Sheep reproduction

What type of breeders are sheep?

Short day breeders

• Breeding season= Aug-Dec

• Lambing season = Dec-May

What is this graph showing?

• Cattle= not seasonal

• Horse= long day breeders

• Sheep short day breeders

Why is seasonal breeding advantageous to the animal?

• Inc temp, graze availability and graze quality in summer

What hormone controls the seasonality of breeding in sheep?

• Melatonin (blocked by light production)

• Reducing pulse frequency of GnRH and blocks cycles

How does the response to melatonin change in a horse compared to a sheep?

How do follicular waves differ in cows compared to sheep?

• More variation in number of waves

• More waves and quicker growth in shorter period of time

• More twin ovulation

Result of this is that it is harder to manipulate and more difficult to predict

How often are the ewes receptive to the ram in the breeding season?

Every 16-18 days

• Will go and seek the ram

How long should the ram be left in with the ewes in breeding season?

At least 35 days

• Allows the ewes which did not conceive when first mater to be bred again at subsequent heat

What are the purposes of raddling ram to mark mated ewes

• Allows ID of infertile rams and ewes

• Allows lambing schedule to be predicted more accurately

What is a normal ewe to ram ratio?

1:30

But very variable with breed and lots of factors to consider

How is artificial insemination usually performed in sheep in the UK?

Laparoscopy due to cervix

• So usually pedigree or performance testing flocks only

List some of the ways repro can be modified in sheep?

• Genetics - breed

• Ram effect

• Day length

• Nutrition - flushing

• Ram and day length

• Melatonin

• Melatonin and genetics

• Nutrition and Day length

• Pharmacological – control of ovulation rate and time

What molecule determines fecundity in sheep?

• Bone Morphometric Protein signalling in OVARY

  • Determines number of follicles that go onto ovulate

What is the 'ram effect'?

• Rams can induce cyclicity in the ewe earlier in season

  • Intro of novel male or after 2+ weeks of male absence

• Can synchronise cycling to some extent

• Fertility improvement

When do ewes ovulate if using a ram introduce to induce cyclicity

• 1st ovulation for some- silent for some and then ovulate again at 25 days (red)

• 19 days (other have 1st ovulation) (green)

Explain the practical aspect of using the ram effect?

• Either vasectomised teaser animals

• Or introduce fertile rams into field in high pen or trailer

When rams are used for synchronisation over how long will the ewes be lambing usually?

Most of lambing within 15 days

How can you manipulate seasonality in sheep?

• Need to shorten day (hard to keep out light)

  • But if you give a light earlier in seasons constantly they switch off responding to light earlier

• This isn't particularly viable currently option is choose less seasonal breed of sheep

How can you give melatonin to ewes?

Regulin- implant by ear

When would you give melatonin to sheep in order to control breeding?

• Less seasonal breed from mid May to June

• More seasonal mule and halfbred flocks from early June to late July

Day 1- remove ram completely, Day 7-implant melatonin Day 42- introduce rams

What are the two windows for nutritional flushing?

Short term- 3-7 days

• Improving current follicle

Long term- 6 to 8 week

• Improving number of follicles from primordial pool

What is this showing?

• Higher plane of nutrition causing a longer cycle in ewes

Explain how you synchronise sheeps with hormones?

• Chronogest (progesterone sponge)

  • Gives them a luteal phase so 'pauses' cycling

  • Leave them intra-vaginal for 12-14 days to get into blood stream

• Combing with PMSG/ecG (FSH) injection at time of sponge removal to stimulate cyclicity out of season

• Oestrus 36-72 hours after sponge removal

• Will lamb in 3 week period, most in 7 days

What ram to ewe ratio would you use if you have sponged your lamb? When should you introduce ram?

• 1 Ram : 10 ewe ratio

• 48 hours after sponge to avoid overmating of sheep that have come in earlier

What is this?

