The Arabian (AR) horse, prized for its beauty, elegance, and enduring athleticism, is considered one of the world’s oldest domesticated equine breeds. The AR horse breed is genetically predisposed to several diseases, such as equine metabolic syndrome.1 As a breed, it is also predisoposed to several diseases specifically affecting the head, including ocular diseases, guttural pouch tympany, and congenital occipitoatlantoaxial malformation (OAAM).2–5
A morphometric study on the conformation of the equine skull revealed that the AR skull differs significantly compared with that of Thoroughbreds (TB) and Standardbreds (SB).6 The skull of the AR has a significantly shorter nasal length compared with TB and SB, and a significantly greater ratio of cranial: nasal length compared with TB.6 The findings of this study also revealed that AR have a significantly higher “nasal profile index” than TB and SB, representing a more concave “dished” facial profile, which is one of the defining features of the AR phenotype.6,7 The authors summarized that, although it is generally thought that AR have smaller heads; in reality, this appearance is due to shorter nasal length rather than overall length.6
In dogs, brachycephalic breeds are known to have significantly shorter and wider skulls compared with mesaticephalic and dolichocephalic breeds.8 These different dimensions give rise to altered anatomy of the nasal passages and pharynx, resulting in a condition known as brachycephalic syndrome, which is a common cause of respiratory distress in affected breeds.8,9 In addition, Pug breeds have significantly altered sinus anatomy as a result of their brachycephalic skull conformation.10 Measurement of craniofacial angles (CFA) in a variety of dog breeds revealed that brachycephalic breeds have significantly smaller angles compared with those of mesaticephalic and dolichicephalic breeds.11 The authors concluded that the shorter skull of the brachycephalic breeds results in a more perpendicular cranium development relative to the facial axis.11 Both brachycephalic dog breeds and AR horses have a genetic predisposition for congenital upper respiratory disorders, that is, brachycephalic syndrome and guttural pouch tympany, respectively.2,3,8–11 Although measurements of CFA in AR horses are yet to be determined, selection for breed standards in this group has led to extreme skull conformation equivalent to that seen in the Pug dog breed.
The Straight Egyptian Arabian (SEAR) horse is a distinct bloodline of the AR horse, defined by The Pyramid Society (Lexington, KY) as a horse that can be traced in every line of its pedigree to The Pyramid Society Studbook for SEAR Horses Worldwide. Therefore, SEAR horses have pedigrees that can be traced back to particular horses bred by the Bedouin tribes of Arabia.12 Although SEAR account for only about 3–5% of all AR horses, it is a popular breed worldwide and is used mostly for show competitions. For this reason, the breed has been subjected to relatively intense genetic selection for conformational traits desired for showing and has evidence of relatively high inbreeding within individuals.12 Genomic studies have shown increased signals overlapping with particular genes in the SEAR horse, which correlates in people with markers at a particular gene associated with the width of the face between the eyes and the relative height of the eyes on the face.12 The authors theorized that this gene in humans mirrors the markedly concave and characteristic nasal bone and domed forehead with large eyes, as is seen in the SEAR horse subgroup.12 The findings of this particular study, which assessed genomic diversity of the AR horse, concluded that the SEAR subgroup, with its relatively high inbreeding, has a sufficient loss of diversity, that it could impact animal health.12 Unsurprisingly, with such intense genetic selection, the SEAR horse has certain bloodlines that have been shown to be predisposed to certain heritable diseases, such as juvenile idiopathic epilepsy and lavender foal syndrome (also called coat color dilution lethal).13,14 For these reasons, and more, the SEAR horse has been flagged as being an advantageous model for future studies on skull morphology.12
In the authors’ clinical experience of working with the Arabian breed, in addition to already well-documented breed predispositions (eg, guttural pouch tympany and OAAM), at the authors’ institution, the AR breed commonly presents with a variety of other diseases of the head that could potentially be attributable to extreme skull morphology. One example is the problem encountered by the authors on the AR breed suffering from dental overcrowding leading to dental disease and chronic secondary sinusitis, with poor sinus drainage. These conditions often require surgical intervention to treat, with surgical approaches taken based on documented landmarks.15 However, traditional surgical approaches to the paranasal sinuses of AR do not provide the same access to underlying structures as in other breeds.15 The primary objective of this study was to use a number of surgically relevant measurements to compare the normal skull morphology of the SEAR horses to that of the TB horses, using computed tomography (CT). A secondary objective was to compare the CFA between the SEAR and TB groups. We hypothesized that the well-documented shorter nasal length and concave facial profile would result in different skull morphology in the SEAR, compared with the TB group, making surgical approaches more challenging. Furthermore, we hypothesized that there would be a significant difference in the CFA between the two groups, with the SEAR group having significantly smaller angles compared with the TB group.
