Exam 3 - Estrous Cycle

Question 1

what is the relevance of puberty for food-producing females?

Answer 1

females that reach puberty & become pregnant have an economic advantage!!!

Question 2

what is the length of gestation for cattle?

Answer 2

282 days

Question 3

when must heifers reach puberty to have an economic advantage in regards to the breeding season? why?

Answer 3

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

Question 4

should a heifer calve earlier than a cow? why?

Answer 4

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

Question 5

when should a heifer calve? where does that put them hitting puberty? why do you want them to calve by 2 years?

Answer 5

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%

Question 6

is puberty synchronous with sexual maturity?

Answer 6

no

Question 7

what is the role of the hypothalamus in puberty?

Answer 7

hypothalamus quiescence limits puberty

responds to E2 positive feedback loop in which sufficient GnRH is then produced

gonadotropin release = gonadal response

Question 8

what is the definition of puberty?

Answer 8

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

Question 9

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?

Answer 9

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

Question 10

what are some things used to evaluate readiness of an animal to breed? what is the primary determinant of puberty?

Answer 10

weight - weight tape placed behind shoulder to measure circumference - primary determinant!!

reproductive tract score

pelvic score

Question 11

why do uterine horns & ovaries get bigger in cows in puberty?

Answer 11

estrogen increases size in uterine horns

ovaries get bigger due to follicular development & corpus luteum

Question 12

what is the minimum pelvic score needed at 12 months when evaluating readiness of an animal to breed? how is this test utilized?

Answer 12

minimum of 150 cm2 at 12 months

used to cull!!! not to increase pelvic size

Question 13

what are some general factors that influence the onset of puberty?

Answer 13

age

genotype - breed

body weight/nutrition

Question 14

how does age affect the onset of puberty in cattle?

Answer 14

average 6-18 months, but usually by 1 year

brahman are later at 19-27 months

Question 15

what is likely the most common cause of delayed puberty in large animals?

Answer 15

energy deficiency - poor BCS/nutrition

Question 16

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?

Answer 16

> 65% mature weight

Question 17

how does age affect the onset of puberty in small ruminants?

Answer 17

6-12 months depending on the season because they are short day breeders

Question 18

how does age affect the onset of puberty in horses?

Answer 18

average 18 months depending on the season because they are long day breeders

Question 19

how does age affect the onset of puberty in pigs? why is it a problem?

Answer 19

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

Question 20

how is pelvic score measured?

Answer 20

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

Question 21

in cows, do bos taurus or bos indicus breeds reach puberty earlier?

Answer 21

bos taurus faster than bos indicus

Question 22

how does inbreeding affect the onset of puberty?

Answer 22

it increases the onset - delayed puberty!!!

Question 23

what are some factors that can be attributed to earlier onset of puberty?

Answer 23

breeds selected for milk & size (beef breeds) & scrotal circumference

Question 24

presence of the male around what food animals causes an earlier onset of puberty?

Answer 24

goats & pigs

Question 25

how does disease affect the onset of puberty?

Answer 25

chronic disease or parasitism slows the animals growth & delays puberty

Question 26

how does climate affect the onset of puberty? what about animals that live close to the equator?

Answer 26

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

Question 27

how does photoperiod affect the onset of puberty in food animals?

Answer 27

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

Question 28

how does temperature affect the onset of puberty in food animals?

Answer 28

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

Question 29

how does excessive heat have a negative effect on reproduction?

Answer 29

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

Question 30

how is the estrous cycle controlled by photoperiod in some animals?

Answer 30

we think it is mediated by the pineal gland through the secretion of melatonin

Question 31

how is the photoperiod related to the estrous cycle in long day breeders?

Answer 31

horses - lengthening in daylight is stimulatory, so the peak of reproductive cyclicity is in the summer (solstice)

Question 32

how is the photoperiod related to the estrous cycle in short day breeders?

Answer 32

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

Question 33

what is anestrus?

Answer 33

without cyclicity - period of sexual quiescence

Question 34

what is the difference between estrus & estrous?

Answer 34

estrus - noun, standing heat estrous - adjective, referring to the cycle

Question 35

T/F: an animal in anestrus can be physiologically normal

Answer 35

true

Question 36

what are some examples of things that may cause anestrus?

Answer 36

season, pregnancy, lactation, presence of offspring, pathology, stress, & age of the animal

Question 37

what are the 2 phases of the estrous cycle? how are they different?

Answer 37

follicular phase - estrogen dominated & low progesterone luteal phase - progesterone dominated

Question 38

what makes up the follicular phase of the estrous cycle?

Answer 38

proestrus - formation of pre-ovulatory follicles & estrogen secretion estrus - sexually receptive period usually with ovulation

Question 39

what makes up the luteal phase of the estrous cycle?

Answer 39

metestrus - CL formation & increasing progesterone secretion diestrus - sustained, elevated luteal progesterone secretion with a mature CL

Question 40

what are signs of estrus in a mare?

