Genetic analysis of dystocia in French draft horses M. Sabbagh, S. Danvy, Anne Ricard

To cite this version:

M. Sabbagh, S. Danvy, Anne Ricard. Genetic analysis of dystocia in French draft horses. 63. Annual Meeting of the European Federation of Animal Science (EAAP), Aug 2012, Bratislava, Slovakia. pp.3- 7, ￿10.3920/978-90-8686-761-5￿. ￿hal-02745253￿

HAL Id: hal-02745253 https://hal.inrae.fr/hal-02745253 Submitted on 3 Jun 2020

HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Genetic analysis of dystocia in French draft horses Sabbagh, M.1, Danvy, S.1 and Ricard, A.2, 1Institut français du cheval et de l’équitation (IFCE), 61310 Exmes, France, 2INRA, GABI, UMR1313, 78350 Jouy­En­Josas, France [email protected]

Background As in many species, dystocia (foaling difficulty) is a significant cause of female and neonatal death in horse breeding, especially in draft horses due to the weight and size of the foal. French breeders associations asked for genetic tools to realize selection to improve their breeds. The aim of this paper was to estimate genetic parameters of dystocia in the main French draft horses breeds.

Material and Method

Data Since 1998, registration forms at birth included a score for the conditions of foaling for draft horses in France. In this study, we focused on the main breeds: Breton (B), Comtois (C), Percheron (P) and as a whole Ardennais, Auxois, Trait du Nord (A) because these 3 later breeds mate together and have very low genetic distance between them (Leroy et al., 2009). For these 4 populations, only intra mates were taken in the analysis from 1998 to 2010. Scores for foaling ease are given by the breeder: “without help”, “easy”, “difficult”, and “intervention of the veterinarian”. It turned out difficult, at the same time for the breeders but also during the data analysis, to make a strict difference between "without help" and "easy". So, during the analysis, the data of these two occurrences were grouped. We distinguished only 3 categories: without help or easy, difficult, intervention of the veterinarian. From 21% to 30% of registration forms had missing data about foaling difficulty but without particular distribution according to region, age of mare, sex of foal or sires. Few observed dystocia (1%) had missing sex of foal, and had unfortunately high scores: the proportion of “difficult” was 31 %, instead of 3% to 7% in the analyzed data. But as sex ratio remained closed to 50% in the analyzed data, we expected that estimates were not biased for the effects included in the model. Finally, the characteristics of the data sets are given in Table 1.

Table1: Number of total births, analyzed births and distribution of scores of foaling ease in the 4 breeds.

Ardennais, Breton Comtois Percheron Auxois, Trait du Nord Number of births 13,631 51,284 51,909 18,240 Number of births with missing score 2,804 10,692 15,831 4,610 Number of births with missing sex 166 422 320 120 Number if birth analyzed 10,610 38,868 35,758 13,274 % births analyzed 77.8% 75.8% 68.9% 72.8% Distribution of scores Easy or without help 90.9% 95.4% 94.7% 93.3% Difficult 7.1% 3.41.% 4.1% 5.0% With veterinarian 1.9% 1.2% 1.3% 1.7%

All available genealogies of mares and foals were used in the analysis. Therefore, between 18,519 and 56,285 animals were included in the analysis according to the breeds (Table 2).

Table 2: Number of horses included in the analysis

Ardennais, Auxois, Trait Breton Comtois Percheron du Nord Nb of mares of foals 3,828 12,781 12,954 4,928 Nb of sires of foals 662 1,483 1,783 446 Nb of sire of mares 911 1,628 1,672 631 Nb of horses 18,519 56,285 52,343 19,399

The mean number of births per mares ranged from 2.8 (A) to 3.0 (B) and the mean number of births per sire ranged from 16.0(A) to 29.8 (P).

Method The following threshold mixed model was assumed:

With: vector of underlying performances for distocya, vector of fixed effects, vector of random direct additive genetic effect of the foal, vector of random maternal additive genetic effect of the mare, vector of random permanent environmental effects common to the different foalings of the mare, vector of residuals, and , were incidence matrices. The distributions of vectors , were assumed normal with variance matrices: and with A the relationship matrix. Fixed effects were the following: - Year of foaling (from 1998 to 2010) - Month of birth (January and February, March, May, June, July and after) - Region of foaling (6 regions differentiating traditional area of each breed and 5 other big regions) - Age of the mare (3, 4, 5 to 9, 10 and more) - Sex of the foal (Male, Female). So that the following genetic parameters were defined: Phenotypic variance : Heritability of direct effect : Heritability of the maternal effect : Genetic correlation between maternal and direct effect : Repeatability between two foalings of the same mare (assuming different sire): To estimate the different parameters, a MCMC Gibbs sampling was used with the TM software (Legarra and al., 2011). For each population, Gibbs sampling was carried out through a unique chain of 100,000 iterations, discarding the first 1,000 iterations and retaining one every 20 samples.

