Managing fertility and manipulating the breeding season 2 Flashcards
Why would you want to manipulate the breeding seasons in cattle and sheep?
Cattle
* Aim for compact breeding season (if seasonal calving farm)
* Aim for consistency and 365 calving interval (if AYR calving farm)
Sheep
* Aim to breed as early as possible to maximise breeding opportunities and capitalise on higher lamb prices in Spring
What are the basic principles of bovine cycle manipulation?
Aim = to remove the CL to induce oestrus
* Induce luteolysis –> shorten CL lifespan –> induce oestrus sooner
◦ Prostaglandin
Aim = to mimic luteal phase of cycle (mimic a CL) –> induce oestrus when withdrawn
* Progesterone releasing devices (CIDR/PRID)
* Prostaglandin usually also used to ensure no functional CL present
Synchronisation programmes typically combine both approaches
How can cycle manipulation be used to maximise submission rate in dairy herds?
- Synchronisation protocols and fixed time AI
◦ Theoretically = SR of 100% - Synchronisation protocols and AI to observed oestrus
◦ Still needs effective oestrus detection
What are the downsides of OvSynch?
Increased drug costs, labour, and reduced conception rate compared to service to observed oestrus mean it isn’t for everyone
Which cows aren’t eligible for OvSynch?
- Not recommended for cows in anoestrus
- Not recommended for maiden heifers (have three follicular waves in cycle and this is designed for 2 follicular waves (older cows))
What is the better alternative to OvSynch for heifers?
CIDR/PRID which has added progesterone
What is the aim of AI to observed oestrus?
Oestrus detection is still needed –> not suitable on farms where this is suboptimal
- Use of drugs to mimic part of the oestrus cycle means ovulation can be predicted with greater certainty
◦ Can be used to ensure lots of cows are served at the same time (seasonal herd)
or
◦ to aid oestrus detection by allowing farmers to direct resources to oestrus detection for a defined window of time
Why is a compact calving pattern important in both beef and dairy cows?
- Beef cows:
◦ Compact calving pattern means that calves are closer in age and the group should be more uniform (in age and size) when ready for sale - Dairy cows:
◦ Compact calving pattern means that the whole herd is at the same stage in lactation and there is a more consistent herd-level lactation curve
What are the common approaches for shortening breeding season?
Synchronise cows so more of them come into oestrus in the first 6 weeks
Some common approaches are:
* Prostaglandin + natural service or AI to observed oestrus
* CIDR/PRIDSynch + FTAI
* CIDR/PRID + natural service or AI to observed oestrus
* CIDR/PRID + chorionic gonadotrophin hormone
When is the CIDR/PRID and chorionic gonadotrophin protocol helpful?
- Useful for non-cycling animals or those in poor bodily condition
- Currently only one CG product available in UK (Chorulon)
- Follow up FTAI with sweeper bull 3 weeks later
What is the most common cause of anoestrus in beef herds? How can you return to cyclicity?
Suckling calves = reduced LH pulse
◦ One of the most common cause of anoestrus in beef herds (other is low BCS) -> use CIDR/PRID-Synch if you believe this is the case
What are the options for advancing the breeding season in sheep? How do they work?
Ram effect
* Advances breeding season by ~2wks
* Entire or vasectomised ram presence –> stimulates ovulation
* Need 2 vasectomised rams per 100 ewes
* Usually left in for a week (although 2 days is sufficient)
* Ewes and rams need to be at least 1 mile apart for at least 6 weeks prior to breeding
◦ Consider neighbouring farms
Melatonin implant
* Advances breeding season by up to 2 months
* Melatonin implant mimics effect of shortening photoperiod
◦ GnRH is produced by hypothalamus at an earlier point in the year
* Success can be variable
◦ Some breeds (e.g. Suffolks and their crosses) respond better than others
◦ Older, well-conditioned animals respond better than gimmers or ewes in poor condition
◦ Melatonin is not effective in animals that are sexually immature
Recommended approach to melatonin implant
* Inject subcutaneously behind the ear
* 30 weeks before intended lambing –> separate all male sheep and goats from ewes to be treated
◦ Needs to be out of sight, sound and smell – the field next door will not be sufficient
- One week later insert the implant (this is 29 weeks before intended lambing)
- 30-40 days (i.e. ~ 5 weeks) after inserting the implant introduce fertile rams to the ewes (this is 24 weeks before expected lambing)
◦ Mating activity will commence 2-3 weeks after introducing rams (22-21 weeks before expected lambing)
◦ Gestation of sheep is ~21 weeks
Progesterone (or synthetic progestogen) + equine Chorionic Gonadotrophin (eCG)
* Advances breeding season by 4 – 6 weeks
* Also synchronises the flock
* Intravaginal devices used +/- eCG injection
* Suitable for cycling and non-cycling ewes
◦ Non-cycling –> eCG is needed otherwise results are poor
◦ Cycling –> eCG is optional but synchronisation is optimised if used
Progestogen sponges + eCG
* Intravaginal devices (sponges) impregnated with a synthetic progesterone (Flugestone acetate)
◦ Suppression of GnRH –> supresses ovulation (when sponge is in place)
* Sponge left in place for 14 days
* 200-400 IU eCG injection administered at time of sponge removed –> optimises synchronisation
◦ If ewes are non-cycling inject 500 IU eCG
Progesterone releasing devices + eCG
* Intravaginal devices impregnated with progesterone
◦ Suppression of GnRH –> supresses ovulation (when device is in place)
◦ These are same as CIDRs for cows but smaller size with lower concentration of progesterone
* CIDR left in place for 12 days
* 200-400 IU eCG injection administered at time of CIDR removed –> optimises synchronisation
◦ If ewes are non-cycling inject 500 IU eCG
