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
When removing a Chronogest sponge, what can it be combined with to stimulate cyclicity out of season?
PMSG (FSH activity) injections
Describe the hormonal activity in a ewe following Chronogest sponge removal and PMSG injections
Oestrus 36-72 hours after sponge removal
Ram : 10 ewe ratio (1:5 out of season)
Ram in 48 hours after sponge out (not earlier)
Lamb in 3 week period, most in 7 days
Name the progesterone device licenced in the UK?
CIDR-ovis
intra-uterine device
How can prostaglandins be used in hormonal manipulation of seasonality?
Cause luteolysis and induce oestrus in cycling animals
On farm, describe the use of prostaglandins
- Not authorised but half the cattle dose of dinoprost or cloprostenol have been used
- CL refractory to PG for 2-4 days
- Oestrus in @ 40 hours
- 2 PG injections 7-11 days apart induce 95% of ewes in 72 hours
Describe how drugs can be used to induce lambing
Dexamethasone injection (Dexafort) from day 140 after ram in
Lambing 40 +/- 7 hours later
Not authorised
Describe some pre-breeding management steps that may occur on farm
- Cull out unproductive ewes. (health / infertility / age).
- Introduce replacement ewes or ewe lambs (19 or 7 months old).
- Check condition score (CS) and separate thin animals for additional feeding
- Check rams and ensure CS 3.5 before breeding
What is the optimal BCS at mating for ewes?
3 - 3.5
What is the gestation length of a ewe?
145 days
What is the gestation length of a ewe?
145 days
How should you feed ewes from conception to day 42?
Maintenance only - grass +/- forage
How should you feed ewes from day 42-90?
Maintenance + 2mj/day
Why should feeding be slightly increased between day 42 and 90?
Considerable placental development during this period – significant restriction of nutrient intake will retard placental (and therefore foetal) growth.
Why is ultrasound used during pregnancy?
Identifies barren ewes and allows those carrying single, twin or multiple lambs to be managed accordingly in the run up to lambing
Describe the features of ultrasound scanning ewes
- Vital management tool
- Non-vet
- External on abdomen
- 70 - 120 days from ram in or 28 days from ram out
- Count lambs and spray mark
Why is good nutrition needed from day 90-parturition in sheep?
- Rapid foetal growth
- Colostrum quality and quantity (mammary development).
- Prevention of metabolic diseases.
Describe a metabolic disease associated with underfeeding ewes from day 90 in pregnancy
Pregnancy toxaemia (twin lamb disease).
Ewes in negative energy balance – usually carrying multiple lambs
Signs: Listless, poor appetite, recumbency, death.
How should you feed ewes from day 90 of pregnancy?
2 X maintenance
- Single foetus: Barley straw and some concentrates will suffice
- Multiple lambs: concentrates and good quality hay is preferred to silage
Describe the features of a pre-breeding ram examination
- Physical exam: feet, brisket, caseous lymphadenitis
- Scrotal measurement (30cm) and examination (firm and even)
- Exteriorise and examine penis & vermiform appendage
- Semen exam
- Libido testing
- Serving capacity test – how many serves in a set time
Name 3 bacterial causes of epididymitis in rams in the UK
- Actinobacillus seminis
- Haemophilus somnus
- Histophilus ovis
What are some risk factors for epididymitis?
Intensive reared, trough fed rams = more time lying
How can epididymitis be treated/prevented?
- Treatment unsuccessful
- Prevent by growing rams in small groups, graze and rotate to clean paddocks
Describe an inguinal hernia in rams
Bowel passes through an enlarged inguinal canal
Usually unilateral
Describe an inguinal hernia in rams
Bowel passes through an enlarged inguinal canal
Usually unilateral
A cryptorchid ram is known as?
A rig
What is cryporchidism?
Uni- or bilateral failure of testis to descend
Can rigs still be used for mating?
Likely reduced fertility if unilateral - do not put with too many ewes
What are the risk factors for testicular degeneration?
Inflammation
Extreme fatness
High environmental temperature
Transport / stress = Showing and sales
How does testicular degeneration impact use as a mating ram?
Small soft testes likely to produce poor and low number of sperm.
May just have poor fertility in first year if ram newly bought
- If OK then return to soundness in 3 months as new sperm develop
What is the cause of scrotal mange?
Chorioptes bovis - sheep adapted strain
What are the impacts of scrotal mange?
- Crusty scabs on lower 1/3 of scrotum
- Crake and expose sore, weeping dermis
- If extensive then raises blood flow and testes temperature => testicular degeneration and reduced sperm quality
How can scrotal mange be diagnosed?
Confirm by skin scraping from several locations as low numbers of mites
How can sheep scrotal mange be treated?
Doramectin effective but not Ivermectin (longer action)
Diazinon sheep dip effective
What is Balanoposthitis?
Inflammation that affects both the glans penis and prepuce
Balanoposthitis is also known as?
Pizzle rot
How does pizzle rot present?
Range from small ulcers and discharge at prepuce to scabbing causing blockage of the prepuce and also fly strike on the effected area
What is the agent that causes pizzle rot?
Corynebacterium renale
Name two risk factors for pizzle rot
High protein concentrates
Lush grass
