317 research outputs found
Breeding against osteochondrosis : phenotypic and genetic analyses in horses and pigs
No full text Osteochondrosis (OC) is a disturbance in the process of endochondral ossification during skeletal growth. The objectives of this thesis were to assess the prevalence and genetic parameters of OC, and to facilitate optimization of breeding against OC in horses and pigs. In the Dutch warm blood horse, 70% of individuals showed joint abnormalities in at least one of the 28 locations examined. Joint abnormalities were divided into flattened bone contours and bone fragments. Genetic parameters were estimated for flattened bone contours, fragments and overall OC. Heritability was 0.08 for flattened bone contours, 0.22 for fragments, and 0.23 for overall OC. In fattening pigs, the prevalence of OC was 41%, and 12% of the individuals had severe OC. The prevalence was highest for individuals kept on a concrete, partially slatted floor with ad libitum feeding (58%), and lowest for individuals kept on a deep litter floor with restricted feeding (34%). These results demonstrate that the prevalence of OC can be reduced by applying deep litter floors and restricted feeding. The differences in growth patterns between pigs with and without OC were investigated also. After 28 days of age, piglets with severe OC at slaughter started to grow faster, and were significantly heavier after 70 days of age than pigs without OC at slaughter. These results suggest that OC might be related to high growth rates during a specific time period. To evaluate prospects for breeding against OC, selection responses were compared between breeding schemes using phenotypic selection based on own performance or progeny testing and genomic selection. The results show that, when genomic information has an equal accuracy as phenotypic information before selection, it will have a lower equilibrium response to selection because it has a larger Bulmer effect. Especially for low heritable traits, genomic selection was of additional value over traditional selection. The general discussion argues that OC has both economical and practical relevance for the current horse industry. Simulations showed potential for genomic selection compared to the current breeding program in the Dutch warmblood horse (KWPN), even with small reference populations. In pigs, OC is a more serious problem in sows than in fattening pigs, because sows live longer. A decrease in OC prevalence will, therefore, yield larger economic and welfare benefits then apparent from results on fattening pigs. Also for pigs, simulations indicated possibilities for genomic selection. The final section of the general discussion proposes directions for future research.</p
Genetics of survival in cannibalistic laying hens: The contribution of social effects
No full textMortality due to cannibalism in laying hens is a worldwide economic and welfare problem occurring in all types of commercial poultry housing systems. Due to prohibition of beak-trimming and the traditional battery system in the European Union in the near future, mortality due to cannibalism in laying hens may increase. To reduce mortality in laying hens, it is possible to use genetic selection. Mortality due to cannibalism, however, depends on social interactions between group members. Traditional selection methods neglect these social interactions, meaning that they ignore the genetic effect an individual has on its group members. These methods are, therefore, not very effective. The main aim of this thesis is to investigate the effect of social interactions on the heritable variance in mortality due to cannibalism in laying hens and to develop a selection method that takes into account social interactions. To investigate the effect of social interactions on the heritable variance in mortality due to cannibalism, genetic parameters for direct and associative effects on survival time in three layer lines were estimated. For all three layer lines it was found that social interactions contribute approximately two-third of the heritable variation in survival time. The heritable variation in survival time is, therefore, substantially larger than suggested by the traditional methods currently used in poultry breeding. To improve traits affected by social interactions in laying hens, a solution is to select individually housed candidates based on the performance of their full sibs kept in family groups. Theoretical results suggest that this selection method offers good opportunities to improve traits affected by social interactions. A selection experiment was applied aiming to improve mortality due to cannibalism in laying hens using selection based on relatives. After one generation, mortality was 10% lower in the selection line compared to the control. In the second generation, no significant effect was found, which seemed to be related to environmental factors. Results in this thesis suggest that prospects for reducing mortality due to cannibalism by means of genetic selection are good. Using selection methods that incorporate social interactions may lead to substantial reduction of one of the major welfare problems in egg production. Further research is needed to investigate the effect of group size and kin recognition on social interactions. <br/
History and structure of the closed pedigreed population of Icelandic Sheepdogs
