References of "Gengler, Nicolas"
     in
Bookmark and Share    
Peer Reviewed
See detailAccounting for heterogeneous variances in multi-trait evaluation of Jersey type traits
Gengler, Nicolas ULg; Wiggans, G. R.; Thornton, L. et al

in Journal of Dairy Science (2005), 88(Suppl. 1), 11-11

Detailed reference viewed: 31 (23 ULg)
Peer Reviewed
See detailStandard errors of solutions in large scale mixed models, application to linear and curvilinear effects of inbreeding on production traits.
Gengler, Nicolas ULg; Croquet, C.

in Journal of Dairy Science (2005), 88(Suppl. 1), 74-74

Detailed reference viewed: 17 (3 ULg)
See detailLes marqueurs génétiques
Renaville, Robert ULg; Parmentier, Isabelle; Falaki, Mohammed et al

in Thewis, André; Bourbouse, A.; Compère, Roger (Eds.) et al Manuel de zootechnie comparée Nord-Sud (2005)

Detailed reference viewed: 29 (0 ULg)
Full Text
Peer Reviewed
See detailAdjustment for heterogeneous covariance due to herd milk yield by transformation of test-day random regressions
Gengler, Nicolas ULg; Wiggans, George; Gillon, Alain ULg

in Journal of Dairy Science (2005), 88

A method of accounting for differences in covariance components of test-day milk records was developed based on transformation of regressions for random effects. Preliminary analysis indicated that ... [more ▼]

A method of accounting for differences in covariance components of test-day milk records was developed based on transformation of regressions for random effects. Preliminary analysis indicated that genetic and nongenetic covariance structures differed by herd milk yield. Differences were found for phenotypic covariances and also for genetic, permanent environmental, and herd-time covariances. Heritabilities for test-day milk yield tended to be lower at the end and especially at the start of lactation; they also were higher (maximum of ∼25%) for high-yield herds and lower (maximum of 15%) for low-yield herds. Permanent environmental variances were on average 10% lower in highyield herds. Relative herd-time variances were ∼10% at start of lactation and then began to decrease regardless of herd yield; high-yield herds increased in midlactation followed by another decrease, and medium-yield herds increased at the end of lactation. Regressors for random regression effects were transformed to adjust for heterogeneity of test-day yield covariances. Some animal reranking occurred because of this transformation of genetic and permanent environmental effects. When genetic correlations between environments were allowed to differ from 1, some additional animal reranking occurred. Correlations of variances of genetic and permanent-environmental regression solutions within herd, test-day, and milking frequency class with class mean milk yields were reduced with adjustment for heterogeneous covariance. The method suggests a number of innovative solutions to issues related to heterogeneous covariance structures, such as adjusted estimates in multibreed evaluation. [less ▲]

Detailed reference viewed: 9 (2 ULg)
Full Text
See detailGenetic evaluation of cow survival using a lactation random regression model
Gengler, Nicolas ULg; Vanderick, Sylvie ULg; Mayeres, Patrick et al

in INTERBULL Bulletin (2005), 33

Detailed reference viewed: 8 (3 ULg)
Full Text
See detailEvaluations génétiques laitières: changement de base
Félix, Alain; Vanderick, Sylvie ULg; Gengler, Nicolas ULg

Article for general public (2005)

Detailed reference viewed: 14 (7 ULg)
Full Text
Peer Reviewed
See detailEstimation of (co)variance components across breeds by a test-day model adapted to New Zealand dairy cattle.
Vanderick, Sylvie ULg; Harris, Bevin; Mayeres, Patrick et al

in Proceedings of the British Society of Animal Science (2005)

Detailed reference viewed: 2 (1 ULg)
Full Text
Peer Reviewed
See detailEstimation of (co)variance components across breeds by a test-day model adapted to New Zealand dairy cattle.
Vanderick, Sylvie ULg; Harris, Bevin; Mayeres, Patrick et al

