Reproduction and production Flashcards
What are the three different types of oestrous cycle ?
What type of oestrous cycle do cows undergo ?
Types of oestrous cycle
What is the two phases of the oestrous cycle in cows ?
Phases of the oestrous cycle
Follicular phase
Begins with luteolysis - ends with ovulation
- luteolysis results in a decline of P4
- gonadotrophins, LH and FSH no longer inhibited and this results in follicles producing oestrogen
- low P4
- high E2
Luteal phase
begins with ovulation - ends with luteolysis
After ovulation the corpora lutea develops which increases P4
- high P4
- comprises 80% of the cycle
Describe the four stages of the oestrous cycle in cattle ?
Stages of the oestrous cycle cattle
1) Pro-estrous
- formation of the ovulatory follicle (up E2)
2) Oestrous
sexual receptivity and a peak in E2
- behavioural signs of oestrous precede ovulation
3) Metoestrus
Cl formation and increase in P4
- slight blood discharge sometimes visible during metoestrous
4) Dioestrus
- high P4 the longest stage
Provide the basic facts of the oestrous cycle in cattle ?
Characteristics of the oestrous cycle in cattle
length = 21 days (17-25) slightly shorter in heifers
Ovulation = 24-30 hrs after the onset of oestrus
LH surge = 24 - 28 hrs
onset of oestrous coincides with a surge in LH and FSH
Duration of oestrus = about 18 hrs (12-30hr)
Luteolysis = day 16 -18 (on average)
Number of follicular waves in a cycle 2-4 per cycle
Describe the changes in hormone concentrations during the luteal phase of the oestrous cycle in cattle ?
Luteal phase - cattle
Concentration of progesterone > 1ng/ml
- progesterone has negative feed back on GnRH and LH secretion
- oestradiol conc is low and negatively feeds back on the secretion of LH and GnRH
Oestrous and ovulation do not occur
Follicle turnover occurs even in the presence of high conc of P4
Draw the hormonal changes which occur during the bovine oestrous cycle ?
Describe the hormonal changes which occur during the follicular phase of the oestrous cycle
Follicular phase
Progesterone < 1ng/ml
- the concentration of oestradiol increases to threshold and positively feeds back on LH and GnRH
- LH surge and ovulation can occur
Describe the hormonal events taking place in the cow which leads to the preovulatory surge ?
Describe the three stages of folliculargenesis (cattle)?
Folliculargenesis = Waves of follicular development which occur during the oestrous cycle in cattle
Emergence, or Recruitment
- a small number of primordial follicles develop to antral follicles
- antral follicles begin to secrete small amounts of oestrodiol
- process takes 3-4 months
Selection
- Some of the recruited follicles undergo atresia - or become selected and begin to secrete moderate amounts of oestrodiol
Dominance
As concentrations of FHS decline (inhibition oestrodiol) one follicle will become larger than the other follicles
- Dominant follicle secrete large quantities of oestrodiol
- if progesterone <1 ng/ml this will trigger the LH surge
Define and describe the physiology behind luteolysis ?
Luteolysis = Decomposition of the CL
Luteolysis occurs at the end of the luteal phase ( day 16-18) after oestrous in the cow
- causes a decline in P4 concentration
- oestrogen stimulates the expression of oxytocin receptor expression in the endometrium
- Oxytocin from the posterior pituitary acts upon these receptors to stimulate the release of PGF2alpha
PGF2alpha travels to the ovary from the uterus through a vascular counter exchange system - causing luteolysis
What is the maternal recognition of pregnancy in cattle ?
Maternal recognition of pregnancy occurs around days 15 to 17
Interferon tau produced by the trophoblastic cells inhibits PGF2A synthesis by the endometrium.
Interferon tau also inhibits the expression of oxytocin receptors
Thus progesterone production by the CL is maintained
Describe the process of parturition in cows ?
Parturition in cows
Parturition is initiated by the foetus
- increased foetal ACTH secretion which in turn stimulates foetal cortisol
- P4 decreases last week of gestation
- oestrodiol increases prepartum
- secretion of relaxin causes a softening of the cervix and relaxation of the palvic ligaments
Oestrogen stimulates the release of PGF2alpha from the myometrial receptors which increases the strength of contraction.