Materials and Methods
Study design, sample size, and study population
The study was a prospective cohort study. Thirty clinically normal, non-pregnant, adult horses (aged 5 years and over) were included comprising 15 SEAR horses and 15 TB horses. Data were collected in both quantitative and descriptive fashion. The study was approved by the Institutional Animal Care and Use Committee (Protocol #2021-1160) of the Equine Veterinary Medical Center.
Data collection
The study was performed on-site at the Equine Veterinary Medical Center, Doha, Qatar.
Physical examinations determined that each horse was healthy for inclusion in the study and to rule out signs of paranasal sinus disease (eg, nasal or ocular discharge, submandibular lymphadenopathy, and halitosis). Body weights (kilograms) were recorded using walk-on digital scales. Horse height at the withers (centimeters) was measured using a measuring stick.
To ensure patient compliance and welfare, horses were sedated with intravenous injections of Xylazine HCL (0.1–1 mg/kg) ± Detomidine (0.004–0.02 mg/kg) ± Butorphanol (0.01–0.04 mg/kg) and Acepromazine (0.02–0.05 mg/kg).
A number of gross morphometric measurements of the horse heads were taken using a measuring tape (Horse Measurement Instructions by Brooks Equine Genetics, IFAS Research, University of Florida). Measurements included:
Eye-to-eye width (centimeters): measured across the forehead between the medial canthi of the eyes, keeping the tape taut and straight.
Jaw width (centimeters): measured across the ventral aspect of the mandible, from the outsides of the mandibles at their widest points, keeping the tape taut and straight.
Head length (centimeters): measured from a line drawn between the top corners of the two nostrils, measured straight to the top of the occipital protruberance.
Muzzle circumference (centimeters): taken at the level just rostral to the facial crest.
Left eye-to-mouth length (centimeters): measured from the lateral canthus of the left eye to the corner of the commissure of the left lip.
Left eye to jaw length (centimeters): measured from the lateral canthus of the left eye to the deepest point of the angle of the mandible.
Anatomic locations for bone flaps commonly used in the adult horse were marked on the skull using radiopaque tape, according to previously described landmarks (Supplementary Figure S1), as follows.15
Maxillary bone flap: rostral margin was a line drawn from the rostral end of the facial crest to the infraorbital foramen; the dorsal margin was a line from the infraorbital foramen to the medial canthus of the eye, the caudal margin was a line (parallel to the rostral margin) from the medial canthus of the eye to the caudal aspect of the facial crest, and the ventral margin was the facial crest.15
Frontonasal bone flap: the caudal margin was a perpendicular line from the dorsal midline to a point midway between the supraorbital foramen and the medial canthus of the eye, the lateral margin began at the caudal margin 2 to 2.5 cm medial to the medial canthus of the eye and extended to a point approximately two-thirds the distance from the medial canthus of the eye to the infraorbital foramen, and the rostral margin was a perpendicular line from the dorsal midline to the rostral extension of the lateral margin.15
Gross measurements of the above bone flaps’ dimensions were taken using a measuring tape (in centimeters).
CT of the skull was performed with the horse under sedation, using a 64-slice Siemens Definition AS Sliding Gantry CT system (Siemens Definition AS, Siemens Healthineers). One-millimeter helical images processed by using a high-frequency convolution kernel were acquired (parameters 35Ma, 140KV, 0.6 mm slice thickness).
CT assessment
CT images were assessed using diagnostic imaging viewing software by a board-certified diplomate of the European College of Veterinary Diagnostic Imaging and the American College of Veterinary Radiology.
