Sheep Reproduction Flashcards
What kind of breeders are sheep?
Short day breeders - seasonally polyestrus
in northern hemisphere = Oct - Feb
During short days, are melatonin levels higher or lower? and what does this mean with regards to cycle?
Higher melatonin
= decreased sensitivity to E2 negative feedback
What is “silent ovulation” and when does it occur?
First ovulation after lambing (in transition period) - ewes are not fertile. Won’t get a full 17 day cycle with this one
“silent” because no progesterone priming to induce estrus behavior beforehand
how long is the ewe estrus cycle?
16-17 days
7 signs of estrus
1) increased movement and vocalization
2) mounting or standing to be mounted
3) tail wagging
4) swelling and hyperemia of vulva
5) male pawing at flanks
6) decreased appetite
7) decreased milk yield (late lactation)
What is the duration of estrus?
24-36 hours
How long is gestation?
147-149 days
depends on breed
at way day during gestation does the CL respond to PGF2a?
28-56d
What day does the placenta take over from CL producing P4?
~day 50
At below what day of gestation can you abort?
anytime below ~ day 60 (after that it will be much harder to abort)
Define “lambing %”
(# lambs born / # ewes put to tup) x100
Define “rearing %”
(# lambs reared / # ewes put to tup) x100
Name 4 reasons for reproductive failure
Low ovulation rate
Low conception rate
High abortion rate
High perinatal losses
What are 5 causes for low ovulation rate?
NUTRITION age season stress/weather genetics
6 reasons for low conception/pregnancy rate
RAMS nutrition season stress/weather genetics disease
7 reasons for high perinatal losses
Poor COLOSTRUM intake, disease, preg tox, bad supervision, mis-mothering, weather, predation
What are the 4 “T”s of checking a ram/tup before mating?
Teeth
Toes
Tone (BCS - 3.5-4)
Testicles (large, firm)
What day can you use ultrasound for diagnosis of pregnancy? (and when is the optimal time?)
From day 35 to 50 onwards
optimal time is 60-90 days
What is an average ram:ewe ratio?
1:40 ?? is that right?
BCS ewe @ tupping (hill, upland, lowland)
hill = 2.5 upland = 3 lowland = 3.5
What things must you do to ensure good nutrition management of ewes in preparation for mating?
Check BCS and modify (takes up to 2 months to change 1 BCS)
“flush” (increase plane of nutrition) for at least 1 cycle
avoid flushing on possible estrogenic pastures
Careful if grazing brassicas
How often should you change a crayon on harness things to detect returns to estrus?
every 2 weeks
From what day can you use Ballottement for pregnancy diagnosis?
day 100
What are 4 ways to advance the ewe breeding season?
The ram effect
Melatonin
Progestagen priming
Lighting
Describe the ram effect.
Introduce ram/teaser to anestrus females (previously isolated from males - large farms/ranges better)
- almost immediate increase in LH pulse and amplitude
- get a silent ovulation 2-3d (not suitable for AI) and then subsequent ovulations
Describe progestagen priming
combined treatment of intravaginal progestagen device and eCG
(sponges or CIDRs for P4 - 14d).
eCG injected @ sponge removal.
in estrus 2-3 d later. fixed time AI 55h after sponge removal
Describe melatonin use in advancing breeding season
Regulin implant
Isolate females from 30 weeks prior to lambing -> after 7d place implant-> 30-40d introduce males -> peak mating @ 25-35d after male introduction
Describe lighting as use for advancing breeding season
House and switch on to short day cycle
Need light proof housing
(intensively managed animals only)
What 3 things can be used to synchronize estrus during the breeding season?
Progestagen devices
PGF2alpha analogues
Teasers
describe synchronizing estrus during breeding season using prostaglandin analogues
[not licensed]
breeding season only
Estrumate, Lutalyse
If randomly cycling: 2 injections 9-11 days apart, estrus 2d after 2nd injection
