W10L2 Tues manipulating domestic animal reproduction 2 Flashcards
Why do we what to decrease fertility of animals?
– Suppression of behaviour (e.g. male aggression)
– Management and stop in-breeding
– Improved growth rates, taste (Boar-taint) * Androstenone and Skatole in fat
How to decrease fertility
– Desexed e.g. castration
– Vaccination- GnRH, GDF-9/ BMP-15
– Immunocastration * GnRH agonists (Deslorelin)
Superovulation
- Genetically superior females undergo multiple ovulation + embryo transfer (MOET) so that they can sire multiple offspinrg, heard improvement
- Synchronisation of donor + recipient female cycles (PGF2a + CIDR)
§ Donor: FSH injections for 4 days to recruit more follicles, GnRH/hCG to trigger ovulation (8-10 ovulations induced producing ~5 transferable embryos), AI then embryo recovery + transfer on day 7
Non-surgical collection of cattle embryos
catheter inserted into utherus + bulb seals behind cervix
→ flushing fluid into uterus
→ release bulb
→ manually squeeze fluid out
→ recover embryos in fluid
step in superovulation and embryo transfer
: superovulation of donor with FSH → artificial insemination (5 days after initiating superovulation) → non-surgical recovery of embryos (6-8 days after mating) with Foley catheter → isolate/classify embryos → storage/ transfer
transfer surgically or non-surgically → pregnancy diagnosis 1-3 months after transfer based on behavior→ birth 9 months
Animal IVF history
- AI first in 1784 in dogs, ET/IVF/IVM in 1890s,
-sex selection via sperm in 1980s
Human IVF
§ Basic IVF in 1967, IVM in 1983, ICSI in 1992, sex selection 1990s (biopsy)
Artificial Reproduction: 2 procedure of Cloning
- Two procedures
1. Embryo splitting or cloning - Multiple copies of OFFSPRING
2. Somatic Cell Nuclear Transfer (SCNT) - Multiple copies of an INDIVIDUAL
Embryo Cloning by splitting
- Embryo splitting → 2 (or more) genetic clones
- Maximises offspring from high genetic value embryos
Ø Donor embryo flushed from uterus (4-5 days after mating) + zona pellucida removed + obtain separate blastomere cells
→ oocyte from other cow + remove zona pellucida/polar body/nucleus = cytoplasm only
→ electrofusion of cytoplasm + blastomere = new embryo
Cloning efficiency of embryo cloning
fertilised egg 34%, two-cell 28%, 4-cell 21%, 8-cell 5%, morula 0%
§ Blastomeres 25%, ESC 10% (loss of totipotency), somatic SCs/differentiated cells 0% (loss of pluripotency)
Somatic cell nuclear transfer (SCNF)
Ø Donor somatic cell from injected into enucleated oocyte → electrofusion → embryo activation → in vitro culture → day 7 blastocyst stage embryo transfer
Ø Requires ‘reprogramming’ of donor cell nucleus back to totipotency
Efficientcy of Somatic cell nuclear transfer (SCNF)
-Very low efficiency, for dolly 1 in 277
-need starvation to return it to F0 phase
-low survival rate of SCNF embryo vs conventional embryo
Why do we clone if it is so inefficient
-Multiplying valuable breeding animals
-Resurrection for breeding (castrated or dead animal)
-Conservation of endangered breeds
Health and wellbeing of clone
- Bovine somatic cell nuclear transfer (NT) is associated with an increased incidence of abnormal placental and fetal development.
- About 10% of transferred NT embryos result in a live calf and only 67% of these survive to weaning at 3 months of age.
- Health problems are commonly reported with neonatal NT calves.
- NT calves that survive to weaning can appear healthy until exposed to external stressors or when examined at post- mortem.
- Lack of data on clone health – Public issue, USFDA risk assessment.
Phenotype Assessments
- Birth to maturity (3 years)
- Response to fasting
- Response to hormonal challenges
