Quartuccio, Fazio et al. (2021) — Italian Journal of Animal Science
Correlation Between Sperm Parameters and Circulating Thyroid Hormones and Testosterone Concentrations in Labrador Retriever Dogs
Published: July 31, 2026
When a stud dog produces poor semen quality, the investigation usually starts with reproductive hormones — testosterone in particular. A study of 26 Labrador Retriever males has added an important dimension to that picture: thyroid hormones are physiologically regulating semen quality in ways that interact directly with testosterone, and dogs with azoospermia show a hormonal profile that differs from normal dogs in directions that point toward thyroid function as a variable breeders and veterinary reproductionists should be routinely assessing. 🐾
Researchers M. Quartuccio, E. Fazio, and their team measured serum thyroxine (T4), free thyroxine (fT4), thyroid-stimulating hormone (TSH), and testosterone concentrations in 26 adult Labrador Retriever dogs — 20 normospermic and 6 azoospermic — alongside comprehensive conventional and kinematic sperm parameter evaluation and clinical ultrasound assessment. The goal was to establish breed-specific hormonal reference ranges and characterise the specific relationships between thyroid hormones, testosterone, and semen quality in this breed.
What the Correlations Actually Show
In the normospermic group — dogs with normal semen parameters — significant correlations emerged between T4 and several key reproductive variables. T4 correlated negatively with testosterone concentration, meaning higher T4 levels were associated with lower testosterone. T4 also correlated negatively with sperm progressive motility — the measure of what percentage of sperm are moving purposefully in the right direction. And T4 showed a positive correlation with non-progressive motility — sperm that are moving but not in a directed, functionally useful way.
The direction of these correlations matters clinically. They suggest that even within the normal physiological range, thyroid hormone levels are not neutral with respect to reproductive function — higher T4 within normal limits appears to be associated with modestly lower testosterone and reduced directional sperm motility. Whether this represents a direct physiological relationship or reflects the regulatory interplay of the hypothalamic-pituitary axis across multiple hormonal axes requires further investigation, but the pattern is consistent enough in this dataset to warrant attention.
The azoospermic group produced the most clinically significant finding. Dogs with azoospermia — complete absence of sperm in ejaculate — showed higher T4, higher fT4, and higher TSH concentrations alongside lower testosterone compared to normospermic dogs. In the azoospermic group, T4 and testosterone showed a positive rather than negative correlation — the relationship between the two hormones reversed direction compared to normospermic dogs, suggesting a fundamentally different hormonal regulatory state rather than simply an exaggeration of the pattern seen in normal dogs.
Why Breed-Specific Reference Ranges Matter ⚠️
A consistent theme in the canine reproductive and endocrinology literature is that reference ranges established across diverse mixed populations may not accurately reflect the normal physiological parameters of specific breeds. Labrador Retrievers, like other breeds, have a specific body composition, metabolic rate, and physiological profile that may produce normal hormone values that sit at different points within or even outside cross-breed reference intervals.
The researchers emphasise this directly — the establishment of breed-specific hormonal and sperm parameter reference ranges for Labrador Retrievers is one of the study’s primary contributions. A testosterone or T4 value assessed against a generic canine reference range may be interpreted as normal when it is actually high or low for this specific breed, leading to missed diagnoses or inappropriate reassurance in reproductive evaluations.
For breeders working with Labrador stud dogs, this has immediate practical implications. A reproductive evaluation that returns hormone values described as within normal range may still be missing clinically relevant information if those values are not being interpreted against breed-appropriate reference data. Azoospermia or reduced semen quality in a Labrador Retriever stud warrants thyroid function evaluation alongside the testosterone assessment that is already standard practice — and the evaluation should be interpreted by a veterinary reproductionist familiar with the breed-specific reference data this research is beginning to establish.
What This Means for Breeding Programme Health 🐕
Thyroid disorders are among the more common endocrine conditions in dogs, and their effects on reproductive function have been documented in both males and females across species. The mechanism proposed in this research — thyroid hormones regulating semen quality through effects on testosterone concentration and through direct effects on sperm motility and viability — provides a physiologically coherent framework for why a dog with apparently normal reproductive anatomy might still produce suboptimal semen.
For breeding programmes where stud dog reproductive performance is critical, routine thyroid hormone screening as part of pre-breeding health evaluation is a straightforward and relatively low-cost addition that this research supports. A stud dog with subclinical hypothyroidism or borderline thyroid dysfunction may present with reduced semen quality that resolves with appropriate management — but only if the thyroid axis is being assessed in the first place.
At Zoeta Dogsoul, physical foundation is always part of the full picture. The health of a breeding animal is not only relevant to the individual dog — it flows directly into the genetic and developmental foundation of every puppy produced. A breeding programme built on thorough endocrine health evaluation, including thyroid function, is a programme that is investing in the physical integrity of the animals it produces. That investment is part of what responsible breeding looks like when it is taken seriously at a biological rather than purely pedigree level. 🐾
Source: Quartuccio, M., Fazio, E., et al. (2021). Correlation between sperm parameters and circulating thyroid hormones and testosterone concentrations in Labrador Retriever dogs. Italian Journal of Animal Science. Published January 1, 2021.