No full textAbstract Background Dog breeds lose genetic diversity because of high selection pressure. Breeding policies aim to minimize kinship and therefore maintain genetic diversity. However, policies like mean kinship and optimal contributions, might be impractical. Cluster analysis of kinship can elucidate the population structure, since this method divides the population in clusters of related individuals. Kinship-based analyses have been carried out on the entire Icelandic Sheepdog population, a sheep-herding breed. Results Analyses showed that despite increasing population size and deliberately transferring dogs, considerable genetic diversity has been lost. When cluster analysis was based on kinships calculated seven generation backwards, as performed in previous studies, results differ markedly from those based on calculations going back to the founder-population, and thus invalidate recommendations based on previous research. When calculated back to the founder-population, kinship-based clustering reveals the distribution of genetic diversity, similarly to strategies using mean kinship. Conclusion Although the base population consisted of 36 Icelandic Sheepdog founders, the current diversity is equivalent to that of only 2.2 equally contributing founders with no loss of founder alleles in descendants. The maximum attainable diversity is 4.7, unlikely achievable in a non-supervised breeding population like the Icelandic Sheepdog. Cluster analysis of kinship coefficients can provide a supporting tool to assess the distribution of available genetic diversity for captive population management.</p
Indirect genetic effects clarify how traits can evolve even when fitness does not
No full textAcknowledgmenets We thank Cortland Griswold, Loeske Kruuk, Alastair Wilson, Piter Bijma, Lucas Marie-Orleach, Joel McGlothlin, and an anonymous reviewer for comments and discussions that helped to improve this manuscript. The authors declare no conflicts of interest.Peer reviewe
Socially Affected Traits animal breeding socially affected traits , Inheritance and Genetic Improvement
No full textSupplemental Material for Bijma, Wientjes and Calus, 2020
No full textThis file contains- R-codes used for simulation- Supplementary Tables S1 and S2- Excel File with empirical regression coefficients</div
Effects of pedigree errors on the efficiency of conservation decisions
No full textAbstract Conservation schemes often aim at increasing genetic diversity by minimizing kinship, and the best method to achieve this goal, when pedigree data is available, is to apply optimal contributions. Optimal contributions calculate contributions per animal so that the weighted average mean kinship among candidate parents is minimized. This approach assumes that pedigree data is correct and complete. However, in practice, pedigrees often contain errors: parents are recorded incorrectly or even missing. We used simulations to investigate the effect of these two types of errors on minimizing kinship. Our findings show that a low percentage of wrong parent information reduces the effect of optimal contributions. When the percentage of wrong parent information is above 15%, the population structure and type of errors, should be taken into account before applying optimal contributions. Optimal contributions based on pedigrees with missing parent information hampers conservation of genetic diversity; however, missing parent information can be corrected. It is crucial to know which animals are founders. We strongly recommend that pedigree registration include whether missing parents are either true founders or non-founders.</p
Genetics of social interactions in laying hens : improving survival and productivity
No full textThrough social interactions, individuals affect one another’s phenotype. The heritable effect of an animal on its own phenotype is referred to as a direct genetic effect (DGE), while the heritable effect of an animal on the phenotype of a conspecific is referred to as an indirect genetic effect (IGE). Both DGEs and IGEs determine a population’s potential to respond to selection, i.e. the total genetic variance. This thesis focusses on the genetic architecture of survival time in laying hens showing feather pecking and cannibalistic behaviour, a well-known social interaction trait. DGEs and IGEs for survival time were estimated in purebred and crossbred laying hens. Unrelated birds of the same line or cross were kept in groups of four. Beaks were kept intact. Results showed that IGEs contribute around half of the total genetic variance in purebreds and the majority of the total genetic variance in crossbreds (up to 87%). The direct-indirect genetic correlations were close to zero in purebreds and moderately to highly negative in crossbreds. Consequently, unlike purebreds, crossbreds would fail to respond positively to mass selection. To ensure positive response to selection, animals should be selected based on their total breeding value. Moreover, increased response to selection can be obtained when including genotypic information. With genomics, the accuracy of estimated breeding values increased with 20 up to 110%, showing the added value of genotypic information. In addition, the genetic correlation between survival time (individual data) and early egg production (pooled data) was calculated. Results showed that, unlike for individual data, pooled data cannot be used to estimate DGEs and IGEs. However, pooled data can be used to estimate total genetic effects. The default bivariate model did not allow all non-genetic correlations between both traits to be fitted and, therefore, resulted in biased genetic parameter estimates. When this issue was resolved, the genetic correlation between survival time and early egg production was slightly negative (-0.09), but not significantly different from zero. Finally, the interpretation of as a measure of inheritance for social interaction traits was discussed. expresses the total genetic variance relative to the phenotypic variance. Throughout this thesis it became clear that, for social interaction traits, the level of data collection (individual vs pooled data) and the within-group relatedness affects the phenotypic variance and, consequently, affects . Therefore, can differ between experimental set-ups, even though the underlying genetic parameters are the same. This is undesirable for the comparison of studies. For survival time, a 30 up to 40% decrease in was observed when using pooled data instead of individual data. This illustrates that , as a measure of inheritance, should be used with care
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