Cold Weather Impacts on Bull Fertility
Severe winter temperatures can compromise bull fertility by causing frostbite to the scrotum and testicles. Even moderate frost damage can impair sperm production and reduce breeding efficiency. Reviewing breeding plans and evaluating the current bull battery is essential following periods of extreme cold.
 
1. How Cold Stress Affects Bull Fertility
Frostbite can damage testicular tissue and disrupt sperm cell development. Depending on severity, fertility losses can range from temporary reductions in sperm quality to permanent impairment.
  • Severe frostbite: Visible scrotal damage; bulls may need to be culled immediately.
  • Moderate frostbite: Often not externally obvious; detected through semen evaluation showing abnormal sperm morphology.
 
2. Importance of a Breeding Soundness Evaluation (BSE)
A comprehensive BSE is the most reliable method for assessing cold-related reproductive damage.
A proper evaluation includes:
  • Physical examination of external and internal reproductive organs
  • Measurement of scrotal circumference
  • Detailed semen analysis (motility, morphology, concentration)
The veterinarian will determine:
  • Whether frost damage occurred
  • Expected recovery timeline
  • Whether the bull should be retained or culled
Because recovery from frostbite may take 8–10 weeks, early evaluation prevents delays in replacing an unsound bull.
 
3. Economic Impact of an Unsound Bull
A bull with reduced fertility can significantly affect calving distribution and total pounds of calf weaned.
Optimal Scenario – 70‑20‑10 Distribution
  • 70% bred in first cycle
  • 20% in second
  • 10% in third
    Result: ~59,440 lb weaned (≈594 lb per cow exposed)
Compromised Bull – 40‑10‑40‑10 Distribution
  • Lower conception early in breeding season
    Result: ~54,820 lb weaned (≈548 lb per cow)
Difference:
  • 46 lb less weaned calf per cow
  • 4,620 lb total loss in a 100‑cow herd
This demonstrates how cold‑related bull infertility can reduce returns the following fall.
 
4. Recommendations for Producers
  • Schedule pre‑breeding BSEs on all bulls, especially following extreme cold.
  • Replace or supplement questionable bulls before breeding season begins.
  • Monitor bulls throughout winter for lameness, frostbite, or illness.
  • Maintain proper bedding and wind protection to reduce frostbite risk.
Early identification of bull fertility problems protects herd reproductive performance and ensures revenue is not lost due to preventable breeding delays.