Small Ruminants: Sheep Reproduction Flashcards
What does it mean that sheep are ‘short day breeders’
Sheeps breeding season (conception) is from August- December when day length is shortest
Lambing season: December to May
Describe how seasonality works
- Light comes into the eye (dependent on photoperiod)
- Optic nerve to the hypothalamus to the super-cervical ganglion
- To the pineal gland- the pineal gland either does or doesn’t produce melatonin
- Light supresses melatonin
- Increased melatonin in sheep from short days increases GnRH pulses
What controls seasonality?
- Oestrogen negative feedback
- Dopamine
- Thyroid hormone
- How long do cycles last in sheep during the breeding season?
- How many follicle waves do they have?
- 16-18 days
- 2-5 waves 50% have 4
How long should rams remain with ewes?
At least 35 days
Allows ewes which did not convieve when first mated to be bred again
How can you identify a ram has mated a ewe?
Rams can be raddled to mark mated ewes
Allows accurate lambing
Allows accurate lambing
Allows identification of infertile rams and ewe and accurate lambing
How many ewes are needed per ram?
Recommended 1 ram for 30 ewes
Some farmers say 1 ram for 120 ewes
How is AI done in sheep?
Laparoscopically due to cervix
Pedigree or performance testing flocks only
How can reproduction be modified in sheep?
- Genetics
- Ram effect
- Day length
- Nutrition
- Ram and day length
- Day length in a bottle (melatonin)
- Melatonin and genetics
- Nutrition and day length
- Pharmacological
How can breed and fecundity (genetics) modify reproduction in sheep?
- Ideal numbers of lambs varies on farm- hill ewe 1 lamb
- Number of lambs sold per ewe is key indicator
- Many breeds/strains developed with higher fecundity
- Genomic selection now identified- Bone morphometric protein signalling in ovary to determine follicle number
Examples:
FecB mutation of BMP receptor 1 in booroola sheep
Fecx1 mutations of BMP 15 in inverdale sheep
FecXg BMP 15 in belcare- 9 lambs or one
What is the ram effect?
- Introduction of ‘novel’ male or after 2 weeks+ of male absence
- Induce cyclicity earlier in the season
- Can synchronise cycling sheep too some extent
Teaser animal can be used to synchronise and advance group for entire
What are the 2 peaks of oestrus activity after ‘ram effect’?
- 1st ovulation silent
- 19 days- non-silent oestrus
- 25 days- second oestrus
Some have 1st ovulation on 19 and 2nd on 25
What is the average sheep gestation?
145 days
Varies with breeds
What happens to cyclicity and fertility after ram introduction after start of short days?
- % of cycling increase
- % fertile matings increase
How can seasonality be manipulated with light?
- Exposing to articifically shortened or lengthened days
- Animals become refractory to continuous signal
- End when become refractory to long days
- Can just treat males and then use the ‘ram effect’ to induce ewes
How can seasonality be manipulated with melatonin?
Give melatonin- regulin (ear implant)
* Breed affects time of usage
* Day 1 move ewes from sight, sound and smell of ram
* Day 7- implant ewes
* Day 42- introduce rams
* Delay of 14-21 days before mating allowing for cycle
* Use vasectomised rams for first 14 days for more compact lambing period
What is flushing?
Altering nutrition to assist in conception
Static effect- ewes in better BCS have higher ovulation rate
Dynamic effect- increasing live weight gain gives higher ovulation rate
Increased more in lower BCS scores
Can give higher quality pasture/silage for week before
Describe hormonal synchronisation with sponges in sheep
- Chronogest- synthetic progesterone in a sponge
- Intravaginal for 12-14 days to get into blood stream
- Combine with PMSG (gonadotrophin- FSH) at removal to stimulate cyclicity out of season
- Oestrus 36-72 hours after sponge removal
- 1:10 ram:ewe, 1:5 out of season
- Rams in 48 hours after sponges out
- Lamb in 3 week period- most 7 days
Sponges get stuck, progesterone immune supressent- vaginitis
How can prostoglandins be used for synchronisation in sheep?
- Use prostoglandin to cause luteolysis and induce oestrus in cycling animals
- Not authorised but half cattle dose has been used
- Oestrus in 40 hours
- can do 2 PG 7-11 days apart to induce 95% in 72 hours
How and when can you induce lambing?
8ml dexamethasone (Dexafort) from day 140 after ram in
Lambing 40±7 hours later
Only if service date known
What should be done and checked with sheep pre-breeding?
- Cull out unproductive ewes- health, infertility, age
- Introduce replacement ewes or ewe lambs
- Check condition score and separate thin animals for additonal feeding- 3.5 optimal
- Check rams and ensure 3.5 BCS
How should ewes be fed for the following periods:
1. Conception to 42 days
2. 42- 90 days
3. 90- parturition
- Maintenance only (grass+/forage)
- Feed for maintenance + 2 MJ/day
- Good nutrition- 2x maintanence by lambing time- appetite reduced
Why in days 42-90 days of pregnancy in sheep is nutrition very important?
- Considerable placental development during this period
- If restriction of nutrient intake will retard placental growth
- And therefore foetal growth
When can sheep be scanned?
- 70-120 days ram in
- 28 ram out
Count and spray
What is done for a ram pre-breeding examination?
- Physical examination- feet, brisket, caseous lympadenitis
- Scrotal measurement- 30cm
- Scrotal palpaiton- firm and even
- Exteriorise and examine penis and vermiform appendage
- Semen evaluation
- Libido testing- mounting ability with ewes in oestrus
- Mating dexterity- intromission
- Serving capacity test- how many serves in a set time
- Why is epididymitis a problem?
- How can it be diagnosed?
- What agents can cause it
- Sperm storage
- Palpable in scrotum and ultrasound
- Actinobacillus seminis, Haemophilus somnus, Histophilus ovis
What is an inguinal hernia?
Bowel passes through enlarged inguinal canal
What is a Rig ram?
Cryptorchidism
What is the problem with cryptorchidism?
- Testes need lower temperature for sperm to develop
- Likely reduced fertility
What determines wether a ram has testicular degeneration or hypoplasia?
Fertility history or previous examination
Degeneration if previous fertility success
Would you pass a ram without a vermiform appendage?
No
* Why has it not got one?
* Likely urolithiasis and removed
* May still have stones
Would you pass a ram without a vermiform appendage?
No
* Why has it not got one?
* Likely urolithiasis and removed
* May still have stones
What can cause degeneration or hypoplasia?
Degeneration
* Small soft testes- produce low number of sperm
* Inflammation, extreme fatness, high environment temp
* Transport/stress
* Poor fertility in first year
Hypoplasia
* uni or bilateral- cryptochidism, hereditary
- What causes scrotal mange?
- Why can it be problematic?
- How is it diagnosed and treated?
- Chorioptes bovis- crusty scabs
- If extensive then raises blood flow and testes temperature- degeneration
- Confirm by skin scrapes, doramectin- diazinon sheep dip
What is pizzle rot?
(balanoposthitis)
How is it treated?
Penis infection
Rams and wethers
* Range from small ulcers and discharge to blockage
* Fly strike
* Corynebacterium renale, also associated with orf
* Produced ammonia from urea in unine
* High protein concentrated and lush grass risk factor
* Castration affects development of area so urinate inside prepuce
- Tx- access to water, salt or ammonium chloride to acidify urine, isolate and clip wool
- treat fly strike
