






































Type of the Paper (Article


 

 
Cluj Vet J 2024, 29, 3 http://clujveterinaryjournal.ro 
  

Article 

Correlations between hypothyroidism and ovarian cysts in 
bitches 
Zoltán-Miklós GÁL1, †), Alexandru-Raul Pop 1, †), Ana Hîruța 2, Alexandra Irimie 3,* and Ioan Ștefan Groza 1 

1 Faculty of Veterinary Medicine, Reproduction Department, University of Agricultural Sciences and Veteri-
nary Medicine, Cluj-Napoca, 400372, Cluj, Romania; alexandra.irimie@usamvcluj.ro 

2 Faculty of Veterinary Medicine, Pathology Department, University of Agricultural Sciences and Veterinary 
Medicine, Cluj-Napoca, 400372, Cluj, Romania. 

3  Faculty of Veterinary Medicine, Anatomy Department, University of Agricultural Sciences and Veterinary 
Medicine, Cluj-Napoca, 400372, Cluj, Romania.  

* Correspondence: alexandra.irimie@usamvcluj.ro 
†) These authors contributed equally to this work. 

Abstract: This study involved 48 canine individuals with ovarian cystic formations larger than 4–5.5 mm in diameter, as identified 
by ultrasound, who were in the diestrus or anestrus phase of the sexual cycle. Both T4 and fT4 levels were measured in all 48 cases. 
The imaging diagnosis of ovarian cystic formations was performed using the stationary ultrasound equipment Esaote MyLab X5, 
and with the owners' consent, samples were collected and the obtained data processed. Peripheral venous blood samples were col-
lected in coagulation activator-lined tubes. Hormone assays were performed using the Biomerieux MiniVidas hormone analyzer. 
The results are automatically calculated by the machine using stored calibration curves and are expressed in µg/dL for T4 and in 
ng/dL for fT4. The objective of this study is to determine the prevalence and extent of hypothyroidism in polycystic ovarian syndrome 
in bitches by measuring the levels of both T4 and fT4 in 48 patients with ovarian cysts. Considering clinical symptoms, borderline 
values were classified as indicative of hypothyroidism. 27% (n = 13) were diagnosed with hypothyroidism, while 73% (n = 35) had 
euthyroidism. Statistically significant differences were found in the results of both T4 and fT4 between the euthyroid and hypothy-
roid groups. This study found a high prevalence of hypothyroidism in female dogs with ovarian cysts. Given the impact of hypothy-
roidism on ovulation in women and its potential effects in dogs, thyroid function testing is recommended for female dogs with 
infertility. 

Keywords: cysts, hypothyroidism, infertility, bitch

 
 

1. Introduction 
Polycystic ovarian syndrome (PCOS) is the leading global cause of infertility in 

women, associated with a high level of comorbidities. This syndrome is linked to exces-
sive ovarian and/or adrenal androgen hormone secretion, anovulation, and often insulin 
resistance and other associated metabolic disorders [1]. PCOS is thus a heterogeneous 
condition involving changes in the reproductive and cardiovascular systems, as well as 
metabolic and oncological implications, with serious health consequences [2].  

Thyroid dysfunction in women can impact fertility through various mechanisms, 
resulting in anovulatory cycles, luteal phase defects, elevated prolactin levels (PRL), and 
disruptions in sex hormone balance. As a result, proper thyroid function is essential for 
fertility, pregnancy, and the maintenance of a healthy pregnancy, even in the early stages 
[3]. 

Thyroid hormones influence the function of nearly every organ in the body; there-
fore, canine hypothyroidism can present a wide range of clinical signs. One factor in de-
termining the effects of the disease is the challenge of confirming a diagnosis of hypothy-
roidism in dogs. Establishing the diagnosis is hindered both by the lack of specificity of 
thyroxine (T4) analysis and the insensitivity of thyrotropin testing. Given that purebred 

Received: 05.08.2024 

Accepted: 10.08.2024 

Published: 12.09.2024 

DOI: 10.52331/t8vsmz64 

 

 

Copyright: © 2024 by the authors. 

Submitted for possible open access 

publication under the terms and 

conditions of the Creative Commons 

Attribution (CC BY) license 

(http://creativecommons.org/licenses

/by/4.0/). 

https://doi.org/10.52331/t8vsmz64


Cluj Vet J 2024, 29, 3 9 of 29 

 

   

dogs are intentionally bred, the impact of hypothyroidism on reproduction holds significant clinical im-
portance. While a wide range of abnormalities occur in women with this disorder, there is limited  

knowledge about the effects of thyroid hormone deficiency on reproductive performance in female 
dogs [4]. 

