Artificial Insemination - Anatomy & Physiology
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BACK TO REPRODUCTIVE SYSTEM
BACK TO REPRODUCTIVE TECHNOLOGIES
Introduction
Artificial insemination involves:
- Collection of semen from the male
- Preservation and extention of sperm
- Insemination of the female
All dairy cattle and a large proportion of beef cattle in the UK are bred by artificial insemination. It is also common practice in Turkeys, Pigs and Horses. Success rates are very dependent on good insemination technique, which can be carried out by an inseminator service or DIY. Generally, success rates are the same or better than natural survice.
Semen Evaluation
- Determine ejaculate volume.
- Estimate the percentage displaying progressive motility (linear motion) at 37◦C.
- Determine sperm concentration.
- Total sperm in ejaculate = ejaculate volume x sperm (ml)
- This determines how many insemination doses are possible from each ejaculate.
- >60% motile sperm = good quality
- <50% motile sperm = discard, especially if it is intended to be frozen
Seminal Extenders
- Extend the number of sperm in the original ejaculate.
- Extend the life of sperm.
- Must be isotonic
- Must minimize cold damage.
- The cell membrane of spermatozoon is sensitive to sudden drops in temperature 'cold shock'.
- Slow, controlled cooling of sperm is important because it minimizes stress on the cell membrane by lowering temperatures gradually.
- A low storage temperature reduces metabolism by about 50% for each 10◦C decline.
- Enables conservation of their fixed amount of metabolic energy.
- Must be a good buffer
- Typical buffers include Sodium Citrate and Sodium Phosphate.
- When the goal is to extend the semen for a sustained period of time (1 week-years) a cryoprotectant is required.
- Protects cells against the cold damage that would occur at 0-50◦C.
- Classified as cell-penetrating (glycerol, DMSO) and non-penetrating (milk protein, egg yolk lipoproteins).
- Glycerol is the dominant cryoprotectant for frozen sperm.
- Milk protein and egg yolk lipoproteins will also provide nutrients.
- Sperm have no anabolic capacity, so cannot synthesize materials for energy and repair.
- Vitality is totally dependent on the environment in which they are suspended.
- Nutrients need to be supplied to maintain metabolism.
- Major nutrients are fructose and glucose.
- Sperm can convert glucose to fructose and metabolize it to fuel motility.
- Semen contains microorganisms which can grow in the ideal environment provided by the extender.
- Antibiotics are normally added to prevent microbial growth.
- Include penicillin, liquamycin, linco-spectin and streptomycin.
Semen Preservation
- For short term use:
- Fresh liquid semen is used after seminal extension.
- In most species this can be cooled and stored at 5◦C for several days-1 week.
- In swine 17-18◦C is optimal.
- Widespread distribution and long-term use:
- Frozen semen
- Freezing and thawing compromises sperm viability in all species.
- Fertility drops much faster either side of ovulation with frozen semen, especially in the sow.
- Hence, artificial insemination with frozen semen is rare in the sow.
Insemination Methods
CATTLE
- Many doses from a single ejaculate.
- Inseminate 6 hours post-oestrus.
- Success rate is 70% from a single insemination (same as natural service)
- Farmers inseminate the herd themselves.
- A hand is used to grasp the cervix of the cow and a delivery pipette is inserted through the cervix into the uterine body which is felt with the index finger.
- Allows further advance of the semen than natural insemination would reach (anterior vagina).
- Only 2-8 million live sperm are required in the semen to achieve fertility in cattle.
SHEEP
- The ewe has a convex cervix with overlapping folds. Insemination is into the internal os of the cervix.
- 0.25 ml or less is delivered by pipette.
- 70-75% conception rate is achieved with fresh semen, but only 5-15% with frozen semen due to the site of delivery being so far from the site of fertilization.