Conformational Defects in the Limbs of Menorca Purebred Horses and Their Relationship to Functionality

Citation: Ripollés-Lobo, M.; Perdomo-González, D.I.; Valera, M.; Gómez, M.D. Conformational Defects in the Limbs of Menorca Purebred Horses and Their Relationship to Functionality. Animals 2024,14, 1071. https://doi.org/10.3390/ ani14071071 Academic Editors: Roberta F. Godoy and David Marlin Received: 4 March 2024 Revised: 28 March 2024 Accepted: 30 March 2024 Published: 31 March 2024 Copyright: © 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). animals Article Conformational Defects in the Limbs of Menorca Purebred Horses and Their Relationship to Functionality Maria Ripollés-Lobo 1, Davinia I. Perdomo-González 1, Mercedes Valera 1and María D. Gómez 2,* 1Departamento de Agronomía, Escuela Técnica Superior de Ingeniería Agronómica, Universidad de Sevilla, Ctra, Utrera Km 1, 41013 Sevilla, Spain; [email protected] (M.R.-L.); dper[email protected] (D.I.P.-G.); [email protected] (M.V.) 2Asociación de Criadores y Propietarios de Caballos de Raza Menorquina, Edificio Sa Roqueta C/Bijuters, 36 Bajos, 07760 Ciutadella de Menorca, Spain *Correspondence: cavallmenor[email protected] Simple Summary: Limb alignments significantly impact the performance and overall well-being of horses, which means that the identification and management of limb-conformation defects is vital for horse owners and breeders. Our study investigates the prevalence of 14 defects in Menorca Purebred horses, along with the environmental factors influencing their occurrence and the genetic parameters for potential inclusion in the official breeding program. Analysis of data from 1120 records from 509 animals reveals a higher prevalence of defects in older females from breeder studs dedicated to breeding, possibly due to limited care. Notably, splay-footed forelimb, closed hocks, camped under, pigeon-toed forelimb and coon foot are the commonest, with a prevalence exceeding that of other equine populations. These defects significantly influence gait scores, particularly in trotting. Heritability estimates range from 0.12 to 0.30, suggesting genetic influence. Genetic correlations show that careful consideration is needed in selective breeding to avoid unintended outcomes. It is therefore advisable to focus selective efforts on the more prevalent defects with higher heritability, as well as to evaluate the inter-defect relationships. Abstract: Limb-conformation defects significantly influence equine performance and welfare, necessitating thorough investigation for effective management. This study examines the prevalence and genetic parameters of 14 limb-conformation defects in Menorca Purebred horses using data from 1120 records (509 animals with an average age of 101.87 ± 1.74 months) collected between 2015 and 2023. Defects were evaluated using a three-class scale by three appraisers, and a Bayesian approach via Gibbs sampling was employed to estimate genetic parameters including gender, birth period, stud selection criteria, evaluation age and appraiser as fixed effects. Splay-footed forelimb and closed hocks were the most prevalent defects (67.20% and 62.53%, respectively). Horses with any of the defects analyzed have been observed to obtain significantly lower scores for both walk and trot. Heritability estimates range from 0.12 (s.d.: 0.025) for closed hock to 0.30 (s.d.: 0.054) for base narrow, confirming the genetic influences on the expression of limb conformation defects. The divergent defect in hind limbs showed the highest genetic correlations with forelimb defects (camped under, − 0.69; s.d: 0.32 and camped out, 0.70; s.d: 0.27). The significant genetic correlations between defects highlight the complexity of the relationships, which requires careful consideration. Keywords: limb defects; equine; genetic parameters; movements; prevalence 1. Introduction Selection for suitable morphological qualities for performance in a sport discipline benefits genetic progress by allowing us to make an early pre-selection of the animals, even before they begin their sport career [ 1 ]. Deviations from optimal limb structure, commonly known as limb conformation defects