The metabolically active fraction of thyroxine (T4), known as free T4 (fT4), is widely acknowledged to 
more closely reflect the thyroid status compared to T4. Determining fT4 through equilibrium dialysis has 
been proposed as an alternative, non-invasive method, and is considered by some authors to be more sensi-
tive and specific than measuring T4. This is because fT4 represents the amount of thyroid hormone available 
for use by the body's cells, whereas the total T4 level can be influenced by binding proteins [5]. In the same 
reference the authors state that the specificity of the low fT4 is between 93–94%. 

In small animal breeding programs, infertility is one of the most critical issues that poses a challenge 
to successful management. Fertility involves achieving conception, followed by a pregnancy through im-
plantation and successfully carrying the pregnancy to full term. 

This study aims to establish the prevalence and degree of involvement of hypothyroidism in polycys-
tic ovarian syndrome in the canine species, by testing the levels of both T4 and fT4 in 48 patients with infer-
tility. 

2. Materials and Methods 
In this study, 48 individuals belonging to the female canine species were included, in which ovarian 

cystic formations larger than 4–5.5 mm in diameter were identified by ultrasound, and they were in the 
diestrus or anestrus phase of the sexual cycle. In all 48 cases both T4 and fT4 levels were measured. 

The diagnosis of females with ovarian cysts, as well as the collection of samples for thyroid hormone 
measurements, were conducted at the Faculty of Veterinary Medicine in Cluj-Napoca within the Reproduc-
tion, Obstetrics, and Reproductive Pathology Department (small animal clinic), as well as at the specialized 
private veterinary clinic Quantas Repro Vet in Cluj-Napoca. 

The imaging diagnosis of ovarian cystic formations was conducted using the stationary ultrasound 
equipment Esaote MyLab X5, with a microconvex probe, followed by measuring the cystic structures using 
the ultrasound machine's software. After diagnosing cases of ovarian cysts, with the owners' consent to col-
lect samples and process the obtained data, peripheral venous blood samples were collected in coagulation 
activator-lined tubes. 

The collected samples were centrifuged at 5000 rotations per minute to obtain serum. The liquid frac-
tion was transferred into 1 ml Eppendorf tubes and stored at a freezing temperature of –18 degrees Celsius 
to conduct the thyroid profile. In most cases, the thyroid profile was conducted for diagnostic purposes, so 
the owners agreed to have T4 and fT4 levels measured. In this scenario, the processing of the samples was 
done directly after collection. Processing samples stored in the freezer involves first allowing them to thaw 
at room temperature for 15 minutes. After thawing, the samples need to be homogenized before testing. 
Hormone assays were performed using the Biomerieux MiniVidas hormone analyzer. This is an automated 
analyzer that utilizes immunoassay techniques for testing infectious markers (viral, bacterial), tumor mark-
ers, hormones, markers for cardiovascular conditions and hemostasis pathology, drug assays, allergology, 
etc. Special kits from the supplier are required for each assay. 

The results are automatically calculated by the machine using stored calibration curves and are ex-
pressed in nmol/L. Samples with concentrations greater than 320 nmol/L need to be retested after dilution 
with 1/2 in T4-free serum (1 volume of sample and 1 volume of T4-free serum) and retested in the VIDAS T4 
test. The results for fT4 are automatically calculated by the machine using stored calibration curves and are 
expressed in pmol/L. 

The obtained fT4 and T4 data were examined for normality using the Shapiro-Wilk test. For the nor-
mal distribution results comparison, the independent samples t-test was applied. In case the normality was 
rejected for the examined data, the Mann-Whitney test was applied. Values of p < 0.05 were considered as 
statistically significant. The statistical analysis was performed using MedCalc® Statistical Software version 
22.032 (MedCalc Software Ltd, Ostend, Belgium). 

