Materials and Methods

Results of MPT, AI and SBI of the Hanoverian Studbook Society (HSS) were made available for this study. Information on 36,441 Hanoverian warmblood horses

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born between 1992 and 2005 were considered. All performance data and pedigree information were made available by the HSS through the national unified animal ownership database (Vereinigte Informationssysteme Tierhaltung w.V., VIT) in Verden at the Aller, Germany.

Mare performance test. MPT data included information on 16,814 performance tested mares. Of these mares 14,500 accomplished their MPT in a one day event in the field (MPTF), whilst only 2,314 mares completed their MPT in stationary performance tests (MPTS). Tests at station included 26 days of standardized training and a final test. If a mare participated in more than one MPT, only the last test result was considered for subsequent analyses. Included MPTs took place in 1995 to 2008.

The number of performance tested mares per year ranged between 855 and 1,286 in MPTF and between 126 and 210 in MPTS. The mares were judged for quality of gaits (walk, trot, and canter under rider), jumping talent (style and ability of free jumping), rideability, and character using a 0.5 scale from 0 (not shown) to 10 (excellently shown). Style and ability of free jumping were scored individually and subsequently averaged to a total score for free jumping. Rideability was separately scored by a judging commission and by a test rider. The character was only judged at MPTS.

Most of the mares completed their MPT until the completion of their fourth year of age (mean age of 3.58 ± 0.91 years in MPTF and 3.54 ± 0.78 years in MPTS).

Performance tests in the field were held at 63 places with on average 26.94 ± 13.19 (1 to 82) judged Hanoverian warmblood mares per date and place. MPTS took place in only 5 places with on average 18.52 ± 6.47 (1 to 30) mares per date and place.

Auction inspection. Horses offered for sale at riding horse auctions of the HSS are preselected by a judging commission. Auction candidates are chosen based on their preliminary performance evaluation. Between 1999 and 2008, 8,081 Hanoverians (5,567 males, 2,514 females) were judged at auction inspections (AI) in a procedure similar to MPTF. Accordingly, presented horses were scored for quality of gaits (walk, trot and canter under rider), jumping talent (style and ability of free jumping, total

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score for free jumping), and rideability. Mean age of evaluated horses at AI was 4.21

± 0.82 years. AI were held at 111 places, with on average 16.77 ± 18.68 (range 1 to 96) inspected horses per date and place.

Studbook inspection. All mares intended to be used for breeding under the HSS must be registered in the Hanoverian studbook. At studbook inspection (SBI) a judging commission gives individual scores for several conformation traits as well as for walk, correctness of gaits in walk and trot at hand, and impetus and elasticity in trot at hand. Scores on a scale from 0 (not shown) to 10 (excellently shown) were assigned for each trait. For more details see Stock and Distl (2006). For this study we considered the SBI results with respect to the three gait-related traits of 29,053 mares, presented between 1995 and 2008 at a mean age of 3.79 ± 1.66 years. There were 182 places of SBI with on average 11.73 ± 12.44 (range 1 to 83) inspected mares per date and place.

3.3.2 Pedigree Data

For the genetic analyses, four ancestral generations of all horses with performance data (SBI, MPT or AI results) were considered. The relationship matrix comprised 80,746 individuals, including 7,486 base animals. The 29,053 mares judged at SBI descended from 1,079 sires and 1,706 maternal grandsires. The sires were on average represented by 26.91 ± 63.5 (range 1 to 998) horses and the maternal grandsires were on average represented by 17.02 ± 41.59 (range 1 to 704) horses. The 24,895 horses that performed at MPT or AI descended from 935 sires and 1,485 maternal grandsires. The sires were on average represented by 26.61 ± 62.59 (range 1 to 941) horses and the maternal grandsires were on average represented by 16.76 ± 40.61 (range 1 to 686) horses. The performance tested Hanoverian population had an average proportion of 0.58 (median = 0.59) Hanoverian genes, 0.23 (median = 0.20) Thoroughbred genes, 0.07 (median = 0.05) Trakehner genes, and 0.05 (median = 0) Holsteiner genes. The proportions of genes provided by Thoroughbred, Trakehner and Holsteiner were calculated for the tested

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Hanoverian population. For this calculation, all available pedigree information was used. Details are described elsewhere (Hamann and Distl, 2008).

