17.4.1: Introduction to farm animal reproduction Flashcards
True/false: you can tell about the cow’s cyclicity from her cervix.
False
Cervix tone is discussed in horses but not in cows
Dominant follicle
* Contains oocyte
* Fluid filled (anechoic on ultrasound)
* Secretes oestradiol -> this drived oestrus
Corpus luteum
* Highly vascularised transient endocrine gland
* Solid (homogenous, medium echogenicity)
* Produces progesterone
1
2
3
4
5
High levels of which hormone lead to an LH surge? What is the effect of the LH surge?
Oestradiol
Effect of LH surge = ovulation
How long is the oestrus cycle in the cow?
How long is the luteal phase?
How long does standing oestrus last?
You see a cow showing signs of oestrus. When should you AI?
Oestrus lasts ~ 1 day so ASAP!
In an ideal world, would AI 6hrs after the onset of oestrus; in practice, just AI as soon as you see oestrus.
What will the ovaries feel like when a cow is on Day 1 of her cycle?
Day 1 = ovulation has just occurred
The ovaries will be small and it might be hard to palpate the tiny CL
If you see a large CL and a large follicle present at the same time, which one is dominant?
The CL
Which structures can you see on this ovary?
There is a small follicle (anechoic structure)
Which structures can you see on this ovary? Which is likely to be dominant?
What phase of her cycle is this cow in?
Follicular phase
These two ovaries are from the same cow. What phase of her cycle is she in? Which structure will be dominant?
- She is mid-luteal phase
- She has a large follicle but the CL will dominate
1
2
3
True/false: the first oestrus after parturition is typically silent.
True
How long after parturition should a dairy cow have had her first ovulation by?
3 weeks after parturition
In which species do we see profound lactational anoestrus (in that while the young are there and suckling, she will not cycle)? What is the hormonal mechanism behind this?
Sow
Prolactin suppresses LH, thus there is no ovulation
Why might we see anoestrus?
- Physiological reasons: gestation, lactation/presence of offspring (species differences), seasonality (long or short day breeders)
- Pathology: metabolic/ heat stress, ovarian pathology e.g. cystic ovarian disorders, inactive ovarian activity
How soon after piglets are weaned would you expect a sow to ovulate?
- Weaning intiates oestrus and there should be an LH surge within 7 days
- This may be affected by length of lactation, timing of weaning
Cystic ovary
True/false: GnRH will induce oestrus.
False
* GnRH induces an LH surge and therefore ovulation (approx. 28hrs later)
* If you give GnRH, AI the cow 6hrs later
* It does not induce oestrus
True/false: we can use GnRH to force ovulation/ luteinisation of cystic structures.
True
Multiple growing follicles on both ovaries
What is the effect of FSH and what are its clinical uses?
FSH stimulates antral follicle growth. There are few products that are FSH-specific; we can use eCG as this has mainly FSH-like activity.
Clinical uses:
* Superovulation: ovulation of more follicles than norma
* Must administer early in the follicular wave for superovulation
* Often requires repeated doses
* Responses are varied
What effect does LH have and how can we use it clinically?
We don’t have an LH-specific product; we use hCG instead as this is LH-like in activity.
This stimulates the final maturation of follicles, causes luteinisation and provides luteal support.
Clinical uses (exact effect influenced by dose)
* Induce ovulation when animals are in oestrus
* To force ovulation when there has been repeated failure of conception in cattle
* Treatment of cystic ovaries in cows and heifers
What effect do progestogens have and what can we use them for clinically?
Progestogens -> negative feedback effect on the pituitary (mimics luteal phase)
Clinical use:
* Suppress the HPG axis
* Used as a method of inducing/ synchronising oestrus by administration and withdrawal of the product
* When we withdraw the product, cow will enter the follicular phase
What is flugestone and what does it do?
- Progestogen vaginal sponge
- Oestrus induction/ synchronisation upon withdrawal
- Often used in combination with eCG
What is a PRID/CIDR and what does it do?
- Vaginal device release progesterone
- Oestrus induction/ synchronisation on removal
- Often used in combination with GnRH
What is altrenogest (a.k.a. Regumate) and what does it do?
Exogenous progestogen
* Oral liquid
* Used for oestrus suppression/ induction/ synchronisation in mares and sows
How old does a CL need to be in the cow to respond to prostaglandin?
Must be over 6 days old to respond
What must you ensure before giving PGF2a to an animal?
Ensure that she is not pregnant
What physiological effects does PGF2a have?
- Lysis of the mature CL, causing progesterone to decline
- Smooth muscle contraction (ecbolic effect on the uterus)
What are the clinical uses of PGF2a?
- Termination of luteal phase to synchronise oestrus
- Induction of abortion
- Induction of parturition
- Ecbolic efect: treatment of chronic metritis, treatment of pyometra is CL is present
How soon after giving PGF2a to lyse a CL will a cow come into oestrus?
3-4 days after PGF2a
Which protocol is pictured here?
P4 and PGF. This is followed by fixed time AI.
This can be used in the cow or heifer.
Which synchronisation protocol is pictured here and what animals is it used in?
OvSynch
Used in cows
Which synchronisation protocol is pictured here and what animals is it used in?
OvSynch with P4
Heifers
True/false: melatonin can be used to induce cyclicity in sheep.
True
True/false: it is common to use 2 doses of PGF2a in sow synchronisation protocols.
False
* Unable to use 2 doses of PGF2a in the sow because CL only responds after day 11
1-4
1-5
1-6