3. Results 
In the following table the levels of both T4 and fT4 in the studied cases are presented (Table 1). The 

prevalence of hypothyroidism among female dogs diagnosed with ovarian cysts and who underwent thy-
roid hormone testing (n = 48) was 12% (n = 6). In 15% of cases (n = 7), thyroid hormone levels were at the 
lower limit. Such cases close to the lower limit were included in the borderline group and were considered 



Cluj Vet J 2024, 29, 3 10 of 29 

 

   

along with those with hypothyroidism, as the clinical history revealed signs of thyroid insufficiency. From 
a clinical perspective, considering that these levels should be interpreted in conjunction with the clinical 
symptoms, we classified the borderline values as indicative of hypothyroidism. Therefore, 27% (n = 13) of 
cases were diagnosed with hypothyroidism and a percentage of 73% (n = 35) of cases were diagnosed with 
euthyroidism. 

Table 1. The levels of the T4 and fT4 in the studied cases 

NR.CRT Breed Age T4 FT4 T4 REF. FT4 REF.  
    µg/dl ng/ml µg/dl ng/ml 

1 Central Asian Shepherd 3 1.56 1.11 1.50–4 0.80–3 
2 Romanian Bocovina Shepherd 4 2.4 1.35 1.50–4 0.80–3 
3 Labrador Retriver 11 1.57 1.05 1.50–4 0.80–3 
4 Bernese Mountain Dog 6 1.37 0.86 1.50–4 0.80–3 
5 American Bully 2 3.34 3.28 1.50–4 0.80–3 
6 Tibetan Mastiff 3 1.31 0.91 1.50–4 0.80–3 
7 French Bulldog 7 2.63 2.21 1.50–4 0.80–3 
8 Central Asian Shepherd 8 1.99 2.79 1.50–4 0.80–3 
9 Malinois Shepherd 7 2.05 2.11 1.50–4 0.80–3 
10 Siberian Husky 2 2.77 1.89 1.50–4 0.80–3 
11 Central Asian Shepherd 8 4.03 2.8 1.50–4 0.80–3 
12 Bernese Mountain Dog 8 1.32 0.74 1.50–4 0.80–3 
13 Cane Corso Italiano 4 1.79 1.83 1.50–4 0.80–3 
14 Belgian Shepherd 4 3.56 2.81 1.50–4 0.80–3 
15 Belgian Shpeherd 4 2.67 1.85 1.50–4 0.80–3 
16 American Bully 4 0.93 0.7 1.50–4 0.80–3 
17 Pero de Pressa Canario 9 1.78 1.35 1.50–4 0.80–3 
18 Akita Inu 10 1.26 1.10 1.50–4 0.80–3 
19 Middle Mixed breed 12 0.74 0.75 1.50–4 0.80–3 
20 Malinois Shepherd 5 2.48 2.31 1.50–4 0.80–3 
21 Pug 4 2.59 1.79 1.50–4 0.80–3 
22 German Shepherd 9 2.52 1.74 1.50–4 0.80–3 
23 German Shepherd 3 1.55 0.77 1.50–4 0.80–3 
24 Bull Terrier 9 2.39 1.85 1.50–4 0.80–3 
25 Middle Mixed Breed 12 1.23 1.02 1.50–4 0.80–3 
26 Malinois Shepherd 7 1.32 1.85 1.50–4 0.80–3 
27 American Bully 2 1.97 1.6 1.50–4 0.80–3 
28 Bichon Maltese 8 2.23 1.72 1.50–4 0.80–3 
29 American Bully 1 4.46 1.67 1.50–4 0.80–3 
30 American Bully 3 2.25 1.23 1.50–4 0.80–3 
31 English Bulldog 1 2.39 1.64 1.50–4 0.80–3 
32 Caucasian Shepherd 7 1.7 1.3 1.50–4 0.80–3 
33 Bernese Mountain Dog 4 1.48 0.87 1.50–4 0.80–3 
34 Wired Dachshund 7 0.57 0.37 1.50–4 0.80–3 
35 American Bully  1 2.25 1.91 1.50–4 0.80–3 
36 American Bully 1 1.31 0.87 1.50–4 0.80–3 



Cluj Vet J 2024, 29, 3 11 of 29 

 

   

NR.CRT Breed Age T4 FT4 T4 REF. FT4 REF.  
    µg/dl ng/ml µg/dl ng/ml 

37 Beagle  11 2.28 1.34 1.50–4 0.80–3 
38 Yorkshire Terrier 6 2.74 1.4 1.50–4 0.80–3 
39 American Bully 1 1.12 1.07 1.50–4 0.80–3 
40 Central Asian Shepherd 5 0.87 0.7 1.50–4 0.80–3 
41 Middle Mixed Breed 16 2.31 1.14 1.50–4 0.80–3 
42 Mini Bullterrier 1 3.2 1.57 1.50–4 0.80–3 
43 American Bully 2 3.49 2.23 1.50–4 0.80–3 
44 German Shepherd 4 2.69 1.41 1.50–4 0.80–3 
45 Alaskan Malamut 6 1.3 1.16 1.50–4 0.80–3 
46 American Bully 4 2.03 1.25 1.50–4 0.80–3 
47 Wired Dachshund 4 1.18 0.91 1.50–4 0.80–3 
48 French Bulldog 1 2.69 1.87 1.50–4 0.80–3 
 