3.3.3 Statistical Analyzes

Statistical analyses included three traits evaluated at SBI, i.e. walk at hand (SBI_Walk), correctness of gaits in walk and trot at hand (SBI_Corr) and impetus and elasticity in trot at hand (SBI_Imp), and five performance test (PT) traits evaluated at MPT and AI, i.e. walk under rider (PT_Walk), trot under rider (PT_Trot), canter under rider (PT_Canter), total score of free jumping (PT_FJT) and rideability scored by judging commission (PT_Ride). Because for some horses individual scores for style and ability of free jumping were not recorded, only the total score for free jumping was considered for all individuals. Horses evaluated at AI were, unlike the ones at MPTs, only scored for rideability by a judging commission, but not by a test rider. For that reason we only included rideability scores from the judging commission for our analyses.

3.3.4 Model Development

The following effects were tested for their influence on distribution of performance trait scores from MPT/AI and SBI: Age at MPT/AI or SBI evaluation as covariate or fixed effect (3-, 4- or ≥ 5 years old); evaluation year (individual years from 1995-2008), evaluation month (individual months), evaluation season (February through April, May through July, August through October, November through January), and evaluation place (182 places of SBI, 111 places of AI, 63 places of MPTF and 5 places of MPTS) as fixed effects; combined date-place effect (2,476 levels for SBI, 482 levels for AI, 537 levels for MPTF, 126 levels for MPTS) as random effect;

proportion of genes (Hanoverian or Thoroughbred, Trakehner, and Holsteiner) as covariate or fixed effect (low, moderate and high proportion of genes of the respective breed). The sex effect (male, female) was tested for the AI traits.

Simple and multiple analyses of variance (ANOVA) were performed using the procedures GLM and MIXED of the Statistical Analysis System (SAS), Version 9.2 (SAS Institute Inc., Cary, NC, USA, 2010). Model choice was based on the model fit

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test statistics and the significance tests. In the final model (Model 1), sex (only for AI) and age group at SBI or MPT/AI evaluation were considered as fixed effects, and the combined date-place effect was considered as random effect. To investigate the impact of accounting for the proportion of genes on results of the genetic analyses, an alternative model (Model 2) was used which additionally included the proportions of genes of Thoroughbred, Trakehner and Holsteiner as fixed effects. Class were formed from the proportions of genes with the aim of having similar numbers of horses in each of three effect levels. Given the uneven representation of breeds, boundaries were set independently for Thoroughbred (≤0.13, >0.13 and <0.30,

≥0.30), Trakehner (≤0.2, >0.2 and <0.8, ≥0.8), and Holsteiner (0.0, >0.0 and <0.3,

≥0.3).

Distributions of performance scores and residuals were analyzed for including tests for normality using Kolmogorov-Smirnov statistics of the UNIVARIATE procedure of SAS. For all analyses, the significance limit was set to 0.05.

3.3.5 Genetic Analyses

Genetic parameters were estimated univariately in a linear animal model with (Residual Maximum Likelihood (REML) using VCE-5, version 5.1.2 (Variance Component Estimation; Kovač et al., 2003). Estimates for environmental and genetic effects were obtained under the same models using Best Linear Unbiased Prediction (BLUP) with the software PEST (Groeneveld et al., 1990).

yijnopq= μ + AGEAI/MPT/SBIi + SEXj + dateAI/MPT/SBI x placeAI/MPT/SBIno [1]

+ ap + eijnopq

yijklmnopq= μ + AGEAI/MPT/SBIi + SEXj + TBk + TRAKl + HOLm [2]

+ dateAI/MPT/SBI x placeAI/MPT/SBIno + ap + eijklmnopq

with yi…q = MPT/AI or SBI score, μ = model constant, AGEAI/MPT/SBIi = fixed effect of age group at performance evaluation (i = 1-3), SEXj = fixed effect of sex (j = 1-2), TBk = proportion of Thoroughbred genes (k = 1-3), TRAKl = proportion of

Trakehner genes (l = 1-3), HOLm = proportion of Holsteiner genes (m = 1-3),

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dateAI/MPT/SBI x placeAI/MPT/SBIno = random effect of interaction between date of performance evaluation and place of MPT/AI or SBI, ap = random additive genetic effect of the individual horse ( r = 1-36,441) and ei…q = residual.

To study the genetic correlations between the analyzed traits and to test the influence of the model on the results of genetic evaluation, Pearson correlation coefficients between breeding values were calculated using the procedure CORR of SAS.