Poster (2005)

Detailed reference viewed: 36 (22 ULg)
Full Text
Peer Reviewed
See detailComparison of external morphological traits of newborns to inner morphological traits of the dam in the double-muscled Belgian Blue Beef breed
Coopman, F.; Gengler, Nicolas ULg; Groen, A. F. et al

in Journal of Animal Breeding & Genetics (2004), 121(2), 128-134

In the double-muscled (DM) Belgian Blue Beef (BBB) breed, caesarean section (CS) is used as a routine management tool to prevent dystocia. This practice is criticized on animal welfare grounds. With ... [more ▼]

In the double-muscled (DM) Belgian Blue Beef (BBB) breed, caesarean section (CS) is used as a routine management tool to prevent dystocia. This practice is criticized on animal welfare grounds. With unassisted (natural) births, difficulties arise because of disproportion between the sizes of the newborn and inner pelvic sizes of the dam. In this study external morphological traits of newborns are compared with inner morphological traits of the dam. Results of this study indicate that in the DM-BBB, CS is the only means to successful calving. Therefore, no calving ease scores are available to select for less dystocia in this breed. Selection for fewer CS must be achieved by focusing on lower birth weight (BW) and decreased muscular conformation at birth, both having a sufficiently high heritability. Simultaneously, pelvic sizes of the dam should be increased. It is very likely that the look of the DM-BBB will change when selecting for less dystocia. [less ▲]

Detailed reference viewed: 16 (2 ULg)
Full Text
Peer Reviewed
See detailPrediction of daily milk, fat, and protein production by a random regression test-day model
Mayeres, P.; Stoll, J.; Bormann, J. et al

in Journal of Dairy Science (2004), 87(6), 1925-1933

Test-day genetic evaluation models have many advantages compared with those based on 305-d lactations; however, the possible use of test-day model (TDM) results for herd management purposes has not been ... [more ▼]

Test-day genetic evaluation models have many advantages compared with those based on 305-d lactations; however, the possible use of test-day model (TDM) results for herd management purposes has not been emphasized. The aim of this paper was to study the ability of a TDM to predict production for the next test day and for the entire lactation. Predictions of future production and detection of outliers are important factors for herd management (e. g., detection of health and management problems and compliance with quota). Because it is not possible to predict the herd-test-day (HTD) effect per se, the fixed HTD effect was split into 3 new effects: a fixed herd-test month-period effect, a fixed herd-year effect, and a random HTD effect. These new effects allow the prediction of future production for improvement of herd management. Predicted test-day yields were compared with observed yields, and the mean prediction error computed across herds was found to be close to zero. Predictions of performance records at the herd level were even more precise. Discarding herds enrolled in milk recording for <1 yr and animals with very few tests in the evaluation file improved correlations between predicted and observed yields at the next test day (correlation of 0.864 for milk in first-lactation cows as compared with a correlation of 0.821 with no records eliminated). Correlations with the observed 305-d production ranged from 0.575 to 1 for predictions based on 0 to 10 test-day records, respectively. Similar results were found for second and third lactation records for milk and milk components. These findings demonstrate the predictive ability of a TDM. [less ▲]

Detailed reference viewed: 22 (4 ULg)
Full Text
Peer Reviewed
See detailType trait (co)variance components for five dairy breeds
Wiggans, G. R.; Gengler, Nicolas ULg; Wright, J. R.

in Journal of Dairy Science (2004), 87(7), 2324-2330

(Co)variance components were estimated for final score and 14 or 15 linear type traits for the Ayrshire, Brown Swiss, Guernsey, Jersey, and Milking Shorthorn breeds. Appraisals from 1995 or later were ... [more ▼]

