The Estrous Cycle

Question 1

Comprise four phases: (range of days)
1. Proestrus
2. Estrus
3. Metestrus
4. Diestrus

Answer 1

1. Proestrus: Day 19-20/21
2. Estrus- Day 0 (17.8 hrs in dairy cows, 15.3 hrs in dairy heifers)
3. Metestrus: Day 1-4
4. Diestrus: Day 5-18

Question 2

Proestrus:
During this stage the _____________ regresses

Answer 2

During this stage, the corpus luteum regresses (progesterone declines)

Question 3

Proestrus:
The pituitary gland of the brain secretes the ______________ that causes the ovary to develop follicles

Answer 3

follicle stimulating hormone

Question 4

Several follicles develop in what is termed ____________, but only one dominant follicle and egg mature for ovulation (rupture of follicle and release of the egg)

Answer 4

follicular waves

Question 5

As the follicle develops, estrogen is secreted by the ______

Answer 5

Estrus:
ovary

Question 6

The egg grows larger as more estrogen is secreted by the ovary

Answer 6

Estrus

Question 7

Estrus:
Estrogen causes __________ and __________ to aid transport of sperm

Answer 7

Estrogen causes estrus “heat” and contractions of the uterus to aid transport of sperm

Question 8

Estrus:
Ovaries contain________

Answer 8

1 (occasionally 2 Graafian follicles which have matured to preovulatory size)

Question 9

Corpus luteum of the preceding cycle has become ______________

Answer 9

Estrus:
Corpus albicans (non-secretory)

Question 10

Uterus shows marked turgidity and is edematous

Answer 10

Estrus

Question 11

Vaginal mucosa is congested

Answer 11

True

Question 12

Estrus:
____and ____________ have high levels of secretory activity

Answer 12

Mucosal cells and cervix

Question 13

The pituitary gland secretes luteinizing hormone (LH) usually in a pulsatile rhythm

Answer 13

Estrus

Question 14

Estrus:
High estrogen from the ovary causes ______________

Answer 14

an LH surge or spike that causes the ovarian follicle to rupture and release egg

Question 15

Some cows may have a bloody vaginal discharge during this stage

Answer 15

Metestrus

Question 16

Duration of estrus

Answer 16

17.8 hours (dairy cows), 15.3 hours (dairy heifers)

Question 17

This indicates that they were in heat a day or two earlier

Answer 17

Metestrus

Question 18

Metestrus:
The site of where the follicle ruptured becomes a _________ that secretes progesterone to inhibit estrus and, if the cow is pregnant, it helps maintain pregnancy

Answer 18

corpus luteum

Question 19

Diestrus:
The _________continues to increase in mass and reaches a mature size by ___________

Answer 19

The CL continues to increase in mass and reaches a mature size by day 7

Question 20

Diestrus:
If the uterine wall does not get a signal by days 16-18 of the estrous cycle indicating that_________________

Answer 20

a fertilized egg has been implanted in the uterine wall, the hormone prostaglandin is secreted from the uterus

Question 21

Diestrus:
Then the CL regresses between _________to complete the reproductive cycle

Answer 21

days 18-20

Question 22

Fertilization:
The cow has such a ____________that breeding or AI times are restricted relative to the time of ovulation

Answer 22

short period of sexual receptivity

Question 23

Fertilization:
AI is most successful when performed from __________________

Answer 23

mid-estrus up to a few hours after the end of estrus

Question 24

Fertilization:
Because the majority of AI programs now use frozen-thawed semen, which has a______________ , breeding too early can result in fewer sperm capable of fertilizing the oocyte

Answer 24

shorter viability span than fresh semen

Question 25

Fertilization:
The oocyte must be fertilized within ____________ if a high rate of fertility is to occur

Answer 25

6 hours after ovulation

Question 26

Fertilization:
The embryo or the unfertilized oocyte enter the uterus __________

Answer 26

72-96 hours from the onset of estrus