Reproductive Cyclicity

Section 1: Estrus vs. Estrous

1. ⭐ What is estrus?
→ The period of sexual receptivity (heat) when the female accepts mating.

2. ⭐ What is estrous?
→ An adjective describing the reproductive cycle (e.g., estrous cycle).

3. What defines an estrous cycle?
→ The predictable sequence of reproductive events from one estrus to the next.

4. What is anestrus?
→ A temporary period without regular estrous cycles.

Section 2: Types of Reproductive Cyclicity

5. ⭐ What are the three classifications of reproductive cyclicity?
→ Polyestrous, seasonally polyestrous, and monoestrous.

6. What is polyestrous?
→ Repeated reproductive cycles throughout the year.

7. ⭐ Which animals are polyestrous?
→ Cattle, swine, rodents, and domestic cats.

8. What is seasonally polyestrous?
→ Multiple reproductive cycles restricted to a particular breeding season.

9. ⭐ Which animals are seasonally polyestrous?
→ Sheep, goats, horses, deer, elk, and wild cats.

10. ⭐ What are long-day breeders?
→ Animals that begin cycling as day length increases.

11. ⭐ Which animals are long-day breeders?
→ Horses and wild cats.

12. ⭐ What are short-day breeders?
→ Animals that begin cycling as day length decreases.

13. ⭐ Which animals are short-day breeders?
→ Sheep, goats, deer, and elk.

14. What is monoestrous?
→ Having approximately one reproductive cycle per year.

15. ⭐ Which animals are monoestrous?
→ Dogs, wolves, foxes, and bears.

16. ⚠ How frequently do domestic dogs typically cycle?
→ Approximately three cycles every two years.

Section 3: Phases and Stages

17. ⭐ What are the two phases of the estrous cycle?
→ Follicular and luteal.

18. ⭐ What dominates the follicular phase?
→ Growing ovarian follicles and estrogen (E₂).

19. ⭐ What dominates the luteal phase?
→ Corpus luteum (CL) and progesterone (P₄).

20. What percentage of the estrous cycle is follicular?
→ Approximately 20%.

21. What percentage is luteal?
→ Approximately 80%.

22. ⭐ What are the four stages of the estrous cycle in order?
→ Proestrus → Estrus → Metestrus → Diestrus.

23. ⭐ Which stages belong to the follicular phase?
→ Proestrus and estrus.

24. ⭐ Which stages belong to the luteal phase?
→ Metestrus and diestrus.

25. What happens during proestrus?
→ Follicles grow, P₄ declines, and E₂ increases.

26. ⭐ What happens during estrus?
→ Sexual receptivity, peak E₂, LH surge, and ovulation.

27. What happens during metestrus?
→ Ovulated follicle luteinizes and the CL begins forming.

28. ⭐ What happens during diestrus?
→ Functional CL secretes sustained P₄.

29. ⚠ What is the longest stage?
→ Diestrus.

30. What causes luteolysis in the lecture’s general estrous-cycle model?
→ Uterine prostaglandin F₂α (PGF₂α).

Section 4: Female Dog

31. ⭐ What is the reproductive cyclicity classification of dogs?
→ Monoestrous.

32. ⭐ What are the stages of the dog’s cycle?
→ Anestrus → Proestrus → Estrus → Diestrus.

33. ⚠ What stage is absent from the dog’s cycle in your lecture?
→ Metestrus.

34. How long is dog anestrus approximately?
→ 20 weeks.

35. How long is dog proestrus approximately?
→ Nine days.

36. What physical signs characterize dog proestrus?
→ Blood-tinged vaginal discharge and vulvar swelling.

37. What happens hormonally during dog proestrus?
→ Follicles grow and E₂ increases, peaking before estrus.

38. When does ovulation occur in the dog?
→ Approximately days 2–3 of estrus.

39. ⭐ What type of oocyte does the dog ovulate?
→ Primary oocyte.

40. ⭐ Why is fertilization delayed in dogs?
→ The primary oocyte must complete maturation after ovulation.

41. How long after ovulation can fertilization occur?
→ Approximately 48–72 hours.

42. What is superfecundation?
→ Fertilization of different ova by sperm from different males, producing a mixed-sire litter.

43. ⭐ Why can nonpregnant dogs experience pseudopregnancy?
→ Pregnant and nonpregnant dogs undergo similar P₄-dominant diestrus.

44. ⚠ Does pregnancy alter the length of diestrus in dogs?
→ No, according to your lecture.

Section 5: Female Cat

45. ⭐ What type of reproductive cyclicity do domestic cats exhibit?
→ Polyestrous.

46. ⭐ Are cats spontaneous or induced ovulators?
→ Induced ovulators.

47. ⭐ What triggers ovulation in cats?
→ Copulation stimulates the GnRH → LH surge pathway.

48. How many copulations may be needed to induce an LH surge?
→ Approximately 4–7, according to your lecture.

49. What happens after induced ovulation in cats?
→ CL formation and luteal activity.

50. ⚠ What happens if a queen does not ovulate?
→ She remains in or returns to follicular cycling rather than forming a functional CL.

51. Can cats enter diestrus?
→ Yes, following ovulation and CL formation.

Section 6: Silent Ovulation

52. ⭐ What is silent ovulation?
→ Ovulation without behavioral estrus.

53. ⭐ Why is the first ovulation after anestrus often silent?
→ The brain has not received prior progesterone priming.

54. ⭐ What is the function of progesterone priming?
→ It optimizes brain sensitivity to estrogen-induced reproductive behavior.

55. ⭐ Why is the second ovulation after anestrus usually not silent?
→ P₄ from the first luteal period primes the brain for E₂-driven estrus.

56. ⚠ Can ovulation occur without visible sexual receptivity?
→ Yes; this is silent ovulation.

Section 7: Seasonal Breeding and Anestrus

57. ⭐ What two factors regulate seasonal breeding?
→ Photoperiod and melatonin.

58. ⭐ What happens to melatonin when darkness increases?
→ Melatonin secretion increases/lasts longer.

59. ⭐ When do long-day breeders cycle?
→ During increasing day length, generally spring/summer.

60. ⭐ When do short-day breeders cycle?
→ During decreasing day length, generally fall/winter.

61. What is the general seasonal reproductive pathway?
→ Photoperiod → melatonin signaling → GnRH → LH/FSH → ovarian activity.

62. ⭐ What are major causes of anestrus?
→ Pregnancy, lactation, season, inadequate nutrition, stress, and disease.

63. What happens hormonally during anestrus?
→ GnRH ↓ → LH/FSH ↓ → minimal follicular growth and ovarian inactivity.

64. How does suckling affect reproductive activity?
→ Suppresses LH secretion, contributing to lactational anestrus.

65. What causes nutritional anestrus?
→ Inadequate energy/protein → decreased GnRH and gonadotropin secretion