…”

Section: Model Inputs and Assumptionsmentioning

confidence: 99%

The cost-benefit of genomic testing of heifers and using sexed semen in pasture-based dairy herds

Newton

Hayes

Pryce

2018

Journal of Dairy Science

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Recent improvements in dairy cow fertility and female reproductive technologies offer an opportunity to apply greater selection pressure to females. This means there may be greater incentive to obtain genomic breeding values for females. We modeled the impact of changes to key parameters on the net benefit from genomic testing of heifer calves with and without usage of sexed semen. This paper builds on earlier cost-benefit studies but uses parameters relevant to pasture-based systems. A deterministic model was used to evaluate the effect on net benefit due to changes in (1) reproduction rate, (2) genomic test costs, (3) availability of parent-derived breeding values (EBV), and (4) replacement rate. When the use of sexed semen was included, we also considered (1) the proportion of heifers and cows mated to sexed semen, (2) decreases in conception rate in inseminations with sexed semen, and (3) the marginal return for surplus heifers. Scenarios with lower replacement rates and no availability of EBV had the largest net benefits. Under current Australian parameters, the net benefit of genomic testing realized over the lifetime of genotyped heifers is expected to range from A$204 to A$1,124 per 100 cows for a herd with median reproductive performance. The cost of a genomic test, a perceived barrier to many farmers, had only a small effect on net benefit. Genomic testing alone was always more profitable than using sexed semen and genomic testing together if the only benefit considered was increased genetic gain in heifer replacements. When other benefits (i.e., the higher sale price of a surplus heifer compared with a male calf) were considered, there were combinations of parameters where net benefit from using sexed semen and genomic testing was higher than the equivalent scenario with genomic testing only. Using sexed semen alongside genomic testing is most likely to be profitable when (1) used in heifers, (2) the marginal return for selling surplus heifers (sale price minus rearing costs) is greater than A$400, and (3) conception rates of no more than 10 percentage points lower than those achieved using conventional semen can be realized. Net benefit was highly dependent on the marginal return. Demonstrating that the initial investment in genomic testing can be recouped within the lifetime of the heifers tested may assist in the development of extension messages to explain the value of genomic testing females at the herd level.

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Theory of nucleus breeding schemes with overlapping generations

Cited by 11 publications

References 4 publications

Open-nucleus breeding strategies compared with population-wide positive assortative mating

Open-nucleus breeding strategies compared with population-wide positive assortative mating

Prediction of effective population size in open nucleus breeding systems

The cost-benefit of genomic testing of heifers and using sexed semen in pasture-based dairy herds

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