A stud dog’s sperm are made a few degrees below body temperature, so a hot summer, a fever or a stuffy kennel can quietly reduce semen quality — and because sperm take about two months to develop, the effect often shows up weeks after the heat wave, just when a booked mating comes around.
The most important first
- Heat stress can lower semen quality. In one controlled study, sperm counts fell within 30 days in heat-stressed dogs and stayed lower.
- Effects are delayed. Sperm production takes about 62 days in the dog, so problems can last one or more cycles after the heat.
- Keep stud dogs cool: shade, ventilation, cool resting surfaces and a healthy weight.
- Plan ahead: consider collecting and freezing semen in cooler months, and evaluate semen before important summer matings.
- Chilled semen needs cold, fast transport. Work with your vet on extender, packaging and courier timing.
Last updated: November 8, 2026
Why heat affects sperm
Theriogenologist Kara Kolster (2022) explains that sperm production happens at temperatures 3–5°C below body temperature, and that raised scrotal temperature causes temporary testicular dysfunction and abnormal sperm. Little change usually appears in the first 10 days after a heat insult, because the sperm ejaculated then were already almost mature. Depending on how severe and long the insult was, abnormalities may last for one or more spermatogenic cycles — 62 days in the dog.
Kolster lists sources of scrotal heat stress beyond the weather, including irritating disinfectants, rough kennel surfaces, scrotal dermatitis, obesity and infection.
What the studies show
The evidence on season is mixed, but heat itself seems to matter:
- Controlled heat stress. Burgio and colleagues (2024) followed 36 crossbred male dogs in southern Italy from May to August, comparing dogs exposed to heat stress with dogs kept in thermoneutral conditions. In the heat-stressed group, sperm concentration and total sperm count fell after 30 days and stayed lower than in the comparison group throughout the trial.
- Hot climates. In Baghdad, Ibrahim and Zaid (2017) found significant drops in sperm motility, sperm numbers and viability in summer, with more abnormal sperm, in both mature and young males.
- Older work. Kuroda and Hiroe (1972), studying ten Spitz dogs in Japan, found semen quality best in spring and worst in summer.
- Temperate climates. In contrast, Strzeżek and colleagues (2015), studying five crossbred dogs in Poland over a year, found seasonal differences in some measures but no clear negative effect of season on semen quality overall.
The practical reading: in hot climates, heat waves and hot kennels, summer can reduce semen quality, while a stud dog kept cool in a temperate climate may be little affected.
In practice
A breeder has a popular stud booked for an August mating. After a hot July, she asks her vet to evaluate his semen two weeks before the bitch is due in season. Sperm numbers are lower than in his spring sample, so she shares the result with the bitch’s owner, and together with both vets they plan an extra insemination and agree to use frozen semen collected in April as a backup.
(Illustrative, composite scenario.)
Keeping a stud dog cool
- Housing: shade, airflow, a cool place to lie, and no rough or chemically irritating floor surfaces.
- Weight: keep him lean — obesity is a recognised source of heat stress.
- Exercise: in the cool of the day.
- Health: treat skin problems and infections promptly.
- Breeding schedule: Kolster suggests reducing heat stress by limiting breedings, or scheduling frozen semen collections in cooler months.
Shipping chilled semen in summer
Chilled semen is diluted in an extender and kept cold during transport. Castro and colleagues (2026) note that a standard Tris-egg yolk extender with antibiotics supports canine semen for up to about three days, and found that an antibiotic-free version stored at 5°C also preserved sperm function in the short term.
- Agree the plan with both vets in advance: extender, packaging, who collects and who inseminates.
- Use proper insulated shipping containers with cold packs, and avoid long waits in hot vans or sorting depots.
- Ship early in the week so a package doesn’t sit over a weekend.
- Have a backup: frozen semen or a second shipment date.
When to call your veterinarian
- Before an important summer mating, for a semen evaluation.
- If a stud dog has a fever, a swollen or painful scrotum, or skin problems on the scrotum.
- After repeated missed matings or small litters.
- Before shipping semen, to agree on extender, packaging and timing.
- If in doubt, call — your vet would rather hear from you early.
Work on it
A few minutes here will teach you more than re-reading the article.
Ask yourself
- How hot does my stud dog’s kennel get on summer afternoons?
- Do I have frozen semen banked from a cool season?
- Would I know if his semen quality dropped after a heat wave?
Find out & check
- Ask your vet about a baseline semen evaluation in spring.
Do one thing
- Put a min-max thermometer where your stud dog sleeps and check it through the next warm spell.
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Sources & further reading
- Kolster K (2022) — Addressing subfertility in stud dogs. Clinical Theriogenology 14:158–161. ivis.org
- Burgio M, Forte L, Prete A, Maggiolino A, De Palo P, Aiudi GG, Rizzo A, Carbonari A, Lacalandra GM, Cicirelli V (2024) — Effects of heat stress on oxidative balance and sperm quality in dogs. Frontiers in Veterinary Science 11:1445058. doi.org
- Ibrahim NS, Zaid NW (2017) — Semen evaluation in local dogs during different season in Baghdad. Iraqi Journal of Veterinary Sciences 31:45–50. doaj.org
- Kuroda H, Hiroe K (1972) — Studies on the metabolism of dog spermatozoa. I. Seasonal variation on the semen quality and of the aerobic metabolism of spermatozoa. Japanese Journal of Animal Reproduction 17:89–98. jstage.jst.go.jp
- Strzeżek R, Szemplińska K, Filipowicz K, Kordan W (2015) — Semen characteristics and selected biochemical markers of canine seminal plasma in various seasons of the year. Polish Journal of Veterinary Sciences 18:13–18. agris.fao.org
- Castro M, Carrasco-Zambrano N, Pezo F, Contreras MJ (2026) — Antibiotic-free short-term storage of canine sperm at 5 °C preserves functional and mitochondrial integrity. Frontiers in Veterinary Science 13:1774926. doi.org
Where evidence is limited, recommendations rest on established practice and expert judgment, and may be updated as knowledge develops. This is general information and does not replace advice from your veterinarian or a veterinary reproduction specialist.
Next steps
- Read next: Raising a litter in summer.
- Related: Heatstroke in breeding dogs and puppies.
- Return to the guide: The breeding dog’s life.