Answer 40

tail elevation/deviation winking of vulva & rhythmic clitoral eversion posturing/stands for male donkeys - mouth clapping

Question 41

T/F: a mare in estrus will virtually show no signs unless a male is present

Answer 41

true

Question 42

what is day 0 in the estrous cycle of a mare?

Answer 42

day 0 - ovulation

Question 43

T/F: a mare remains in estrus post-ovulation

Answer 43

true

Question 44

when are the 2 follicular waves of FSH in the estrous cycle of mares? why do they occur?

Answer 44

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)

Question 45

if a mare isn't pregnant by day 14 of the cycle, what happens?

Answer 45

PGF2a is released by the endometrium of the uterus which lyses the CL & causes a rapid decrease in progesterone

Question 46

what should the cervix, uterus, & ovaries feel like upon palpation of a mare in estrus?

Answer 46

cervix - relaxed, short, soft, & wide uterus - flaccid!!! ovaries - large follicle (>25-30mm follicle, but most often >35mm)

Question 47

what should the cervix, uterus, & ovaries feel like upon palpation of a mare in diestrus?

Answer 47

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

Question 48

what direction does the cervix in a mare relax during estrus?

Answer 48

cervix relaxes cranial to caudal

Question 49

what is the primary sign of a cow in estrus?

Answer 49

stands for mounting

Question 50

what are secondary signs of a cow in estrus?

Answer 50

mounting others, clear vaginal mucus, hyperactivity (bellowing), & vulvar edema (unreliable)

Question 51

T/F: in cattle, ovulation occurs during standing heat

Answer 51

false - doesn't occur during, occurs after during metestrus 12-16 hours after estrus!!!

Question 52

if you feel a large CL on a cow ovary during rectal palpation, what stage of the estrous cycle is she in? why?

Answer 52

diestrus - because you can feel the CL

Question 53

what is weird about LH in the estrous cycle of the mare?

Answer 53

there is not really an actual surge of LH - it is rising throughout estrus & actually peaks after ovulation has occurred

Question 54

when do cows ovulate in the estrous cycle?

Answer 54

12-18 hours after the end of estrus

Question 55

what should the cervix, uterus, & ovaries feel like upon palpation of a cow in estrus?

Answer 55

cervix - no palpable changes because it doesn't respond to hormonal changes!! uterus - tonic ovaries - CL < 1cm, follicle 1.5-2.5cm

Question 56

what should you feel upon rectal palpation of a cow in metestrus? what is the significance of this?

Answer 56

pitting edema post-ovulation with 'bloody' mucus - too late to breed them!

Question 57

what should the cervix, uterus, & ovaries feel like upon palpation of a cow in diestrus?

Answer 57

cervix - no palpable changes uterus - flaccid ovaries - CL = 3cm, follicles <1cm you can feel the CL!!!

Question 58

what are the primary signs of estrus in sows?

Answer 58

stands for mounting!!!! response to pressure on the back - increased by the presence of a male!

Question 59

what are secondary signs of estrus in a sow?

Answer 59

anorexia, restlessness, salivation, grunting, champing jaws, & swollen vulva

Question 60

how long does estrus last in sows?

Answer 60

1-4 days

Question 61

when do sows ovulate?

Answer 61

ovulate 36-44 hours after the onset of estrus

Question 62

what is the primary sign of estrus in ewes & does?

Answer 62

stands for mounting

Question 63

what are secondary signs of estrus in ewes & does?

Answer 63

restlessness, tail swishing, seeking a male, vocalization, +/- vulvar edema

Question 64

what is the importance of a male for detecting estrus in ewes & sows?

Answer 64

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

Question 65

how long does estrus last in ewes?

Answer 65

24-48 hour estrus

Question 66

T/F: in the estrous cycle of ewes, there are multiple FSH waves that occur throughout the period

Answer 66

true

Question 67

how long after the LH surge does ovulation occur in ewes?

Answer 67

24 hours after LH surge

Question 68

when is prostaglandin secreted in the estrous cycle of the ewe?

Answer 68

days 14-17

Question 69

when is prostaglandin secreted in the estrous cycle of the cow?

Answer 69

day 15

Question 70

when is prostaglandin secreted in the estrous cycle of the mare?

Answer 70

around day 14 - followed by rise in estrogen & FSH causing the rise of LH & starts estrus

Question 71

when is prostaglandin secreted in the estrous cycle of the sow?

Answer 71

days 13-15 followed rise in estrogen on day 18-20, LH surge 20-21 & ovulation near day 21

Question 72

how long does estrus last in sows?

Answer 72

1-4 days

Question 73

what is the effect of seasonality on puberty in ewes?

Answer 73

lambs born in early spring will reach puberty the same year while lambs born in late spring reach puberty the following year

Question 74

what is the only food animal that doesn't ovulate during estrus?

Answer 74

cattle - ovulate after

Question 75

what is the average length of the estrous cycle in food animals? what is the exception to this average?

Answer 75

21 days for most species 17 days for sheep!!!