9 Reproductive Physiology 2 Flashcards
How do we sperm sex
X bearing chromosomes have 4% more DNA and are heavier than Y bearing
Labeled with fluorochrome DNA stain (diff for X and Y)
Advantages of sexed semen
- producing replacement heifers
- flexibility in culling/sale decisions
- less dystocia
- profitable on genetically superior animals
- rapid genetic progress
Disadvantages of sexed semen
- cost
- lower conception rates
- more straws needed
- widespread use = surplus heifers
How does sex semen lower CR
Sorting process affect sperm viability/fertility
Fewer sperm packaged per straw
Further decrease in CR when used on multiparous animals
Rationale for embryo transfer
- faster propagation of superior donor females
- transfer to recipients of inferior genetic merit
- sexing of embryos
- freezing of embryos
Main advantages of embryo transfer
- rapid genetic improvement
- introduce genetics with virtually no health risks
- export and import bovine genetics
Number of OVA/embryos collected from dairy in Canada? tranferable ones?
51,317 (10.6 per flush)
28,696 (5.9 pf)
Steps involved in ET
- superovulation of donor cow
- AI of donor cow
- flushing for embryo collection
- transfer to synchronized recipient
What to expect when doing MOET
Multiple ovulation embryo transfer
- poor or no response to FSH
- extreme response in some cases
- range of 0 to 45 embryos
- on average 6 transferable embryos per donor
What is ovum pick up
Transfer of oocytes instead of embryos
In vitro fertilization, culture then embryos are transferred or frozen
Ovum pick up AKA
Transvaginal oocyte collection
Pros of OPU (5)
- simple and quick
- weekly collections possible
- 12 to 20 oocytes per OPU, 4 to 6 transferable embryos/animal
- minimal risk to health and fertility of donor
- commercial service available
Advantages of OPU
- oocytes may be harvested in pre-pubertal heifers, post-pubertal cows, even during pregnancy
- used on donors who do not respond to super ovulation
- ovaries can be recovered at slaughter for IVF (ovary brought back to lab and oocytes collected)
How could you combine genomic selection and reproductive technologies in heifers to achieve rapid genetic gain
Genotype either all heifers or only top and bottom heifers
Use top 5% for OPU/IVF/ET
Next 20% used for AI using sexed semen
Bottom 5% beef semen or cull
20% after those used as embryo recipients
Slide 31***
Problems with measuring calving interval
- biased bc accounts for only a portion of the herd (1st lactation cows excluded, cows failed to conceive second time around not included)
