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Bjørg Heringstad - One of the best experts on this subject based on the ideXlab platform.

  • short communication validation of two animal models for estimation of Genetic Trends for female fertility in norwegian dairy cattle
    Journal of Dairy Science, 2003
    Co-Authors: I M Andersenranberg, Gunnar Klemetsdal, Bjørg Heringstad
    Abstract:

    Two animal models were compared with respect to potential bias in Genetic Trend estimates for female fertility and for their predictive ability. In addition to either a fixed effect for month of first insemination or for month-year of first insemination, the models had fixed effects of age and double insemination and random effects of herd-year and animal. The model with a fixed effect of month of first insemination had a larger positive Genetic Trend for 56-d nonreturn rate in virgin heifers (0.16% yr), smaller downward bias, and somewhat higher predictive ability. These results demonstrate the importance of verifying models to be used in the calculation of breeding values.

  • variance components and Genetic Trend for somatic cell count in norwegian cattle
    Livestock Production Science, 2003
    Co-Authors: Jorgen Odegard, G Klemetsdal, Bjørg Heringstad
    Abstract:

    Abstract First-lactation mean somatic cell score (LSCS) in Norwegian Cattle, sampled during 1978–1995 for 1.3 million cows from 2043 sires, were used in Genetic analyses. Variance components and Genetic Trends were estimated for four linear sire models with alternative definitions of contemporary group effects. Model validation demonstrated necessity to separate environmental time Trends from Genetic Trends by modelling contemporary groups as fixed. A model with fixed effect of herd×year was chosen, because it was the simplest and had less significant bias. The heritability estimate for LSCS using this model was 0.11. The resulting Genetic Trend for all relevant progeny tested bulls was approximately flat, but bull sires born 1984, onwards, showed consistently favourable selection differential for LSCS, most likely due to indirect selection resulting from selection on clinical mastitis.

  • short communication validation of estimates of Genetic Trend in the norwegian cattle population
    Journal of Dairy Science, 1999
    Co-Authors: Bjørg Heringstad, Gunnar Klemetsdal, John Ruane
    Abstract:

    Abstract We examined alternative definitions of herd × year effects in models used to estimate Genetic Trends for clinical mastitis in Norwegian Cattle. The model with random herd x year effects showed significant bias and clearly overestimated Genetic Trend. To obtain unbiased estimates of Genetic Trend for clinical mastitis with this data, herd x year should be defined as fixed. Our results emphasized the importance of validating estimates of Genetic Trend.

Vincent Ducrocq - One of the best experts on this subject based on the ideXlab platform.

  • A general approach for international Genetic evaluations robust to inconsistencies of Genetic Trends in national evaluations
    Interbull Bulletin, 2020
    Co-Authors: Vincent Ducrocq, Didier Boichard, I Delaunay, S Mattalia
    Abstract:

    This paper is a contribution from the PROTEJE project. It presents an approach which makes uses in a sire model of annual information (= average daughter yield deviations per year of performance and lactation number) for each sire. It is shown that with a suitable sire model (including a year x country effect, a lactation x country effect and a within country regression on age of the sire when his daughters are born), the Genetic parameters and the sire solutions obtained are robust to overor under-estimation of Genetic Trend in the national models. The approach has other benefits: validation of Genetic Trends is no longer critical (although obviously desirable), deregression becomes obsolete. An extension to categorical or survival traits is briefly described and a general strategy for the computation of equivalent daughter contributions and daughter yield deviations and their validation is proposed.

  • An approximate multitrait model for Genetic evaluation in dairy cattle with a robust estimation of Genetic Trends (Open Access publication)
    Genetics Selection Evolution, 2007
    Co-Authors: Jan Lassen, Morten Kargo Sørensen, Per Madsen, Vincent Ducrocq
    Abstract:

    In a stochastic simulation study of a dairy cattle population three multitrait models for estimation of Genetic parameters and prediction of breeding values were compared. The first model was an approximate multitrait model using a two-step procedure. The first step was a single trait model for all traits. The solutions for fixed effects from these analyses were subtracted from the phenotypes. A multitrait model only containing an overall mean, an additive Genetic and a residual term was applied on these preadjusted data. The second model was similar to the first model, but the multitrait model also contained a year effect. The third model was a full multitrait model. Genetic Trends for total merit and for the individual traits in the breeding goal were compared for the three scenarios to rank the models. The full multitrait model gave the highest Genetic response, but was not significantly better than the approximate multitrait model including a year effect. The inclusion of a year effect into the second step of the approximate multitrait model significantly improved the Genetic Trend for total merit. In this study, estimation of Genetic parameters for breeding value estimation using models corresponding to the ones used for prediction of breeding values increased the accuracy on the breeding values and thereby the Genetic progress.

