Reproduction
Adapted from SPH

• Introduction
• Ewe reproduction
• Ram reproduction
• Efficiency
• Techniques
• Systems

Ewe reproductive anatomy and physiology (from SPH)

Hypothalamus

• Integrates internal and external cues about reproductive status
  • If signals indicate no reproductive activity then "hypothalamic pulse generator," and electrical signal generator, is inactive
  • If signals indicate that there should be reproductive activity, then the "hypothalamic pulse generator" causes the hypothalamus to secrete GnRH with each pulse
• GnRH goes to the pituitary gland which then secretes luteinizing hormone (LH) and follicle stimulating hormone (FSH) into the circulatory system by which these gonadotropins (hormones affecting the gonads) get to the ovaries

Ovaries

• Respond to gonadotropins by growing follicles which mature and release eggs at the time of ovulation
  • As follicles increase in size, they secrete estradiol-17ß which targets the brain
  • When follicles reach 0.2 to 0.4 inches in diameter, estradiol concentration is maximized and stimulates the release of a surge of LH which causes ovulation about 24 hours later

Follicles

• After ovulation, corpus luteum is formed from follicle
• Corpus luteum begins secreting progesterone three days after ovulation
• Progesterone signals the hypothalamus to stop stimulating pituitary to produce LH so that ovulation is suppressed

Cervix

• Convoluted barrier into uterus from vagina
• The anatomy of the ewe cervix makes nonsurgical AI difficult

Uterus

• Note that the sheep uterus is bifurcated into to horns (What are the implications for multiple fetuses?)
• If egg is not fertilized, uterus secretes prostaglandin F_2α (PGF_2α) beginning at about day 11 after estrus with increasing concentrations to day 16 or 17.
• PGF_2α causes lysis of the CL on the ovaries, which decreases progesterone, which removes the negative feedback to the hypothalamus, so that the cycle starts again

• If an egg is fertilized and pregnancy is established, the uterus is signaled to recognize the pregnancy by a signaling protein, like interferon tau or ovine trphoblastic protein (oTP-1), secreted by the embryo which causes the uterus to secret other forms of prostaglandin that may help to maintain the CL.
• Duration of estrus

• Length of estrus cycle:

Average estrous cycle length is assumed to be 17 days.

Progesterone monitoring of reproduction

Pregnancy

Egg fertilized in oviduct

Placenta

J. M. Wallace, D. A. Bourke, R. P. Aitken, and M. A. Cruickshank. Switching maternal dietary intake at the end of the first trimester has profound effects on placental development and fetal growth in adolescent ewes carrying singleton fetuses. Biol Reprod 61 (1):101-110, 1999.

Nutritional requirements of pregnancy

Signs of parturition

• Udder development
• Swollen vulva
• Ewe isolation (if given the opportunity)
• "Nest" building

Malpresentations resulting in dystocia