or orthopedic diseases, are widespread concerns in equine sporting breeds, and transcend geographical and disciplinary boundaries. Animals 2024,14, 1071. https://doi.org/10.3390/ani14071071 https://www.mdpi.com/journal/animals Animals 2024,14, 1071 2 of 14 Furthermore, limb alignments play an important role in sport performance, compromising the horse’s biomechanical efficiency, the horse’s overall well-being and the general health of horse populations. For all these reasons, conformation is a significant indicator of potential soundness and performance, which is pivotal in horse evaluation for purchase, with substantial economic repercussions for owners and breeders, as poor conformation significantly diminishes a horse’s value [ 2 – 4 ]. Conformation defects are often caused by underlying complex genetic effects, which may be breed-specific or common in certain types of horses [5]. The economic impact of these defects arises from the diminished athletic capacity and a greater associated risk of musculoskeletal injuries, which can slow down or impede the ideal performance of the animals in different equestrian sports [ 6 ]. Changes in conformation shift the center of gravity forward, resulting in variations in gait that impose asymmetrical loads on the musculoskeletal system, predisposing horses to injuries [ 7 ]. In this regard, musculoskeletal injury is the most significant cause of wastage in the horse industry [ 8 , 9 ], and accounts for the greater part of culling in riding horses (50–70%) [ 10 – 12 ]. Consequently, owners and breeders invest considerable resources in the training and upkeep of their equine athletes, making the identification and mitigation of limb conformation defects crucial for warranting a considerable investment in time and money. Therefore, the primary objective of animal breeders and breeding associations is to improve the genetic potential of the animals over generations [ 13 ], with limb conformation serving as a key selection criterion. Focusing on the common defects shared among different breeds, we aim to explore the potential efficacy of implementing genetic selection as a proactive measure to curb the prevalence of limb-conformation defects, using Menorca Purebred horses (PRMe) as an example. The PRMe is an endangered native breed primarily found in Menorca (Balearic Islands, Spain), and widely known for its role in the regional festivities called “Jaleo Menorquin” [ 14 ]. It is a black-coated animal predominantly utilized as a saddle breed, for Classic and Menorcan Dressage. Menorcan Dressage is a different variety of Dressage with specific rules recognized in the Menorca Island. It is a riding modality characterized by its way of holding the reins (using only the left hand), its style of clothing and its horse and rider equipment. The official reprises include typical dressage exercises, but also special Menorca movements (bot, in which the horse stands or walks on its hind limbs; front limb pirouettes, with the forelimb rotating around the haunches at trot; and hindlimb pirouettes, with the hindlimb rotating around the shoulders at trot) [ 14 , 15 ] and they are evaluated at both the recreational and national level [15]. Through a comprehensive examination of limb-conformation defects in the PRMe population, our research seeks to provide valuable insights into the feasibility and impact of genetic interventions for mitigating limb-conformation defects in equine populations dedicated to sport disciplines without losing sight of the main aim of the breeders and breeding organizations, which is to improve the genetic potential of the animals over generations. In this context, our study explores the prevalence of 14 limb-conformation defects that are present in the PRMe population in different degrees, in order to determine the environmental factors that can condition their presence in the population, their influence on walk and trot scores and the genetic parameters (heritability values and genetic correlations) used to evaluate their possible inclusion in the official breeding program. Hopefully, this will provide a promising avenue for breeders and owners to enhance the overall soundness and performance of their equine stock. 