  • An approximate multitrait model for Genetic evaluation in dairy cattle with a robust estimation of Genetic Trends.
    Genetics Selection Evolution, 2007
    Co-Authors: Jan Lassen, Morten Kargo Sørensen, Per Madsen, Vincent Ducrocq
    Abstract:

    : In a stochastic simulation study of a dairy cattle population three multitrait models for estimation of Genetic parameters and prediction of breeding values were compared. The first model was an approximate multitrait model using a two-step procedure. The first step was a single trait model for all traits. The solutions for fixed effects from these analyses were subtracted from the phenotypes. A multitrait model only containing an overall mean, an additive Genetic and a residual term was applied on these preadjusted data. The second model was similar to the first model, but the multitrait model also contained a year effect. The third model was a full multitrait model. Genetic Trends for total merit and for the individual traits in the breeding goal were compared for the three scenarios to rank the models. The full multitrait model gave the highest Genetic response, but was not significantly better than the approximate multitrait model including a year effect. The inclusion of a year effect into the second step of the approximate multitrait model significantly improved the Genetic Trend for total merit. In this study, estimation of Genetic parameters for breeding value estimation using models corresponding to the ones used for prediction of breeding values increased the accuracy on the breeding values and thereby the Genetic progress.

  • Validation of an approximate approach to compute Genetic correlations between longevity and linear traits
    Genetics Selection Evolution, 2006
    Co-Authors: Joaquim Tarrés, Jesús Piedrafita, Vincent Ducrocq
    Abstract:

    The estimation of Genetic correlations between a nonlinear trait such as longevity and linear traits is computationally difficult on large datasets. A two-step approach was proposed and was checked via simulation. First, univariate analyses were performed to get Genetic variance estimates and to compute pseudo-records and their associated weights. These pseudo-records were virtual performances free of all environmental effects that can be used in a BLUP animal model, leading to the same breeding values as in the (possibly nonlinear) initial analyses. By combining these pseudo-records in a multiple trait model and fixing the Genetic and residual variances to their values computed during the first step, we obtained correlation estimates by AI-REML and approximate MT-BLUP predicted breeding values that blend direct and indirect information on longevity. Mean Genetic correlations and reliabilities obtained on simulated data confirmed the suitability of this approach in a wide range of situations. When nonzero residual correlations exist between traits, a sire model gave nearly unbiased estimates of Genetic correlations, while the animal model estimates were biased upwards. Finally, when an incorrect Genetic Trend was simulated to lead to biased pseudo-records, a joint analysis including a time effect could adequately correct for this bias.

Didier Boichard - One of the best experts on this subject based on the ideXlab platform.

  • A general approach for international Genetic evaluations robust to inconsistencies of Genetic Trends in national evaluations
    Interbull Bulletin, 2020
    Co-Authors: Vincent Ducrocq, Didier Boichard, I Delaunay, S Mattalia
    Abstract:

    This paper is a contribution from the PROTEJE project. It presents an approach which makes uses in a sire model of annual information (= average daughter yield deviations per year of performance and lactation number) for each sire. It is shown that with a suitable sire model (including a year x country effect, a lactation x country effect and a within country regression on age of the sire when his daughters are born), the Genetic parameters and the sire solutions obtained are robust to overor under-estimation of Genetic Trend in the national models. The approach has other benefits: validation of Genetic Trends is no longer critical (although obviously desirable), deregression becomes obsolete. An extension to categorical or survival traits is briefly described and a general strategy for the computation of equivalent daughter contributions and daughter yield deviations and their validation is proposed.

  • a simulation study of the effect of connectedness on Genetic Trend
    Genetics Selection Evolution, 1996
    Co-Authors: E Hanocq, Didier Boichard, J L Foulley
    Abstract:

    Un schema de selection constitue de quatre sous-populations est simule durant sept generations separees. Les mâles sont selectionnes a l'issue de leur testage sur descendance. Des mâles de connexion sont utilises en proportion variable afin d'estimer le niveau genetique de chaque sous-population, ou groupe de taureaux. La politique de renouvellement adoptee permet l'existence de flux de genes entre les sous-populations. En l'absence de connexion, les differences genetiques entre groupes de taureaux ne sont pas estimables et le progres genetique global est limite. En presence de connexions en faible quantite (proportion de taureaux de connexion de 1/16), la precision des contrastes entre sous-populations est reduite mais le flux de genes existant permet l'augmentation du progres genetique global, en particulier a la premiere generation de selection. Un degre de connexion important ameliore la precision de l'evaluation genetique mais l'accroissement supplementaire du progres genetique est faible.

