# The first report of quadricuspid aortic valve in cattle: clinical, anatomical and histological findings in three Holstein cattle

Samuel Kalpers, Sander Prins, Katherine Ings, Jayne Orr, Mark P Dagleish

<figure><img src="image_1.png" /></figure>

## To cite this version:

Samuel Kalpers, Sander Prins, Katherine Ings, Jayne Orr, Mark P Dagleish. The first report of quadricuspid aortic valve in cattle: clinical, anatomical and histological findings in three Holstein cattle. Journal of Comparative Pathology, 2025, 220, pp.40-46. 10.1016/j.jcpa.2025.06.002. hal-05509038

HAL Id: hal-05509038

https://hal.inrae.fr/hal-05509038v1

Submitted on 13 Feb 2026

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
<figure><img src="image_3.png" /></figure>

# The first report of quadricuspid aortic valve in cattle: clinical, anatomical and histological findings in three Holstein cattle

Samuel Kalpers<sup>a, *, b, c</sup>, Sander Prins<sup>b, c, d</sup>, Katherine Ings<sup>a, d</sup>, Jayne Orr<sup>b</sup>, Mark P. Dagleish<sup>a, d</sup>

<figure><img src="image_4.png" /></figure>

## ARTICLE INFO

Handling Editor: Samuel Kalpers

### Keywords:

Aortic valve

Cattle

Congenital anomaly

Heart

Holstein

Quadricuspid

## ABSTRACT

Quadricuspid aortic valve (QAV) is a rare congenital heart condition in which the aortic valve is comprised of four, rather than three, sinuses and cusps. The clinical significance of QAV is unclear; it is diagnosed most frequently in humans and has not been reported in cattle. QAV was identified in three female Holstein cattle at necropsy for unrelated clinical conditions. Although heart murmurs were identified on clinical examination, no animal had heart failure. In all three cases the non-coronary cusp of the aortic valve was comprised of two separate cusps, resulting in a quadricuspid valve. Histological examination of the abnormal valves did not reveal consistent significant microscopic lesions. The clinicopathological consequences, genetic basis and incidence of QAV in cattle are unclear; however, veterinarians and pathologists should be aware of this condition as a possible differential diagnosis in cattle with heart murmurs.

## 1. Introduction

Quadricuspid aortic valve (QAV) is a rare congenital heart condition in which the aortic valve is composed of four aortic sinuses and four cusps, rather than the normal three. QAV is reported most frequently in humans, but the specific aetiology is currently unknown [1,2]. Historically, QAV was detected incidentally in human patients undergoing open heart surgery or autopsy. Ante-mortem diagnosis of QAV in humans has improved due to the widespread use of echocardiography [2] and advancement in imaging techniques, including cardiac computed tomography and magnetic resonance imaging [3]. Functionally, QAV can manifest as aortic regurgitation, which may progress to aortic stenosis, although the exact pathogenesis remains undetermined [3]. Most affected humans are asymptomatic until they are over 60 years old, at which stage the major clinical sign is congestive heart failure [2]. Typically, QAV is diagnosed as a sole condition, although concurrent congenital anomalies have been reported occasionally, including coronary artery and ostium anomalies, atrial septal defect, ventricular septal defect (VSD), patent ductus arteriosus and tetralogy of Fallot [3]. Rarely, infective endocarditis may occur due to endothelial damage secondary to poor coaptation of the valves [3].

In humans, QAV is classified according to morphology into one of

seven different morphologies, denoted A to G [4]; an additional presentation, H, was subsequently reported by Vali *et al* [5]. In addition, Nakamura *et al* published an alternative classification system dividing the morphologies into four broader categories [6]. Currently, both systems are used in human cardiology, although a lack of correlation between morphological categories and clinical outcomes is reported [2].

