Natural Animal Reproduction
Unit: Animal Science and the Industry
Problem Area: Animal Reproduction
Lesson: Natural Animal Reproduction
¢ Student Learning Objectives. Instruction in this lesson should result in students
achieving the following objectives:
1
2
3
4
Discuss the importance and explain the basics of animal reproduction.
5
Discuss the events that occur leading up to, during, and after parturition and
describe the problems that may be encountered during parturition.
Describe the phases of the estrous cycle.
Describe the process of fertilization in mammals.
Determine the gestation length of common agricultural animals and define
parturition.
¢ List of Resources. The following resources may be useful in teaching this lesson:
Corresponding E-unit(s). Danville, IL: CAERT, Inc. www.mycaert.com
¢ List of Equipment, Tools, Supplies, and Facilities
ü Copies of sample test
ü Visuals from accompanying masters
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¢ Terms. The following terms are presented in this lesson (shown in bold italics):
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anestrus
artificial insemination
breed
breeding
copulation
diestrus
differentiation
dystocia
embryo
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estrous cycle
estrus
fertilization
fetus
gestation
infundibulum
insemination
metestrus
natural insemination
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ovulation
parturition
placenta
proestrus
progesterone
reproduction
reproductive efficiency
semen
umbilical cord
¢ Interest Approach. Use an interest approach that will prepare the students for the
lesson. Teachers often develop approaches for their unique class and student situations. A
possible approach is included here.
Write the words “Animal Reproduction” on the chalkboard. Ask students to tell
you what that means. Use this discussion to guide students to the lesson by
asking students what various ways exist to manage reproduction within a herd.
SUMMARY OF CONTENT AND
TEACHING STRATEGIES
Objective 1: Discuss the importance and explain the basics of animal reproduction.
Anticipated Problem: What are some of the basics of animal reproduction?
I. Reproduction is the process by which offspring are produced. The offspring are of the
same species and have traits similar to their parents. Reproduction is not essential for
an organism to live; however, it is essential if a species is to stay in existence.
Without reproduction, there would be no new animals. In learning about animal
reproduction, there are several basic concepts that a producer must understand.
A. The placing of sperm in the reproductive tract of the female is called
insemination. Natural insemination is the process of the male depositing
semen, the fluid containing sperm, in the reproductive tract of the female. This
occurs during copulation or mating. Copulation is the sexual union of a male and
female animal. Artificial insemination involves a technician collecting semen
from a male and placing it in the reproductive tract of a female.
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B. Breeding is promoting animal reproduction so the desired offspring result. A
breed is a group of animals of the same species that share common traits.
C. Reproductive efficiency is the timely and prolific replacement of a species. This
is the difference between success and failure in animal production. The
fertilization of an egg may not always produce a new, healthy individual. The
developing animal may die before birth or hatching. These losses lower
reproductive efficiency.
There are many techniques that can be used to assist students in mastering this
material. Students need material to aid in understanding the basics of animal
reproduction. Use VM–A to aid in the discussion on this topic. In addition, a
possible technique to review this objective with students is the matching activity
with students. After introducing this objective, pass out index cards with a term
or definition on each card. Students must find their “match.” After students feel
they have completed the activity, discuss the activity with the students to assess
their understanding of the material. The following terms and definitions may be
used on index cards:
t Reproduction
t Semen
t Copulation
t Breed
t Insemination
t Natural insemination
t Artificial insemination
t The placing of sperm in the reproductive tract
t The process of the male animal depositing sperm in a female animal’s
reproductive tract
t The fluid containing sperm
t Sexual union of a male and female animal
t A group of animals of the same species that share common traits
t The process by which a technician collects semen from a male and places it in
a female
t The process by which offspring are produced
Objective 2: Describe the phases of the estrous cycle.
Anticipated Problem: What happens in the various phases of the estrous cycle?
II. The estrous cycle is the time between periods of estrus. The estrous cycle of female
mammals has four periods. These are cyclical, except during gestation or pregnancy,
for many animals, such as cattle or swine. Some animals are seasonal breeders. They
may go through periods of cycling and periods of anestrus. Anestrus is the absence
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of cycling. Anestrus is often related to the number of hours of light in a day. Examples
of seasonal breeders include sheep, cats, goats, and horses. The four periods of the
estrous cycle are:
A. Estrus—Estrus, also know as heat, is the period when the female is receptive to
the male and will stand for mating. The length of estrus varies between species.