Quantitative CT measurements were taken as follows (Supplementary Figure S2):
Length of the facial crest (centimeter) was measured with the images viewed in an oblique plane to align with the facial crest;
Maximal diameter of the globe (centimeter) was measured in a dorsal plane, parallel to the hard palate;
Distance from the caudal-most aspect of the globe and the rostral-most aspect of the mandibular condylar process (centimeter) was taken in a dorsal plane, skull aligned parallel with the hard palate and midline sagittal plane;
Lengths of the frontal, caudal, and rostral maxillary sinuses (centimeter) were taken from the rostral extent to the caudal extent, skull aligned parallel with the hard palate and midline sagittal plane;
Minimal height of the nasomaxillary aperture (millimiter) measured with skull aligned parallel with the hard palate and midline sagittal plane (considered as the minimal height obtained from the rostral extent to the caudal extent);
Distance of the septal bulla to the rostral aspect of the CRIBRIFORM plate (left olfactory bulb interface) (centimeter), measurement taken parallel with the hard palate and midline sagittal plane;
Distance from the caudal maxillary flap margin (radiopaque marker) to the distal-most margin of the 211 tooth root (centimeter), measurement taken with skull parallel with the hard palate and midline sagittal plane;
CFA was measured according to the description by Regodón et al. (1993), as the angle formed by the basilar and facial axes.11 The basilar axis was a line between the basioccipital bone and the caudal margin of the chiasmatic groove (sulcus chiasmatis). The facial axis was formed by making a line continuous with the hard palate. In the multiplanar reconstruction (MPR) image, the x-axis is initially aligned to the palatine bone. Using the sagittal MPR image, the z-axis is moved to the level of the facial crest, making the facial axis parallel with the palatine bone.
Data analysis
The Shapiro-Wilk test was used to examine the normality of the data for each group, and normality was not rejected (P > .05) for all the data. Therefore, data were presented as mean ± standard deviation (SD), and a t-test was used to compare each group’s means.
The absolute measurements were converted into ratios to assess the significant differences in the measured features between groups and the same analysis was performed on all variables (except for body weight), using head length (centimeters) as a denominator for all ratios. A ratio of skull length to body height was also calculated for each breed. Again, the Shapiro-Wilk test was used to examine the normality of data for each breed, and normality was not rejected when P > .05 for all the data. Data were presented as mean ± SD and t-tests were used to compare the means in each group.
Results
Measurements were taken from 29 clinically normal, non-pregnant, adult horses (+5 years), including 15 SEAR horses (all mares; mean age 10.4 ± 3.59 years; mean body weight 405.33 ± 29.91 kg) and 14 TB (12 mares, 2 geldings; mean age 7.47 ± 2.25 years; mean body weight 502.79 ± 44.36 kg). One TB was excluded due to an unacceptable motion artefact on the CT. Descriptive statistics were performed for a total of 23 variables (Table 1) and all data were normally distributed. Several variables were identified as being significantly different between groups (P < .05), in all cases being greater in TB than SEAR horses. These included: the length of the facial crest (Figure 1), distance from the caudal-most globe and rostral aspect of the mandibular condylar process, length of the frontal sinus, length of the caudal maxillary sinus, the minimal height of nasomaxillary aperture (Figure 2), distance of septal bulla from the rostral aspect of CRIBRIFORM plate, lateral length of the maxillary flap, body height, body weight, eye-to-eye width, jaw width, head length, muzzle circumference, left eye-to-mouth length, and left eye-to-jaw length.
Computed tomography (CT) quantitative data and gross morphometric measurements in Straight Egyptian Arabians (SEAR) and Thoroughbred (TB) horses.