In animals, QAV has been reported in dogs [7–9], horses [10,11], Syrian hamsters [12,13], a cat [14] and a greater white-toothed shrew (*Crocidura russula*) [1]. Ultrasound findings in horses and dogs suggest QAV may cause a degree of aortic regurgitation (as in humans) with variable, possibly species-dependent, clinical consequences [7,9–11]. For instance, aortic regurgitation in horses with QAV was implicated in the development of heart failure [10,11], whereas in dogs the consequences of QAV reportedly range from subclinical [9] to cardiac failure [7].

Additionally, concurrent congenital cardiac anomalies have been reported in dogs, including VSD [7,8], patent ductus arteriosus, abnormal coronary ostium and degenerative mitral valve disease [7]. A single coronary artery is reported in a greater white-toothed shrew with QAV [1], while concurrent VSD and tetralogy of Fallot have been reported in horses with QAV [11,15].

This is the first report of QAV in cattle and it describes the clinical,

<footnote><sup>a</sup> Division of Pathology, Public Health and Disease Investigation, School of Biodiversity, One Health and Veterinary Medicine, University of Glasgow, UK</footnote>

<footnote><sup>b</sup> Scottish Centre for Production Animal Health & Food Safety, School of Biodiversity, One Health and Veterinary Medicine, University of Glasgow, UK</footnote>

<footnote><sup>c</sup> Université Clermont Auvergne, INRAE, VetAgro Sup, UMR Herbivores, Saint-Genès-Champanelle, 63122, France</footnote>

<footnote>* Corresponding author.
E-mail address: skalpers@gmail.com (S. Kalpers).</footnote>
gross and histological findings in three female Holstein cattle.

## 2. Materials and methods

### 2.1. Clinical history

All cases were submitted to the Scottish Centre for Production Animal Health and Food Security (SCPAHFS), School of Biodiversity, One Health and Veterinary Medicine, Glasgow University, Scotland, UK, for clinical investigation and teaching purposes. Case 1, a 10-month-old female Holstein heifer weighing 240 kg, was referred in September 2023 for mastitis and a heart murmur. Case 2, a 7-month-old female Holstein heifer weighing 82 kg, was referred in September 2023 for chronic pneumonia, bilateral heart murmur and ill thrift. Case 3, a 5-year-old, 2nd lactation, non-gravid Holstein cow weighing 614 kg, was referred in January 2024 for a heart murmur and poor milk production. Cases 2 and 3 were from the same farm. Samples were also taken from a cow with normal aortic valve anatomy for use as a negative control; this was 2.5-years-old female Holstein cow, 270 days in milk, that was 7 months pregnant. It was sent for post-mortem examination following a short duration illness characterized by anorexia and cessation of lactation. Veterinary examination suggested gastrointestinal blockage and the animal was euthanized on farm.

### 2.2. Post-mortem examination

All three affected animals were euthanized by overdose of barbiturate and, along with the negative control case, subjected to standard gross post-mortem examination (excluding brain and spinal cord) and the heart examined using the inflow-outflow method [16]. Individual aortic valve cusps were measured at the attached base and free margin, along with the circumferences of the aortic and pulmonary arteries. All measurements were taken by the same person (SK) by tracing the relevant margins with string, then measuring the string length.

### 2.3. Histological examination

The whole heart (case 1) or the interventricular septum, aortic and pulmonic valves (cases 2 and 3 and negative control) were fixed in 10% buffered formal saline. Sagittal sections of each aortic valve were taken from the middle of the free margin of each cusp to the base of the valve and the underlying myocardium or aorta. Samples were processed routinely through graded alcohols prior to being embedded in paraffin wax. Semi-serial sections (4 µm) were placed on glass microscope slides and subjected to haematoxylin and eosin (HE), Alcian blue, Masson's trichrome and Verhoëff's method for elastic fibres stains.

## 3. Results

### 3.1. Clinical data

#### 3.1.1. General clinical findings

In all three cases, the heart rate/rhythm, pulse rate/rhythm, mucous membrane colour and capillary refill time (CRT) were normal, and there were no signs of jugular pulsation or oedema, although case 3 had mild jugular distention. All three cases had different dams and sires. No clinical notes were available for the negative control animal.

