Bovine and Small Ruminant Repro Flashcards
What type of breeders are bovine?
polyestrous
What type of ovulators are bovine?
monovulatory - one egg per estrus phase
After puberty, what is the cyclicity like in the bovine for the rest of its life?
routine normal cyclicity that continues throughout its life unless inhibited by disease or pregnancy
What is the length of the estrous cycle in the bovine?
21 days on average (range: 17-24 days)
What are the two centers in the hypothalamus for GnRH release?
surge center and tonic center
How does the surge center work in releasing GnRH?
it is what dictates the huge surge of GnRH that causes ovulation
How does the tonic center work in releasing GnRH?
it allows for a constant release of GnRH no matter where we are in the estrous cycle
When is the tonic center stimulated to begin GnRH release?
during puberty
What two hormones are released from the anterior pituitary that are involved in the estrous cycle?
FSH and LH
What is the role of FSH?
it is needed for the recruitment of follicles and the growth of follicles
What is the role of LH?
final maturation of the ovary for ovulation
What two cells are important in estrous?
granulosa cells and theca cells
What do granulosa cells and theca cells produce?
estrogen
How many folicular waves are there typically in a bovine estrous cycle?
two to three
What is progesterones role in the estrous cycle?
it is the gate keeper; it dictates what happens on the ovary, if present the ovary cannot ovulate
What decreases the level of progesterone in the estrous cycle?
natural luteolysis
If the estrous cycle is 18-19 days long, how many follicular waves will the bovine most likely have?
two
If the estrous cycle is 24 days long, how many folliclular waves will the bovine have?
three
During recruitment, what are hormone levels of FSH, LH, and estrogen like?
FSH is high for follicular growth, LH is limited because it is reserved for ovulation, and there are insignificant levels of recruitment
During selection, what are hormone levels of FSH, LH, and estrogen like?
there is not much FSH because follicles are growing, increased LG and more estrogen is being produced than in recruitment
What is inhibins role in selection?
it is involved to make sure that only one follicle is released during ovulation
In selection, what is inhibin released from?
the dominant follicle to suppress its cohorts
What are the hromone levels like during dominance?
inhibin levels keep increasing, there is an LH surge for ovulation, and increased estrogen
What are the two types of inhibin and what are their roles?
alpha and beta, alpha allows for litters and multiple dominant follicles, beta only allows for one dominant follicle
How and when is estrogen involved in negative feedback?
for the majority of the estrous cycle, if estrogen is produced/present and progesterone levels are high (present) then the system is told that no more estrogen is needed so it is not produced
How and when is estrogen involved in positive feedback?
when progesterone is gone during the estrus phase, estrogen levels increase its production because it is needed
What are the two phases of the estrous cycle?
follicular and luteal phase
What are the two sub phases of the follicular phase?
proestrous and estrus
What are the two sub phases of the luteal phase?
metestrus and diestrus
What is the follicular phase?
the period from regression of the corpus lutea to ovulation
What primary ovarian structures are involved in the follicular phase?
growing dominant follicle and regressing CL
What primary hormone is involved in the follicular phase?
estrogen
When does proestrus occur?
after diestrus or anestrous immediately preceeding estrus when progesterone declines from resulting luteolysis
How long is proestrus usually?
between 2-5 days
What transition period occurs during proestrus?
the transition between progesterone dominance to estrogen dominance
What is estrus characterized as?
a period of sexual receptivity
What are some physical signs that a bovine is in estrus?
increased locomotion, vocal expression, nervousness, and mounting
How long does estrus typically last in the bovine?
16 hours
When do bovine typically ovulate?
12-16 hours post standing estrus
What is the time from standing estrous to ovulation?
typically 30 hours
If a cow is in standing estrus in the morning, when would we typically inseminate?
in the PM
If a cow is in standing estrus in the evening when would we typically inseminate?
in the morning
What is released from the anterior pituitary during the follicular phase?
everything
Why is FSH released in the follicular phase?
for follicle stimulation
What part of the estrous cycle has the highest estrogen period?
estrus
What does blood on the tail indicate?
that a cow probably just went past her heat a couple of days prior
What causes blood on the tail?
estrogen will cause blood vessels to burst
What are some methods, aside from physical signs, that can be used to help determine if a cow is in standing estrus?
paint on the tails (if it rubs off, she has been mounted) and a pressure detector (a lot of pressure will change the color of the detector)
What is the longest phase of the estrous cycle?
the luteal phase
When does the luteal phase occur?
it is the period from ovulation of the dominant follicle to the regressionof the corpus lutea
What is the primary ovarian structure during the luteal phase?
the corpus luteum
What is the primary hormone of the luteal phase?
progesterone
What happens to follicles during the luteal phase?
they are constantly growing and regressing but they do not produce enough estrogen to proceed into the follicular phase
When does metestrus occur?
it is the period between ovulation and formation of the CL
What are hormone levels like early on in metestrus?
progesterone and estrogen are low
What do granulosa and theca cells turn into in the metestrus phase?
