Bull Vet Inst Pulawy 56, 623-629, 2012 DOI: 10.2478/v10213-012-0110-5

MORPHOLOGICAL DIFFERENTIATION OF POLISH ARABIAN - MULTIVARIATE ANALYSIS

DOROTA SOBCZUK AND MARCIN KOMOSA1

Department of Animal Breeding and Use, Faculty of Agricultural Sciences in Zamosc, University of Life Sciences in Lublin, 22-400 Zamosc, 1Department of Animal Anatomy, University of Life Sciences in Poznan, 60-625 Poznan, Poland. [email protected]

Received: July 28, 2012 Accepted: December 12, 2012

Abstract

The aim of the study was to show the variability of exterior type in Arabian horses bred in three leading farms in Poland. A total of 334 adult animals from the basic herd of stud farms in Bialka, Janow Podlaski, and Michalow were studied. Each underwent 26 exterior measurements. In the first stage, the method of exploration of multidimensional data - principal component analysis, was used, and subsequently, a stepwise canonical discriminant analysis. It was found that each stud farm breeds horses with a different metrical pattern. Horses bred in Bialka represent clearly different morphotype comparing to horses from the other stud farms. Individuals from Janow Podlaski are more similar to horses originating from Michalow but morphological variation also occurs between them. From among the 26 metric traits, 10 parameters have a meaningful discriminative power. These include in particular such parameters as the length of the metatarsus, pelvis, arm, and neck, and depth of the chest.

Key words: Arabian horses, morphological type, biometry, exterior.

The value of the Arabian horses is mainly characteristics, such as a rapid increase in limb growth associated with their exterior conformation, because this rate and resistance to injuries of bones (8, 11). In the particular breed is used primarily for presentations. countries of other geographical latitudes, the conditions Therefore, the major criterion for their assessment is for breeding Arabian horses are different, which their aesthetic value, as well as, their correct body consequently may impinge on the change of their composition. Arabian horses have been bred in Poland intrinsic features. Therefore, the comparison of different for many years and can boast a high reputation in the populations of the Arabian horses across the world, may world. Although the rearing of this horse breed is be particularly interesting from the researcher’s point of overseen by the World Organisation view. In Poland, the subject has been recently (WAHO), it is extremely difficult to provide one single undertaken; however, the study was limited to only three definition of the ideal pattern of the exterior. Therefore, basic biometric parameters (3, 10, 14-16). judging during the shows is a matter of subjectivity. Therefore, the study aims at answering the Attempts to characterise the morphometrical question whether the Polish Arabians are uniform group pattern have been taken repeatedly for many horse in terms of biometry and demonstrating metric breeds in recent years (1, 7, 17). Biometric studies differences in body parts between individuals reared in narrowed down only to Arabian horses mainly apply to three major stud farms in Poland. populations in , Iran and, Egypt (2, 4, 13). On the basis of the Spanish population it was found that some of the exterior parameters revealed significant Material and Methods differences between animals bred for morphological shows and for endurance races (2). In view of these data, The study was conducted on 334 a question arises whether Arabian horses represent a Arabian horses (50 and 284 mares) with a different metric model in the countries where they are completed process of growth and development. The bred. The homeland of the breed is the Arabian horses originated from the basic herds of the following Peninsula, where there are specific climate conditions stud farms: Bialka, Janow Podlaski, and Michalow. that have contributed to the formation of the unique For each horse, 26 biometric measurements features of such horses. Hence, this breed is not only were conducted. Some of them are standard parameters interesting for its exterior but also for a peculiar that are commonly used to characterise , conformation of anatomical-physiological 624 however, the remaining part of measurements fell circumference (22), neck length (23), head length (24), outside the common standards (Fig. 1). Horses were chest circumference (25), and chest depth (26). measured with the use of a certified equipment including The statistical methods used in the study belong standard measuring stick, measuring tape, and to the category of multivariate analyses. The first compasses dedicated to biometric measurements. method, the so-called exploratory one, which served to highlight the diversity of the exterior of the horses, was the principal component analysis (PCA). In PCA, the varimax rotation strategy was applied. The goal of this strategy was to obtain a clear pattern of the dependency between metric features and components. Eigenvalues showed the share of a given component in total variance. Subsequently, the stepwise canonical discriminant analysis (CDA), which in details indicates differentiating traits in three studs of Arabian horses, was used. Additionally, basic statistical analysis for most important biometric traits was used. The analytical calculations were performed using programme Statistica 9.0.