#### 3.1.2. Case 1

Clinical examination revealed a body condition score (BCS) of 3/5, a heart rate of 72 beats per minute (BPM), pink mucous membranes, a CRT of less than 2 s and a pulse of normal strength and rhythm. Auscultation revealed a 3/6 right-sided heart murmur and a quieter (ungraded) murmur on the left side. A partially reducible, approximately 8 cm in diameter, umbilical hernia was present. No other clinical abnormalities were seen. Cardiac ultrasound (model and make absent from clinical

notes) revealed aortic valve insufficiency and mild tricuspid valve insufficiency. Lung ultrasound was normal. The animal was treated for digital dermatitis with topical chlortetracycline (Cyclo Spray; Dechra Veterinary Products, www.dechra.co.uk) and subcutaneous meloxicam (0.5 mg/kg bodyweight [BW]) (Recocam; Bimeda Laboratories, www.bimeda.co.uk). Routine biochemistry and haematology revealed increases in the concentration of albumin (37 g/L; reference interval [RI], 21–34 g/L) and glutamate dehydrogenase activity (GLDH, 54.9 U/L; RI, 0–10 U/L) (Supplementary Table 1).

#### 3.1.3. Case 2

Clinical examination revealed a BCS of 1/5, bilateral clear nasal discharge, a respiratory rate of 50 breaths per minute, heart rate of 100 BPM, pink mucous membranes, a CRT of less than 2 s and a pulse of normal strength and rhythm. Auscultation identified bilateral adventitious lung sounds and a left-sided heart murmur, but the adventitious lung sounds precluded grading the murmur. Ultrasound (Easy-Scan:Go Bovine ultrasound scanner, curved probe 3–7Mhz, depth 12 cm; IMV imaging, www.imv-imaging.com) revealed multifocal, bilateral, prominent B-lines in the cranioventral and craniodorsal lung fields, and a hypoechoic area in the right cranial lung field. Cardiac ultrasound was not performed. The animal was treated for pneumonia for 7 days with a variety of medications including, initially, intramuscular penicillin and streptomycin (8 mg/kg BW procaine penicillin and 10 mg/kg BW dihydrostreptomycin sulphate) (Pen & Strep Suspension for Injection; Norbrook Laboratories Ltd, www.norbrook.com) and subcutaneous meloxicam (0.5 mg/kg BW) (Recocam, Bimeda Laboratories), then intramuscular florfenicol (20 mg/kg BW) (Nuflor 300, MSD Animal Health Hub, www.msd-animal-health-hub.co.uk). Plasma biochemistry revealed increased activities of GLDH (162.8 U/L; RI, 0–10 U/L), gamma-glutamyl transferase (GGT, 77 U/L; RI, 0–27 U/L) and aspartate transferase (AST, 154 U/L; RI, 0–140 U/L), and decreased creatinine concentration (42 µmol/L; RI, 53–132 µmol/L) (Supplementary Table 1). Haematology revealed a decreased haematocrit (21.6%; RI, 24.0–46.0%), haemoglobin concentration (6.5 g/dL; RI, 8.0–15.0 g/dL) and lymphocyte count (2.17 × 10⁹/L; RI, 2.5–7.5 × 10⁹/L) (Supplementary Table 1).

#### 3.1.4. Case 3

Clinical examination identified a BCS of 2.5/5, unilateral right-sided clear nasal discharge, a heart rate of 52 BPM, pink mucous membranes, a CRT of less than 2 s, a pulse of normal strength and rhythm and mild jugular distention, although the jugular refill test was within normal limits. A diastolic grade 5/6 right-sided heart murmur and a grade 4/6 left-sided heart murmur were present. All other clinical parameters were within normal reference values. Cardiac ultrasound (model and make absent from clinical notes) showed severe aortic valve regurgitation and tricuspid valve regurgitation with thickening of the aortic and mitral valves and mild thickening of the tricuspid valve. Haematology and biochemistry revealed increases in GLDH (32.9 U/L; RI, 0–10 U/L) and GGT (67 U/L; RI, 0–27 U/L) activities (Supplementary Table 1).

