Sheep reproduction 1 + 2 Flashcards
What type of breeders are sheep?
Short day breeders
When is the breeding season for sheep?
August - December
When is the lambing season for sheep?
December - May
Describe how the brain controls seasonality in sheep
- In spring melatonin production is decreased as light increases: light blocks melatonin production
- Light comes into the eye – travels through the optic nerve to the hypothalamus and superior cervical ganglion -> pineal gland – controls melatonin
Describe how melatonin is involved in sheep being short day breeders
Sheep are short day breeders so light -> less melatonin release -> no cycles
In comparison: Horses are long day breeders so light -> less melatonin releases -> cycles
Name some hormones involved in the control of seasonality
Oestrogen
Dopamine
Thyroid hormone
Melatonin
When is melatonin secreted?
During the hours of darkness
How many follicular waves do sheep have in a cycle?
2- 5 waves but 50% have 4 waves and 35% have 3 waves
How long is a sheeps cycle?
16 days
Describe how low progesterone affects the cycle
When progesterone is low you get more frequent, less intense LH peaks which drives follicular growth
Describe how high progesterone affects the cycle
When progesterone is high you get less frequent more intense LH waves.
How is ovulation induced?
Progesterone levels fall and the dominant follicle grows -> LH surge
Describe the process of breeding using natural service
- Ewes ovulate and are receptive to the ram every 16 - 18 days during the breeding season.
- Rams should remain with the ewes (1 ram / ~30 ewes) for at least 35 days
- This allows ewes which did not conceive when first mated to be bred again at the subsequent heat
Why is it important to have marking devices on rams when using natural service?
Allows identification of infertile rams and ewes.
Allows lambing schedule to be predicted accurately.
Artificial insemination is used by which flocks?
Pedigree or performance testing flocks only.
How is AI carried out in sheep, why?
Commercially by laparoscopy due to cervix.
List some features of reproduction that can be modified in sheep
- Genetics
- Ram effect
- Day length
- Nutrition
- Day length in a bottle (melatonin)
What is the key indicator on farm for breed/fecundity?
Number of lambs sold per ewe
What is the ‘ram effect’?
Introduction of a novel male or after 2+ weeks of male absence
Pheromones of the ram stimulate the reproductive hormones of the ewes
Why would farms want to use the ‘ram effect’?
- Induce cyclicity earlier in the season
- Can synchronise cycling sheep too some extent
Why are teaser males used?
To synchronise and advance group for breeding males to be introduced
How can you use melatonin to manipulate seasonality - describe the schedule used?
Regulin = implant in the ear
- Day 1 (30 weeks before want to lamb) move ewes from sight, sound and smell of ram
- Day 7: Implant ewes at the base of the ear;
- Day 42 (30-40 days after implantation) introduce rams
- Delay of 14-21 days before mating, peaking at 25-35 days
What is flushing?
The practice of increasing nutrient intake and body condition prior to and during breeding
Describe how flushing can manipulate seasonality?
- Short-term 3–7 days (need synchronisation?)
- Longer term 6 to 8 week
- “Static effect” = Ewes in better BCS have higher ovulation rate
- “Dynamic effect” = Increasing live weight gain gives higher ovulation rate
Describe how Chronogest is used as a hormonal synchronisation method?
- Synthetic progesterone in a sponge
- Intra-vaginal for 12-14d to get into blood stream