Periods of estrus are triggered by the hormone estrogen. Many changes take
place, such as restlessness, mucus discharge, a swollen vulva, and standing to be
ridden by other animals. Ovulation takes place during estrus for most species. The
cat however only ovulates after mating. Ovulation is when a mature ovum is
released by the ovary. The number of eggs ovulated varies between species.
B. Metestrus—The period following estrus is metestrus. Ovulation occurs during
metestrus in cattle and goats. During this period luteinizing hormone (LH) triggers
the corpus lutea (CL) to develop from follicular tissue that remains after release of
the ova. The corpus luteum (yellow body) is important n maintaining pregnancy.
C. Diestrus—Diestrus is the period in the cycle in which the system assumes
pregnancy. A fully functional corpus luteum (yellow body) releases high levels of
progesterone. Progesterone is the hormone that maintains pregnancy. This is
when the uterus is prepared for pregnancy.
D. Proestrus—Proestrus begins with the regression of the corpus luteum and a drop
in the hormone progesterone. Late in this period, changes in behavior may occur
as estrus approaches.
There are many techniques that can be used to assist students in mastering this
material. Students need material to aid in understanding the phases of the
estrous cycle. Use VM–B to aid in the discussion on this topic. In addition, one
technique to review with students is to have students construct a flip chart of the
estrous cycle. After stapling six like-sized pieces of construction paper together,
have students label each stage of the estrous cycle in order on the front of each
page. The top of the flip chart is for a title labeled Estrous Cycle. On the back of
each page labeled for a separate stage of the cycle, students should describe
the steps of each cycle.
Objective 3: Describe the process of fertilization in mammals.
Anticipated Problem: How does fertilization happen in mammals?
III. The definition of fertilization as the union of a sperm and an egg is constant
between all mammals. However, the “roadmap” or process of how fertilization occurs
differs slightly between mammals based upon each animal’s reproductive tract
differences. In addition, it is important to note that the only system in mammals that
varies between sexes in a species is the reproductive system. However, without these
different systems working together the process of fertilization would not occur.
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A. This process begins by the male mammal depositing sperm in a female mammal’s
reproductive tract during mating. After this sperm is deposited, the sperm
gradually travels through the female’s reproductive tract until it reaches the
infundibulum, which is where ovum rest during ovulation. At this point in the
process, the sperm cell will pierce an egg cell if it is present. Although many
sperm cells are present in a reproductive tract after copulation, only one sperm
cell may fertilize an egg cell. Thus, fertilization occurs.
B. It is important to the process of fertilization to time the presence of egg cells and
live sperm cells in a mammal at coinciding times. Often times, after an egg cell is
released in a female mammal’s reproductive tract, it has less than 12 hours to
become fertilized by a sperm cell. In turn, sperm cells cannot survive for a long
duration in a female mammal’s reproductive tract.
There are many techniques that can be used to assist students in mastering this
material. Students need material to aid in understanding the process of
fertilization. Use VM–A to aid in the discussion on this topic. Another technique
to review the objective with students is to have students replicate visually the
fertilization process discussed in class. Ask students to draw the steps of the
fertilization process.
Objective 4: Determine the gestation length of common agricultural animals and
define parturition.
Anticipated Problem: How do gestation lengths vary between agricultural animals?
IV. After fertilization has occurred, the process of gestation begins in the reproductive
cycle. Gestation is defined as the period of time in which an animal is pregnant. The
periods of gestation vary between species, but should be calculated to determine the
expected date of birth, which ends the stage of gestation and begins the stage of
parturition.
A. After fertilization occurs, the gestation process continues as a series of cell
divisions occur without growth as the new animal or embryo moves toward the
uterus within three to four days. Here, the embryo engages in a rapid growth cycle
called differentiation that develops major organs in the embryo. After
differentiation, the new animal is known as a fetus. At this point, the fetus,
surrounded by a watery fluid enclosed in membranes, grows slowly in the uterus.