### 3.2. Post-mortem examination

At post-mortem examination the BCSs of cases 1, 2 and 3 were 1.5–2/5, 1.5/5 and 1.5/5, respectively, and that of the negative control animal was 1/5. In all three affected animals the non-coronary cusp of the aortic valve was subdivided by a firm, pale pink, thin septum extending from the base of the valve to the free margin, forming two separate cusps (Figs. 1 and 2). The aortic semilunar valve cusps were labelled from 1 to 4 corresponding to the left coronary cusp (valve 1), right coronary cusp (valve 2), first non-coronary cusp (valve 3) and second non-coronary cusp (valve 4). Cases 1 and 2 had one small valve 3 and one large valve 4, and case 3 had one large valve 3 and one small valve 4 (Fig. 2 and Table 1). All the semilunar valves were pale yellow to pale pink, had smooth surfaces and were diffusely and irregularly thickened up to 5
<figure><img src="image_5.png" /><figcaption>**Fig. 1.** Quadricuspid aortic valve, cattle. Quadricuspid aortic valves (arrows) and normal mitral valve (stars). (A) Case 1. (B) Case 2. Younger animal. (C) Case 3. (D) Negative control animal. Bar, 10 cm.</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>**Fig. 2.** Quadricuspid aortic valve, cattle. A septum (arrow) divides the non-coronary cusp into two different cusps. Left coronal cusp (1), right coronal cusp (2), first non-coronal cusp (3), second non-coronal cusp (4). (A) Case 1. (B) Case 2. Younger animal. (C) Case 3. (D) Negative control animal. Bar, 5 cm.</figcaption></figure>

mm.

Additional findings in the three affected animals included a moderate, non-strangling umbilical hernia and moderate fibrosis in the left hind quarter of the mammary gland (case 1), moderate to marked suppurative chronic-active bronchopneumonia, hydropericardium, keratomalacia and renal petechiae (case 2) and subaortic stenosis and fibrous pleural-pericardial adhesions (case 3).

The control animal had an acute, focally extensive, severe, fibrinous peritonitis and acute, multifocal to coalescing, severe fibrinonecrotizing abomasitis.

### 3.3. Histological examination

Histological examination of the three animals with QAV did not

reveal any significant microscopic changes in the aortic valves following staining with HE (Fig. 3), Alcian blue (Fig. 4), Masson's trichrome (Fig. 5) or Verhoëff's method for elastic fibres (Fig. 6). All the valves from cows with QAV had similar proportions of collagen, mucins, elastic fibres and smooth muscle compared with the valve tissue of the negative control animal. Due to sectioning and processing artefact, the nature of the grossly appreciable irregular thickening was unclear and the plane of section from all the animals could not be entirely comparable.

### 4. Discussion

This is the first report of QAV in cattle, which is surprising given the condition was found in three animals from two different premises over a relatively short period of time. All cases were female Holstein cattle,
<table><caption>**Table 1**
Dimensions of the aortic semilunar valves at the cusp base and free margin and the aortic and pulmonary valve circumferences.</caption><thead><tr><th></th><th></th><th>Case 1</th><th>Case 2</th><th>Case 3</th><th>Negative control</th></tr></thead><tbody><tr><td rowspan="2">Valve 1 (mm)</td><td>Cusp base</td><td>92</td><td>46</td><td>112</td><td>74</td></tr><tr><td>Free margin</td><td>51</td><td>33</td><td>76</td><td>52</td></tr><tr><td rowspan="2">Valve 2 (mm)</td><td>Cusp base</td><td>61</td><td>51</td><td>116</td><td>77</td></tr><tr><td>Free margin</td><td>46</td><td>25</td><td>68</td><td>52</td></tr><tr><td rowspan="2">Valve 3 (mm)</td><td>Cusp base</td><td>49</td><td>37</td><td>98</td><td>81</td></tr><tr><td>Free margin</td><td>23</td><td>10</td><td>63</td><td>57</td></tr><tr><td rowspan="2">Valve 4 (mm)</td><td>Cusp base</td><td>66</td><td>55</td><td>70</td><td>N/A</td></tr><tr><td>Free margin</td><td>49</td><td>34</td><td>40</td><td>N/A</td></tr><tr><td>Total aortic circumference (mm)</td><td>Cusp base</td><td>141</td><td>67</td><td>202</td><td>133</td></tr><tr><td>Pulmonary valve circumference (mm)</td><td>Cusp base</td><td>117</td><td>81</td><td>131</td><td>111</td></tr></tbody></table>