2. Materials and Methods 2.1. Description of Traits and Database For this analysis, we used data of PRMe horses provided by the Asociación de Criadores y Propietarios de Caballos de Raza Menorquina (ACPCRMe) and collected between 2015 and 2023. A total of 1120 records were recorded from 503 animals (266 males and 237 females, with 605 and 515 records, respectively) belonging to 179 different studs for Animals 2024,14, 1071 3 of 14 14 limb-conformation defects in visits to studs, sport competitions and morphological events featuring PRMe. The average number of records was 2.20 per animal. The animals’ minimum age was 36 months and the maximum was 242 months, with an average age of 101.87 ± 1.74 months. All the individuals included in the analysis were healthy animals, without orthopedic treatments or veterinary interventions. Limb-conformation defects were evaluated by three different appraisers, previously trained and periodically tested to reduce subjective evaluation, using three classes in a scale, where 0 represents the absence of defect (correct limb conformation), 1 is the slight presence of a defect and 2 the evident presence of a defect. A graphic representation of the defects analyzed and the description of the scale used is shown in Table 1and the written description is included in supplementary Table S1. Of the animals included, 77.14% were evaluated by more than one appraiser. Additional information of walk and trot scores were also obtained in the corresponding morphological events, by the same appraisers, considering the general characteristics of each gait using a scale of 7 points. Walk score was the mean value for activity, clarity, amplitude and suppleness at walk, while trot score was the mean value for amplitude, suppleness, impulsion, equilibrium and suspension at trot. The walk-score mean value was 5.9 (SD: 1.52) and the trot-score mean value was 5.6 (SD: 1.77). 2.2. Statistical and Genetic Analysis Prevalence of the 14 limb-conformation defects was estimated in a generic way (classes 1 + 2: slight and evident presence of a defect) and for each level (0, 1 and 2: no defect, a slight defect and an evident defect). Prevalence was also estimated by each factor analyzed within a defect: gender (two levels: male and female), birth period (three levels: before year 2000, between 2001 and 2010 and after 2010), stud selection criteria for animals’ purchase or replacement (four levels: (1) functionality (sportive performance), (2) conformation or breed quality, (3) equestrian routes and (4) breeding purpose), evaluation age (two levels: young (<48 months) and adult ( ≥ 48 months)) and appraiser (three levels). The stud selection criteria effect was included since the management of the animals in the studs is conditioned by their main use. A preliminary analysis of variance was carried out to assess the statistical significance of the non-genetic effects that could influence the defect traits analyzed in the PRMe horses. A Generalized Non-Linear Model (GLZ) with a multinomial distribution and a logit link function was used to analyze the effect of gender, birth period, stud selection criteria, evaluation age and appraiser in Statistical for Windows software v.11 [ 16 ]. The GLZ represents a methodological approach analogous to a GLM (General Linear Model), with the key distinction being the absence of a continuous Gaussian distribution assumption. Instead, the model assumes other distributions based on the nature of the data being analyzed. Furthermore, to assess the potential impact of limb-conformation defects at different levels on the scores acquired by the animals when both walking and trotting, we employed a GLM followed by a Tukey post hoc test. To estimate the genetic parameters (heritability and genetic correlations), we set up a multivariate animal model with a Bayesian approach via Gibbs sampling using GIBBSF90+ and POSTGIBBS modules of the BLUPF90 software [ 17 ]. The equation in matrix notation was: y=Xb +Zu +Wpe +e where yis the vector of observations, Xthe incidence matrix of systematic effect, Zthe incidence matrix of animal genetic effect, Wthe incidence matrix of random permanent