Here, the fetus has an umbilical cord that is connected from its navel to the
placenta, which lies along the wall of the uterus. This connection of the umbilical
cord serves many purposes for the fetus. This cord contains blood vessels which
supply nutrients and oxygen to the fetus as well as exit waste products. In
addition, the exchange of these nutrients and oxygen happen between the fetus
and its mother, which occurs through the diffusion of the placenta.
B. During the gestation period, the head, nervous system, and blood vessels develop
first. Although the process of a growing fetus is slow, the majority of this growth
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happens in the last stage of the gestation period, which is when the bones and
limbs fully mature. In addition, the position of the fetus shifts as the gestation
period comes to a close.
C. The events of a gestation period are the same throughout every mammal,
however, the timing of these events vary by species as the gestation periods differ
in length among species. For example, the average length of gestation for a cattle
species is 283 days and the differentiation cycle is complete on Day 45. Whereas,
with the swine species the differentiation cycle is complete on Day 28 and the
average length of gestation is 114 days. In sheep, the length of gestation
averages 148 days. In goats, the average length of gestation is 151 days. The
average length of gestation in horses lasts 336 days, almost one year.
There are many techniques that can be used to assist students in mastering this
material. Students need material to aid in understanding the gestation cycle
among mammals used in livestock production. Use VM–C to aid in the
discussion on this topic. Another technique to review material covered
throughout this objective with students could be to ask students to construct a
paper cube or dice. On each side of the cube, students can draw a picture of
the species and identify its length of gestation.
Objective 5: Discuss the events that occur leading up to, during, and after parturition
and describe the problems that may be encountered during parturition.
Anticipated Problem: What events occur before, during, and after parturition? What
problems can occur?
V. Parturition is the process of a pregnant organism or animal giving birth to a fetus.
Sometimes referred to as labor, animals often express many physical and behavioral
indications of when they plan to give birth. In addition, many scientific methods of
determining when an animal is to give birth have been established. It is important for
animal producers to recognize these indicators and methods so that they can be
prepared for new offspring and certain management techniques can be applied.
A. The parturition process varies among animals and it is important to understand
the terminology, stages, and problems that can arise throughout this process.
Many domesticated animals have a specific term that describes the process of
parturition. Yet, despite these changes in terms, all animals engage in the same
three stage process in order to give birth. During the birthing process, problems
can arise, especially with younger and older animals. Understanding parturition
and the problems a producer may face is critical to raising animals and managing
live births.
B. The process of giving birth is referred to differently between species. For example,
with cattle the parturition process is called calving and with felines the process is
called queening. Other examples include, farrowing for swine, foaling for horses,
lambing for sheep, whelping for dogs, and kidding for goats. Each of these terms
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refer to the process of giving birth for the species and many of these terms evolve
from the term for their young offspring, such as foals for horses and lambs for
sheep. Queening for cats evolves from the term queen or a sexually mature
female cat, while whelping in dogs is simply the process of giving birth.
C. As the parturition process begins all animals go through a three stage process to
give birth. Each stage of the process prepares the female’s body and her fetus to
be released into its new environment. The first stage of parturition deals with the
start of uterine contractions and the reproductive organs prepare for the birthing
process. The birth canal begins to open and the female’s muscles begin to relax
as the fetus prepares to pass. The fetus begins to align with the canal and the
mother’s respiratory rate increases. The second stage begins as abdominal
muscular contraction occurs and the mother starts to strain to pass the fetus.
Also, fluid is released from the uterine body as a lubricant. This stage concludes
with the birth of the fetus. The third stage of parturition deals with the expulsion of
the placenta. The mother’s straining ends and she begins to relax. The placenta
detaches from the uterine wall and the fetal membranes are released.
D. Parturition is not always a smooth and simple process as many problems can
occur. Mothers can experience difficulties when trying to pass their fetus through
the birth canal. Problems during the parturition process are called dystocia, which
is typical in younger animals as their muscles are not fully developed and in older
animals as their muscles weaken with age. Dystocia can also occur when females
are mated to males with a reputation for producing large fetuses. Producers
should be cautious when assisting in the birthing process. Both the mother and
the fetus can be injured or even killed if assistance is applied too early in stages.