Valve 1, left coronary cusp; valve 2, right coronary cusp; valve 3, first non-coronary cusp; valve 4, second non-coronary cusp; N/A, not applicable.

which may represent a population bias as most adult cattle submitted to the SCPAHFS are female and most dairy cattle submitted are Holsteins. Examination of the breeding records failed to find any direct genetic relationship. However, as all the affected cattle were of the Holstein breed, a genetic aetiology for QAV cannot be excluded. Conversely, as they all originated from a localized geographical area, the possibility of an environmental aetiology must also be considered.

In all three cases the non-coronary cusp of the aortic valve formed two separate cusps, a change also reported in a dog [9], a cat [14] and a horse [10]. In veterinary medicine, the Hurwitz and Roberts's classification of QAV [4] has been used in Syrian hamsters [17], dogs [7,9], horses [10,11] and a cat [14]. In addition, a study in Syrian hamsters has independently reported four categories of quadricuspid and

quadricuspid-like morphologies, although the authors did not identify any correlation between morphological category and clinicopathological outcomes [12].

Case 1 had three equal cusps and one smaller cusp, case 2 two equal larger cusps and two unequal smaller cusps, and case 3 one large, two intermediate and one small cusp, which, using the Hurwitz and Roberts classification system, would be attributed to B, F and D morphologies, respectively [4]. However, there is no evidence that this classification system is clinically relevant in animals, and even studies in human cardiology highlight a lack of correlation between the morphology of the QAV and clinicopathological consequences [2]. Similarly, no meaningful relationship between QAV morphology and clinicopathological outcome was identified in these three cattle, especially as none of the cases had clinical or post-mortem evidence of (left-sided) heart failure. Furthermore, even though case 3 had concurrent subaortic stenosis, this did not appear to have any clinical consequences despite multiple examinations over a period of 6 weeks.

In humans, aortic valve incompetence due to QAV does not usually occur in young patients [4,18], although progression to heart failure [6, 19] due to the development of aortic regurgitation in the fifth to sixth decades of life has been reported [2,3,20]. The cattle in this study were all young animals and if QAV in cattle follows a similar pathogenesis to that in humans, it is tempting to speculate that these animals may have developed clinical signs with advancing age. In dogs, two cases of QAV in young individuals did not appear to cause any clinical disease, including one case with ultrasonographic evidence of very mild aortic regurgitation [9]. In horses, heart failure was reported in one case; however, this may have been the result of a concurrent VSD rather than a direct effect of QAV as the authors suggested the latter only caused mild aortic regurgitation [11]. Similarly, a case of cardiac failure was reported in a 3-day-old alpaca cria that had QAV with concurrent VSD, patent foramen ovale and a common arterial trunk anomaly [21].

