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					                                        Agriscience 102
                          Applied Agricultural Science and Technology
                                             8407
                                  Methods of Animal Breeding
                                       TEKS: (c)(4)(D)
Topic Goal:
The student shall be provided the opportunity to discuss animal breeding as a means of performing
technical skills related to animal science and technology.

Topic Objectives:
After completing the topic, the student will be able to:
  1. define and explain advantages of breeding systems: grading up, crossbreeding, etc.,
  2. identify puberty age, breeding age, and female reproductive cycle for various livestock classes,
  3. describe factors considered in selecting traditional/non-traditional mating methods; and
  4. explain synchronization of estrus and procedures for embryo transfer.

                                             CLASS NOTES

INTRODUCTION

Nearly every successful livestock breeding operation considers the environmental, economical, and
technological factors that affect the choices made concerning breeding systems, breeding seasons, times
of breeding, and ______________ of breeding. Producers must be prepared to successfully breed
livestock by using the appropriate technology and by applying a thorough working knowledge of animal
_________________ as well as animal reproduction and physiology.

BREEDING SYSTEMS

Breeding systems are a set of ___________________ practices that are used by producers to ensure the
transmission of certain traits from parents to offspring, particularly those traits that the producer desires
to be inherited. No one breeding system or method of breeding livestock will fit ________ producers.
For example, some systems may include grading up, _______________________, purebred breeding,
linebreeding, and inbreeding.

Several factors to be considered in determining the breeding system to use are:
     ________________ conditions
     Types of markets
     Knowledge of ________________
     Size of operation

                                                    -1-
     ________________ preferences
     Available resources
     Goals of the ______________

Crossbreeding

Crossbreeding is the mating of two animals of _________________ breeds. Usually, both animals are
_________________. However, commercial breeders will often mate purebred sires to females that are
considered ___________ animals with the resulting offspring or progeny also considered “crossbreds”
or F1s. This system may be referred to as _________________________ crossbreeding.

Crossbreeding is done to improve the overall performance of offspring that result from mating
individuals with different but _______________________ breed values. Another reason for
crossbreeding is to produce hybrid vigor or _________________ for traits such as fertility and
survivability.

Advantages of crossbreeding are:
     Weaknesses can be improved upon or ___________________ by breeding an animal “strong” in a
      particular trait to an animal that is considered to be lacking or “weak” for the trait in question.
     The average ______________________ of the offspring is increased over either parent.
     Crossbreds are more ______________ than their purebred parents.
     Crossbreds wean heavier _________________ than do purebreds.
     Crossbreds are more ________________ than purebreds.

Several crossbreeding methods are used by livestock producers; therefore, crossbreeding is the most
popular breeding system practiced in ___________________ livestock operations. However, some
methods     work       better   for   certain   ______________       than    others.    Three     types     of
_______________________ to be discussed in this topic are grading up, backcrossing, and three-breed
rotational crossing.

Grading Up

Grading up is the process of mating purebred males to ___________________ females, with the
ultimate goal of eventually creating a purebred herd or flock. The purpose is to improve quality, develop
uniformity, and increase performance in the _________________. Breeding replacement females from
within a commercial herd back to purebred sires results in offspring that are more
                                      -2-
____________________ similar to the purebred sire. A noticeable improvement through the
_____________ generation can be expected when using this system. After the fourth generation, the
herd will carry 94% of the characteristics of the purebred sire. However, progress is much slower for the
succeeding generations. The purebred sires should be products of different production-tested herds, thus
helping to ensure higher ____________________ among the offspring.

Backcrossing

Backcrossing is the mating of an individual to any other individual with which it has one or more
_________________ breeds or lines in common. The backcross method is ______________ in
commercial cattle operations. This system crosses two purebreds, and then the resulting offspring is bred
back to one of the original parent breeds, but not the same _____________ animal. This method of
breeding productive female offspring to related breeds of superior ___________ can be continued for
several generations.    Repeated backcrossing is used to incorporate a specific trait found in one
population into a _________________ population, while maintaining selective traits found in the second
population. However, when using this system the breeder may risk losing some ______________vigor
in later generations.

Three-breed Rotational Crossing

Another type of crossbreeding that is popular with swine breeders is the three-breed
___________________ cross method. This system involves breeding _________________ females to
purebred males. The rotation of purebred males from ___________ breeds on subsequent generations of
selected crossbred females can be continued for several generations.

Inbreeding

Inbreeding is the mating of individuals over several generations that are more ______________ related
than average for the population they represent. Inbreeding is used more in ________________
operations than in commercial operations. When inbreeding is practiced for several generations, it is
called _________________ inbreeding. However, if “overused” this is the form that often gives
inbreeding a ________________ connotation. When used appropriately, the purposes for inbreeding are
to concentrate the inheritance of desirable traits and eliminate ____________________ traits for a given
group of animals. If starting with a desirable group of animals, a breeder can make further
______________________ by inbreeding. This system has been used to develop many
____________________ herds. Other ways in which inbreeding can be used to improve livestock are to
                                            -3-
form families, produce ________________ stock, develop lines for crossing, and determine the genetic
value of an individual. Some potential disadvantages of inbreeding may be a decrease in reproductive
efficiency, vigor, ________________ rate, and growth rate.