| Breed | Straight Egyptian Arabians (n = 15) | Thoroughbreds (n = 14) | ||||
|---|---|---|---|---|---|---|
| Measurements | Mean | SD | Mean | SD | P value | |
| Length of facial crest (cm) | 13.45 | 0.72 | 15.12a | 0.63 | < .001 | |
| Maximum diameter of the globe (cm) | 4.71 | 0.16 | 4.58 | 0.23 | NSD | |
| Distance from the caudal-most aspect of the globe to the rostral-most aspect of the mandibular condylar process (cm) | 5.43 | 0.44 | 6.16a | 0.52 | .001 | |
| Length of the frontal sinus (cm) | 13.48 | 1.22 | 14.56a | 1.57 | .049 | |
| Length of the caudal maxillary sinus (cm) | 7.68 | 1.63 | 9.60a | 1.51 | .002 | |
| Length of the rostral maxillary sinus (cm) | 7.00 | 1.23 | 8.19 | 1.80 | NSD | |
| Minimal height of the nasomaxillary aperture (mm) | 0.86 | 0.17 | 1.20a | 0.41 | .011 | |
| Distance of the septal bulla from the rostral aspect of the cribriform plate (cm) | 3.02 | 1.03 | 3.95a | 1.02 | .021 | |
| Distance from the caudal maxillary flap to the distal-most margin of the 211 tooth (cm) | 2.77 | 1.08 | 2.21 | 0.71 | NSD | |
| Height at withers (cm) | 147.87 | 3.14 | 160.38a | 4.15 | < .001 | |
| Body weight (kg) | 405.33 | 30.96 | 502.79a | 46.03 | < .001 | |
| Eye-to-eye length (cm) | 18.29 | 0.87 | 19.64a | 1.01 | < .001 | |
| Jaw width (cm) | 12.34 | 1.01 | 15.38a | 1.48 | < .001 | |
| Head length (cm) | 49.39 | 0.96 | 55.70a | 1.66 | < .001 | |
| Muzzle circumference (cm) | 57.62 | 1.99 | 63.64a | 4.05 | < .001 | |
| Left eye-to-mouth length (cm) | 28.72 | 0.70 | 32.66a | 0.92 | < .001 | |
| Left eye-to-jaw length (cm) | 22.73 | 1.32 | 24.27a | 1.20 | .002 | |
| Maxillary flap length | Caudal (cm) | 6.21 | 0.43 | 6.18 | 0.51 | NSD |
| Lateral (cm) | 6.73 | 1.18 | 8.52a | 0.81 | < .001 | |
| Rostral (cm) | 5.91 | 0.77 | 5.76 | 0.54 | NSD | |
| Frontal flap length | Caudal (cm) | 6.41 | 0.51 | 6.15 | 0.62 | NSD |
| Lateral (cm) | 9.91 | 1.02 | 10.14 | 0.78 | NSD | |
| Rostral (cm) | 5.32 | 0.59 | 4.92 | 0.68 | NSD | |
Measurements indicate a significant difference between breeds (P < .05).
Sagittal oblique computed tomography (CT) multiplanar reconstruction (MPR) image (WW1500 WL 300) showing facial crest length (between the arrows), from the rostral facial crest to the most rostral junction of the temporal process of the zygomatic bone and zygomatic process of the temporal bone, of a to the Thoroughbred (TB) (a) measuring 16.2 cm, compared with a Straight Egyptian Arabian (SEAR) (b) measuring 13.5 cm. D = dorsal. V = ventral. R = rostral. C = caudal.
Citation: American Journal of Veterinary Research 84, 5; 10.2460/ajvr.22.11.0191
Transverse computed tomography (CT) multiplanar reconstruction (MPR) image (WW1400 WL −500) showing left and right nasomaxillary apertures (arrow heads) of a Thoroughbred (TB) (a) with minimal height measuring 2.2 mm, compared with a Straight Egyptian Arabian (SEAR) (b) measuring 0.6 mm. D = dorsal. V = ventral. L = lateral.
Citation: American Journal of Veterinary Research 84, 5; 10.2460/ajvr.22.11.0191
Regarding the ratios of variables to head length, descriptive statistics were performed for a total of 21 variables (Table 2) and all data were normally distributed. When expressed as a ratio to head length, 12 variables were found to be significantly different between breeds. Ten variables were found to have ratios significantly larger in SEAR than TB horses: maximum diameter of the globe, distance from the caudal maxillary flap to the distal-most margin of 211, height at withers, eye to eye width, jaw width, left eye to jaw length; caudal, lateral, and rostral frontal flap dimensions; and caudal and rostral maxillary flap dimensions. Ratios for jaw width and lateral length of the maxillary flap were significantly smaller in SEAR than in TB group.
Ratios of 21 variables (not including head length or body weight), using head length as a denominator.