All three cases in this study had mildly increased plasma GLDH levels and cases 2 and 3 also had increased plasma GGT levels. In cattle, elevated GGT is used as an indicator of hepatobiliary disease [22] whereas elevated GLDH is specific for hepatocellular insult [23]. These findings suggest hepatobiliary injury in cases 2 and 3 and hepatocellular injury in all cases. No macroscopic hepatic lesions were identified in

<figure><img src="image_7.png" /><figcaption>**Fig. 3.** Quadricuspid aortic valve, cattle. (A) Case 1. (B) Case 2. Younger animal. (C) Case 3. (D) Negative control animal. HE. Bar, 250 µm.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**Fig. 4.** Quadricuspid aortic valve, cattle. (A) Case 1. (B) Case 2. Younger animal. (C) Case 3. (D) Negative control animal. Alcian blue. Bar, 250 µm. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>**Fig. 5.** Quadricuspid aortic valve, cattle. (A) Case 1. (B) Case 2. Younger animal. (C) Case 3. (D) Negative control animal. Masson's trichrome. Bar, 250 µm.</figcaption></figure>

these animals and as the livers were not sampled for histological examination, the cause of these changes is unclear.

Identification of heart murmurs in cattle has both a low sensitivity and specificity for cardiac diseases, as they can be physiological [24]. Although diagnosis of QAV was achieved *ante mortem* in two horses using echocardiography [10,11], *ante-mortem* definitive diagnosis of heart diseases in cattle remains challenging as echocardiography is not performed routinely [24,25]. Therefore, it remains unclear whether QAV can be diagnosed in cattle by ultrasound examination.

The embryogenesis of aortic valves is complex but appears to be relatively similar across mammalian species. The aortic valve is formed by the growth of two mesenchymal cushions, also referred to as ridges or swellings, dividing the lumen of the conotruncus into the aortic and pulmonary tracts, and in each tract three further mesenchymal swellings go on to form the valve cushions [4,13,18]. The mechanism of QAV development has only been reported in Syrian hamsters, where it is thought that QAV forms following the additional division of one of the cushions by invagination of the endothelial layer on the luminal side
<figure><img src="image_10.png" /><figcaption>**Fig. 6.** Quadricuspid aortic valve, cattle. (A) Case 1. (B) Case 2. Younger animal. (C) Case 3. (D) Negative control animal. Verhoëff's method for elastic fibres. Bar, 250 µm.</figcaption></figure>

early in valve formation [26]. More recent work on Syrian hamsters suggests a continuum between tricuspid and quadricuspid aortic valves in this species in which some individuals develop tricuspid aortic valves with an incomplete raphe-like ridge in one of the aortic valves [12,17].

Histological examination using HE, Alcian blue, Masson's trichrome and Verhoëff's method for elastic fibres stains did not reveal any consistent changes in the valves of the QAV animals compared with the aortic valve tissue of the negative control animal. Unfortunately, apart from Syrian hamsters [27], there are no published detailed histological descriptions of QAV.

Detailed examination of the aortic valves may not always be undertaken during cattle necropsies, which may explain why QAV has not previously been diagnosed in cattle. Further studies are required to determine the true prevalence of QAV in Holstein and other breeds of cattle and a slaughterhouse survey may be an expedient way to undertake this.

This study has several limitations. The clinical data were retrospective in nature and recorded by undergraduate veterinary students. Consistent with published reports, and due to a different assessment methodology of the BCS inherent to the examination of cadavers in lateral recumbency, there were discrepancies between the BCS attributed during the ante-mortem clinical examination versus the post-mortem examination [28]. Furthermore, reliable measurement of aortic valve leaflets is challenging due to their morphology and histological assessment is restricted due to the size of standard tissue cassettes such that the sections of valves examined are unlikely to be identical within or between cases.

## 5. Conclusion

This is the first report of QAV in cattle, a poorly characterized congenital anomaly in any species, yet three cases were diagnosed in cattle over a 9-month period. The clinicopathological consequences, genetic basis and incidence of QAV in cattle are unclear, as in other species in which the condition has been reported. However, clinicians and pathologists should be aware of this probably underreported condition during clinical and post-mortem examinations. More extensive

studies are required to further characterize the prevalence, pathogenesis and clinical relevance of this condition.

