Response to mass selection when the genotype by environment interaction is modelled as a linear reaction norm

Kolmodin, Rebecka; Bijma, P.

doi:10.1186/1297-9686-36-4-435

Cited by 60 publications

(37 citation statements)

References 15 publications

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“…Consequently, there may be less genetic variability of production in this zone. Importantly, the optimum selection environment depends not only on the breed type of the animals (tropically adapted or poorly adapted), but also depends on the heritability, on the degree of G × E and on the correlation between level and slope of the reaction norms (Kolmodin and Bijma, 2004).…”

Section: Discussionmentioning

confidence: 99%

Genetics of heat tolerance for milk yield and quality in Holsteins

Júnior

Bignardi

Pereira

et al. 2017

Animal

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Tropical and sub-tropical climates are characterized by high temperature and humidity, during at least part of the year. Consequently, heat stress is common in Holstein cattle and productive and reproductive losses are frequent. Our objectives were as follows: (1) to quantify losses in production and quality of milk due to heat stress; (2) to estimate genetic correlations within and between milk yield (MY) and milk quality traits; and (3) to evaluate the trends of genetic components of tolerance to heat stress in multiple lactations of Brazilian Holstein cows. Thus, nine analyses using two-trait random regression animal models were carried out to estimate variance components and genetic parameters over temperature-humidity index (THI) values for MY and milk quality traits (three lactations: MY × fat percentage (F%), MY × protein percentage (P%) and MY × somatic cell score (SCS)) of Brazilian Holstein cattle. It was demonstrated that the effects of heat stress can be harmful for traits related to milk production and milk quality of Holstein cattle even though most herds were maintained in a modified environment, for example, with fans and sprinklers. For MY, the effect of heat stress was more detrimental in advanced lactations (−0.22 to −0.52 kg/day per increase of 1 THI unit). In general, the mean heritability estimates were higher for lower THI values and longer days in milk for all traits. In contrast, the heritability estimates for SCS increased with increasing THI values in the second and third lactation. For each trait studied, lower genetic correlations (different from unity) were observed between opposite extremes of THI (THI 47 v. THI 80) and in advanced lactations. The genetic correlations between MY and milk quality trait varied across the THI scale and lactations. The genotype × environment interaction due to heat stress was more important for MY and SCS, particularly in advanced lactations, and can affect the genetic relationship between MY and milk quality traits. Selection for higher MY, F% or P% may result in a poor response of the animals to heat stress, as a genetic antagonism was observed between the general production level and specific ability to respond to heat stress for these traits. Genetic trends confirm the adverse responses in the genetic components of heat stress over the years for milk production and quality. Consequently, the selection of Holstein cattle raised in modified environments in both tropical and sub-tropical regions should take into consideration the genetic variation in heat stress.

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Section: Discussionmentioning

confidence: 99%

Genetics of heat tolerance for milk yield and quality in Holsteins

Júnior

Bignardi

Pereira

et al. 2017

Animal

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“…The genetic variance in host performance as a function of pathogen burden was calculated as xk PB Gx PB (Kolmodin & Bijma, 2004), where…”

Section: (Iv) Genetic Analysis Of Simulated Datamentioning

confidence: 99%

Genetic analysis of tolerance to infections using random regressions: a simulation study

Kause

2011

Genet. Res.

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SummaryTolerance to infections is the ability of a host to limit the impact of a given pathogen burden on host performance. This simulation study demonstrated the merit of using random regressions to estimate unbiased genetic variances for tolerance slope and its genetic correlations with other traits, which could not be obtained using the previously implemented statistical methods. Genetic variance in tolerance was estimated as genetic variance in regression slopes of host performance along an increasing pathogen burden level. Random regressions combined with covariance functions allowed genetic variance for host performance to be estimated at any point along the pathogen burden trajectory, providing a novel means to analyse infection-induced changes in genetic variation of host performance. Yet, the results implied that decreasing family size as well as a non-zero environmental or genetic correlation between initial host performance before infection and pathogen burden led to biased estimates for tolerance genetic variance. In both cases, genetic correlation between tolerance slope and host performance in a pathogen-free environment became artificially negative, implying a genetic trade-off when it did not exist. Moreover, recording a normally distributed pathogen burden as a threshold trait is not a realistic way of obtaining unbiased estimates for tolerance genetic variance. The results show that random regressions are suitable for the genetic analysis of tolerance, given suitable data structure collected either under field or experimental conditions.

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“…A special case is one threshold, in which the terms relating to the second threshold in equations (8a) and (8b) can be omitted. An example is the avoidance of poor animal performance that may reduce consumer acceptance of the production system, so an objective may be to reduce the proportion of animals below a certain threshold [22].…”

Section: Differential Profit Based On Thresholdsmentioning

confidence: 99%

Selection for uniformity in livestock by exploiting genetic heterogeneity of residual variance

2007

Self Cite

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-In some situations, it is worthwhile to change not only the mean, but also the variability of traits by selection. Genetic variation in residual variance may be utilised to improve uniformity in livestock populations by selection. The objective was to investigate the effects of genetic parameters, breeding goal, number of progeny per sire and breeding scheme on selection responses in mean and variance when applying index selection. Genetic parameters were obtained from the literature. Economic values for the mean and variance were derived for some standard non-linear profit equations, e.g. for traits with an intermediate optimum. The economic value of variance was in most situations negative, indicating that selection for reduced variance increases profit. Predicted responses in residual variance after one generation of selection were large, in some cases when the number of progeny per sire was at least 50, by more than 10% of the current residual variance. Progeny testing schemes were more efficient than sib-testing schemes in decreasing residual variance. With optimum traits, selection pressure shifts gradually from the mean to the variance when approaching the optimum. Genetic improvement of uniformity is particularly interesting for traits where the current population mean is near an intermediate optimum.heterogeneity of variance / index selection / uniformity / economic value / optimum trait

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Response to mass selection when the genotype by environment interaction is modelled as a linear reaction norm

Cited by 60 publications

References 15 publications

Genetics of heat tolerance for milk yield and quality in Holsteins

Genetics of heat tolerance for milk yield and quality in Holsteins

Genetic analysis of tolerance to infections using random regressions: a simulation study

Selection for uniformity in livestock by exploiting genetic heterogeneity of residual variance

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