| Breed | Straight Egyptian Arabians (n = 15) | Thoroughbreds (n = 14) | ||||
|---|---|---|---|---|---|---|
| Measurement: head length ratio | Mean | SD | Mean | SD | P value | |
| Length of facial crest (cm) | 0.27 | 0.01 | 0.27 | 0.01 | NSD | |
| Maximum diameter of the globe (cm) | 0.10 | 0.00 | 0.08a | 0.00 | < .001 | |
| Distance from the caudal-most aspect of the globe to the rostral-most aspect of the mandibular condylar process (cm) | 0.11 | 0.01 | 0.11 | 0.01 | NSD | |
| Length of the frontal sinus (cm) | 0.27 | 0.02 | 0.26 | 0.06 | NSD | |
| Length of the caudal maxillary sinus (cm) | 0.16 | 0.03 | 0.17 | 0.03 | NSD | |
| Length of the rostral maxillary sinus (cm) | 0.14 | 0.03 | 0.15 | 0.03 | NSD | |
| Minimal height of the nasomaxillary aperture (mm) | 0.02 | 0.00 | 0.02 | 0.01 | NSD | |
| Distance of the septal bulla from the rostral aspect of the CRIBRIFORM plate (cm) | 0.06 | 0.02 | 0.07 | 0.02 | NSD | |
| Distance from the caudal maxillary flap to the distal-most margin of the 211 tooth (cm) | 0.06 | 0.02 | 0.04a | 0.01 | .022 | |
| Height at withers (cm) | 2.99 | 0.06 | 2.88a | 0.09 | < .001 | |
| Eye to Eye length (cm) | 0.36 | 0.02 | 0.35a | 0.02 | .013 | |
| Jaw width (cm) | 0.25 | 0.02 | 0.28a | 0.03 | .01 | |
| Muzzle circumference (cm) | 1.17 | 0.05 | 1.14 | 0.06 | NSD | |
| Left eye to mouth length (cm) | 0.58 | 0.01 | 0.59 | 0.01 | NSD | |
| Left eye to jaw length (cm) | 0.46 | 0.02 | 0.44a | 0.02 | .007 | |
| Maxillary flap length | Caudal (cm) | 0.13 | 0.01 | 0.11a | 0.01 | < .001 |
| Lateral (cm) | 0.14 | 0.02 | 0.15a | 0.01 | .031 | |
| Rostral (cm) | 0.12 | 0.02 | 0.10a | 0.10 | .003 | |
| Frontal flap length | Caudal (cm) | 0.13 | 0.01 | 0.11a | 0.01 | <.001 |
| Lateral (cm) | 0.20 | 0.02 | 0.18a | 0.02 | .011 | |
| Rostral | 0.11 | 0.01 | 0.09a | 0.01 | <.001 | |
Data are normally distributed. A mean value of <1 means that the dimension for this variable is a fraction of head length.
Measurements indicate a significant difference between breeds (P < .05).
Regarding the skull length-to-body height ratio for each breed, the results indicated that the TB group (0.35 ± 0.01) had a significantly greater (P value < .001) skull length-to-body height ratio compared with the SEAR group (0.33 ± 0.01).
For the CFA, skull CTs including the external acoustic meatus (for measurement of the basilar axis) were only available for a total of 6 SEAR and 6 TB horses. Results showed that there was a significant difference in CFA between the 2 groups with TB (8.79 ± 4.37) having significantly greater (P value = .018) angles than SEAR (2.18 ± 4.15).
Discussion
The results of this study highlighted several significant differences in the skull morphology of the SEAR compared with the TB horses, which should be taken into consideration when planning surgical approaches to the skull, in particular to the paranasal sinuses for the treatment of sinusitis or other sinus-related diseases.
In contrast to previous findings, the head length was significantly shorter in SEAR compared with TB horses.6 This could be a unique feature of the individuals included in the SEAR group.7 Previous research has shown differences between different lineages of Arabian horses. For example, the SEAR and Desert Breed Arabian horses have significantly shorter skull lengths compared with the Polish Arabian horses.7 Furthermore, the results of the current study suggest that head length is shorter relative to body height in SEAR compared with TB horses. Despite having several smaller skull dimensions, SEAR do not have significantly different globe dimensions compared with TB horses. However, when expressed as a ratio to head length, the SEAR globe diameter was found to be significantly greater compared with TB. This finding is in agreement with the SEAR-reported phenotype.7 Therefore, when performing costmetic globe surgery, orbital implants or intraocular prostheses used in other horse breeds are likely to be of an appropriate size for SEAR horses.16
Regarding the frontal sinuses, there were no significant differences between the groups for the frontonasal bone flap dimensions; however, the length of the frontal sinus was found to be significantly shorter in SEAR than TB horses. Therefore, it may be warranted to revisit landmarks for conventional frontonasal bone flaps in the SEAR breed, taking into consideration their shorter frontal sinus length to avoid complications such as hemorrhage due to trauma of the ethmoid tubinates. It has been the authors’ experience that access to the maxillary septal bulla in the Arabian breed is more difficult through a conventional conchofrontal trephination site compared with other breeds. With a significantly shorter distance from the maxillary septal bulla to the rostral aspect of the CRIBRIFORM plate in SEAR compared with TB horses (Figure 3), the results of the present study suggest that the maxillary septal bulla is located more caudally in this breed, making the septal bulla fenestration angle more vertical. Therefore, a trephine site located more caudal than the traditionally recommended 0.5 cm caudal to the medial canthus of the eye, might be considered in a SEAR horse if fenestration of the maxillary septal bulla is anticipated to gain access to the ventral conchal and rostral maxillary sinuses.15
Transverse computed tomography (CT) multiplanar reconstruction (MPR) image (WW1500 WL 300) showing distance (blue arrow) of the septal bulla to the rostral aspect of the cribriform plate in a Thoroughbred (TB) (a) measuring 5.39 cm compared with a Straight Egyptian Arabian (SEAR) horse (b) measuring 3.21 cm. R = rostral. C = caudal. L = lateral.
