Investigating poor fertility in sheep flocks Flashcards
What are some consequences of poor reproduction in sheep flocks?
Low lambing/marking % = less saleable meat lambs
Disruption of flock structure (in self-replacing flocks) → old flocks
- High disease risk
- High culling %
- Introduction of external sheep = costly/intro of dz
Table of reproductive stages where losses may occur
What are some causes of losses in sheep occuring at joining?
How do each of these present clinically?
How would they be detected?
Sheep in anoestrus
- Signs: low conception rate, protracted lambing
- Dx: ram harnesses (mark ewes when mounted)
Low OV rate
- Signs: low twin/triplet %, low lambing rate
- Dx: indetectable bar above parameters
What are the 5 major factors which determine whether a ewe will be in anoestrus at joining?
Age - too young/too old
BCS/nutrition
- low growth rate in maidens → delayed puberty
- critical mating weight, below which ewes in anoestrus
Season - short-day breeders (TF anoestrus in summer)
Stressors - mgt (e.g. shearing during joining)
Toxins - e.g. lucerne/white clover
What is the relationship b/w onset of puberty & the oestrous cycle?
Onset of puberty in ewes = 6-15mo old
- Hoggets which grow faster before puberty experience an earlier onset of puberty (TF higher lambing % observed)
What is the ideal BCS for a ewe at joining & lambing?
What is the consequence on reproduction for being above & below this score?
Ideal BCS = 3 (balance b/w fat enough for good OV rate but avoids requirement for lots of supplementary feed/high cost)
- BCS > 3 → increased # lambs but more prone to dystocia/preg tox/lameness
- BCS < 3 → lower OV rate + potential acyclcity if below CMW
What is the OV rate?
What factor has the biggest influence on OV rate & how?
OV rate = # follicles ovulated by a ewe in a single cycle
Strong correlation w b.w./BCS
- Absolute value (rather than change in BCS during pregnancy - “flushing”) biggest driver of BCS
What possible factors with the rams may cause failure of insemination of ewes at joining (5)?
Poor ram libido
Balanoposthitics (knob rot)
MSK problems/lameness
Poor nutrition/BCS
Testicular abnormalities/disease
What are the 5 T’s of a ram breeding soundness exam (BSE)?
How do these factors influence ram fertility?
Teeth = adequate grazing/nutritional status
Torso = BCS (3.5-4) as joining is hard work!
Toes = MSK soundness/lameness/mobility affect mounting behaviour + ability to graze
Tossle = check for factors which prevent normal function (pizzle rot, scarring, etc.)
Testes = circumference + no abnormalities on palpation (as influences sperm output/viability)
What is the normal ratio for rams:ewes in a natural mating flock?
1% + 1 fit/healthy rams
E.g. 2 rams:100 ewes
When should a BSE on rams be conducted (relative to joining)?
6 wks prior
What are some issues with a ram’s testicles which could cause poor insemination rates at joining?
Poor sperm output - small testes, too few rams
Poor semen quality - heat (dt dz/env T), orchitis
What infectious diseases may cause infertility in rams in Australia?
Ovine Brucellosis (B. ovis)
Actinobacillosis (A. seminis)
Ovine Brucellosis:
- Location & character of inflammation
- Tm
- Clinical signs in rams
- Clinical signs in ewes
- Epididymitis (spermatic granulomas) + orchitis
- Tm = STI
- mechanical b/w rams via mating the same ewe
- direct via homosexual activity
- Rams = enlarged inflamed testicles/epididymis, fever, scrotal oedema → testicular atrophy
- Ewes = no clinical signs
Dx of ovine brucellosis
Mgt of ovine brucellosis
Dx:
- testicular palpation (epididymal tail granulomas)
- serology (CFT/ELISA of paired sera)
Mgt options (no tx available):
- Small flocks = cull all rams & replace from an accredited flock
- Large flocks = test & slaughter
- positive test = spermatic granuloma OR seropositive
What flock-level signs indicate a potential problem with ovine brucellosis?
Low marking %
Delayed/protracted lambing
Testicular abnormalities found on ram BSE
What are some causes of failure of fertilisation of a ewe with + w/o return to service?
With return to service:
- Oestrogenic clover disease
- Young ewes
Without return to service: interruption of oestrous cycle
- seasonal anoestrus
- shearing/stress during joining/pregnancy
- nutritional stress
What is clover disease?
What clinical signs?
What clinical forms (& in what sheep classes)?
Clover disease = ingestion of oestrogenic clovers → uterine changes (more mucus) impede sperm transport to ovum
- Signs = more old/dry ewes, increased teat length, precocious lactation, enlarged/swollen genitals
-
Forms:
- Temporary clover dz (young ewes) = return of infertility after removal from pasture
- Permanent clover dz (old ewes) = permanent infertility dt cystic glandular hyperplasia
Dx + Mgt of clover disease in ewes
Dx = clinical signs + histolopath of uterus/cervix
Mgt:
- avoid risk pastures near joining
- cast for age at younger age
- graze cattle/wethers (as unaffected)
- decrease stocking rate (allows grass growth)
- pasture renovation
How does EEL present in a flock of ewes?
Looks like failure of fertilisation/return to service
Causes of abortion in ewes
Over-/under nutrition post-mating (EEL)
Heat stress (EEL)
Se deficiency (EEL)
Onion grass toxicity (EEL)
Pestivirus (Border dz)
Listeriosis (>3mo gestation)
Toxoplasmosis (>3mo gestation)
Campylobacteriosis (>3mo gestation)
Summary table of infectious abortion in ewes
- Agents
- Zoonotic?
- Route of infection
- Epidemiology
- Lesions
- Dx
Tx + prevention of:
- Campylobacteriosis
- Toxoplasmosis
- Listeriosis
Campylobacteriosis:
- Tx = oxytet + isolate cases
- Prevention = vax, expose pre-joining (natural immunity)
Toxoplasmosis:
- Tx = oxytet
- Prevention = vax, minimise contact w cats/feral cat access to pasture, coccidiostats during pregnancy
Listeriosis:
- Tx = penicillin/oxytet
- Prevention = manage feed sources (silage)