environmental genetic effect, b the vector of systematic effects, u the vector of direct animal genetic effects, pe the vector of random permanent environmental genetic effect and e the vector of residuals. The prior distributions for the systematic effects and the variance components were assumed to be bounded uniform, and the prior distributions for the genetic effects were Gaussian distributions with mean zero and variance defined as follows: Animals 2024,14, 1071 4 of 14 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Closed hock CH Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Convergent Conv Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Divergent Diver Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Camped under CU Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Camped out CO Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Pigeontoed forelimb PTF Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Splay-footed forelimb SFF Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Base narrow BN Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Base wide BW Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Coon foot CF Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Broken and upright foot BUF Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Sloping foot Sloping Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024, 14, x 4 of 15 Table 1. Graphic description of the 14 limb-conformation defects analyzed in the Menorca Purebred horse population, including the definition of the evaluation scale (between 0 to 2). Defect Class Defect Class 0 (Correct) 2 (Evident) 0 (Correct) 2 (Evident) Open hock OH Closed hock CH Convergent Conv Divergent Diver Camped under CU Camped out CO Pigeon-toed forelimb PTF Splay-footed forelimb SFF Base narrow BN Base wide BW Coon foot CF Broken and upright foot BUF Sloping foot Sloping Club foot Straight Animals 2024,14, 1071 5 of 14 var  u pe e  =  Aσ2 u0 0 0Aσ2 pe 0 0 0 Iσ2 e  (1) where σ2 u , σ2 pe , and σ2 e are the additive, random permanent environmental and residual variances. Ais the numerator relationship matrix and Iis the identity matrix. More specifically, b included gender (2), birth period (3), stud selection criteria (4), evaluation age (2) and appraiser (3). The Gibbs sampler was run for 250,000 rounds, with the first 50,000 considered as burn-in and then every sample saved for later analysis. Posterior means and standard deviations were calculated to obtain estimates of (co) variance components. Convergence of the posterior distributions generated was assessed using the Geweke’s Z criterion [ 18 ], and Monte Carlo sampling error (MCse). The pedigree data for the estimation of the genetic parameters was composed of 1017 animals born between 1961 and 2020 (448 males and 569 females), including between 2 to 5 generations of the animals registered in the official PRMe Studbook, with an average of 2.5 generations. 3. Results The prevalence of the limb-conformation defects analyzed in the PRMe population is outlined in Table 2. Most of the individuals (>50%) are included in the group of unaffected animals (class 0) for most of the defects analyzed, except closed hock, camped under and splay-footed forelimb, with a lower percentage of animals included in class 0 (37.47%, 44.58% and 32.80%, respectively). Table 2. Prevalence of the 14 limb-conformation defects analyzed in Menorca Purebred horses according to the class. Limb Defect N Class 0 1 2 1 + 2 n%n%n%n% Open hock OH 343 238 69.39 100 29.15 5 1.46 105 30.61 Closed hock CH 483 181 37.47 233 48.24 69 14.29 302 62.53 Convergent Conv 412 252 61.17 122 29.61 38 9.22 160 38.83 Divergent Diver 432 251 58.10 148 34.26 33 7.64 181 41.90 Camped under CU 507 226 44.58 257 50.69 24 4.73 281 55.42 Camped out CO 356 341 95.79 15 4.21 0 0 15 4.21 Pigeon-toed forelimb PTF 318 178 55.97 126 39.62 14 4.40 140 44.02 Splay-footed forelimb SFF 439 144 32.80 255 58.09 40 9.11 295 67.20 Base narrow BN 467 374 80.09 82 17.56 11 2.36 93 19.92 Base wide BW 476 363 76.26 108 22.69 5 1.05 113 23.74 Broken and upright foot BUF 418 311 74.4 98 23.44 9 2.15 107 25.59 Coon foot CF 477 268 56.18 184 38.57 25 5.24 209 43.81 Club foot