Citation: American Journal of Veterinary Research 84, 5; 10.2460/ajvr.22.11.0191
For the maxillary bone flaps, while the heights of the rostral and caudal margins were similar, the length of the lateral margin of the flap was significantly shorter in SEAR than TB horses. This is consistent with the authors’ clinical experience; whereby, maxillary flaps tend to be short and result in poor access to the maxillary sinus in SEAR horses. This is likely also due to SEAR’s significantly shorter facial crest length. Although the caudal maxillary sinus was significantly shorter in SEAR than TB horses, the maximal length of the rostral maxillary sinus was not significantly different between breeds, suggesting that this sinus is proportionately larger for the size of the skulls in SEAR compared with TB horses.
Finally, the significant difference between the 2 groups for the CFA measurements, being significantly smaller in SEAR than TB horses (Figure 4), suggests that there appear to be similarities between the SEAR horse and brachcephalic dog breeds with respect to skull dimensions. This anatomical feature could potentially be playing a role in the variety of pathologies of the skull seen in this equine breed; however, this would require further investigation to elucidate.
Sagittal oblique computed tomography (CT) multiplanar reconstruction (MPR) image (WW1500 WL 300) showing cranial facial angle (CFA) of a Thoroughbred (TB) (a) measuring 17.4 degrees, compared with a Straight Egyptian Arabian (SEAR) horse (b) measuring 3.9 degrees. D = dorsal. V = ventral. R = rostral. C = caudal.
Citation: American Journal of Veterinary Research 84, 5; 10.2460/ajvr.22.11.0191
Limitations of this study include the small sample sizes for both groups. In addition, the Arabian horse population consisted only of SEAR horses, which is known to have a relatively high degree of inbreeding; therefore, it is possible that the horses in the SEAR group had a high degree of relatedness.12
The findings of this study confirm the authors’ clinical impression that the SEAR horses skull morphology differs significantly from the TB, and that their phenotype can make surgical approaches for common diseases of the head more challenging. Whilst frontal sinus dimensions appear to be relatively unaffected, the shorter facial crest and caudal maxillary sinus, combined with the shorter lateral length of the maxillary bone flap, could potentially impede surgical access to the maxillary sinus. The more caudally located maxillary septal bulla should be considered when deciding on a trephination site of the conchofrontal sinus. The significantly shorter skull length and smaller CFA in the SEAR compared with the TB horses suggests similarities with brachycephalic dog breeds; however, further investigation is warranted to establish whether the skull dimensions of SEAR breed are consistent with brachycephaly.
Supplementary Materials
Supplementary materials are posted online at the journal website: avmajournals.avma.org.
Acknowledgments
The authors would like to express their gratitude to Dr. Carla Troteaga Alvarez for her hard work and contribution to the project; and to thank Dr. Daniel Schmidt, Dr. Samantha A. Brooks, Sarah Johnson, as well as the supporting hospital staff of the Equine Veterinary Medical Center, for their precious help. We also would like to thank Dr. Guy Beauchamp DVM, PhD, for his biostatistics expertise, as well as Al Shaqab and Al Rayyan farms, for their support with this project.
The authors declare no conflict of interest related to this report.
This study was funded by the Equine Veterinary Medical Center, Member of Qatar Foundation - Intramural grant program; Grant No. RG21_JJ1 (J.P.J.).
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