Clyclicity Flashcards
2 types of repro cycles
Oestous
Menstural
Oestrous
Predicable series of events from one ovulation to the next
Copulation occurs during this time
Oestrus
Noun - the mare is in oestrus
Oestrous
Length of cycle
Typrs of eostrus
Polyestrus Seasonally polyestrus (short day ewe, long day mare)
Monoestrus (dog)
Phases of oestrous cycle
Follicular phase Luteal Phase (CL dominant structure)
Follicular Phase
Follicles dominant structure
E2 secreted from follicles
From regression of CL to ovulation
Initiates sexual receptivity
20% of cycle
Luteal Phase
CL dominant Structure
CL produces progesterone p4
From ovulation to regression of CL
80% of cycle
Follicles grow and regress but do not preduce high concentrations of e2
Stages of Oestrous cycle - 4
Follicular phase
- Proestrus
- Oestrus
Luteal Phase
- Metoestrus
- Dioestrus
Proestrus
Period immediately before estrus
Transitions from progesterone to oestrogen dominance
Progesterone declines as result of luteolysus and ends at onset of oestrus
Oestrus
Part when female allows mating
Oestradiol is dominant hormone
Standing Oestrus - lordosis (back arching)
Metoestrus
Oestrogen dominance to P4 dominance
(ovulation to functional CL)
Newly ovulated follicle undergoes cellular and structural remodelling to become an intr-ovarian endocrine gland = CL
Called luteinisation
Diestrus
Maximum luteal function
Dominated by progesterone
Longest phase of cycle
No sexual receptivity
Ends when CL destroyed (luteolysis)
Canine Oestrous cycle
Proestrus (9d), oestrus (9d), diestrus 2 months), anoestrus (5 months)
Cats
Induced ovulators
proestrus, oestrus, postoestrus, dioestrus and anoestrus
Anoestrus
Cyclicity is interrupted by Pregnancy Nursing Season Nutriotion Stress Infection
Due to insufficient GnRH release from the hypothalamus to stimulate and maintain gonadotrophin release
Ovaries inactive- no ovulatory follicles or functional CL
Eliminating Anoestrus
Improve nutrition
Remove offspring
Eliminate stress
Consider season
Gestational Anoestrus
Oestrous cycles dont occur during pregnancy
P4 from CL induces negative feedback on hypo = no FSH, LH release
Postpartum Anoestrus
Time after parturition where female doesnt cycle
Uterus indergoes involution to support next preg
Silent ovulation
First ovulation after seasonal anoestrus is often silent in ewes
No behavioural estrus
No CL at end of anoestrus there is no progesterone
Return to seasonal cyclicity
GnRH secretion must increase sufficienty to cause LH and FSH release by pituitary
Photoperiod important
Melatonin involved
Melatonin
Hormone from pineal gland
Synthesised and released only at night
Stimulated GnRH in short day breeders
Inhibits GnRH on long day breeders
Lactational Anoestrus
Caused by sight, smell, sound of calf
Not in bitches
