Progesterone

Introduction

• Overview of the lecture focused on progesterone during:
  • The vicious cycle of the dog's reproductive system.
  • Pregnancy management in dogs.
• Purpose:
  • Breeding management for those unfamiliar with using progesterone for breeding timing.
  • Pregnancy management and well-being timing.

Unique Aspects of Canine Reproductive Cycles

• Canine reproductive cycle shows unique characteristics:
  • In dogs, progesterone levels rise before ovulation while in other species, it increases post-ovulation.
  • Dogs typically cycle twice a year; some may cycle once.
  • The reproductive cycle remains consistent regardless of pregnancy status.
  • Dogs ovulate a primary oocyte that must mature for approximately 48 hours before it can be fertilized.

Implications for Breeding Management

• Timing of semen introduction is crucial:
  • Sperm should be waiting after the egg is matured.
  • Breeding typically occurs after ovulation in dogs, allowing time for the oocyte to mature.

Vaginal Cytology in Breeding Management

• Useful tool for understanding breeding timing but not a standalone method:
  • Vaginal cytology monitors changes in vaginal epithelium in response to estrogen.
  • In proestrus, thickening of the epithelium is observable as the cells detach due to lack of blood supply.
• Different cell types observed:
  • Parabasal cells: Round, small.
  • Intermediate cells: Slightly larger, round.
  • Cornified (superficial) cells: Angular, may lose nucleus, and appear dark and small in size.
• Proestrus cytology may include red blood cells due to bleeding.

Progesterone Levels and Corpus Luteum

• Progesterone is produced by the corpus luteum after ovulation:
  • This structure forms from the ruptured follicle and shifts from estrogen to progesterone production.
  • Key phases in follicle development:
  • From primordial follicles to antral follicles, then ovulation.
  • Presence of varying levels of corpus luteum as the cycle repeats.
• Role of progesterone:
  • Maintains the pregnancy phase and prevents return to heat.

Testing for Progesterone

• Testing Methods:
  • ELISA tests: Subjective colorimetric test indicating progesterone levels.
  • Color intensity correlates with hormone levels, cannot provide exact measurements.
  • Chemiluminescence: Preferred method providing exact quantification of progesterone levels.
  • Reliable results within 3-4 hours from local labs.
• Importance of reliable equipment:
  • Verify any in-house testing machines for accuracy and reliability before purchasing.

Normal Progesterone Levels and Implications

• Expected values during the cycle:
  • 2-3 ng/mL indicates an LH surge approximately 48 hours before ovulation.
  • Values of 4-10 ng/mL indicate approach to ovulation.
  • Values over 10 ng/mL confirm that ovulation is complete.
• Testing protocol:
  • Begin testing around day 6 of bleeding; repeat every 2-3 days depending on semen type.
• Note for LH testing: Helpful but expensive to conduct daily; typically used once the LH surge is hypothesized.

Practical Breeding Management Example

• Example Scenario:
  • Initial progesterone level of 0.4 ng/mL indicates basal levels in proestrus.
  • Subsequent tests on Monday (2.4 ng/mL) showing 100% cornified cells indicates potential ovulation.
  • Wednesday shows a progesterone level of 7.3 ng/mL confirming transition towards fertile ovulation.
  • Conclusively, ovulation would likely occur on the following Wednesday tested again at 15 ng/mL.
• Fertile window for breed is noted to be days 2-4 after ovulation.

Complications in the Reproductive Cycle

• Possible complications:
  • Prolonged Proestrus: Extended bleeding presence without rising progesterone levels.
  • Split Heat: Cycle occasionally resumes without fertile ovulation.
  • Failure to Ovulate: Follicular cysts can stabilize progesterone levels without ovulation occurring.
• Regular monitoring of vaginal cytology alongside progesterone testing can confirm stage and possible complications during the cycle.

Breeding Techniques

• Methods of artificial insemination:
  • Vaginal Insemination: Cost-effective for fresh or cooled semen.
  • Transcervical Insemination (TCI): More reliable than surgical AI, and requires skill in navigating the cervix during insemination.
  • Surgical AI: Last resort for difficult cases where TCI is not feasible.

Pregnancy Management

• The reproductive hormones remain stable throughout pregnancy, typically maintaining a 60-day (± 1 day) diestrous phase.
• Pregnancy diagnostics:
  • Ultrasounds at around 30 days enable assessment of viability and fetal heartbeats but not exact puppy counts.
  • Relaxin test: Blood test checking for pregnancy presence, though less effective with smaller litters.
• Progesterone levels during pregnancy should maintain above 2 ng/mL and optimally between 8-10 ng/mL.
  • Supplementation can occur post-day 45 if levels drop, but consider risks to puppies.

Modern Monitoring Technologies

• WhelpWise: A technological solution for monitoring uterine contractions, offering real-time data analysis for better reproductive management during high-risk pregnancies.
• Monitoring temperature alongside progesterone levels aids in timing the whelping process, anticipating a drop around the time of parturition.

Singleton Litter Risks and Management

• Singleton or small litters (1-2 puppies) have a higher risk of requiring emergency C-sections due to insufficient stimulation for whelping.
  • Proper ovulation timing is suggested to prevent difficult deliveries.

Indications for Veterinary Involvement

• If temperature drops without puppies in 24 hours, or prolonged labor is observed, consult a veterinarian.
• Early intervention is crucial if discharge is green, or if active straining exceeds normal intervals without results.

Conclusion

• Continual monitoring and appropriate breeding practices are crucial for successful canine reproductive management.
• Various complications can arise, necessitating a thorough understanding and proactive response from breeders to ensure healthy litters and mothers.
• Encourage your veterinarian’s involvement throughout to navigate challenges efficiently and ethically.