Straight 467 313 67.02 143 30.62 11 2.36 154 32.98 Sloping foot Sloping 452 310 68.58 137 30.31 5 1.11 142 31.42 Abbreviations of limb-conformation defects are listed in Table 1. Key: the number of animals is indicated as N or n, class 0 is no defect, class 1 is slight defect and class 2 is evident defect. Notably, the most prevalent defects included splay-footed forelimb with an overall prevalence (class 1 and 2) of 67.20%, closed hock with 62.53%, camped under with 55.42%, pigeon-toed forelimb with 44.02%, coon foot with 43.81% and divergent with 41.90%. The majority of the defects identified are present in a slight form (class 1), with splay-footed forelimb and camped under being the most frequent defects (58.09% and 50.69% of prevalence for class 1, respectively), and closed hock being the limb defect with the highest prevalence in class 2 (evident defect). In contrast, the defects which presented the lowest prevalence values for the evident presence of a defect (all lower than 5%) were camped out (0%), base wide (1.05%), sloping (1.11%), broken and upright foot (2.15%), base narrow and straight (2.36%), open hock (1.46%), pigeon-toed forelimb (4.40%) and camped under (4.73%). Animals 2024,14, 1071 6 of 14 The relationship of each limb conformation defect with the scores obtained by the animals in the evaluation of walk and trot gaits are shown in the Table 3. Significant differences were detected mainly for the trot scores in the majority of the defects analyzed (64.29%), whereas the walk scores were only influenced by the presence of splay-footed forelimb,coon foot and sloping. Table 3. Generalized Linear Model and post hoc analysis (Tukey LSD) of the scores obtained by the animals for walk and trot in the official evaluations within the breeding program, depending on the level of each of the defects analyzed in the Menorca Purebred horses. Defect Level N Walk Trot Defect Level N Walk Trot OH 1 231 5.99 5.97 b SFF 1 143 6.07 b5.75 b 2 98 5.74 5.37 a2 252 5.89 b5.56 ab 3 5 6.84 5.29 ab 3 40 5.18 a4.94 a CH 1 175 5.93 5.84 b BN 1 369 5.89 5.61 2 231 5.95 5.51 b2 83 5.51 5.21 3 67 5.48 4.85 a3 10 5.52 5.74 Conv 1 244 5.95 5.74 b BW 1 358 5.88 5.62 2 122 5.77 5.43 ab 2 108 5.86 5.30 3 37 5.37 4.89 a3 5 6.63 5.29 Diver 1 244 5.86 5.53 ab BUF 1 308 5.98 5.77 b 2 147 5.97 5.79 b2 98 5.78 4.98 a 3 33 5.91 4.97 a3 9 5.84 4.72 ab CO 1 337 5.96 5.70 b CF 1 263 6.02 b5.64 2 15 5.61 4.83 a2 183 5.64 a5.46 3 0 - - 3 25 5.60 ab 5.62 CU 1 221 5.85 5.70 Sloping 1 305 5.98 b5.70 2 256 5.88 5.42 2 136 5.56 a5.29 3 24 5.65 5.01 3 6 5.96 ab 5.61 PTF 1 175 6.12 6.06 b Straight 1 308 5.91 5.73 b 2 126 5.88 5.22 a2 143 5.78 5.17 a 3 14 5.56 5.42 ab 3 11 5.07 4.39 a Abbreviations of limb-conformation defects are listed in Table 1. Different superscript letters (a and b) indicate a statistically significant difference between groups (p< 0.05). The GLZ (Table 4) revealed that all the effects included in the analysis were significant for some of the limb-conformation defects analyzed, with significance coefficients below 0.05. It is important to emphasize that the appraiser effect was significant for most of the defects included in this analysis (92.86% of the defects analyzed), whereas the evaluation age group was not significant for most of these effects (78.57%), being significant only for open hock, closed hock and convergent. The prevalence of the different defects is shown in Table S2. In general, females presented a higher proportion of limb-conformation defects than males, except for divergent, splay-footed forelimb, base narrow, coon foot and sloping foot. Also, the older animals (with year of birth ≤ 2000) showed a higher proportion of limb-conformation defects (78.57%) than the other birth-date groups included in the analysis. Surprisingly, animals selected for breeding and conformation (individuals belonging to studs that select their animals for purchase and replacement using breeding and breed-quality criteria) showed the highest prevalence values in most of the traits analyzed (50%), with animals belonging to studs with clear conformation objectives presenting the lowest prevalence values. In line with the results obtained for the year of