  • three methods to validate the estimation of Genetic Trend for dairy cattle
    Journal of Dairy Science, 1995
    Co-Authors: Didier Boichard, B Bonaiti, Anne Barbat, S Mattalia
    Abstract:

    Abstract Three methods are proposed to validate the estimation of Genetic Trend for dairy cattle. With the first method, official evaluations, which are generally derived from a repeatability animal model applied to lactation records from several parities, are compared with evaluations based only on first parity to determine whether estimates of Genetic Trend are similar. With the second method, daughter yield deviations are analyzed within sire by calving year to determine whether these deviations remain stable over time. With the third method, variations of successive official evaluations are analyzed by regression to determine any systematic Trend associated with information from additional daughters. Access to raw data is needed for the first two methods, but only published evaluations are needed for the third method. The three methods were applied to French Holstein evaluations calculated with 1990 and 1993 animal models and validated estimates of Genetic Trend based on information from the 1993 animal model.

  • three methods to validate the estimation of Genetic Trend in dairy cattle
    Interbull Bulletin, 1994
    Co-Authors: B Bonaiti, Didier Boichard, Anne Barbat, S Mattalia
    Abstract:

    - Threc mttods are proposed to validate the estimation of Genetic rend in dairy spccies. In the first one, the official prodfs, gencrally derived from a repearabil-iry animal model afplied to several lactaDons, are compared to proofs derivcd from firsr lacrarion dam only. Estimated genctic trcnds with both methods are lxpected to be similar. In thc second method, the within-sire daughter yield dcviations ar. e analysed by production year and are expected to remain stable. The rhird m6rhod analyscs variations of official proofs over timc by rcgrcssion. Any sysrematical Trend associated wirh new daughters information is an estimate of thi bias of the estimited gcnctic rcnd. The first two mcthod.s requirc ^a free access to raw data while the third one can be applied using published proofs. An application of thesc mcthods to the French Holsrein evaluation for ririlk yield is-piesented. '

E Ezra - One of the best experts on this subject based on the ideXlab platform.

  • Genetic analysis of somatic cell score and female fertility of israeli holsteins with an individual animal model
    Journal of Dairy Science, 1997
    Co-Authors: J I Weller, E Ezra
    Abstract:

    The individual animal model was used to analyze the conception index, defined as the inverse of the number of inseminations to conception, and mean lactation somatic cell scores (SCS) of Israeli Holsteins. In addition, multitrait variance components were estimated for these traits and for milk production traits. The animal model analyses included 440,558 lactation records for conception index and 224,869 SCS records collected over 10 yr. First parity heritabilities were 0.035 for conception index and 0.158 for SCS. Genetic correlations were negative between conception index and milk production traits and positive between SCS and milk production traits. Genetic correlations between first and second lactations were 0.9 for conception index and 0.7 for SCS. Phenotypic correlations were 0.08 and 0.3, respectively. Despite the low heritability for conception index, the standard deviation of the sire evaluations was 2%, and the range of evaluations was 10%. Predicted Genetic Trends for conception index and SCS were computed based on the current selection index of Israel. The realized Genetic Trend for the conception index was slightly positive, despite the predicted negative Trend, and the realized Genetic Trend for SCS, although positive as predicted, was fourfold the predicted value. The reasons for these discrepancies are not known.

L.d. Van Vleck - One of the best experts on this subject based on the ideXlab platform.

  • estimates of Genetic parameters and Genetic Trend for reproduction weight and wool characteristics of polypay sheep
    Livestock Science, 2006
    Co-Authors: K J Hanford, L.d. Van Vleck, G D Snowder
    Abstract:

    Abstract The objective was to describe Genetic parameters and Genetic changes in litter sizes at birth and weaning (LB and LW, n  = 9081), birth weight (BW, n  = 11,896), weaning weight (WW, n  = 11,104), fleece weight and grade (FW and FG, n  = 8872), and staple length (SL, n  = 1805) of Polypay sheep. Direct heritability estimates from single-trait analyses were 0.11 for LB, 0.02 for LW, 0.17 for BW, 0.18 for WW, 0.68 for FW, 0.36 for FG, and 0.76 for SL. Estimates of direct Genetic correlation were 0.40 between LB and LW, 0.57 between BW and WW, 0.65 between FW and SL, − 0.37 between FW and FG and − 0.70 between SL and FG. Breeding values (BV) from both single-trait and seven-trait analyses calculated using the parameters estimated from single-trait and two-trait analyses were compared across years of birth with respect to Genetic Trends. Estimated BV from both analyses for LB, LW, BW, WW and FW increased over time, while those for FG and SL were unchanged. Estimated changes in BV over time did not differ substantially for single-trait and seven-trait analyses, except for traits highly correlated with another trait that was responding to selection (i.e., LB, which was highly correlated to both LW and WW).