Results

Principal components analysis. In the first stage of the study, the PCA, which allows an assessment Fig. 1. Some of the metric features. Numbering of morphometric differences of the horses from Bialka, consistent with the text (missing features: 1, 2, 3, 6, 11, Janow Podlaski, and Michalow , was used. Based 14, 20, 22, 23, 24, 25 are defined below this figure). on the eigenvalue parameter, from 26 original measurements, the number of new principal components As it can be noticed, that is a list of all the metric was limited to seven. These components were chosen features: withers height (1), metacarpus circumference because each eigenvalue is greater than 1.0. They (2), croup height (3), greater trunk length – distance explain 63.13% of the variability conditioned by all the between the greater tubercle (tuberculum majus) of measurements. The first component (PC1) describes humerus and the ischial tuberosity (tuber ischiadicum) 18.5%, whereas the second component (PC2) 15.9% of (4), smaller trunk length – distance between the greater the total variability. Both components plotted on a two- tubercle of the humerus and coxal tuber (tuber coxae) of dimensional graph showed a variation of individuals the ilium (5), chest width (6), scapula length – distance under the study (Fig. 2). from the shoulder joint through the spina of scapulae to The grouping variable, which is denoted on the the withers (7), arm length – distance between the plot in the study, was the particular stud farm as a place greater tubercle of humerus and the olecranal tuberosity of horses' origin. It turns out that specimens coming (tuber olecrani) (8), forearm length – distance between from the Bialka stud farm significantly differ from the the olecranal tuberosity and the accessory carpal bone horses from the Michalow stables. It can be assumed (os carpi accessorium) (9), metacarpus length – distance that these two stud farms breed their horses in between the proximal epiphysis of the third metacarpal completely different metric types. The third cohort bone and the metacarpophalangeal joint (10), fore includes horses from the Janow Podlaski stud farm. pastern length (11), fore autopodium length – distance Specimens in this group represent an intermediate type, between the accessory carpal bone and the ground (12), which connects the plot of the other two types. pelvis length – distance between the coxal tuber of the To illustrate the relationship between the ilium and ischial tuberosity (13), pelvis width – distance measurements and the principal components, the between the right and left coxal tuber of the ilium (14), strategy of varimax rotation (Table 1) was used. On this croup depth – distance between the coxal tuber of the basis, PC 1 was strongly associated with only two metric ilium and patella (15), croup length – distance between features of the exterior: the length of the fore pastern the sacral tuber (tuber sacrale) and the ischial tuberosity and the length of the hind pastern. There was also a (16), femur length – distance between the greater medium correlation between the withers height, the trochanter (trochanter majus) of the femur and patella croup height, and the fore autopodium length. PC2 was (17), crust length – distance between the patella and the also strongly linked to only two measurements: the trochlea of the talus (trochlea tali) (18), metatarsus scapula length and arm length. length – distance between the proximal epiphysis of the Canonical discriminant analysis. The purpose third metatarsal bone and metacarpophalangeal joint of the stepwise CDA was to identify metric features (19), Hind pastern length (20), Hind autopodium length among 26 under the consideration, which would mainly – distance between the distal prominence of calcaneus classify the individual into one of the three stud farms. (sustentaculum tali) and ground (21), metatarsus The analysis of the 26 traits indicated 10 traits, which were in turn used to build a model. The features, 625 grouped from the strongest to the weakest are presented that these two populations are distinctive, whereas the in Table 2. Other features, which are not shown in the horses coming from Janow Podlaski have a similar Table, do not matter in relation to distinguishing types metric pattern to the horses bred in Michalow. This is of Arabian horses under the present study. proved by the fact that the two clouds of points on the For the discrimination of horses from different plot overlap to some extent. The tendency to distinguish stables, two functions were isolated. The first function between these types is, however, evident. separates primarily horses originating from the Bialka In the last part of the study, mean values and farm from those bred in Michalow and Janow Podlaski. standard deviation of the top 10 morphometric traits, The second discriminant function differentiates mainly which according to the CDA are important in horses of the latter two stud farms (Fig. 4). distinguishing horses from different stud farms, were There is a large distance between horses from presented. These features are shown both separately for Białka, and horses originating from Michałów. The each group of horses, as well as, totally for the general analysis confirmed the initial assumption of the PCA population of Polish Arabian horses (Table 3).

