Exam 3 - Estrous Cycle Flashcards
what is the relevance of puberty for food-producing females?
females that reach puberty & become pregnant have an economic advantage!!!
what is the length of gestation for cattle?
282 days
when must heifers reach puberty to have an economic advantage in regards to the breeding season? why?
must reach puberty 42 days prior to the start of the breeding season
pregnancy rates on cycles 1-2 are lower than the 3rd - better chance of getting them pregnant
should a heifer calve earlier than a cow? why?
yes - economic advantage
have all of your heifers calve together (which will be before your cows) & then have your cows calve after
heifers will take longer to come back into heat, so whenever you have them go earlier, you breed the cows/heifers all back at the same time
when should a heifer calve? where does that put them hitting puberty? why do you want them to calve by 2 years?
calve by 2 years - hit puberty by 12.5 months to get them pregnant at 15 months
if they have a delayed puberty, you will lose economic value of 42%
is puberty synchronous with sexual maturity?
no
what is the role of the hypothalamus in puberty?
hypothalamus quiescence limits puberty
responds to E2 positive feedback loop in which sufficient GnRH is then produced
gonadotropin release = gonadal response
what is the definition of puberty?
male/female onset of sexual maturity
age at first estrus - first ovulation accompanied by a NORMAL LUTEAL PHASE in which pregnancy can be safely supported
in the pre-pubertal stage for female cows, what is going on with estrogen secretion? what happens in the peri-pubertal stage that ultimately gets them to puberty?
pre-pubertal: the follicle diameters on the ovaries are very small, so there is very little estrogen production, so GNrH & LH secretion are not affected by it keeping them out of puberty
peri-pubertal: the follicle diameters start to increase, so GNrH & LH are slightly more affected & increasing mildly in secretion, but there is not enough estrogen to have positive feedback yet
once the follicles are big enough, enough estrogen is secreted by them which then has positive feedback which increases GNrH & LH secretion finally pushing them into puberty
what are some things used to evaluate readiness of an animal to breed? what is the primary determinant of puberty?
weight - weight tape placed behind shoulder to measure circumference - primary determinant!!
reproductive tract score
pelvic score
why do uterine horns & ovaries get bigger in cows in puberty?
estrogen increases size in uterine horns
ovaries get bigger due to follicular development & corpus luteum
what is the minimum pelvic score needed at 12 months when evaluating readiness of an animal to breed? how is this test utilized?
minimum of 150 cm2 at 12 months
used to cull!!! not to increase pelvic size
what are some general factors that influence the onset of puberty?
age
genotype - breed
body weight/nutrition
how does age affect the onset of puberty in cattle?
average 6-18 months, but usually by 1 year
brahman are later at 19-27 months
what is likely the most common cause of delayed puberty in large animals?
energy deficiency - poor BCS/nutrition
in all species, the age of onset of puberty is closely related to body weight, so the animal must reach how much to hit puberty?
> 65% mature weight
how does age affect the onset of puberty in small ruminants?
6-12 months depending on the season because they are short day breeders
how does age affect the onset of puberty in horses?
average 18 months depending on the season because they are long day breeders
how does age affect the onset of puberty in pigs? why is it a problem?
5-8 months, average of 6 months - delayed puberty is a major constraint to reproductive efficiency
it is reasonably heritable, so it can be passed on to offspring & provide selection pressure
how is pelvic score measured?
device is inserted & you measure in two dimensions & then multiply them to get the area
start evaluating them in advance to be able to identify animals with small pelvises
in cows, do bos taurus or bos indicus breeds reach puberty earlier?
bos taurus faster than bos indicus
how does inbreeding affect the onset of puberty?
it increases the onset - delayed puberty!!!
what are some factors that can be attributed to earlier onset of puberty?
breeds selected for milk & size (beef breeds) & scrotal circumference
presence of the male around what food animals causes an earlier onset of puberty?
goats & pigs
how does disease affect the onset of puberty?
chronic disease or parasitism slows the animals growth & delays puberty
how does climate affect the onset of puberty? what about animals that live close to the equator?
tropical climates reach puberty earlier than temperate climates (due to temperature, photoperiod, or other factors)
equator animals - very consistent climate, so they will enter puberty earlier
how does photoperiod affect the onset of puberty in food animals?
seasonal breeders, horses, sheep, & goats (especially sheep!!), are influenced by the date of birth & will not begin to have estrous cycles until proper season occurs
how does temperature affect the onset of puberty in food animals?
pigs - even though they are not considered to be seasonal breeders, hot summer months can delay puberty or increase the incidence of silent estrus/anestrus
secondary effect of temperature - pigs & dairy cows
how does excessive heat have a negative effect on reproduction?
excessive heat leads to an increase in early embryonic death in cattle & pigs (horses too but not as severe)
behavioral estrus is shorter & less intense in cattle in hot summer months
excessive heat leads to a decrease in dry matter (feed) intake (DMI) which leads to a longer interval in postpartum anestrus in cattle/swine
how is the estrous cycle controlled by photoperiod in some animals?
we think it is mediated by the pineal gland through the secretion of melatonin
how is the photoperiod related to the estrous cycle in long day breeders?
horses - lengthening in daylight is stimulatory, so the peak of reproductive cyclicity is in the summer (solstice)
how is the photoperiod related to the estrous cycle in short day breeders?
sheep/goats - onset of the breeding season coincides with shortening day length in the late summer & autumn, so their peak reproductive cyclicity is in late fall
what is anestrus?