  • Genetic Trend and environmental effects in a population of cattle selected for twinning
    Journal of Animal Science, 1996
    Co-Authors: L.d. Van Vleck, K E Gregory
    Abstract:

    : A selection experiment was established in 1981 to increase twinning rate in cattle. Results reported are through 1993 calf crops. Estimates of Genetic parameters for a two-trait twinning and ovulation rate model with Genetic groups were as follows: heritabilities of .03 for twinning and .07 for ovulation rates with a Genetic correlation of nearly 1.00 and fractional permanent environmental variances of .06 for twinning and .05 for ovulation rate. Corresponding estimates when group effects were ignored were as follows: heritabilities of .08 and .08 and fractional permanent environmental variances of .02 and .04 for twinning and ovulation rates, respectively. Twinning rate (percentage) in the project at the U.S. Meat Animal Research Center has increased in all cows born in the project by year of calving from 3.4% in 1982 to 28.5% in 1993, a phenotypic increase of 25.1%. The estimated Genetic change in twinning of cows by year of calving using the groups model has been 15.2%. The increase in average Genetic value by year of birth has been 18.2% in twinning and 15.0% in ovulation rate from 1980 through 1991. Solutions for seven selected groups of foundation animals ranged from -6.0 to 33.1% and influenced Genetic Trend.

  • breed comparisons for growth traits adjusted for within breed Genetic Trend using expected progeny differences
    Journal of Animal Science, 1993
    Co-Authors: Rafael Nunezdominguez, L.d. Van Vleck, L V Cundiff
    Abstract:

    : Records (2,910) of birth (BWT), weaning (WW), and yearling weight (YW) of F1 calves produced in a top-cross experiment involving Angus, Hereford, Pooled Hereford, Charolais, Limousin, Simmental, Gelbvieh, Maine-Anjou, Chianina, Tarentaise, Shorthorn, and Salers bulls mated to Hereford and Angus cows and records (4,592) of WW on three-breed-cross calves out of 986 F1 females of the same breed crosses were used in this study. The purposes were to estimate how much of the EPD of the sires was realized in crossbred calves and to estimate sire breed effects for the traits adjusted for Genetic Trend and sire sampling. Published EPD for BWT, WW, YW, net maternal ability (MLK), and maternal WW (MAT) were used. Average regressions (kilograms/kilogram +/- SE) of BWT, WW, and YW of F1 calves on EPD of the sire were 1.04 +/- .10, .88 +/- .11, and 1.40 +/- .11, respectively. The regressions (b, kilograms/kilogram) were similar to the expected values of 1.0 except for YW. For WW of three-way-cross calves on MLK EPD of the maternal grandsire, b was 1.02 +/- .11, which was not different from the expected value of 1.0. Estimated sire-breed means were adjusted to a 1982 Genetic base by adding b times the difference of the 1982-breed-mean EPD and mean EPD of sires used in the study. Three different adjustments were compared using the b pooled across breeds, a separate b for each breed, and the expected b of 1.0. In general, the adjustments tended to regress breed of sire means toward the average of all breeds, particularly for BWT and WW of F1 calves, and for WW of three-breed crosses. The effect of type of adjustment varied among breeds, but in most cases small differences resulted from using average or expected b. For WW, the range for net maternal effects among breeds was larger than that for direct breed effects.

  • Estimation of heritability and Genetic Trend in populations at a physiological limit
    Theoretical and Applied Genetics, 1990
    Co-Authors: T. R. Famula, L.d. Van Vleck
    Abstract:

    Limits on physiological processes, though perhaps unknown, must exist. The reported simulations evaluate the effect of a physiological limit on the estimation of Genetic parameters and Genetic progress. Simulation experiments reveal no change in the estimate of heritability, even for limits as restrictive as 1.5 phenotypic standard deviations above the population mean. However, estimates of additive Genetic and environmental variance shrink as limits on performance increase in severity. Simulated physiological limits do not affect the rate of Genetic progress. However, absolute measures of estimated Genetic change are less than those predicted by response equations.