birth, animals when evaluated as adults presented the highest prevalence values in the majority of the defects analyzed (71.43%). Finally, appraiser number 2 was shown to be the most severe, with the highest prevalence values in 85.71% of the limb defects analyzed, whereas appraiser number 3 showed the lowest prevalence values, and therefore the lowest requirement levels in data collection. Animals 2024,14, 1071 7 of 14 Table 4. Generalized Non-linear Model for the 14 limb-conformation defects analyzed in the Menorca Purebred horses based on their non-genetic effects (p-value). Defects Effects Gender Birth Period Stud Selection Criteria Evaluation Age Appraiser OH 0.965 <0.001 0.388 0.009 0.068 CH 0.699 0.031 0.005 0.015 <0.001 Conv 0.689 0.005 <0.001 0.004 <0.001 Diver 0.071 <0.001 0.355 0.387 0.001 CU 0.115 0.005 0.015 0.414 <0.001 CO 0.615 0.047 0.410 0.333 <0.001 PTF 0.283 0.123 <0.001 0.134 0.002 SFF <0.001 0.315 <0.001 0.368 <0.001 BN 0.079 0.323 0.027 0.347 <0.001 BW 0.213 0.018 0.125 0.344 <0.001 BUF 0.003 <0.001 0.499 0.387 <0.001 CF <0.001 0.005 0.077 0.823 0.001 Straight 0.415 <0.001 0.271 0.431 <0.001 Sloping 0.010 <0.001 0.021 0.449 0.034 Abbreviations of limb-conformation defects are listed in Table 1. The heritability, estimated variances and convergence parameters values of the defects analyzed are shown in Table 5. The MCse results for all the variables were less than or equal to 0.001, ranging between 0.00053 (closed hock) and 0.00116 (divergent), and Geweke’s Z-scores for all the variables were included in the range of − 2 to +2. All the heritability values were of low-to-medium range, varying between 0.12 (s.d.: 0.025) for closed hock and 0.30 (s.d.: 0.054) for base narrow. Only 14% of the estimated heritability values were higher than 0.25. Table 5. Genetic parameters for limb-conformation defects analyzed in the Menorca Purebred horse population. Defects σpe σuσeh2 (s.d.) HPD 95% Mean Median HPD 95% Mean Median HPD 95% Mean Median HPD 95% OH 542.23 539.20 373.60– 715.00 367.04 363.50 224.10– 515.30 1415.60 1413.00 1264.00– 1573.00 0.16 (0.029) 0.100– 0.215 CH 276.32 275.00 195.90– 359.90 138.89 137.20 77.410– 201.80 784.17 782.70 705.10– 870.80 0.12 (0.025) 0.067– 0.165 Conv 631.57 630.60 444.80– 814.90 487.25 478.00 282.80– 709.90 944.30 942.30 839.80– 1050.00 0.24 (0.047) 0.147– 0.329 Diver 593.19 592.00 406.30– 788.40 308.43 300.50 142.40– 488.20 853.16 851.30 757.70– 951.90 0.18 (0.048) 0.086– 0.270 CU 26.07 25.83 15.43– 37.12 32.03 31.52 17.60– 48.11 132.83 132.60 119.30– 147.20 0.17 (0.037) 0.095– 0.240 CO 461.32 457.00 286.60– 638.30 584.53 576.20 349.40– 831.00 1309.90 1307.00 1166.00– 1457.00 0.25 (0.045) 0.161– 0.335 PTF 903.71 900.20 662.20– 1146.00 618.70 609.40 360.10– 888.30 1046.00 1044.00 929.60– 1163.00 0.24 (0.046) 0.152– 0.332 SFF 636.58 634.20 452.30– 824.60 374.52 365.80 192.80– 570.30 755.11 753.50 673.00– 840.90 0.21 (0.051) 0.117– 0.311 BN 267.23 265.80 170.80– 362.70 384.72 379.60 230.60– 553.60 633.99 632.70 564.20– 705.80 0.30 (0.054) 0.196– 0.401 BW 270.58 269.00 177.80– 367.40 315.13 310.90 189.10– 447.90 584.43 583.30 521.70– 649.40 0.27 (0.048) 0.175– 0.363 BUF 457.33 454.50 294.50– 619.00 477.58 472.10 281.20– 681.20 1124.10 1122.00 1008.00– 1251.00 0.23 (0.044) 0.147– 0.316 CF 294.29 292.10 195.80– 397.90 240.99 236.90 137.40– 352.40 692.73 691.60 622.10– 767.90 0.20 (0.040) 0.118– 0.274 Straight 342.65 339.20 222.10– 469.90 288.71 283.90 162.20– 422.90 940.42 938.70 840.90– 1039.00 0.18 (0.038) 0.110– 0.258 Sloping 411.64 408.70 283.30– 547.30 368.72 362.90 230.00– 517.80 906.70 905.00 813.20– 1006.00 0.22 (0.038) 0.145– 0.293 Abbreviations of limb-conformation defects are listed in Table 1. σpe : additive genetic variances of random permanent environmental effect; σu : additive genetic variances of animal; σe : residual variances; HPD 95%: 95% higher posterior density; h2: heritability value; s.d.: standard deviation. Animals 2024,14, 1071 8 of 14 Finally, the genetic correlations between the traits analyzed and their standard deviations are shown in Table 6, of which 64.29% were significant and 40.74% minus values. The 12.96% of the significant correlations can be considered high, with