Overview of Manipulation of Bovine Cycle Flashcards
why do we need to synchronize estruous cycles, and why are there so many protocols
One main aim is to enhance the submission rate but also to have the correct time of the submission
Ultimate goal is to have planned the timing of the calving in the subsequent calving period
Enhance the pregnancy rate if the submission rate is maintained
Usually designed to incorporate AI
What do we want to influence
Herd reproductive performance:
- Submission rate
- Pregnancy rate
- Calving rate
- Time of calving
- Genetic merit
what are the general options for synch of estrus and/or ovulation (4)
- Only synchronous luteolysis (PGF2a treatments)
- Prevent estrus and ovulation in all animals for a pre-determined time (progesterone treatments)
- Induce ovulations and then cause synchronous luteolysis and follicular phase, leading to synchronized ovulation (GnRH plus PGF2a treatments)
- Combinations of all treatments above
how is luteolysis synchronized
PGF2a in animals that have a functional CL
how does PGF2a synch luteolysis
PGF2alpha injection in the presence of a corpus luteum (estrumate)
On day 18 of cycle luteolysis occurs
To synchronize a whole group which are in different stages of the cycle, the majority with be in the luteal phase
If animals have functional CL they will respond to a single injection of PGF2alpha
CL lifespan will be cut short and they will enter the follicular phase
what are the problems with synchronizing luteolysis using PGF2a
Variable intervals from PGF to estrus
Depending on which follicle wave the animal is on
If first wave dominant follicle is become atretic, the emergence of second follicle wave has to grow the dominant follicle and induce the LH surge
- This process takes longer
- Estrus would not occur 5-7 days after the PGF injection
how can luteolysis synchronization be improved using PGF2a
double PGF2alpha regime
Two injection of PGF2alpha will be administered 11 days apart
The first injection will cause ovulation and we won’t know exactly what days this will happen (between 2d and 7d)
The second injection is administered on day 7 of the next cycle in the heifers (first wave dominant follicle will be present) will cause ovulation within 3rd or 4th day after the second injection
can fixed timed AI be used in a double PGF2a synch
yes
AI from 60h + from 84h
what occurs if ovulation is late after the first PGF2a injection in a double PGF2a synch program
After second injection the corpus luteum is only on day 3 or 4 cycle which means it is not responsive to PGF2alpha injection
Animals will not come into heat
No luteolysis
No estrus
No pregnancy after fixed time AI
what is the verdict on synchronizing luteolysis
normal fertility to AI on heat
syncrhony not good enough for successful single fixed time AI
when are the double PGF2a injections given
11 or 14 days apart
when can insemination occur when using PGF2a to synch
At observed heat after every injection
At observed heat to second injection
Single (from end of 3rd day ex. from 72h) or double (3rd + 4th day ex. from 60+ from 84h in dairy cows) fixed time AI after 2nd PGF
what do progesterone treatments do
prevent estrus and ovulation for a pre determined time
what are progesterone treatments combined with and why
PGF2a to induce luteolysis before device removal
allows better syncrhony due to follicle wave management ensuring dominant follicle is present at end
describe the 10d CIDR/PRID synch protocol
Utilizing the negative feedback of progesterone on the hypothalamus which prevents GnRH surges and suppressing GnRH pulsatility and therefore LH pulsatility
Selected dominant follicles rely on being supported on LH pulses —> no LH pulses means they will become atretic
Achieve follicle wave management:
- Control follicle growth
- Ensuring that at the end of follicle there is a new dominant follicle present
- During inserting time animals may have a CL present and may still have a CL present when device is removed
Combined with PGF2alpha to induce luteolysis
can fixed timed AI be used with CIDR/PRID synch protocols
yes
10d: AI from 36h + 60h
8d: AI from 48h + 72h
describe the physiology of the 10 CIDR/PRID synch protocol
The FSH/LH surge coincides with estrus causing an FSH rise leading to the emergence of first follicle wave
CL begins to emerge and progesterone rises
10 day CIDR/PRID which leads to absorption of extra progesterone and rapid rise causes suppression of GnRH and LH pulsatility
The first selected dominant follicle becomes atretic earlier and causes a rise of a second follicular wave (earlier than normal)
Selection of 2nd DF occurs day 12 of cycle
3 day period during which DF is supported
When PGF administered, the CL will regress and lead to a rapid decline in P, a small amount of P still absorbed but the LH pulses will increase but GnRH surges are prevented so the DF is able to mature longer
Once CIDR is pulled out, bring into follicular phase and surge will occur on 2nd day after device removal
Because estrous is synchronous we can combine with a timed AI protocol
what is the importance of DF selection status at GnRH1
If there is no DF present there is a likelihood that PGF2a is administered at a time where there is no DF that could continue onto the follicular phase
When GnRH2 is administered there isn’t a DF present that could respond
Not synchronized and no synchronized ovulation
Cannot conceive to insemination
how is ovsynch improved using CIDR/PRID devices
PRID/CIDR between GnRH1 and PGF2a
Allows animals coming on heat after PGF2a injection or protocol is continued on and fixed time AI
Shown to improve pregnancy/AI and 6-week PR when administered to cyclic and anovulatory dairy cows
Reason may be higher progesterone exposure of growing DF and its oocyte
- Beneficial to the quality of the follicle and the oocyte that it will ovulate
how can ovsynch be used for anestrous cows
Needs pre-synchronization/progesterone exposure
Follicles that have not grown in a normal luteal phase (low progesterone)
Fertility of oocyte is not as high as we would expect it to be
