Lecture 5 -- Reproduction, Luteolysis, Fertilisation & the Early Embryo

What are the four stages in bitches

1. Pro-oestrus

   • 9days

   • Estrogen peaks

     • Drive behaviour changes/ Vulva swollen/ Bloody discharge

     • Attract male but does not mate,

2. Oestrus

   • 9days

   • Accept male

   • Ovulation usually D2

3. Dioestrus = Metoestrus

   • 60-70days

   • CL progesterone dominant

     • Produce lots of progesterone

   • No early luteolysis in bitches = Corpus luteum lasts about the same length of time as a normal pregnancy would

4. Anoestrus

   • Ovarian inactive between end of dioestrus and start next pro-oestrus

What are the characteristic of bitch’s oestrus cycle?

• Spontaneous ovulators

• Only 1-3 seasons per year

• Pro-oestrus + oestrus last ~9days

• Ovulation occurs ~48-72 hours after LH surge

• Corpus luteum last 60-70days → No luteolytic mechanism

• Progesterone start increasing few days before ovulation

Why bitches have a higher change of pregnancy?

→ Longer ovulation period ~ 2-3days

→ Egg viable for 5 days → Fertilisation period lasts for 2-5days after ovulation

→ Sperm viability 9-11days

= Can mate from the start of oestrus

How long does an ovum typically remain viable?

Less than 24 hours

How long can spermatozoa remain viable in the female tract?

• Spermatozoa much last for longer than ovum

• Species dependent

  • E.g. Last longer in mare trat compared with cow’s tract

What makes successful fertilization?

1. Transverse the cervix

2. Transport through the utreus to the oviduct

   • Only small % can reach to the isthmus

   • Phagocytosis by macrophages

   • Ejected back out of vagina

3. Capacitation

   • In epididymis, sperm are not capable of fertilisation → Surface molecules of sperm are coated with seminal plasma protein, masking membrane molecule → Stop them from binding to the ovum

   • In female tract, the seminal plasma coating and some surface molecules are removed to allow the sperm to bind with zona pellucida of oocyte

   • Completed in oviduct, where sprem develop a hyperactive motility pattern that facilitate sperm-oocyte contact

4. Acrosomal reaction

   • Acrosome of sperm swell → Its membrane fuse with over-laying plasma membrane sperm → Vesicle form → Release of proteolytic enzyme through exocytosis → Work with zona pellucida of oocyte

5. Prevention of polyspermy

   • When the sperm membrane fuse with oocyte membrane, it causes the oocyte to release Ca → Secretion of cortical granules → Cortical granules then secrete enzyme that cleave the binding site of ZP3 → Prevent attachment and fertilisation by more than 1 sperm

What is syngamy?

→ Haploid spermatozoa penetrates the zona pellucida of secondary oocyte → Oocyte undergoes 2nd meiotic division
→ The fusion of male and female pronuclei to form a zygote.

What is cleavage in the context of early development?

Rapid mitotic division of the zygote, producing progressively smaller cells = Blastomeres

Describe the progression from early cell division to blastocyst hatching.

• Since the zona pellucida stays, as the cells are dividing, those cells are getting smaller and smaller because they have to fit within the zona pellucida -> The bunch of cells within the zona pellucida = Morula

• Morula transforms into the blastocyst, which begins to differentiate into the inner cell mass → Ultimately becomes embryo

• The outer layer of cells begins to adhere to the inner lining and is surrounded by the zona pellucida. Eventually, the zona pellucida ruptures → Hatching of the blastocyst

• Once the blastocyst hatches, it attaches itself to the uterine wall

What is the role of progesterone in pregnancy?

Progesterone is essential for maintaining pregnancy and preventing luteolysis.

What is maternal recognition of pregnancy?

It is the process where the luteolytic signal is blocked to maintain pregnancy.

Do bitches require maternal recognition of pregnancy?

No, bitches do not have a luteolytic signal, increasing chances of maintaining pregnancy.

Describe the anatomy of oviduct

• Infundibulum

• Ampulla

  • Wider part of oviduct near to ovary

• Isthmus

  • Narrower part of oviduct next to utero-tubal junction (Junction between uterine horn and oviduct)

  • Storage of sperm (Arrive after 2-7 hours of mating)

Where does the sperm of cows, sheeps, dogs and cats be deposited?

Vagina

Where does the sperm of pigs be deposited?

Cervix

Where does the sperm of horses be deposited?

Cervical lumen

What aids in the transportation of sperm within the female tract?

→ Smooth muscle contraction of female tract
→ Sperm motility