## Statement of author contributions

**Samuel Kalpers:** Post-mortem examination; Photographs; Trimming of tissue; Histological examination; Writing. **Sander Prins:** Clinical examination; Data collection; Writing. **Katherine Ings:** Post-mortem examination; Histological examination: Writing. **Jayne Orr:** Clinical examination; Data collection; Writing. **Mark Dagleish:** Post-mortem examination; Histological examination; Writing.

## Funding

The authors received no financial support for the research, authorship or publication of this article.

## Declaration of competing interests

The authors declared no conflicts of interest in relation to the research, authorship or publication of this article.

## Acknowledgments

The authors thank the post-mortem room staff and histology team of the Veterinary Diagnostic Services, University of Glasgow, as well as David Sutton, Weipers Centre Equine Hospital, University of Glasgow, for performing ultrasound and George King, SCAPHS, University of Glasgow, for performing ultrasound and clinical examination of the cases.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jcpa.2025.06.002.
## References

[1] Duran AC. Quadricuspid aortic valve and single coronary artery in a greater white-toothed shrew, *Crocidura russula*. J Wildl Dis 1996;32(4):658–60. https://doi.org/10.7589/0090-3558-32.4.658.

[2] Saith S, Saith S, Murthy A. Quadricuspid aortic valve: an introduction for clinicians. Cardiol Res 2022;13(1):2–10. https://doi.org/10.14740/cr1308.

[3] Yuan SM. Quadricuspid aortic valve: a comprehensive review. Braz J Cardiovasc Surg 2016;31(6):454–60. https://doi.org/10.5935/1678-9741.20160090.

[4] Hurwitz LE, Roberts WC. Quadricuspid semilunar valve. Am J Cardiol 1973;31(5):623–6. https://doi.org/10.1016/0002-9149(73)90332-9.

[5] Vali Y, Rajendra R, Nishtar S. A previously undescribed type of quadricuspid aortic valve: type H. J heart valve. Dis 2010;19(6):792–3.

[6] Nakamura Y, Taniguchi I, Saiki M, Morimoto K, Yamaga T. Quadricuspid aortic valve associated with aortic stenosis and regurgitation. Jpn J Thorac Cardiovasc Surg 2001;49:714–6.

[7] Serres F, Chetboul V, Sampedrano CC, Gouni V, Pouchelon JL. Quadricuspid aortic valve and associated abnormalities in the dog: report of six cases. J Vet Cardiol 2008;10(1):25–31. https://doi.org/10.1016/j.jvc.2008.03.003.

[8] Kettner F, Cote E, Kirberger RM. Quadricuspid aortic valve and associated abnormalities in a dog. J Am Anim Hosp Assoc 2005;41(6):406–12. https://doi.org/10.5326/0410406.

[9] Sisson D, Riepe R. Congenital quadricuspid aortic valve anomaly in two dogs. J Vet Cardiol 2000;2(2):23–6. https://doi.org/10.1016/S1760-2734(06)70008-X.

[10] Vitale V, Laurberg M, van Galen G. Transthoracic echocardiography and its limitations in the diagnosis of congenital supernumerary aortic valve in a thoroughbred. Vet Med Sci 2023;9(2):712–6. https://doi.org/10.1002/vms3.472.

[11] Michlik KM, Biazik AK, Henklewski RZ, Szmigielska MA, Nicpon JM, Pasławska U. Quadricuspid aortic valve and a ventricular septal defect in a horse. BMC Vet Res 2014;10:142. https://doi.org/10.1186/1746-6148-10-142.

[12] Lopez-Garcia A, Carmen Fernandez M, Duran AC, Sans-Coma V, Fernandez B. Quadricuspid aortic valves in Syrian hamsters and their formation according to current knowledge on valvulogenesis. Jpn J Vet Res 2015;63(1):37–43.

[13] Fernandez B, Duran AC, Thiene G, Cardo M, Arque JM, Sans-Coma V. Embryological evidence for the formation of a quadricuspid aortic valve in the Syrian hamster. Cardiovasc Pathol 1994;3(4):287–91. https://doi.org/10.1016/1054-8807(94)90017-5.

