Puberty, Estrous Cycles, Reproductive Behavior Flashcards
Puberty is a ______
Process
- acquisition of reproductive competence
- occurs when there is secretion of GnRH in appropriate frequency and quantity to stimulate gonadotropin release by the pituitary
The hypothalamus in inherently _____
Female
- has both a surge and tonic center
The male hypothalamus only has a ____
Tonic center
- allows for slow release of GnRH that allows for continuous production of sperm
Fetal testis
Secretes testosterone that defeminizes hypothalamus and eliminates GnRH surge center
Testosterone is converted to ____ in the brain
Estrogen
- allows for defeminization of the brain
Alfa-fetoprotein
In females, binds E2 and prevents crossing of blood-brain barrier
- estrogen does not enter the brain!!
Definitions of puberty in females
- age at first heat (estrus) –> easy to detect
- age at first ovulation –> difficult to detect
- age at which pregnancy can be maintained without deleterious effects –> 65% of adult body weight
What are possible ways to detect ovulation?
- palpate for a corpus luteum
- do a blood sample to detect presence of progesterone
- ultrasound the ovary to see follicle (or absence of)
Process of pubery in males (in order of increasing age)
- expression of behavioral traits
- first ejaculation
- when sperm appear in the ejaculate
- when sperm appear in the urine
- when ejaculate contains a threshold number of sperm (to achieve pregnancy)
Puberty is influenced by
- plane of nutrition (fatness)
- threshold body size and composition
- exposure to environmental and social cues
- genetics
How do genetics influence puberty?
Breed variations
- ex: brahman reach puberty later, large dogs reach puberty later
Scrotal circumference in bulls and early puberty
- larger SC will have female offspring that reach puberty 4 days earlier per increased centimeter size
Environmental and social cues
- season of birth in seasonal breeders (sheep, goats, cats)
- photoperiod in seasonal breeders (sheep, goats, cats)
- presence or absence of opposite sex (ewe, sow, cow, rodents)
- density of same sex groups (small groups = later, large groups = sooner)
Spring born versus fall born ewe lambs
- spring born: breed in fall and deliver in spring
- fall born: will not reach puberty until next fall (1 yr later)
- due to short day breeding season*
What is a major limit on puberty onset?
Failure of hypothalamus to produce sufficient quantities of GnRH to cause gonadotropin release
GnRH is the limiting step!
Prepubertal female
- tonic center in hypothalamus releases small quantities of GnRH at low frequency
- provides insufficient stimulation of pituitary
- minimal follicular development cannot release enough E2 to trigger surge center to release large amounts of GnRH
Pubertal transition
- tonic center is very sensitive to neg feedback on GnRH at low levels of E2
- neg feedback is slowly lost = higher levels of GnRH = more E2
- eventually, the E2 is high enough to cause surge center to discharge large quantities of GnRH = ovulation and puberty
Prepubertal male
- small amounts of testosterone/estradiol have neg feedback at hypothalamus
- GnRH neurons are less sensitive to T and E2 as puberty approaches
- more T and E2 required to inhibit GnRH neurons
- decreased sensitivity to neg feedback of T = hypothalamus produces more GnRH and more FSH/LH produced
Age at puberty
- equine: 14 mos
- bovine: 11 mos
- canine/feline: 9 mos
- ovine: 7 mos
- porcine: 7 mos
What is the difference between estrus and estrous?
- estrus = noun (behavior)
- estrous = adjective
Estrus is the period of ________
Sexual receptivity
- referred to as heat when female will stand for breeding