values ≥ 0.50, in absolute value, while 22.22% of them can be considered of a low range, with values ≤ 0.25. The highest correlations were obtained between camped out and divergent (0.70, s.d.: 0.273), and between coon foot and base narrow (0.69, s.d.: 0.305) and between camped under and divergent ( − 0.69, s.d.: 0.319), the latter being a minus value, while the lowest correlation was obtained between broken and upright foot and splay-footed forelimb (0.19, s.d.: 0.179). Table 6. Genetic correlations and standard deviation (between brackets) among the 14 limbconformation defects analyzed in Menorca Purebred horses. Conv Diver CU CO PTF SFF BN BW BUF CF Straight Sloping OH −0.36 (0.127) 0.54 (0.127) 0.38 (0.153) −0.20 (0.143) 0.13 (0.152) −0.23 (0.154) 0.49 (0.134) 0.31 (0.464) −0.14 (0.160) 0.40 (0.158) 0.36 (0.466) 0.55 (0.128) CH 0.23 (0.145) −0.45 (0.149) −0.21 (0.434) 0.07 (0.152) 0.28 (0.154) 0.12 (0.247) −0.49 (0.143) 0.09 (0.170) 0.48 (0.140) −0.35 (0.164) 0.26 (0.167) −0.07 (0.106) Conv - - 0.14 (0.366) −0.30 (0.153) −0.26 (0.158) −0.26 (0.368) −0.33 (0.099) 0.24 (0.183) −0.11 (0.190) −0.39 (0.296) −0.31 (0.184) −0.12 (0.174) Diver - - −0.69 (0.319) 0.70 (0.273) −0.33 (0.346) 0.37 (0.326) 0.28 (0.192) −0.19 (0.192) −0.22 (0.190) 0.28 (0.200) −0.33 (0.401) 0.43 (0.154) CU - - −0.20 (0.158) 0.21 (0.184) 0.20 (0.171) 0.02 (0.188) 0.42 (0.380) 0.05 (0.187) −0.26 (0.168) 0.24 (0.178) CO - - 0.21 (0.152) −0.09 (0.171) −0.10 (0.427) −0.33 (0.150) 0.09 (0.162) 0.08 (0.169) 0.11 (0.173) −0.06 (0.389) PTF - - 0.32 (0.139) −0.39 (0.146) −0.35 (0.320) 0.08 (0.169) −0.28 (0.465) 0.33 (0.300) SFF - - −0.24 (0.161) 0.36 (0.163) 0.19 (0.179) 0.42 (0.440) 0.50 (0.436) −0.26 (0.474) BN - - −0.21 (0.154) 0.42 (0.440) 0.21 (0.310) 0.65 (0.300) BW - - 0.27 (0.155) 0.69 (0.305) 0.44 (0.380) 0.26 (0.146) BUF - - −0.47 (0.133) 0.46 (0.146) CF - - −0.23 (0.161) 0.48 (0.123) Abbreviations of limb-conformation defects are listed in Table 1. 4. Discussion Limbs are essential in horse functionality and their conformation affects the horse’s susceptibility to injury [ 2 ], especially to musculoskeletal injuries, which are the most significant cause of financial loss in the horse industry [ 8 , 9 ]. At the same time, limb conformation is a key factor used by buyers when evaluating horses, where straight conformation is preferred [ 19 ]. Thus, the identification of potential predisposing factors, such as specific conformational abnormalities, is a worthwhile aim, given considerable savings in time and money it can bring [2]. Morphological defects in any species, including horses, have origins that are both polygenic [ 20 , 21 ] and multifactorial [ 22 ], and selection is usually based on data collected during the evaluation of an animal’s conformation by technicians and/or appraisers under field conditions. Angular limb deformities usually are of congenital origin, but they can also be developmental and have numerous causes, such as genetics, nutrition, amount of exercise, weight bearing or veterinary interventions, among others, which can all influence the conformation of the adult horse [23]. Here, we analyzed limb-conformation defects in the PRMe population in order to evidence the prevalence of these problems and evaluate their possible inclusion in the official breeding program of this population. Thus, according to the results obtained (Table 2), the most common defects were found to be splay-footed forelimb,closed hocks,camped under, pigeon-toed forelimb and coon foot, and, on the whole, the prevalence percentages obtained in the population analyzed are higher than those reported in other equine populations Animals 2024,14, 1071 9 of 14 for the same defects. As has been observed in Pura Raza Española horses [ 24 ], with a prevalence of 74.12%, convergent hock defect is one of the most prevalent limb defects in the population analyzed in our study, albeit with a lower prevalence (38.83%). Closed hock is also a common defect in the PRMe population, showing lower prevalence values than the Pura Raza Española horses analyzed [ 5 ] (22.09%). Furthermore, lower prevalence rates were reported for closed hock in Swedish Warmbloods (4.30%; [ 25 ]) and