Sexual Cycle in Sheep
• Age of puberty is 6-9 months in sheep.
• Domestic breeds can be used for breeding starting from 7-15 months of age.
• In sheep, which are among the seasonally polyestric animals, the onset of sexual activity is related to daylight length.
• The reduction of light exposure with the day length decrease results in increasing the melatonin release from the pineal gland.
• Increase of blood melatonin level stimulates GnRH release from the hypothelamus and the increased GnRH release stimulates FSH release by affecting the frontal lobe of hypophysis.
• FSH travels to the ovaries through blood and initiates follicular developments.
Sexual cycle in sheep:
• Proestrus (2-3 days)
• Estrus (30-36 hours)
• Metaestrus (2 days)
• Diestrus (10-12 days)
• Anestrus (seasonal)
Sexual Cycle in
Sheep
Proestrus
• Lasts 2-3 days.
• is faint.
• Outer changes may not be observed.
Sexual Cycle in
Sheep
E
strus
• Lasts 30-36 hours (depending on ram effect, age and race of sheep, light exposure time)
• Ovulation occurs closer to the end of estrus.
• Determining the sheep in estrus morning and evening with teaser rams is a necessity.
• Behaviour of sheep in estrus is evident when there is a ram and the distinct sign is smelling rams testicles.
Sexual Cycle in
Sheep
• Detection of estrus by observation is not as easy as it is in cows.
• The most distinct sign of sheep in estrus; smelling rams scrotum and standing in front of the ram.
• Other than these; restlessness, tail wagging, vulvar swelling and edema, open cervix and sometimes a cervical originated mucous discharge may be observed throughout estrus.
• Usage of teaser ram is needed for correct detection of estrus.
Sexual Cycle in
Sheep
Metaestrus
• Lasts 2 days.
• is considered to be the phase in which corpus luteum is formed.
• Corpus Luteum is active and progesterone release is initiated.
Sexual Cycle in
Sheep
Diestrus
• is the longest phase of the cycle and lasts 10-12 days.
• With the effect of progesterone secreted from Corpus Luteum uterine milk is secreted from the uterine glands and it prepares the uterus for gestation.
• If there a viable embryo does not exist by day 13, corpus luteum begins regressing with the effect of PGF2 secreted from the uterus.