8

6

4

2

PC2 0

-2

-4

-6 -6 -4 -2 0 2 4 6 8 PC1 Białka Stud Farm Janów Podlaski Stud Farm Michałów Stud Farm

Fig. 2. Principal component (PC) plot: PC1 versus PC2. Grouping variable is the stud farm.

6 5 4 3 2 1 0

CAN2 -1 -2 -3 -4 -5 -6 -6 -4 -2 0 2 4 6 8 10 CAN1 Białka Stud Farm Janów Podlaski Stud Farm Michałów Stud Farm

Fig. 3. Plot of the first (CAN1) and the second (CAN2) canonical discriminant function 626

Table 1 Component loading matrix after varimax rotation for two most important components. Component loadings in bold express a strong relation of a given component with the primary feature.

Metric feature PC 1 PC 2 Withers height 0.57 0.33 Croup height 0.58 0.37 Metacarpus circumference 0.42 0.38 Greater trunk length 0.01 0.15 Smaller trunk length 0.04 -0.16 Scapula length 0.01 0.78 Arm length -0.18 0.81 Forearm length 0.21 0.37 Metacarpus length 0.06 0.09 Fore pastern length 0.79 -0.20 Fore autopodium length 0.48 -0.10 Pelvis length -0.10 0.60 Pelvis width 0.14 -0.11 Croup depth -0.04 0.04 Croup length -0.04 0.42 Femur length 0.00 0.14 Crust length 0.39 -0.15 Metatarsus length -0.01 0.10 Hind pastern length 0.70 -0.11 Hind autopodium length 0.25 -0.19 Metatarsus circumference 0.12 0.14 Chest circumference 0.17 0.31 Chest depth 0.21 0.19 Chest width -0.02 0.32 Neck length 0.21 -0.08 Head length 0.29 0.05

Table 2 Results of the canonical discriminant analysis.

Variable Wilks’ Partial Wilks’ F value lambda lambda (2.322) Metatarsus length 0.087 0.74 56.546 Pelvis length 0.081 0.792 42.148 Arm length 0.078 0.823 34.66 Chest depth 0.077 0.833 32.159 Neck length 0.073 0.871 23.738 Hind autopodium length 0.072 0.89 19.925 Forearm length 0.072 0.892 19.477 Scapula length 0.071 0.899 17.977 Greater trunk length 0.071 0.90 17.823 Withers height 0.07 0.91 15.828 627

Table 3 Basic statistics of the main morphometric features

Metric feature Stud farm Mean value Standard Mean for all stud (cm) deviation farms (cm) Michalow 41.4 1.1 Metatarsus length Janow Podlaski 42.5 1.5 41.4

Bialka 38.7 2.3 Michalow 44.1 1.9 Pelvis length Janow Podlaski 46.2 3.1 46.3 Bialka 52.2 2.5 Michalow 34.9 2.0 Arm length Janow Podlaski 38.5 2.2 37.0

Bialka 39.2 1.6 Michalow 63.1 2.1 Chest depth Janow Podlaski 63.9 2.7 63.2

Bialka 62.0 2.9 Michalow 79.7 2.7 Neck length Janow Podlaski 78.8 3.2 78.2

Bialka 73.0 4.4 Michalow 57.9 1.7 Hind autopodium length Janow Podlaski 57.4 2.2 56.7

