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26 Cards in this Set

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What is the normal estrous cycle length for ewes and does?
Ewe 16-17 days
Doe 21 days
When is the breeding season for most sheep?
Fall and Winter
What is the major physiologic signal that regulates LH secretion?
Photoperiod
What causes melatonin release and what effect does it have?
Melatonin is released from the pineal gland at night. Melatonin permits increased GnRH pulse generation.
When is the breeding season for most goats?
August - March with peak during October - December
At what body weight can a first year ewe or doe be bred?
60-70% mature weight
How long does estrus last in the ewe and the doe?
Doe: 36 hours
Ewe: 15-45 hours (average 30)
What is a "silent estrus"?
The first ovulation doesn't show signs because of the lack of P4 priming.
Estrus behavior requires 12 days of progesterone priming.
When is the onset of estrus in terms of hormone levels?
Estrus coincides with the LH surge.
What are some behaviors that indicate estrus in the ewe?
Ewe stands still with head lowered
Wags tail
Looks for and seeks the ram
Allows mounting multiple times
When does ovulation occur in the ewe?
24-30 hours after the LH surge
What is the ram/buck effect?
The female does not exhibit signs of estrus when the ram is not present
Pheromones identified in wax from the wool of rams has stimulated both estrus and ovulation in ewes
When does a PGF pulse occur and what tissue does it come from?
From the endometrium of the uterus on day 11-13
If there isn't maternal recognition of pregnancy (ovine interferon from blastocysts), then the uterus synthesizes and releases prostaglandin
How are does and ewes different in terms of pregnancy maintenance?
Does need CL to maintain pregnancy
Sheep only need CL for 45 days, pregnancy will go on without ovaries
How can you tell if a doe is in heat?
Estrous does are restless, wag tails (spread pheromones), vocalize, have swollen vulva with clear mucus, increased urination frequency
When do does ovulate?
12-36 hours after the onset of estrus
What does it mean if the doe has cloudy mucus?
Late in estrus, this is the fertile period
How should replacement ewes be selected?
Select at weaning
Should weigh 65-70% of mature body weight at time of breeding
Select from early-born animals that were twins or triplets (higher fertility)
Maintain moderate BCS
True or False:
Ewes are always bred for the first time at one year of age
False! Commercial operations usually breed first year ewe lambs, but range ewes usually lamb for the first time at two years
Females will ovulate after ___ days of ram/buck exposure?
~6 days (silent heat if it's the first ovulation of the season)
What is a good ram:ewe ratio?
1:50
Male will breed 3-5 females a day.
What are some ways to try and increase ovulation rates?
Immunization against androstenedione (allows more FSH to be released, only in Australia)
Immunization against inhibin (not commercial)
Gonadotropins (LH, FSH, PMSG)
Melatonin (affects seasonality, not really ovulation)
Flushing effect (doesn't work in fat animals)
Why would you administer PGF? What day in the cycle should you give it?
It's used to lyse the CL to allow the onset of estrus in 30-60 hours.
This only works if they are in the luteal phase. They should be susceptible by day 5-6 post ovulation.
What is the STAR program?
An accelerated breeding program which allows continuous production of market lambs.
Ultimate goal = 5 lambings in 3 years
When do you perform AI in ewes?
How much do you need?
12-24 hours after onset of estrus
20-400 x 10^6 PMS
True or False:
Transcervical insemination is the most practical way to AI sheep.
False! Transcervical is pretty much impossible. You just have to deposit the semen in the cranial vagina (SID method = shot in the dark)