Generally, it is encouraged for producers to observe parturition to prevent injury.
The duration of the three stages of parturition vary among species.
1. It takes a mare one to four hours to complete stage one, ¼ to a half hour to
complete the second stage and an additional hour to complete stage three.
2. With cows, it takes two to six hours to complete stage one, ½ to one hour for
completion of stage two and an additional six to twelve hours for completion of
stage three.
3. It takes sows two to twelve hours to complete stage one, two and half to three
hours to complete stage two, and an additional one to four hours to complete
the process.
4. A ewe can take up to six hours to complete stage one, ½ to two hours to complete stage two and an additional ½ to eight hours to complete stage three of
parturition.
5. A producer should note advanced steps of stage two by recognizing exposed
feet, head, or tail. In this case, an experienced producer or veterinarian should
assist the animal with birth.
6. Assistance should never be provided for the third stage of parturition. Only a
veterinarian should treat an animal that has not completed the final stage of
the parturition process.
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E. The process of giving birth by female animals is a critical time for animal
producers. If dystocia occurs, an animal producer needs to immediately contact
assistance or a veterinarian. Many producers have a specially designed area or
stalls where mothers can safely give birth to their young. However, without
physical or behavioral signs, it would be more challenging to prepare for
parturition. Through these signs, a producer can estimate within a few days that
parturition can occur.
1. The physical signs displayed by an expecting mother are some of the most
obvious indication of how soon parturition will occur.
a. The abdomen continues to enlarge throughout pregnancy and reaches its
maximum size just before giving birth.
b. The mammary glands or udder continually develop in the later stages of
pregnancy and become firm prior to parturition. A milky substance is
secreted shortly before birth.
c. Many animals will begin to discharge a mucus type of material from the
vulva. This is especially common in cows and may appear as if parturition
has already occurred.
d. After careful examination a producer should notice that the abdominal
muscles are relaxed causing the belly region to drop and the rump is
sunken on both sides of the tail head. These are all physical signs that
parturition is approaching.
2. Expecting mothers will display behavioral signs prior to parturition. Unlike physical signs, the behavioral signs suggest that the expecting mother is within a
few days of giving birth.
a. She will display nervous types of behavior that includes restlessness,
frequently lying down and getting up, pacing around a small area, and
frequent urination.
b. Dogs and sows will attempt to build large nests to give birth in. A dog will
usually use blankets, towels, or other available materials to build her nests.
A sow will gather straw, grass, sticks, and even dig into the ground for a
nest. They typically select a private location out of sight and general traffic
areas.
c. The respiratory rate of a sow will increase in a six hour period and peak just
before parturition.
d. Once behavioral signs are observed a producer should move the pregnant
mother to a safe location appropriate for the parturition process.
e. In addition to these signs, it is beneficial to have an approximate breeding
date recorded so that a gestation chart can predict the expected parturition
date.
f. Also, there are managerial techniques that can be practiced to determine
the birthing date of an animal. Both the gestation table and the managerial
techniques are not exact calculations of when birth will occur, but more of
a confirmation that an animal is pregnant and a prediction of a birthing
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date. This prepares the producer for arranging for the birth of the new
offspring.
There are many techniques that can be used to assist students in mastering this
material. Students need material to aid in understanding the three steps
associated with the parturition process in livestock production. Use VM–D and
VM–E to aid in the discussion on this topic. In addition, another technique to
review material covered throughout this objective with students could be to pass
out index cards labeled with events that occur throughout the parturition process
and students have to arrange themselves with their respective cards in order of
occurrence from beginning to the end of the parturition process.
¢ Review/Summary. Use the student learning objectives to summarize the lesson.
Have students explain the content associated with each objective. Student responses can
be used in determining which objectives need to be reviewed or taught from a different
angle. Questions at end of chapters in the textbook may also be used in the
review/summary.
¢ Application. Have students complete the Semen Evaluation exercise described on
pages 35–37 in the Activity Manual for Introduction to Livestock and Companion Animals.
¢ Evaluation. Evaluation should focus on student achievement of the objectives for each
lesson. Various techniques can be used, such as performance on the application activities.
The sample written test can also be used.
¢ Answers to Sample Test:
Part One: Matching
1.
2.
3.
