1. Colorado Agriscience Curriculum
Animal Science
Unit 4 – Reproduction and Genetics
Lesson 9 – Fertilization, Pregnancy and Parturition

2. Stages of Prenatal Growth
Fertilization – When the sperm and egg unite. When fertilization occurs, cell division occurs. It starts with 2, 4, 6, 8 and so on.
Attachment – The embryo that has gone through much cell division attaches itself to the uterus for further development.
Embryonic Stage – The period when body parts and organs start to form. The length of time differs between species
Fetal Period – Period that lasts until birth is mainly a time when body parts and organs mature.

3. Gestation and Gestation Periods for Different Species
1. Gestation – Length of Pregnancy
2. Gestation time:
Human: Days
Cow: 285 Days
Ewe: 147 Days
Mare: 336 Days
Sow: 114 Days

4. Gestation
3. The fetus develops in uterus, most of growth is in the last 1/3 of gestation.
4. Umbilical cord connects the navel to the placenta, where food, oxygen and wastes are exchanged.

5. Parturition and Problems with Parturition
Parturition – Signals the end of gestation. The process is started by the release of cortisol. This release causes progesterone levels to decline and estrogen, prostaglandin, and oxytocin to increase. All these hormonal changes cause relaxation of the cervix and contractions to occur. These events allow for the fetus to be born outside the body.
Abnormal positions (Dystocia) – Piglets don’t assume any particular position during birth and it doesn’t seem to affect the ease of birth. However calves, lambs and foals may present themselves in abnormal positions. The next slide shows normal and abnormal positions.

6. Normal Birth vs. Dystocia
Taylor, Robert E., Scientific Farm Animal Production, 4th ed.

7. Lambing: The Birth Of Twins
A pictorial study of parturition.

8. The First Lamb This Suffolk ewe gave birth to twins.
This is the first lamb to be born.
She is licking it clean.

9. The lamb is yellow because of the amniotic fluid.

10. The Wait for the New Lamb
You can see the new lamb’s head.

11. The ewe is straining while the lamb is being born.
Part of the new lamb’s body is showing.

12. Now the two lambs are born.
They are ewe lambs.

13. The ewe is starting to lick the new lamb.

14. And licking.

15. And licking.
The lamb is trying to stand.

16. The ewe lamb is looking for her first drink of colostrum.

17. Now she is standing.
The afterbirth is being expelled.

18. Both lambs are standing and ready to find the ewe’s udder.

19. They have both nursed and are resting. Being born is tiring.