(Co)variance components were estimated for final score and 14 or 15 linear type traits for the Ayrshire, Brown Swiss, Guernsey, Jersey, and Milking Shorthorn breeds. Appraisals from 1995 or later were used. New estimates were calculated to accommodate changes in scoring of traits and because of a change from multiplicative to additive adjustment for age and lactation stage. The adjustment method was changed for better support of the adjustment for heterogeneous variance within iteration, which was implemented in 2002. The largest changes in heritability were an increase of 0.10 for rump angle for Milking Shorthorns and a decrease of 0.11 for udder depth for Jerseys. The new estimates of (co)variance components should provide improved accuracy of type evaluations, particularly for traits that have had variance changes over time. [less ▲]

Detailed reference viewed: 14 (1 ULg)
Full Text
Peer Reviewed
See detailEstimated heterogeneity of phenotypic variance of test-day yield with a structural variance model
Gengler, Nicolas ULg; Wiggans, George; Gillon, Alain ULg

in Journal of Dairy Science (2004), 87

First-lactation test-day milk, fat, and protein yields from New York, Wisconsin, and California herds from 1990 through 2000 were adjusted additively for age and lactation stage. A random regression model ... [more ▼]

First-lactation test-day milk, fat, and protein yields from New York, Wisconsin, and California herds from 1990 through 2000 were adjusted additively for age and lactation stage. A random regression model with thirdorder Legendre polynomials for permanent environmental and genetic effects was used. The model included a random effect with the same polynomial regressions for 2 yr of calvings within herd (herd-time effect) to provide herd-specific lactation curves that can change every 2 yr. (Co)variance components were estimated using expectation-maximization REML simultaneously with phenotypic variances that were modeled using a structural variance model. Maximum heritability for test-day milk yield was estimated to be ∼20% around 200 to 250 d in milk; heritabilities were slightly lower for test-day fat and protein yields. Herd-time effects explained 12 to 20% of phenotypic variance and had the greatest impact at start of lactation. Variances of test-day yields increased with time, subclass size, and milking frequency. Test month had limited influence on variance. Variance increased for cows in herds with low and high milk yields and for early and late lactation stages. Repeatabilities of variances observed for a given class of herd, test-day, and milking frequency were 14 to 17% across nested variance subclasses based on lactation stage. [less ▲]

Detailed reference viewed: 4 (2 ULg)
Peer Reviewed
See detailPit-I and other somatotrope candidate genes to optimize selection for milk traits in bovine species: the 21 century's strategy.
Parmentier, Isabelle; Gillard, Nathalie; Abras, Sven et al

Poster (2003, February)

Detailed reference viewed: 7 (0 ULg)
Full Text
Peer Reviewed
See detailWithin-herd effects of age at test day and lactation stage on test-day yields
Bormann, J.; Wiggans, G. R.; Druet, Tom ULg et al

in Journal of Dairy Science (2003), 86(11), 3765-3774

Variance ratios were estimated for random within-herd effects of age at test day and lactation stage, on test-day yield and somatic cell score to determine whether including these effects would improve ... [more ▼]

Variance ratios were estimated for random within-herd effects of age at test day and lactation stage, on test-day yield and somatic cell score to determine whether including these effects would improve the accuracy of estimation. Test-day data starting with 1990 calvings for the entire US Jersey population and Holsteins from California, Pennsylvania, Wisconsin, and Texas were analyzed. Test-day yields were adjusted for across-herd effects using solutions from a regional analysis. Estimates of the relative variance ( fraction of total variance) due to within-herd age effects were small, indicating that regional adjustments for age were adequate. The relative variances for within-herd lactation stage were large enough to indicate that accuracy of genetic evaluations could be improved by including herd stage effects in the model for milk, fat, and protein, but not for somatic cell score. Because the within-herd lactation stage effect is assumed to be random, the effect is regressed toward the regional effects for small herds, but in large herds, lactation curves become herd specific. Model comparisons demonstrated the greater explanatory power of the model with a within-herd-stage effect as prediction error standard deviations were greater for the model without this effect. The benefit of the within-herd-stage effects was confirmed in a random regression model by comparing variance components from models with and without random within-herd regressions and through log-likelihood ratio tests. [less ▲]