Thoroughbred horses (31%; [ 26 ]). The Thoroughbred breed exhibited a prevalence of 30.10% for splayfooted forelimb defect and 19.39% for pigeon-toed forelimb defect [2], both of which are lower than those obtained in the current analysis. Additionally, camped under shown a higher prevalence in the PRMe population than in Swedish Warmbloods (5.60%; [ 25 ]), but lower than in Thoroughbred horses (58%; [ 26 ]). Various methodologies are utilized to investigate conformational defects in horses, encompassing visual evaluation, physical examination, static conformation analysis, dynamic assessment of movement, gait analysis, diagnostic imaging, and computer-aided modeling. It is worth mentioning that, in the above work mentioned, while Swedish Warmbloods horses were evaluated directly on the animals [ 25 ], the data obtained from Thoroughbred horses [ 26 ] were made by photographic images that were later analyzed. On the other hand, in Pura Raza Española horses [ 5 ], these defects were analyzed in a similar way to the PRMe, with a three-level scale, where 0 is the absence of defect and the other levels reflect the presence of defect in different levels (1 is scarce and 2 is evident). These approaches collectively offer insights into skeletal alignment, musculoskeletal health and biomechanical performance, crucial for assessing the impact of conformational abnormalities on the horses’ soundness and athletic potential. The relationship between walk and trot and conformational defects in sport horses is important for understanding their performance capabilities. Conformational abnormalities can significantly impact movement biomechanics, leading to irregularities in gaits such as the walk and trot [ 5 ]. Horses with structural deviations may experience choppy or uneven gaits. Furthermore, certain conformational defects can predispose horses to lameness issues or musculoskeletal injuries, particularly during high-intensity activities like trotting or galloping, thus affecting their soundness and long-term athletic potential. A poor stance of the forelimbs predisposes horses to lower soundness and durability, due to the role of heels and pasterns as shock absorbers during movement [ 27 ]. Toe-in and toe-out appearance, which often accompanies angular deformities, is a concurrent rotational deformity [ 23 ]. In this context, the prevalence of splay-footed forelimb and pigeon-toed forelimb in PRMe is more than double that of the Thoroughbreds analyzed [ 2 ]. These authors highlighted the relationship of both limb defects with poor racing performance in horses with severe defects. In this regard, the limb-conformation defects analyzed in the PRMe population exert a greater influence on trotting than walk scores (Table 3). The presence of splay-footed forelimb affects both walk and trot scores, while camped under, base narrow and base wide are the only defects without any influence on either of these gait scores. We can therefore conclude that limb-conformation defects significantly impact gait scores in PRMe individuals, as they are crucial factors in their use for riding, in which dressage ability is conditioned by the quality of the gait. The significant effect of forelimb toe-in and toe-out on the likelihood of contracting carpitis has been demonstrated [ 28 ]. Additionally, toe-in and toe-out had the strongest phenotypic effects on health from an orthopedic and locomotive standpoint, along with straight pasterns and changes in lateral hock angles [ 29 ]. Furthermore, stride length, smoothness of gait, soundness of limbs and power of propulsion depend on the structure of the forelimbs [ 30 , 31 ], with alterations in the foot axis (pastern-hoof) increasing cases of concussion, stilting the horse’s action and diminishing its spring and freedom of gait, which are crucial features of stride [ 31 , 32 ]. Therefore, the significant prevalence detected for coon foot is a key finding in the analysis of this population, due to its negative effects on performance, health and soundness. The hock plays an important role in propulsion and helps to decrease the harmful effects of concussion, as it is the region where the propulsive efforts of the extensor muscles