The T4 values for canine females diagnosed with ovarian cysts were compared in the euthyrotic (n = 

35) and hypothyrotic (n = 13) groups. Since the normality of the T4 values in both groups was accepted, the 
independent sample t-test was applied. The results indicated a statistically significant difference (p = 0.001) 
in T4 values between the euthyrotic group and the hypothyrotic group. 

The fT4 values for canine females diagnosed with ovarian cysts were compared in the euthyrotic (n = 
35) and hypothyrotic (n = 13) groups. Since the normality of the data was rejected for the fT4 in the hypothy-
rotic group, the Mann-Whitney test was applied. The results indicated a statistically significant difference (p 
= 0.0001) in fT4 values between the euthyrotic group and the hypothyrotic group. 

Six cases of hypothyroidism have been identified in females with ovarian cysts, and 7 cases with thy-
roid parameter values at the lower limit, borderline, classified as hypothyroidism. The cases of hypothyroid-
ism and diagnosed cystic formations (n = 13) were from the categories of giant breeds (n = 5), large breeds 
(n = 2), medium breeds (n = 4), and small breeds (n = 2). Thus, we observed a prevalence of 38.5% in giant 
breed individuals, 30.8% in medium-sized females, and 15.4% in patients of large and small sizes. 

4. Discussion 
Fertility issues are typically categorized into one of four groups: abnormal estrous cycles, normal es-

trous cycles, unsuccessful breeding, or failure to carry a litter to full term. This classification system helps in 
creating a list of potential causes and conducting a systematic evaluation of all possibilities [6]. 

Thyroid hormones influence the function of nearly every organ in the body; therefore, canine hypo-
thyroidism can present a wide range of clinical signs. 

In women, hypothyroidism is linked to a wide range of reproductive disorders, from abnormal sexual 
development to menstrual irregularities and infertility. The importance of this disorder on the menstrual 
cycle, in women, has been studied and know since 1950s [7]. Hypothyroidism disrupts the normal physio-
logical secretion of GnRH, which is essential for normal follicular development and ovulation. A delay in 
LH response can result in insufficient progesterone secretion by the corpus luteum [7]. Both gonadotropins 
and thyroxine seem to be essential for achieving optimal fertilization rates and blastocyst development [7]. 
On a cellular level, thyroid hormones work together with FSH to directly stimulate granulosa cell functions, 
including morphological differentiation. Thyroid hormones assist in FSH-induced LH/HCG receptor activa-
tion and progesterone secretion. Therefore, insufficient availability of thyroid hormones at the ovarian level 
may contribute to gonadal dysfunction [8]. In a study, the author observed primary and secondary infertility 
in 6.2% of 16 overtly hypothyroid women. This prevalence was similar, 4.8% in the euthyroid group with 
goiter and 2.4% in normal control women (unknown thyroid function) [9]. 

The clinical signs of canine hypothyroidism include low metabolic rate, dermatological conditions 
(dermatological abnormalities are reported in 60–80% of hypothyroid dogs), reproductive abnormalities 
(prolonged interestrus, silent estrus, lack of cyclicality, spontaneous abortion, small size puppies or low 
postpartum weight compared to the breed characteristics, uterine inertia, and weak or stillborn puppies); 



Cluj Vet J 2024, 29, 3 12 of 29 

 

   

however, evidence for this association is limited. If hypothyroidism is a cause of female reproductive dys-
function, it seems to frequently pass undiagnosed in veterinary practice. For example, a single case of hy-
perprolactinemia in a dog with primary hypothyroidism has been reported in the veterinary literature [10]. 