- PGF2alpha stimulates release of maternal oxytocin from the posterior pituitary - +ve feed-back on PGF2alpha
Describe the postpartum events and their timing ?
Post partum events
Expulsion of placenta <12 hr
Uterine involution takes about 30 days
process involves - reduction in uterine size, expulsion of Iochia (vaginal discahrge), tissue sloughing, reepitheliaisation and removal of bacteria
Most cattle cycle within 4 weeks post partum - can be much longer
Optimum fertility achieved 60-90 days postpartum
What factors do we need for an ideal pregnancy test for cattle ?
What is the purpose of pregnancy testing ?
What methods can we utilise to detect pregnancy in cattle (5) ?
Methods for pregnancy diagnosis in cattle
- observation
- laboratory test
- rectal palpation
- electronic methods
- abdominal ballottement
What observations would indicate pregnancy in cattle ?
Observational indications for pregnancy
Failure to return to oestrus
- cows will usually return to oestrous 18-24 days post ovulation
External indicators (non specific indicators of pregnancy)
- change in size and shape of the abdomen
- foetal movements
enlargement of mammary glands
- enlargement and softening of the vulva
Note looks may be deceiving pseudopregnancy.
Why would the absence/ presence of oestrus not be definitive ?
Oestrus may not indicate pregnancy
False positive
- prolonged luteal phase
- embryonic loss
- pseudo pregnancy (dogs, sows)
- Anoestrus
- Abortion after the formation of endometrial cups
-failure to detect oestrus
False negative
- some pregnant animals may show behavioural signs of oestrus
What three laboratory test could be carried out to detect pregnancy ?
Detecting pregnancy through laboratory tests
Progesterone concentration (non specific indicator of pregnancy)
Oestrone sulphate
Pregnancy specific protein B (PAGS)
How can progesterone indicate pregnancy ?
Why is it a non specific indicatory of pregnancy ?
Progesterone
Test
- animal is tested around the time of expected return to oestrus (milk, plasma)
- A test for non pregnancy = a low concentration
- 18-24 days post ovulation high concentrations indicate the Prescence of a functional CL and pregnancy
Why is it a non specific indicator
False positive - presence of a persistent CL
How does oestrone sulphate indicate pregnancy ?
What are the problems with using oestrone sulphate as an indicator ?
Oestrone sulphate
Produce by the foetal placental unit
- a positive test indicates a viable foetal placental unit
- can be used as a test for foetal viability
Problems with oestrone sulphate
Pregnancy must be >100 days
- cost $3 an animal
- recommend that non pregnant cows are tested prior to culling
How dose a pregnancy glycoproteins test work ?, and what are the cons ?
Pregnancy associated glycoproteins
PAGS are proteins produced by the trophoblastic cells of the placenta early in pregnancy
- they enter the blood stream around the time the conceptus becomes closely associated with the uterine lining
- can detect pregnancy down to 28 days
- serum, plasma or milk tests are available
Plasma sensitivity 99%, specificity 95%
Negative
- early embryonic loss / foetal death may produce a false positive
- cows 60< days post partum may produce a false positive
- delayed results may make test to inefficient
- cost $5 a test
Describe abdominal ballottement for pregnancy diagnosis in cattle ?
What two electronic methods can be used for the detection of pregnancy in cattle ?
Describe B mode ultrasonography ?
B mode ultrasonography
Highly effective
- heifers 26 days
- cows day 29
Cows diagnosed as non pregnant scanned <5 weeks should be rechecked once over the five weeks of gestation.
Advantage
- early diagnosis
- diagnose multiple pregnancies
- uterine pathology
- determine stage of gestation, sex and foetal viability
- assess post partum involution
Disadvantage
- cost and portability which are coming down
What are the advantages and negatives of pregnancy diagnosis through rectal palpation ?
Describe the anatomy of the mares reproductive tract, why is the mare so unique ?
