The document summarizes the estrous and menstrual cycles. It describes: - The estrous cycle has two phases: the follicular phase dominated by estrogen, and the luteal phase dominated by progesterone. It occurs over approximately 21 days in cows. - The menstrual cycle also has two phases but the follicular and luteal phases are of equal length at around 14 days each. Ovulation occurs in the middle of the cycle. The cycle culminates in menstruation and lasts around 28 days total. - Key differences are that the estrous cycle has a short follicular phase and ovulation occurs at the start or end of estrus, while the menstrual cycle has a longer, equal follicular phase

1. THER 608 Lecture # 8
Physiology of Reproduction
Prof. Dr. Nasim Ahmad
Reproductive Cyclicity: Physiology of
estrous cycle: Stages, (Phases), Hormones,
Menstrual cycle
1

2. During the follicular phase:
• Follicles = the dominant ovarian structure
• Estrogens by the follicles = dominant
hormone
2
During the luteal phase:
• Corpora lutea = the dominant ovarian
structure
• Progesterone by the CL = dominant
hormone

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4. Estrous Cycle
• Physiological properties are cyclical in nature.
The cycle can be interrupted or elongated by
pregnancy or some other abnormal situation eg.,
cyst formation
• Cycle is controlled by hormones
• Cycle is divided into proestrus, estrus,
metestrus, diestrus
• From endocrine point estrous cycle is divided
into
– Follicular Phase
– Luteal Phase
4

5. Stages of Estrous Cycle
• Proestrus (Before desire)
– Preparation for mating, high E2,
• Estrus (Desire) “sting or frenzy”
– Sexual receptivity, “Lordosis”, E2 is
very high, Ovulation occur
• Metestrus (After desire)
– E2, P4 is low, Prep for pregnancy
• Diestrus (Between desire)
– P4 is high, animal is in quiescent
stage
• Anestrus (Without desire)
– No signs of heat
5
Anestrus
(acyclicity) can
be caused by:
•Pregnancy
•Lactation
•Presence of
offspring
•Season
•Stress
•Pathology

6. Europe North
America
Explanation Incorrect
Oestrus Estrus 18-24 hr period
of sexual
receptivity
Oestrous
Oestrous
cycle
Estrous
cycle
21 day sexual
cycle
Estrus cycle
or oestrus
cycle
Estrus is a noun.
The cow is displaying estrus
Estrous is an adjective.
The length of the estrous cycle in cows is 21 days
IMPORTANT TERMINOLGY

7. FOUR STAGES OF ESTROUS CYCLE
7
Follicular Phase = Proestrus + Estrus
Luteal Phase = Metestrus + Diestrus
True Anestrus
Apparent aestrus
Silent ovulation
Anestrus can result from
negative energy
balance

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11. REPRODUCTIVE PHENOMENA OF DOMESTIC
FEMALES
Cow Ewe Mare
Estrus duration (hrs) 16 30 6
(days)
Ovulation Time after
beginning of estrus
(hrs)
30 26 5
(days)
Cycle duration
(days)
21 17 21
11

12. The estrous cycle
begins and ends with
estrus and or
ovulation. The
follicular phase is
short and the luteal
phase long
12
The menstrual cycle
begins (day 0) and
ends with the start of
menses (day 28).
Ovulation occur in
middle. The FP and
the LP are of same
length (14 days)

13. COMPARISON BETWEEN THE ESTROUS
CYCLE AND MENSTRUAL CYCLE
Event Estrous Cycle Menstrual cycle
Follicular phase Short (20%) Long (50%)
Ovulation At beginning or
end of estrus
Middle of cycle
Luteal Phase 80% 50%
Fertile Period 24 hrs Up to 6 days
Endometrial sloughing None After luteolysis
Luteolysis Uterine PGF2α Ovarian PGF2α
Sexual receptivity Well defined Uniform
P4 function & sex
receptivity
Inhibit GnRH
Inhibit sex. Rec.
Inhibit GnRH
does not inf. SEX.
Menopuase None described Well characterized 13
•Thankyou

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