40 Questions
What is a significant advantage of using artificial insemination (AI) in sheep production?
All of the above
What makes transcervical artificial insemination (TCAI) in sheep more challenging than in cattle?
The ovine cervix has a more complex anatomy
What is the purpose of the cervical rings in the ovine cervix?
To provide a physical barrier to external contamination
Where is the semen deposited in intracervical/transcervical AI?
At the entrance to the cervix
What is the role of the duck-billed speculum in the AI process?
To guide the insemination pipette
Why is the ewe's hindquarters elevated during the AI process?
To aid in the insemination process
How far into the cervical canal is the semen deposited in transcervical AI?
10-20 mm
How many ewes can a skilled operator inseminate per hour using the transcervical method?
100 ewes
When is the ram effect most effective?
Just before the start of the natural breeding season
What happens to ewes that are already cycling when introduced to the ram?
They do not respond
What percentage of ewes ovulate within a certain number of days of the ram introduction?
The majority
What is often followed by one or two short cycles?
The first oestrus
What can improve the efficiency of the ram effect?
Treatment with progesterone
What is the reason for the ram effect not being synchronised tightly enough for fixed time insemination?
The ram effect induces unpredictable short cycles
What is based on the use of progesterone or its analogues?
Progestagen-based methods
What do progestagen-based methods act on in cyclic females?
Pituitary release of gonadotrophins
What is melatonin considered to be in relation to the photoperiod?
The chemical trigger that allows the photoperiod to control hormone secretion
When is melatonin mainly produced by the pineal gland?
During the hours of darkness
What is the purpose of using exogenous melatonin in controlling the breeding season?
To advance the breeding season
How long must elevated blood concentrations of melatonin be maintained to advance the breeding season?
At least five weeks
What is the effect of melatonin treatment on ovulation rate?
It increases ovulation rate
What is often used in conjunction with slow-release melatonin implants?
The ram effect
What is the similarity between cattle and sheep regarding pregnancy recognition?
Progesterone levels during early luteal phase
In the Northern Hemisphere, when are melatonin implants typically used in adult ewes?
Around the summer solstice
What is the purpose of using melatonin implants in commercial Mediterranean flocks?
To advance the breeding season
What is affected by progesterone concentration during early luteal phase?
Embryonic and foetal survival
What was found by Dixon et al (2007) regarding pregnancy?
Lower progesterone levels on day 25 or 45 are predictive of pregnancy loss
What is the effect of immunisation against inhibin?
It increases the ovulation rate
What may affect early luteal function and contribute to lower pregnancy rates?
Timing of breeding in or out of season
What is the role of androstenedione in ovulation rate?
It has a regulatory effect on ovulation rate through its feedback action on the hypothalamic-pituitary axis
What did Mitchell et al (2002) find regarding the breeding season?
The breeding season does not affect the numbers of corpora lutea per ewe, nor the numbers of ova recovered
What is the possible consequence of seasonal shifts in LH secretion and/or follicular function?
Increased fertilisation failure
What is the importance of timing in vaccination for immunisation?
Ewes must be sexually active when the rams are introduced
What is the purpose of priming the ewe flock with progesterone sponges and PMSG?
To stimulate oestrus activity out-of-season
What is more probable to be associated with lower pregnancy rates in ewes bred outside the normal reproductive season?
Low ovulation rate and poor oocyte quality
What was found to be lower in October than in April by Mitchell et al (2002)?
The proportion of unfertilised/degenerate ova recovered
What is the expected fertilisation rate in ewes under natural mating conditions?
90%-95%
What is the effect of using biotechnical methods involving artificial insemination on fertilisation rates?
It decreases the fertilisation rate
What is a complication in interpreting the data on embryonic losses in sheep?
The ewe can often ovulate more than one oocyte
What is a limitation of the available data on embryonic losses in sheep?
Most studies have focused on early embryonic survival or perinatal mortality
Study Notes
Ovine Reproduction
- Artificial insemination (AI) brings benefits for sheep production, but its use in sheep differs from its use in cattle due to the ovine cervix's anatomy.
- The lumen of the ovine cervical canal is convoluted and tortuous, making transcervical artificial insemination (TCAI) challenging.
- TCAI involves depositing a small volume of diluted semen just inside the external os of the cervix, with the ewe's hindquarters elevated and the inseminator guiding the pipette into the cervix.
- This method is only effective at certain times of the year, usually just before the natural breeding season, and is not effective for ewes already cycling or in deep anoestrus.
Ram Effect
- The ram effect is a technique used to induce oestrus in ewes, but it does not synchronize oestrus and ovulation tightly enough to allow for fixed-time artificial insemination.
- The efficacy of the ram effect varies with factors such as breed, location, time of year, nutritional status, and age of the animals.
Progestagen-based Methods
- Progestagen-based methods use progesterone or its analogues to synchronize oestrus in ewes.
- The degree of synchronization and the interval between treatment and onset of oestrus depend on the product used.
- Progestagen-based methods suppress pre-ovulatory pituitary release of gonadotrophins, follicular development, and ovulation in cyclic females.
Melatonin
- Melatonin is a hormone produced by the pineal gland that triggers the photoperiod's control of hormone secretion by the pituitary gland.
- Exogenous melatonin can be used to control the timing of the breeding season.
- Melatonin implants are often used in conjunction with other environmental techniques, such as the ram effect, especially in extensively managed flocks that do not practice artificial insemination.
Immunisation Techniques
- Immunisation reduces the inhibitory effect of ovarian steroids or ovarian inhibin on the hypothalamus and pituitary, resulting in an increase in ovulation rate.
- Immunisation against inhibin has been tested experimentally, but this technique is not yet widely used.
Fertilisation Rate and Embryonic Losses in Sheep
- Fertilisation rates in sheep are typically 90%-95% under natural mating conditions, but lower with artificial insemination, especially with frozen semen.
- Embryonic losses in sheep are less well-studied than in cattle, but may be affected by luteal function and placentation.
This quiz covers the benefits and challenges of using artificial insemination in sheep breeding, including its impact on milk production, feed conversion, and growth rates.
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