8/27/10
Chapter 7
The Estrus Cycle
(Also see powerpoint posted on website)
Preview Questions
1) What is the estrous cycle?
- Definition: E to E, time of sexual receptivity and follicular growth
2) What are the phases of the estrous cycle?
1) Proestrus
2) Estrus
3) Metestrus
4) Diestrus
3) What is anestrous and what are some causes?
- No cycles
- Tiny ovaries
- Low GnRH (amino acid structure – 10 AA in length) from hypothalamus
- True (actually not cycling) vs. apparent (common in cattle; low heat periods, not watching well)
- Poor heat detection is a huge cause of apparent anestrus in dairy cows along with mastitis
- Causes:
1) Gestational anestrus
2) Postpartum anestrus
3) Seasonal anestrus
4) Seasonal Cyclicity
5) Lactational anestrus
6) Nutritional anestrus
· Estrus – failsafe mechanism to get pregnant (if not now, then later so come back into heat)
- Copulation – only time when female allows this is estrus
· Anestrus
- Normal
- Pathogenic
· Parturition
· Uterine involution
· Lactation
· Terminology
- Estrus vs. Oestrus (British spelling) – originates from Estridae gadfly attacks on cows
- Estrual – estrus event
- Heat – usually equivalent to estrus, not always (be careful /w clients)
- Season – estrus or part of estrus?
- Anestrus – absence of cycles
- Polyestrus – many estrus cycles
- “us” vs. “ous” – “us” = noun; “ous” = adjective
· Types of Cyclicity
- Polyestrus – one cycle after another all year round; constant intervals between cycles
- Cow, pig, rodents
- Seasonal Polyestrus – cycle during certain seasons
- Long (spring breeding season) – mare, queen
- Short (autumn breeding season) – ewe, doe, elk, nanny
- Monoestrus – one cycle/year (7.5 months between cycles)
- Dog, wolf, fox, bear
· Phases of the Cycle
1) Follicular
- 20% of the cycle
- Luteal regression
- Follicle growth
-Estradiol out of the follicles (steroid hormone)
2) Luteal
- 80%
- Corpus luteum
- Progesterone secreted by CL (steroid hormone)
- Follicular waves
- Follicle selected as progesterone drops
· 4 Stages of Cycle (Cow)
1) Proestrus – Follicular phase
- Luteal regression occurs first (P4 decline) – CL controls cycle events
- 2-5 days duration, varies /w species (none)
- LH/FSH (Glycoprotein hormones) – stimulate the gonads
2) Estrus – Follicular phase
- Behavioral estrus
- Standing
- Lordosis (cats – back down vs. kyphosis when back arched up)
- Vocalization
- Copulation
- Rise in Estradiol
- Duration – when species covered
** Stages of Estrus (Bitch) (goes estrus à diestrus)
- Very long proestrus – no progesterone before estrus in dogs, like other species
- Very long estrus – rising progesterone (very key clinically)
- Metestrus – not really present in the bitch
** Stages of Estrus (Queen)
- Cats can do 6 things during heat (3 things right now)
1) Induced ovulators (need to be bred enough times/sufficient LH stimulation to ovulate)
2) Follicle regresses w/o being bred – no follicle, no CL à dormant ovary (short anestrus) and then back into heat again (1-14 days later)
3) If bred and ovulates, makes a CL /w high progesterone; if not pregnant, CL dies, anestrus, then back into heat
- If pregnant, will carry, birth, short anestrus, back into heat
3) Metestrus – the time of corpora lutea development; Luteal phase
- Right after estrus
- Luteinization
- Rising progesterone
4) Diestrus – longest phase; Luteal phase
- Luteal dominance
- Progesgterone dominance
- Luteal regression ends – allows follicle to grow again
5) Anestrus
· Casues of Anestrus
1) Gestational anestrus – how people tell if animal pregnant (if animal doesn’t come back into heat or show signs of heat; usually pregnant if don’t show signs, may show slight signs even if pregnant)
- P4 inhibits estrus
2) Postpartum anestrus – allows body to return to normal after birthing
- Species dependent – takes cows longer; mares come back into heat 9 days after foaling; cats sort of have an anestrus
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kasatka