Learning Reproduction in Farm Animals

Learning Objectives

To understand the events of oogenesis and how it differs from spermatogenesis as far as the number of gametes produced and when it occurs.
 

Oogenesis
 

Learning Objectives

To understand how ovulation occurs

To understand what causes cystic follicles

General Events
 

1. Maturation of oocyte cytoplasm & nucleus

 
 
2. Cumulus oophorus & oocyte free of granulosa cells

 
 
3. Follicle wall thins & ruptures

 

 

Specific changes
• LH-FSH surge stimulates meiosis I to start again in preovulatory oocyte.

 
 
• LH surge causes increase in follicular fluid - (edema) follicle swells and makes granulosa convert to progesterone production.

 
 
• Enzymes in follicle begin breaking down the follicle wall.

 
 
• Collagenase attacks collagen in theca externa and tunica albuginea.

 

 

Maximum number of oocytes ovulated for a cow
17 cycles/year x 8 year = 136 oocytes ovulated/lifespan
 
 

Two types of ovulators:

1. Induced - Rabbit, Cat and Camel

 

 
 
 

Intromission stimulates the surge of LH ovulation in rabbit is 10-13 hours after stimulation.
 
 

2. Spontaneous - Farm animals and humans controlled by

 events of estrus cycle and not affected by intromission.
 
 

Causes:
 
 
1. Stress - High producing dairy cows

 
 
2.  Seasonal changes

 
 
3. Genetics

 
4. Other

 

• Insufficient LH released to cause ovulation

 
• Ovary does not respond well to LH

 
Types of Ovarian Cysts
 
• Follicular cysts - Grow & regress and cause nymphomania and short cycles; Increase LH levels to make cysts ovulate.

 
 

 
 
 

• Luteal cysts - LH induces luteinization of follicle wall, high levels of progesterone are produced and anestrus occurs. Give PGF2a to make cysts regress.

 

 
 

Learning Objectives:

• To understand the changes sperm undergo in order to fertilize the oocyte.
• To understand the oocyte events of fertilization, how polyspermy is prevented and why.

 
 
• Capacitation of sperm - A biochemical change to sperm that allows the true acrosome    reaction to occur.

 
• Occurs in the uterus and oviduct.
• Time required before sperm can undergo true acrosome reaction:

 
FOLLICULAR PHASE RABBIT
Uterus - 10 hours

Oviduct - 13 hours

both - 6 hours

Luteal phase takes 24 hours.
• Time for capacitation
Cow ?

Pig 3 hours

Ewe 1-2 hours

Horse ?

• Decapacitation factors - Glycoproteins from epididymis coat the sperm; Oviductal and uterine fluid remove coat and allow capacitation.

 

Sperm Penetration to the Oocyte
 

Fertilization and Cleavage
 

Oocyte blocks to polyspermy
 
 
• Zona reaction

 
 
• Vitelline block

 

 

Mechanisms of blocks
 
• Sperm attaches to vitteline membrane

 
• Cortical granules fuse to vitteline membrane and release contents

 
• Cortical granule components alter zona, i.e. less penetrable by sperm

 
• Vitelline membrane altered - less penetrable by sperm

 
• Species variation

 
• Zona reaction most important in sheep and dog

 
• Vitelline block most important in rabbits

 
 
Sperm Attachment and Egg Activation
 
• Factors causing decreased effectiveness of blocks to polyspermy:

 
1. Age of ova

 
 
2. Heating ova

 
 
3. Excessive sperm numbers

 

 
 
 
 
 

Coordination of events for fertilization to occur, i.e. Time of breeding relative to ovulation.

• Optimize sperm transport and reservoir formation.
• Breed early enough for capacitation - If too early, sperm will die before the oocyte is in the

oviduct.
• Breed late enough so fertile life span of sperm and oocyte overlap.

Illustrated Notes

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