Results

Thresholds The Table 3 gives the two thresholds of underlying liability of dystocia leading to the category “difficult” and “with veterinarian”, assuming that the mean of population was a reference mare of 5 to 9 years old, foaling a female in May 1998 in the traditional area of the breed. These thresholds are expressed in phenotypic standard deviation unit. Table3. Thresholds leading to 1) difficult foaling and 2) intervention of veterinarian in phenotypic standard deviation

Ardennais, Auxois, Trait Breton Comtois Percheron du Nord First threshold 1.66 1.60 1.90 1.59 Second threshold 2.37 2.18 2.51 2.18

Estimates of fixed effects All estimates were presented in phenotypic standard deviation unit.

Year of foaling The effect of the year for the Breton breed showed a clear decrease with time, therefore an environmental improvement of conditions of foaling (from 5% in 1998 of foaling with problems to 2% in 2010). But we felt to understand the causes of such improvement and a different interpretation of scoring with time could not be totally avoided. For the other breeds, the annual differences remained moderate (<1/3 of standard deviation between maximum of variation).

Figure 1. Year of foaling effect (in phenotypic standard deviation)

Month of foaling The latter the foaling takes place in the year, the better it is: the month of June had more favorable conditions of foaling than May and May than April. Births which took place very early in the year, in January or very late in July seemed to have particularly favorable effect, perhaps due to specific behavior of the breeder for these rare cases.

Figure 2. Month of foaling effect (in phenotypic standard deviation)

Region of foaling Traditional areas were not the more favorable for an easy foaling. But differences between regions remained low (<1/3 phenotypic standard deviation). Age of the mare Young mares, and especially 3 years old ones, had more problems at foaling than older one (Figure 3). In order to take into account the difference between age effect itself and primiparous effect, further analysis will distinguish the two aspects when recovering all registration forms, including missing scores one in order to have the information of the rank of parity. This is the major fixed effect.

Figure 3. Age of mare effect (in phenotypic standard deviation)

Sex of the foal As expected due to the size of the foals, the effect of the sex of the foal was favorable for females (Figure 4).

Figure 4. Sex of the foal effect (in phenotypic standard deviation)

Genetic parameters Repeatability was homogeneous among breeds: from 0.26 (P) to 0.33 (A). Heritability of direct effect ranged from 0.12 (B) to 0.31 (A), heritability of maternal effect ranged from 0.11 (C) to 0.22 (A), and was always lower than the direct one except for (B) (0.21). The genetic correlation was unfavorable for 3 populations from ­0.42 (P) to ­0.27 (A) and neutral for C (­0.02) (Table 4).

Table 4: Genetic parameters of distocya (standard deviation in parenthesis)

Ardennais, Auxois, Breton Comtois Percheron Trait du Nord Repeatability 0.33 (0.03) 0.30 (0.02) 0.28 (0.02) 0.26 (0.03) h² direct foal effect 0.31 (0.06) 0.12 (0.03) 0.20 (0.04) 0.21 (0.05) h² maternal effect 0.22 (0.01) 0.21 (0.04) 0.11 (0.02) 0.17 (0.05) Genetic correlation -0.27 (0.14) -0.38 (0.13) -0.02 (0.15) -0.42 (0.21) Estimated breeding values The genetic values of all the horses included in the analysis were calculated. At present, only estimated breeding values (EBVs) of stallions with reliability higher than 0.20 are published. Four stallions of Comtois breed are given in the table 5.

Table 5: EBV for 4 Comtois stallions

Direct Age Maternal effect effect Probabilit Probability EBV Reliability y EBV Reliability Daughter** Mate* QUAINE 7 Not DES 0.33 0.45 publishe BOIS 4.2% d QUEL 7 Not SUCCE -0.17 0.51 publishe S 2.4% d INOUK 14 0.06 0.72 3.1% -0.45 0.50 1.7% CIMBALI 20 0.71 0.40 6.1% 0.66 0.39 5.8% *Probability for a mate with this stallion to have difficult or with veterinarian foaling **Probability for a daughter of this stallion to have difficult or with veterinarian foaling

Discussion No references were found on genetic parameters for dystocia in horse breeding. In dairy cattle, heritability of direct effect was within the range 0.01with raw data to 0.17 with threshold model and heritability of maternal effect was within the range 0.04 with threshold model and 0.14with raw data (Lopez de Maturana et al., 2007; Johanson et al., 2011). Typically the direct heritability estimate was twice the magnitude of the maternal heritability estimate. In beef cattle, estimates were on the same magnitude (Phocas and Laloe, 2003, 2004). Therefore, estimates of this study were inside the range but rather among high estimates. It is common for genetic correlations between direct and maternal effects to be negative and estimates of the present study were similar to those found in dairy or beef cattle breeds. For these breeds, it will be thus difficult to select at the same time a sire improving the easiness of foaling when mate with him and easiness of foaling for its daughters.

Conclusion The estimation of such genetic parameters for dystocia in French horse breeding was the first one. The EBV produced will allow the breeders to obtain additional information on sires. It is however necessary to notice that we have to wait at least 5 years to be able to have an EBV on maternal effect for a stallion. In addition to these evaluations, another study was conducted on morphological traits. Therefore, we have planned to estimate genetic correlation between dystocia and these morphological traits. We expect to find a correlation between one or several criteria of morphology and direct or maternal effects on dystocia to have earlier genetic tools to select stallions.

References

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