without cyclicity - period of sexual quiescence
what is the difference between estrus & estrous?
estrus - noun, standing heat
estrous - adjective, referring to the cycle
T/F: an animal in anestrus can be physiologically normal
true
what are some examples of things that may cause anestrus?
season, pregnancy, lactation, presence of offspring, pathology, stress, & age of the animal
what are the 2 phases of the estrous cycle? how are they different?
follicular phase - estrogen dominated & low progesterone
luteal phase - progesterone dominated
what makes up the follicular phase of the estrous cycle?
proestrus - formation of pre-ovulatory follicles & estrogen secretion
estrus - sexually receptive period usually with ovulation
what makes up the luteal phase of the estrous cycle?
metestrus - CL formation & increasing progesterone secretion
diestrus - sustained, elevated luteal progesterone secretion with a mature CL
what are signs of estrus in a mare?
tail elevation/deviation
winking of vulva & rhythmic clitoral eversion
posturing/stands for male
donkeys - mouth clapping
T/F: a mare in estrus will virtually show no signs unless a male is present
true
what is day 0 in the estrous cycle of a mare?
day 0 - ovulation
T/F: a mare remains in estrus post-ovulation
true
when are the 2 follicular waves of FSH in the estrous cycle of mares? why do they occur?
1st FSH wave occurs during diestrus - lack of inhibin from follicles allows for release of FSH from the AP, so follicles will grow and produce estrogen
2nd FSH wave occurs after the release of PGF2a from the endometrium, surge in FSH causes increase in estrogen, then causing the LH surge bringing the horse back into estrus (leading us back to day 0 of the cycle)
if a mare isn’t pregnant by day 14 of the cycle, what happens?
PGF2a is released by the endometrium of the uterus which lyses the CL & causes a rapid decrease in progesterone
what should the cervix, uterus, & ovaries feel like upon palpation of a mare in estrus?
cervix - relaxed, short, soft, & wide
uterus - flaccid!!!
ovaries - large follicle (>25-30mm follicle, but most often >35mm)
what should the cervix, uterus, & ovaries feel like upon palpation of a mare in diestrus?
cervix - tight!! long, firm, & narrow
uterus - tonic
ovaries - CL not palpable because the it is encased within the ovary, often medium to small follicles (<30mm) sometimes pre-ovulatory size
what direction does the cervix in a mare relax during estrus?
cervix relaxes cranial to caudal
what is the primary sign of a cow in estrus?
stands for mounting
what are secondary signs of a cow in estrus?
mounting others, clear vaginal mucus, hyperactivity (bellowing), & vulvar edema (unreliable)
T/F: in cattle, ovulation occurs during standing heat
false - doesn’t occur during, occurs after during metestrus 12-16 hours after estrus!!!
if you feel a large CL on a cow ovary during rectal palpation, what stage of the estrous cycle is she in? why?
diestrus - because you can feel the CL
what is weird about LH in the estrous cycle of the mare?
there is not really an actual surge of LH - it is rising throughout estrus & actually peaks after ovulation has occurred
when do cows ovulate in the estrous cycle?
12-18 hours after the end of estrus
what should the cervix, uterus, & ovaries feel like upon palpation of a cow in estrus?
cervix - no palpable changes because it doesn’t respond to hormonal changes!!
uterus - tonic
ovaries - CL < 1cm, follicle 1.5-2.5cm
what should you feel upon rectal palpation of a cow in metestrus? what is the significance of this?
pitting edema post-ovulation with ‘bloody’ mucus - too late to breed them!
what should the cervix, uterus, & ovaries feel like upon palpation of a cow in diestrus?
cervix - no palpable changes
uterus - flaccid
ovaries - CL = 3cm, follicles <1cm
you can feel the CL!!!
what are the primary signs of estrus in sows?
stands for mounting!!!!
response to pressure on the back - increased by the presence of a male!
what are secondary signs of estrus in a sow?
anorexia, restlessness, salivation, grunting, champing jaws, & swollen vulva
how long does estrus last in sows?
1-4 days
when do sows ovulate?
ovulate 36-44 hours after the onset of estrus
what is the primary sign of estrus in ewes & does?
stands for mounting
what are secondary signs of estrus in ewes & does?
restlessness, tail swishing, seeking a male, vocalization, +/- vulvar edema
what is the importance of a male for detecting estrus in ewes & sows?
ewes will show minimal signs of estrus without a male presence
does will be more demonstrable - but will be even more clear with a male present or pheromones
how long does estrus last in ewes?
24-48 hour estrus
T/F: in the estrous cycle of ewes, there are multiple FSH waves that occur throughout the period
true
how long after the LH surge does ovulation occur in ewes?
24 hours after LH surge
when is prostaglandin secreted in the estrous cycle of the ewe?
days 14-17
when is prostaglandin secreted in the estrous cycle of the cow?
day 15
when is prostaglandin secreted in the estrous cycle of the mare?
around day 14 - followed by rise in estrogen & FSH causing the rise of LH & starts estrus
when is prostaglandin secreted in the estrous cycle of the sow?
days 13-15 followed rise in estrogen on day 18-20, LH surge 20-21 & ovulation near day 21
how long does estrus last in sows?
1-4 days
what is the effect of seasonality on puberty in ewes?
lambs born in early spring will reach puberty the same year while lambs born in late spring reach puberty the following year
what is the only food animal that doesn’t ovulate during estrus?
cattle - ovulate after
what is the average length of the estrous cycle in food animals? what is the exception to this average?
21 days for most species
17 days for sheep!!!