Detailed reference viewed: 16 (0 ULg)
Full Text
Peer Reviewed
See detailEstimating internal pelvic sizes using external body measurements in the double-muscled Belgian Blue beef breed
Coopman, F.; de Smet, S.; Gengler, Nicolas ULg et al

in Animal Science (2003), 76(Part 2), 229-235

In the double-muscled (DM) Belgian Blue beef (BBB) breed, caesarean section (CS) is being applied systematically as a management tool to prevent dystocia. As a matter of fact, CS is the only possible way ... [more ▼]

In the double-muscled (DM) Belgian Blue beef (BBB) breed, caesarean section (CS) is being applied systematically as a management tool to prevent dystocia. As a matter of fact, CS is the only possible way of calving in the breed. High birth weight and a relatively small pelvic area are the main causes of dystocia and, in the DM-BBB breed, the reasons for the systematically applied CS. Selection for lower birth weight and larger pelvic sizes might reduce dystocia and routine CS. Few data on inner pelvic sizes of pedigree animals are available. Using external measurements to estimate the inner pelvic sizes might be an option to resolve this problem. In this study, animals of the DM-BBB breed were measured and weighed on farms and in abattoirs. External and internal pelvic sizes increased with live weight and age of the animals. Gender had a significant influence on inner pelvic traits. Increased muscular conformation was associated with decreased inner pelvic dimensions. Models with weight, gender, age, withers height and outer pelvic width (TcTc) can be used to estimate inner pelvic sizes (R-2 between 0.35 and 0.77). The estimated inner pelvic sizes can then be used to genetically evaluate pelvic traits in the DM-BBB breed. Improving weight, withers height and TcTc width in combination with lowering muscular conformation may help to decrease the high rate of caesarean section in the DM-BBB. [less ▲]

Detailed reference viewed: 64 (2 ULg)
Full Text
See detailIntegrated detection and correction of outliers in a random regression test-day model
Mayeres, Patrick; Gillon, Alain ULg; Gengler, Nicolas ULg

in INTERBULL Bulletin (2003), 31

Detailed reference viewed: 13 (4 ULg)
See detailEvaluations génétiques des bovins laitiers en Wallonie (Belgique)
Gengler, Nicolas ULg; Vanderick, Sylvie ULg; Mayeres, Patrick et al

Computer development (2002)

Detailed reference viewed: 19 (8 ULg)
Full Text
See detailAnalysis of longitudinal data for selection and management
Gengler, Nicolas ULg; Mayeres, Patrick

in Book of Abstracts of the 53rd Annual Meeting of the European Association for Animal Production (2002, September)

Until recently the description of dynamic biological processes was done using static models even if those biological processes such as lactation or growth provided us with longitudinal data. A classical ... [more ▼]

Until recently the description of dynamic biological processes was done using static models even if those biological processes such as lactation or growth provided us with longitudinal data. A classical example was the use of lactational milk yields even if individual test-days describing the underlying lactation curves were available. Similarly for growth, weights were corrected phenotypically to fit into categories like weaning or yearling weights. Several recent developments stimulated the research on alternative methods describing the evolution of the mean and the variances of continuos dynamic biological processes. These developments were especially the extension of repeatability models towards random regressions and the development of the (co)variance function approach, but the development of better computers allowing the storage and the processing of a huge quantity of data. Despite this the analysis of certain types of longitudinal data as test-day yields in large populations and/or international settings is still a major challenge. But a very important aspect of the analysis of longitudinal data is often forgotten: they give us other information than the one classically extracted from genetic evaluation systems. In fact, the detailed modeling of dynamic biological processes provides opportunities for the development of advanced management tools. This may have a large influence on the way genetic evaluation systems may evolve in the future, making them integrated systems for the management and selection of animals. [less ▲]

Detailed reference viewed: 14 (3 ULg)