4.
5.
6.
7.
8.
b
d
a
h
f
e
c
g
Part Two: Completion
1.
2.
3.
4.
ovulation
Fertilization
Gestation
Natural
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Part Three: Short Answer
1. Estrus, Metestrus, Diestrus, Proestrus
2. Stage one deals with uterine contractions beginning and the reproductive organs
prepare for the birthing process. The birth canal begins to open and the female’s
muscles begin to relax as the fetus prepares to pass. The fetus begins to align with
the canal and the mother’s respiratory rate increases. The second stage witnesses
abdominal muscular contraction occurring and the mother starts to strain to pass
the fetus. Fluid is released from the uterine body as a lubricant. The birth of the
fetus happens. The third stage exhibits the expulsion of the placenta. The mother’s
straining ends and she begins to relax. The placenta detaches from the uterine wall
and the fetal membranes are released.
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Sample Test
Name ________________________________________
Natural Animal Reproduction
u Part One: Matching
Instructions: Match the term with the correct definition.
a.
b.
c.
d.
gestation
diestrus
progesterone
parturition
e.
f.
g.
h.
estrus
fetus
placenta
dystocia
_____1. The period in the cycle in which the system assumes pregnancy
_____2. The process of giving birth
_____3. Stage that ends with birth of an animal
_____4. Problems that emerge with animals giving birth
_____5. A developed embryo housed in the uterus of a female
_____6. The period when the female is receptive to the male and will stand for mating
_____7. The hormone that maintains pregnancy
_____8. Lies along the wall of the uterus
u Part Two: Completion
Instructions: Provide the word or words to complete the following statements.
1. Puberty in female animals is the age of the first estrus with _________________________.
2. The process of _________________________ is defined as the union of a sperm and egg.
3. The period of time in which an animal is pregnant is defined as
_________________________.
4. _________________________ insemination is the process of the male depositing semen in
the reproductive tract of the female.
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u Part Three: Short Answer
Instructions: Complete the following.
1. List the four periods of the estrous cycle.
2. Define the three stages of the parturition process.
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VM–A
BASIC ANIMAL REPRODUCTION
Sperm
Egg
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VM–B
PHASES OF
THE ESTROUS CYCLE
Estrous Cycle
(days)
Length of Estrus
(heat)
Cow
21
12–18 hours
Mare
22
6–8 days
Doe (goat)
21
30–40 hours
Doe (rabbit)
Constant
Constant
Sow
20–21
40–72 hours
mid estrus
Ewe
17
24–36 hours
late estrus
Bitch (dog)
—
9 days
1–2 days after estrus begins
Queen (cat)
14–21*
5 days
24 hours after mating
Species
Ovulation
10–14 hours after estrus
1–2 days before estrus ends
at the end of or just after estrus
8–10 hours after mating
*Estrous cycle influenced by length of daylight, with mating season typically when there are more than 12 hours of daylight in one day.
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VM–C
AVERAGE GESTATION TIMES
FOR MAMMALS
Average Length of
Name of Species
Gestation
Cattle
283 Days
Swine
114 Days
Sheep
148 Days
Goats
151 Days
Horses
336 Days
Dogs
63 Days
Cats
60 Days
Rabbits
30 Days
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VM–D
SPECIES BIRTHING TERMS
Name of Species
Term For Giving Birth
Cattle
Calving
Swine
Farrowing
Sheep
Lambing
Goats
Kidding
Horses
Foaling
Dogs
Whelping
Cats
Queening
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VM–E
THREE STAGES OF THE
PARTURITION PROCESS
Stage of
Parturition Process
Description of Events During Stage
Stage I
Uterine contractions begin and the reproductive
organs prepare for the birthing process. The birth
canal begins to open and the female’s muscles
begin to relax as the fetus prepares to pass. The
fetus begins to align with the canal and the
mother’s respiratory rate increases.
Stage II
Abdominal muscular contraction occurs and the
mother starts to strain to pass the fetus. Fluid is
released from the uterine body as a lubricant.
The birth of the fetus happens.
Stage III
The expulsion of the placenta happens. The
mother’s straining ends and she begins to relax.
The placenta detaches from the uterine wall and
the fetal membranes are released.
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