CIDR

• 12 days and then eCG removal

• Alternative to sponging

What hormone can you use to cause luteolysis and induce cycling in sheep?

Prostanglandin

• Not licensed but can use half the cattle dose

• Can use when removing sponges or by itself if you want a shorter period of time

• CL refractory to PG for 2-4 days, oestrus at 40 hrs

• Or 2PG injection 7-11 days apart

What can you use to induce lambing if service date known?

• 8ml dexamathasone injection from day 140 after ram

• Lambing 40 +/- 7 hours later

• Not authorised by can use under cascade

What steps should you take pre breeding to ensure better fertility?

• Cull out unproductive ewes

• Introduce replacement ewes or ewe lambs

• Check condition score and separate thing animals for additional feeding

• Check rams and ensure BCS 3.5 before breeding

  • Allow 60 days of no interventions bc sperm takes that long to develop

How much feed should you be giving the ewe at different stages of gestation?

• 0-42 days: maintenance only (grass +/- forage)

• 42-90 days: maintenance + 2MJ/ day (grass +/- forage)

• Day 90+: separate single, twins or multiples and feed accordingly

Food provision should be at 2x maintenance by lambing time

When do you scan ewes for identifying number of foetuses?

• 70-120 days from ram in

• 28 days from ram out

What nutrition is preferred for ewes with single foetus vs multiple lambs

• Ewe with single foetus: Barley straw and some concentrates will suffice.

• Ewes with multiple lambs: concentrates and good quality hay is preferred to silage

What should you do once a vasectomy is performed

• Store vas deferens when removed (send to lab is gold standard)

• Identify animal

What should you examine in a ram before breeding?

• Physical exam: feet, brisket CLA

• Scrotal measurement: 30cm

• Scrotal palpation: firm and even

• Exteriorise and examine penis and vermiform appendage

• Semen exam

• Libido test- mounting ability with ewes in oestrus

• Mating dexterity- intromission

• Serving capacity testing- how many serves in a set time

What is this?

Electroejaculator

How can you idnetify epididymitis?

Palpable in scrotum and ultrasound

What agents cause epididymitis?

• In UK – Actinobacillus seminis, Haemophilus somnus, Histophilus ovis

• Other Countries – Brucella ovis

What can cause epididymitis?

• From UTI

• Intensive reared can cause spread through group

What problems can you get with rams related to fertility?

• Epididymitis

• Inguinal hernia

• Cryptorichidism (Rig)

• Testicular degeneration or hypoplasia

• Scrotal mange

• Balanoposthitis

How does testicular degeneration present?

• Bilateral unless specific injury.

• Soft small testes, likely to produce poor and low n° of sperm

• Due to inflammation, Extreme fatness, High environmental temperature, transport / stress = Showing and sales

• Poor fertility in first year if ram newly bought

• If OK then return to soundness in 3 months as new sperm develop

How does scrotal mange present in rams?

• Crusty scabs on lower 1/3 of scrotum

• Crake and expose sore, weeping dermis

• Sore as get “gratification reflex” when handled

• Can occur on lower legs and poll of head

• If extensive then raises blood flow and testes temperature => testicular degeneration and reduced sperm quality (proven experimentally)

How is scrotal mange confirmed and treated?

• Skin scape confirms

• Doramectin effective, Ivermectin NOT

• Diazinon sheep dip effective

What are the signs of balanoposthitis?

• From small ulcers and discharge at prepuce to scabbing causing blockage of the prepuce and also fly strike on the effected area

• Produces ammonia from urea in urine

What are the risk factors for balanposthitis?

High protein concentrates and lush grass a risk factor

How is balanoposthitis treated?

• Access to water, salt or ammonium chloride to increase drinking and acidify urine

• Isolate animals to reduce environmental contamination

• Clip wool away and clean area

• Systemic antibiotics +/- fly treatment

What agent causes balanoposthitis?

• Corynebacterium renale, also associated with orf