[14] Nakamura T, Sawada T, Takagi M. Incidental echocardiographic findings of a quadricuspid aortic valve associated with aortic regurgitation in a cat. JFMS Open Rep 2015;1(2):2055116915596356. https://doi.org/10.1177/2055116915596356.

[15] Gesell S, Brandes K. Fallotsche Tetralogie bei einem 7-jährigen Wallach. Pferdeheilkunde 2006;22(4):427–30.

[16] Robinson WF, Robinson NA. Cardiovascular system. In: Maxie MG, editor. Jubb, Kennedy & Palmer's pathology of domestic animals. 6th ed., vol. 3. St. Louis: Elsevier; 2016. p. 1–101.

[17] Fernández B, Fernández MC, Durán AC, López D, Martire A, Sans-Coma V. Anatomy and formation of congenital bicuspid and quadricuspid pulmonary valves in Syrian hamsters. Anat Rec 1998;250(1):70–9. https://doi.org/10.1002/(sici)1097-0185(199801)250:1<70::Aid-ar7>3.0.CO;2-i.

[18] Timperley J, Milner R, Marshall AJ, Gilbert TJ. Quadricuspid aortic valves. Clin Cardiol 2002;25:548–52.

[19] Jagannath AD, Johri AM, Liberthson R, Larobina M, Passeri J, Tighe D, et al. Quadricuspid aortic valve: a report of 12 cases and a review of the literature. Echocardiography 2011;28(9):1035–40. https://doi.org/10.1111/j.1540-8175.2011.01477.x.

[20] Soares FR, Branco C, Coutinho GF, Prieto D, Antunes MJ. Quadricuspid aortic valve with a hidden left ostium: case report and literature review. Rev Port Cardiol (Engl Ed) 2021;40(1):63 e1–e5. https://doi.org/10.1016/j.repc.2018.04.012.

[21] Kurosawa TA, Gunasekaran T, Sanders R, Carr E. Common arterial trunk in a 3-day-old alpaca cria. Case Rep Vet Med 2016;2016:4609126. https://doi.org/10.1155/2016/4609126.

[22] Braun JP, Benard P, Burgat V, Rico AG. Gamma glutamyl transferase in domestic animals. Vet Res Commun 1983;6(2):77–90. https://doi.org/10.1007/BF02214900.

[23] Barnouin J, Mialot M, Levieux D. [Evaluation of hepatic pathology of bovines by a blood sample. Relations with histopathologic findings]. Ann Rech Vet 1982;12(4):363–9.

[24] Buczinski S, Rezakhani A, Boerboom D. Heart disease in cattle: diagnosis, therapeutic approaches and prognosis. Vet J 2010;184(3):258–63. https://doi.org/10.1016/j.tvjl.2009.05.005.

[25] Mitchell KJ, Schwarzwald CC. Echocardiography for the assessment of congenital heart defects in calves. Vet Clin North Am Food Anim Pract 2016;32(1):37–54. https://doi.org/10.1016/j.cvfa.2015.09.002.

[26] Fernandez B, Duran AC, Martire A, Lopez D, Sans-Coma V. New embryological evidence for the formation of quadricuspid aortic valves in the Syrian hamster (*Mesocricetus auratus*). J Comp Pathol 1999;121(1):89–94. https://doi.org/10.1053/jcpa.1998.0299.

[27] Fernandez B, Soto-Navarrete MT, Lopez-Garcia A, Lopez-Unzu MA, Duran AC, Fernandez MC. Bicuspid aortic valve in 2 model species and review of the literature. Vet Pathol 2020;57(2):321–31. https://doi.org/10.1177/0300985819900018.

[28] Munro R, Munro HMC. Animal abuse and unlawful killing: forensic veterinary pathology. Edinburgh/New York: Elsevier Saunders; 2008.