Bialka 51.9 2.8 Michalow 40.8 1.4 Forearm length Janów Podlaski 40.6 1.5 41.1

Białka 42.8 1.6 Michałów 60.7 2.2 Scapula length Janow Podlaski 65.3 3.0 63.5

Bialka 66.9 3.9 Michalow 154.6 4.1 Greater trunk length Janów Podlaski 152.5 5.1 154.4

Białka 157.9 5.3 Michałów 151.6 3.1 Withers height Janow Podlaski 150.9 3.2 151.1

Bialka 150.5 3.0

Discussion Michalow, which has been in operation since the middle of 20th century. The horses bred there predominantly The first conclusion of the study is that in each come from the Saklawi type. Out of the three, Bialłka is stud farm, Arabian horses are morphologically diverse. the youngest stud farm. The farm started to breed horses Therefore, it is needed to look at their origins and the only in 1980. The breeding herd largely came from the breeding history of the farms. Of the three stud farms, first two stud farms, so it is based on a similar genetic Janow Podlaski can boast the longest breeding. The farm material. The examined horses represent a total of eight has operated since the early 19th century. It is believed sire lines. The largest group comes from the line of the that horses bred there represent the type of Kuhailan Saklawi I , and next from the line of the Kuhailan horses. The stud farm, which has a shorter tradition is Haifi stallion. Therefore, these two stallions must have had the greatest influence on the shaping of the 628 examined population of Arabians. It is worth noting that these studies, PC1 is connected with the parameters in each of the stud farms there is, however, a significant influencing the size of animals, while PC2 is interpreted number of horses that come from each of these stallion as a factor of "thickness". These two components founders. Thus, morphometric distinctness of the three classify Arabian horses alongside such breeds as the stud farm horses should not depend on the sire lines. In Connemara Pony, Mountain Horse, Morgan, Appaloosa, other words, there is no relationship between the stud and . There is, however, little research when it farm and the founder sire if a horse's morphotype is comes to a comparison of the same breed or type of taken into account. horses in different countries. The example is the analysis There is a similar situation when it comes to the of metric features of racehorses in and Ireland. It dam lines. Among the fifteen families, the most was also found that differ from other numerous is the Milordka dam line, and then the dam breeds, not only with regard to segment lengths but also line of Gazella. The mtDNA research has shown that with regard to joint angles (18). Similarly, the quadratic there is a clear genetic distinction of Polish Arabian form of silhouette generally applies to race breeds (9). mare lines, with only a few exceptions (5). However, it This principle can also apply to the Arabian horses. is worth emphasising that in each of the stud farms there Interestingly, the comparison of Arabians with are horses deriving from these lines. It is particularly Thoroughbreds showed that limb injuries are problematic why, despite a similar origin, horses born in significantly less frequent in Arabian horses (11). these three stud farms differ morphometrically. It seems Perhaps this is due to the fact that Arabians have usually that the variability of the metric model of horses can be a correct anatomy of forelegs, especially their autopodial affected by sublines, which have been currently created segments (carpus, metacarpus and phalanges). in the three farms. Moreover, a consistently conducted In conclusion, three leading Arabian horse stud selection and breeding by various breeders can account farms in Poland breed horses with various morphometric for the differences. In the Arabian horse breeding, in types. Horses from Janow Podlaski represent a similar addition to inherent characteristics of demonstration, type to individuals originating from Michalow. Horses what is particularly sought after, is racing prowess of bred in Bialka are clearly distinctive, especially in horses. The interaction between these aspects may relation to horses from Michalow. Among metric finally lead to the preferences of a slightly different features, the largest discriminative power is especially model of the Arabian horse in the farms under study. seen in the length of the metatarsus, pelvis, and arms, Out of the 26 metric traits, 10 features are and in the depth of the chest and neck. increasingly significant. Among them, as one of the primary trait, one should point to the length of the Acknowledgements: The authors wish to metatarsus. It is the longest in horses from Janow acknowledge the help of Janow Podlaski, Michalow, and Podlaski and the shortest in horses originating from Bialka stud farms in possibility of data collection and to Bialka. 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