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Reproductive Cyclicity
- Estrus (noun) (European: oestrus, oestrous)
Termed “in season” for seasonal animals (i.e., mare)
- Estrous cycle (Estrous adjective)
Continual throughout adult lifetime, can be temporarily interrupted by:
Pregnancy, nursing, season of year (species specific), inadequate nutrition, stressful environment & (or) management conditions, pathologic conditions
Known as: ______________________ (noun)
Types (Fig 7-1)
________________________________ (cattle, swine, rodents, domestic cats)
Can become pregnant throughout year
_____________________________________ (sheep, goats, horses, deer, elk, wild cats)
Become pregnant only during specific season
Altered by management: light in mares during winter
_________________________________________ (sheep, goats, elk, deer)
Began estrous cycles w/ day length
__________________________________________ (horses, wild cats)
Began estrous cycles w/ day length
____________________________________ (dogs, wolves, fox, bear)
Duration of estrus, several days
Domestic canine: typically 3 estrous cycles in two years
Phases of estrous cycle
Follicle phase (20% of estrous cycle) __________________________________________
___________________________ (2-5 days)
FSH/LH primary hormones
_____________________________ (hours to days species dependent)_
Presence of mature dominant ovulatory follicle(s)
Estrogen drives behavioral estrus (in absence of progesterone)
Sexual receptivity + peak estrogen + ovulation
Luteal phase (80% of estrous cycle) _____________________________________________
__________________________ (Period between ovulation & initial CL formation)
Fig 7- 1
Table 7-1. Characteristics of estrous cycles in domestic animals
Length of estrous cycle Duration of estrus (^) Time from onset of estrus to ovulation
Time from LH surge to
Species Classification Mean Range Mean Range^ ovulation
Alpaca Polyestrus 15 d (11-18 d) 5 d (4-5 d) Induced ovulator 26 - 36 h
Bitch Monoestrus 6 mo (3-9 mo) 9 d (4-21 d) 4 - 24 d 2 - 3 d Cow Polyestrus 21 d ( 17 - 24 d) 15 h ( 6 - 24 hd) 24 - 32 h 28 h
Ewe
Seasonally Polyestrus (Short day)
17 d ( 13 - 19 d) 30 h ( 18 - 48 h) 24 - 30 h 26 h
Llama Polyestrus 10 d ( 8 - 12 d) 5 d (4-5 d) Induced ovulator 26 - 36 h
Mare
Seasonally Polyestrus (Long day)
21 d ( 15 - 26 d) 7 d ( 2 - 12 d) 5 d 2 d
Queen Polyestrus 17 d (4- 30 d) 9 d (2-19 d) Induced ovulator 30 - 40 h Sow Polyestrus 21 d (17- 25 d) 50 h (19-96 h) 36 - 44 h 40 h
Estrous cycle in bitch
Reproductive quiescence, results in three estrous cycles in two years
Large follicles, estrogen & peaks before estrus
Bitch begins to accept male @ end of proestrus
Shortly after peak estrogen, behavioral estrus begins
LH/FSH peak early in estrus
Delay in fertilization due to ovulation of primary oocyte
Used as indicator as to when ovulation occurs (mating purposes)
________________________________________________________
________________________________________________________________________
________________________________________________________________________
Non-pregnant often considered pseudo-pregnant
Progesterone peaks about 15 d after estrus
General comments
Wild canids: one estrus period per year, usually seasonal
Domestic canids: one to two estrus periods per year, four possible
Estrus most frequent Feb to May
Queen
Proestrus, estrus, postestrus, diestrus, anestrus
Female remains in constant follicular phase
Copulation: CL formation (no true luteal phase)
60 d gestation, parturition, lactation, estrus (no lactational anestrus)
Fig 7- 4
Fig 7-7 The effect of photoperiod on short day breeders
Fig 7- 6
Onset of seasonal cyclicity example: short day breeders (Fig 7-7)
Anestrous driven by lack of GnRH & LH/FSH secretion
_________________________________________________________________
Lactational anestrus (not consistent across species)
Dog: no lactational anestrus, bitch enters anestrus after parturition
Cat: may have lactational anestrus, but not uniform
Sow: cyclicity totally suppressed during lactation, weaning initiates estrus (2-3 d)
Horses: estrus right after foaling, no true lactational anestrous
Beef cows: delayed until 40-60 d post parturition, weaning initiates estrus (3-30 d)
Suckling ≤ 2x per day hastens onset of estrus, ≥ 3 no effect (Fig. 7 -8)
___________________________________________________________________ (Fig. 7-9)
Removal of neural stimulation does not totally remove (-) FB
Other factors (+) lactational anestrous
Nutritional anestrus (cattle, pigs, humans, horse to lesser extent)
Table 7-2. Cycle event comparison between estrous cycle and menstrual cycle
Events Estrous cycle Menstrual Cycle
Follicular Phase Short (20% or less of cycle duration) Long (50% of the cycle duration)
Ovulation At the beginning and end of the cycle Middle of cycle (day 14) Luteal Phase 80% of cycle 50% of the cycle
Fertile Period 24 hours or less (5% of cycle) Up to 6 days before ovulation (18% of cycle) Endometrial sloughing None After luteolysis Luteolysis Uterine PGF Ovarian PGF Sexual Receptivity Well defined Relatively uniform throughout the cycle
Progesterone function and sexual receptivity
Inhibits GnRH release Inhibits sexual receptivity
Inhibits GnRH release Does not influence sexual receptivity Menopause None described Well characterized (Follicular depletion)
- Amenorrhea: ____________________________________________________________________
_____________________________________________________________________________
Athletes with sustained high levels of intense training (marathon runners)
Lactational amenorrhea (Fig 7-11)
- Menopause (analogous to anestrus)
Depletion of ovarian follicles, no estrogen, no LH surge, no ovulation, no CL
Fig 7- 11