Mare anatomy
The mare is unique
- “inside out” compared to other species
- thick tunica albuginea covers most of the ovary except the ovulation fossa
- ovulation occurs only through the ovulation fossa
- follicles may be palpated but not the corpus luteum
Provide the basic facts about equine reproduction eg age at puberty, gestation length, oestrous cycle length and time of ovulation etc ?
Basic facts mare reproduction
- seasonally polyoestrous
- most mares exhibit anoestrus during winter
Age at puberty = filly 14 months (10-24) and colts 18months (12-19)
Gestation length = 11months
Length of oestrous cycle 21 days (range 18-24days)
Dioestrus less variable - 14 to 16 days
Ovulation occurs on the last or second last day of behavioural oestrus (14% of mares after the end of oestrus).
1-2 follicular waves per cycle
Peak PGF2alpha levels occur on day 14 post ovulation ( non pregnant mare) - causing lysis of the corpus luteum
What occurs during the spring transition period in horses ?
Mares are seasonally polyoestrous
The spring transition period
Melatonin is secreted at night so as day length increases less melatonin is secreted (long day breeders)
Melatonin inhibits GnRH secretion
- GnRH secretion increases
- FSH secretion increases
- follicles develop on the ovaries, but they secrete little oestrogen
- more follicles develop secreting increasing quantities of oestrogen
- eventually a follicle is produced which secretes enough oestrogen to stimulate an LH surge
- ovulation
- the mare than enters dioestrus and normal cycles should continue
Describe the oestrous cycle of the mare ?
The oestrous cycle
Oestrogen
- causes the mare to be sexually receptive and induces swelling / odema / softening of the reproductive tract
LH
- Induces ovulation of a dominant follicle (or two)
Progesterone
- suppresses sexual receptivity, inhibits GnRH (LH, FSH, oestrogen) thus blocking the LH surge
FSH
- Induces waves of follicular development. This mare has two follicular waves per cycle
PGF2A
- causes lysis of the Corpus luteum(s) and therefore a drop in progesterone levels
What four tools can be utilised to monitor the oestrous cycle in the mare ?
Tools to monitor the oestrous cycle in the mare
- Teasing
- Rectal palpation
- Transrectal ultrasound of the reproductive tract
- Vaginal speculum to observe the cervix (digital palpation of the cervix)
Describe the scoring system for teasing ?
Is this process fool proof ?
Describe the process of rectal palpation ?
What changes would you feel in the cervix, uterus and ovaries?
Rectal palpation
Used to asses the size and tone of reproductive structures - dependant on hormonal influence
Cervix
- High tone (tubular) when progesterone levels are high in dioestrus
- softens as mare come into oestrous
- very soft and open as the mare approaches ovulation (might not be palpable at this stage)
- low tone during anoestrous
Uterus
- High tone (tubular during dioestrous (progesterone)
- Becomes soft and oedematous / swollen during oestrus (oestrogen)
- low tone during anoestrus (progesterone and oestrogen at basal levels)
Ovaries
- Small and form during anoestrous (inactive)
- Large in a cycling mare (roughly plum sized, but bean shaped)
- During oestrous follicles of varying size and softness may be palpable
- A pre ovulatory follicle will become progressively bigger (35mm and over) and softer as ovulation approaches
Corpus luteum in dioestrus is not palpable ( due to inside out nature of the ovary and thick tunica albuginea covering the ovary.
How could transrectal ultrasonography be used to detect stages of the oestrous cycle in the mare ?
Transrectal ultrasonography
During oestrous
- endometrial oedema is visualised as a distinct pattern (wagon wheel or orange segments) to the uterus
- as oestrus progresses one follicle (perhaps two) will enlarge to over 35mm in diameter as ovulation approaches
- the oedema is due to high levels of oestrogen
During Dioestrus
- Corpora lutea can have a range of appearances, but they are always HYPERECHOIC (grey white tissue echogenicity) where as a follicle is ANECHOIC (black, fluid echogenicity) on ultrasound.
Describe what you would observe with a vaginal speculum exam ?
