Assisted Reproductive Technologies in Sheep Flashcards
what are reproductive technologies
= technologies that enhance or improve fertility
e.g.
~ AI (insemination of semen into repro tract)
~ semen cryopreservation (freezing of sperm)
~ embryo transfer (transfer of embroyo from doner to recipient ewe)
~ cloning
~ transgenesis (DNA of one organism into another)
~ IVF
~ in vitro embryo production (fertilised oocyte cultured in lab until point of embryo) (quick turnaround for donor)
~ store semen (chilled, frozen)
~ oestrus synchronisation (all animals brought into oestrus at same time)
Sheep oestrus cycle
- length = 17 days
- ovilation occurs between day 0 and 2
- day 2 = corpus luteum begins to be formed
- day 14 = luteolysis (structual demise of CL)
(diagram in folder) - oestrodidol does most functions for oestrogen
detecting oestrus
- oestrus last 24-42 hours
~ signs - restlessness, stamping feet, sniffing male- - 6-8% ewes in oestrus each day of breeding season - at least 17 days to inseminate a flock naturally cycling ewes
- ewes can be mised and labor intensive
oestrus synchronisation
= use of synthetic hormones to syncronise oestrus in a flock
advantages of oestrus synchronisation
- well established method
- determine expected time of ovulation (less labour)
- multiple insemination at one time point
- ewes lamb in unison = facilitating management during preg/parturition, all lambs in short time span,manage nutrition at same stage
- stimulate ovulation = increase fertility (more ewes preg) and fecundity (more offspring per female)
- out of season breeding (mar-sept)
- no need to observe and draft off females in oestrus
- no teaser male required to detect oestrus
disadvantages of oestrus synchronisation
- can be costly
- reduced fertility (if not managed properly)
~ e.g. 300 ewes brought into oestrus but not used for artificial insemination program
~ put out for natural ating with few rams
= unable to mate with all
= lower fertility rates
oestrus synchronisation
- progesterone method
(diagram in folder)
- adv - cheap (£4-5 per ewe)
- quickest (days to ovulation) and most reliable method of synchronisation
- dis - enviro contamination: residue progesterone/antibiotics (accumulate in tissues) not ethical/green/clean (waste disposal important)
- preg rates lower than untreated ewes
artificial insemination
- def
- advantages
= the deposition of semen into the female reproductive tract by artificial means
- ease of transport (frozen semen), cheaper to transport than whole animal
~ allow transport of sperm between countries that dont allow import/export of live animals
- increase breeding efficiency = remove sub-fertile rams (collect and assess semen) and inseminate all females
- lower ram maintenance
- prevention/control disease (no male/female contact, less transport rams)
- use of incapacitated males e.g. old, injured
~ identify why cant mate (hereditary/genetic trait)
- synchronised breeding
- out of season breeding = use in semen semen (impaired func/integrity if take sperm out of season, lower fertility rate)
- increase rate of genetic gain (ram naturally 50 ewes/years vs AI 1000 ewes/2-3 weeks)
Disadvantaegs of artificial insemination
relatively small if managed correctly
- Inbreeding
~ More prevalent in a small flock or herd.
~ Care must be made to ensure selection intensity is not too high.
~ Can have opposite effect (more sires available). - Reduced fertility
~ Pregnancy rates can be less than with natural mating.
~ Can be caused by incorrect handling of semen or unsuccessful oestrous synchronisation.
~ ability of person undertaking AI affect - Cost
~ Technician, drugs, hormones, semen.
~ Cost per insemination relatively low, cost of labour, drugs and hormones is greatest.
AI sites of deposition and dose (number of sperm)
- laproscopic ~ 20 million sperm ~ 70% fertility with FT sperm - Cervical ~ up to 180m sperm ~ 70% fertility with fresh sperm ~ less than 20% with frozen - Vaginal ~ 300m fresh sperm ~ 70% fertility (seen 80-90% commonly) ~ FT semen not effective
Timing of AI
- Timing of semen deposition relative to ovulation is critical
- Timing of AI dependent on site of semen deposition
- if too early = sperm sat in repro tract, frozen sperm die quickly
~ Cervical AI: optimal fertility 55h after pessary (sponge/CIDR) removal (further to travel to fertilise oocyte)
~ Intra-uterine AI: Optimal fertility 60-66h after sponge removal - Should AI prior to but close to ovulation
~ Fresh sperm viable for 3-5d in repro tract
~ Cryopreserved semen have reduced fertility (max. 12 h)
~ Oocyte viable for 24h post-ovulation
~ need to ensure sperm already moving in repro tract when ovulating
~ Advantages to using ovulation-inducing agents (GnRH/PMSG) = ovulation occur at time expected to
limitations of cervical ai
- Using fresh semen:
~ Fertility rates average 70%
~ BUT fresh-semen is only viable for 24 hours (some advances with cooled semen) - Using cryopreserved (or frozen-thawed) semen so stored for years:
~ Fertility rates approx. 20%
~ Lambing rates range from 6.7 – 57 % (not commercially viable) - better results cryopreserved rather than chilled
Effect of sperm storage on fertility
- Sperm storage reduces sperm integrity and function
- Sperm storage reduces motility in utero (4h post-AI) however stored sperm still give viable fertility rates
- Sperm storage reduces movement of sperm through the cervix
- Cervical AI with stored sperm is unviable (low fertility rates)
= Transit of stored sperm through the cervix is impaired
what is sperm transit in the cervix affected by
- Changes to cervical mucus composition with oestrous synchronisation
~ sperm interact and need to get through mucus - Changes to sperm membrane structure and biochemistry during storage
Laproscopic AI - disadvantages
- Will by-pass the cervix
- Costly at approx. £20/ewe (AB Europe 1-10 ewes) cost reduced if more ewes
- Time consuming
- Requires technical ability
- Not considered welfare friendly = anaesthesia, put into cradal upside down, rumen push on lungs, vomiting, injected directly into uterine horn
- need to be upside down so rumen goes down and visualise uterus easily
- Can only be used in recognised sheep breeding schemes and performed by a veterinarian/technician