luteal cells
Is diestrus or metestrus longer?
diestrus
What happens in diestrus?
the corpus luteum is fully functional and production of progesterone is high
When does diestrus end?
at luteolysis or termination of pregnancy; by the activation of prostaglandin release
What is the precursor for all androgens, progesterone, and estrogens?
cholesterol
When will the highest level of progesterone occur in the estrous cycle?
at approximately day 11
Can you palpate a cow to tell what day she is in her estrous cycle?
no
If a follicle gets to 8mm what will it become?
the dominant follicle - will grow to 16-18 mm follicle
What is anestrus?
the condition where a heifer/cow has not been seen in estrus
What can cause anestrus?
delayed puberty and post-partum anestrous causes
What can cause post-partum anestrous?
too short time since calving, negative energy balance, health issues, or lactational issues
What happens to hormones in postpartum anestrus?
elimination of progesterone and estrogens at parturition and relatively long suppression of FSH and LH during late gestation
What is the voluntary wait period?
the period of time where dairies woll not breed an animal post partum (55-75 days)
When signifies resumption of cycle?
it is the first FSH increase within 3-5 days postpartum, however, it typically does not have other components to finish the cycle
When do dairy cattle typically resume their cycle?
15-45 days postpartum
When do beef cattle typically resume their cycle?
30-130 days postpartum
Why do dairy cattle resume cyclicity before beef cattle?
most likely because the calf is removed in order to prevent diseases
Why would a calf have an effect on cyclicity in a cow?
it inhibits GnRH and LH frequency and surge; it establishes the negative feedback of estrogen on the hypothalamus
How can lactation inhibit signs of estrus?
prolactin will suppress GnRH therefore suppress the LH surge
What is the purpose of exogenous drugs used in reproduction?
treatment of disease processes, control the estrous cycle, and alter the estrous cycle
What is MRP?
maternal recognition of pregnancy
When must MRP occur?
prior to luteolysis
What hormone must be present for MRP and why?
progesterone to allow changes in the endometrium
What molecule signals to the cow that she is pregnant?
interferon-T
What is interferon-T produced by and what is its specific function?
it is produced by the trophoblast cells in the embryo and blocks the release of prostaglandin from the endometrium by blocking oxytocin receptors
What cells make up the placenta?
trophoblasts
When does attachment of the embryo start and when is it completed?
it starts at day 20 and is completed by day 40
What type of connection do cattle have with their embryo (placentation) and how many layers between the two?
syndesmochorial; 6 layers
What type of placenta do cattle have?
cotyledonary: cotyledon from the fetus and caruncle from the mother
What are the three parts of the ruminant placenta?
amnion, allantois, chorion
What is the function of the amnion?
it provides nutrients to the fetus
What is the function of the chorion?
it attaches to the endometrium of the maternal side
How can pregnancy be diagnosed?
rectal palpation, ultrasound, and blood tests (least effective)
What is the average gestational length of the bovine?
283 days
What dictates the length of gestation?
fetus
What hormone is needed throughout gestation?
progesterone
What is the primary source of progesterone for the first 5 months?
CL
What is the primary source of progesterone 6-8 months into pregnancy?
the placenta
What takes over progesterone production in the last month of gestation?
CL
How many stages of parturition are there?
3
What occurs during the first stage of parturition?
myometrial contractions and cervical dilation
How long does stage 1 of parturition usually take?
2-6 hours
What are the typical signs of stage 1 of parturition?
separating from the herd, mild contractions and moving around, pelvic ligaments relax
What occurs during the second stage of parturition?
fetal expulsion: straining and strong contractions, breaking of the allantoic sac, breaking of the amnion sac
How long does fetal expulsion usually take?
30-60 minutes in cows and 2 hours in heifers
What does straining and strong contraction allow for?
stimulation of oxytocin release for dilation of the cervix
What occurs in stage three of parturition?
fetal membrane expulsion
How long does fetal membrane expulsion usually take?
6-12 hours
When does a cow considered to have a retained fetal membrane?
when it hasn’t been expelled 12 hours after fetal expulsion
How is the fetal membrane expelled?
chorionic villi must dislodge from crypts and endometrium (caruncles)
On average, when do goats and sheep hit puberty?
6 months
What is the average length of the goat estrous cycle?
21
What is the average length of the sheep estrous cycle?
17
After estrus, when does the goat usually ovulate?
12-36 hours
After estrus, when does the sheep usually ovulate?
24-30 hours
What is the main difference between the estrous cycle in small ruminants and the bovine?
they are short day seasonal breeders
How long is gestation in goats?
147-155 days
How long is gestation in sheep?
145-150 days
Typically how many follicular waves do small ruminants have?
three to four
What is the dominant follicular size in the small ruminant?
5 mm
What do long light days do in the small ruminant?
inhibit the pineal gland from releasing melatonin
What is seasonal breeding regulated by?
RF amide-relatedd peptide neurons that are present in the mediobasal hypothalamus
What are RFRP neurons regulated by?
melatonin