A study assessed the influence of short-term induced hypothyroidism on fertility, gestation, parturi-
tion, and neonatal health in female dogs. There was no difference in the estrous cycle interval, litter size, or 
gestation length between the hypothyroid group and the control dogs. The duration of uterine contractions 
was longer, but the strength of contractions was weaker in the hypothyroid group compared to the control 
dogs; however, the interval between puppies was not affected. Postpartum puppy mortality was signifi-
cantly higher among females with hypothyroidism [4]. It is not clear why the female dogs in this study did 
not develop the common reproductive abnormalities associated with hypothyroidism in women. One pos-
sible reason could be the relatively short duration of the present study and, consequently, of the hypothy-
roidism, for reproductive abnormalities associated with hypothyroidism to manifest. It is possible that thy-
roid insufficiency gradually develops in the case of spontaneous hypothyroidism, compared to the sudden 
induction of severe hypothyroid status for experimental purposes discussed in this study. Therefore, pro-
longed hypothyroidism may occur in natural disease as it progresses from subclinical to more severe mani-
festations, becoming evident over time [4]. 

Infertility and insulin resistance are the result of glucose metabolism abnormalities in women with 
Polycystic Ovary Syndrome (PCOS). PCOS is the most common cause of anovulatory infertility, while hy-
perinsulinemia in women leads to increased androgen production and the presence of insulin resistance 
(IR). Patients with IR and PCOS may have elevated plasma levels of homocysteine, which can influence both 
short-term reproductive function and long-term cardiovascular complications associated with insulin-re-
sistant PCOS [11]. Patients with hypothyroidism frequently experience insulin resistance, which results in 
increased serum gonadotropin (LH) levels. This stimulates the ovaries to produce excessive androgens, thus 
triggering or worsening PCOS [12]. A study discovered that 22.5% of PCOS patients also had subclinical 
hypothyroidism (SCH), in contrast to only 8.3% of the normal control group [13] compared to another study 
that the prevalence of subclinical hypothyroidism (SCH) in PCOS patients was 43.6% [12]. Xing et. Al [14] 
reported an increased prevalence of SCH in PCOS women at 26.97%. In our investigation, among all the 
cases diagnosed with ovarian cysts and infertility, 27% had T4 and fT4 values indicative of hypothyroidism, 
which aligns with the previous mentioned studies. Statistically, there was a significant difference in results 
for both T4 and fT4 between the euthyroid and hypothyroid groups. On the canine species we did not find 
studies that indicate a correlation between these 2 disorders. The limitations of our study are comparable to 
those of Fatima et al.'s study [12], such as the absence of a temporal understanding between the two disor-
ders, clinical outcomes following hypothyroidism treatment, and the correlation with other disorders like 
diabetes or obesity. 

5. Conclusions 
Given the recognized significance and impact of hypothyroidism on the physiological process of ov-

ulation in women, and its lesser-studied effects in canine species, there should be increased consideration of 
this disorder in the pathological evaluation of infertility in female dogs. This study revealed a notable prev-
alence of hypothyroidism in female dogs with ovarian cysts. Specifically, one-third of the canine females in 
the research group with ovarian cysts were also diagnosed with hypothyroidism, indicating a significant 
correlation between the two conditions. As ovarian cystic pathology can lead to infertility, this study sug-
gests testing thyroid functions in female dogs with a clinical history of infertility. Another noteworthy find-
ing in this study is that middle and giant breeds are more prone to hypothyroidism. Therefore, there is a 
high likelihood that hypothyroidism could be the underlying cause of infertility in these breeds. Cases ex-
hibiting clinical signs such as infertility, skin lesions, obesity tendency, high blood pressure, etc., along with 
borderline values of the T4 and fT4 indicators, should be regarded as hypothyroidism cases. 

Author Contributions: Conceptualization, Z.-M.G. and I.Ș.G.; methodology, A.-R.P., A.H. and A.I.; statistical analysis, 
Z.-M.G.; resources, A.-R.P.; data curation, A.H.; writing—original draft preparation, Z.-M.G., A.H. and A.I.; writing—
review and editing, A.I.; supervision, I.Ș.G. All authors have read and agreed to the published version of the manuscript. 

Funding: This research was founded by the Discipline of Animal Reproduction at the Faculty of Veterinary Medicine 
Cluj-Napoca.  

Acknowledgments: The authors extend their gratitude to the Discipline of Animal Reproduction at the Faculty of Vet-
erinary Medicine Cluj-Napoca, and the private practice reproduction referral clinic Quantas Repro Vet SRL in Cluj-
Napoca for their help in collecting the samples. 



Cluj Vet J 2024, 29, 3 13 of 29 

 

   

Conflicts of Interest: The authors declare no conflict of interest. 

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