Linebreeding

Linebreeding is a “milder” form of ___________________ designed to maintain a degree of relationship
to highly regarded ancestors, without resulting in a level of inbreeding that is harmful. Similar to
inbreeding, linebreeding is more often used in ________________ operations. Animals are
___________ mated that are closer than half-brothers or half-sisters.

A breeder using the linebreeding system should recognize its _________________ and limitations.
However, linebreeding is only successful in herds that have a high degree of excellence and possess
outstanding individuals as indicated by ______________ tests.

Purebred Breeding

Inbred lines are established _____________, and rather than referring to the process or method of
mating purebred individuals of the same breed as “inbreeding,” it is known as purebreeding or
straightbreeding. Purebreeding is the mating of animals within the same breed that are either
___________________ in a breed association or are eligible for registry. A purebred animal’s
______________ can be traced to the original foundation animals of the breed, which were those
animals first accepted for registry.

Being a purebred does not necessarily guarantee that an animal is ________________. Yet, purebred
animals may be preferable in many respects when compared to ___________ animals.

METHODS OF BREEDING

The two methods of breeding for livestock species are natural breeding and assisted reproductive
______________________. The method of breeding a producer uses depends on several factors: type
and size of the operation, available labor, number of males and females in the herd or flock,
___________________, financial resources, breed registry policies, and personal preference.




                                                  -4-
Natural Breeding

Hand Mating

Hand mating, where the male is kept separate from the female except during the act of breeding, is used
primarily by purebred breeders to control _____________. Under this system, when the female comes
into __________ (estrus) she is brought to the male and mated individually. Advantages of this system
are that a male can service more females, the act of mating is ___________________, and accurate
records (breeding dates, etc.) are easier to keep. Additional labor is required because the female must be
checked for heat ___________ daily during the breeding season and also brought to the male when
mating is to occur.

Pasture Mating

Pasture mating allows the male to be with the females throughout the ________________ season or for
the entire year. However, if uniformity in size of offspring and time of ____________________ are
important, then exposure to males must be limited to only the breeding season. This system may be used
for all ______________ of livestock. In addition, the pasture mating method requires less ___________
because it involves less handling of the animals. Also, in the case of registered herds, records are more
_________________ to keep when more than one male is used for pasture mating. So, when
___________ records are desired, use the recommended number of females per male and keep them in
separate pastures.

Corral Mating

This system is used mostly by horse breeders and involves putting the mare and stallion together in a
strongly   fenced     _____________.      There     is   no   human   assistance   required,   other   than
______________________ the animal to the corral. Both mare and stallion are returned to their
respective pens after ______________.

Flock Mating

This system is popular with ______________ breeders. Flock mating allows a number of males to be
placed with an _____________ flock of females. On average, a placement ratio of 12 to _______ males
per 100 females is practiced in poultry breeding flocks. There tends to be a high _________________
rate with this system and it requires less labor.


                                                     -5-
Pen Mating

Pen mating is another breeding method used primarily by ______________ breeders. However, instead
of the whole flock being together, pen mating places one male with 8 to _______ females in a single
pen. This mating system makes it easier for a producer to know the parents of every chick and to
evaluate a male's ______________________ performance. But, fertility is generally not as good in pen
mating as compared to ___________ mating because the females cannot choose their mate, and there is
no competition occurring between males for mates.

Assisted Reproductive Technology (Artificial Breeding)

Technology offers new approaches for the artificial breeding of animals and can assist in addressing
problems of ____________________. Modern reproductive technologies include artificial insemination,
semen freezing, embryo transfer, and ______________. In recent years, these techniques have been
applied to produce animals with new genes, which has benefited not only the production of food and
fiber but animal and human _____________ as well.

Artificial Insemination (A.I.)

Artificial insemination is a reproductive technology in which ___________ is collected from males and
then used to breed females.

Advantages of artificial insemination
     It allows the use of superior, ____________________-tested sires.
     Records for ___________________ can be improved.
     The number of ______________ that can be bred to one superior male increases.
     The chance of spreading ______________ is reduced.
     The chances of ________________-related injuries are reduced.

Disadvantages of artificial insemination
     A trained ____________________ is required.
     More time and supervision of the females are required; therefore, more ___________ is needed.
     Special handling facilities and ______________ equipment are required.
     The __________ may be a problem for some producers.




                                                 -6-
Embryo Transfer

Embryo transfer is the process of removing an embryo during the early stages of _________________
development from a female's reproductive tract, and then transferring the embryo to another female's
reproductive tract for further development and subsequent birth. Embryo transfer procedures are more
_________________ and labor intensive than other methods and are used more often in cattle than in
other species of livestock. Yet, through the use of artificial insemination and embryo transfer, there can
be a greater _____________ of offspring produced from genetically superior sires and dams.

Estrous Synchronization

Estrous synchronization is a process that uses chemically manipulated ________________. It can be
used in conjunction with any breeding program to ensure that all of the females come into heat (estrus)
at or near the same __________. Estrous synchronization of several females can be
___________________ for producers. It reduces the number of days needed to inseminate or transfer a
herd, thus concentrating ___________ needs to specific breeding and birthing times.

Cloning

Cloning is a reproductive technology that may be used to produce genetically _________________
(homozygous) individuals. There are several methods of cloning such as embryo _________________
and nuclear transplantation.

Embryo splitting, or bisection, involves cutting the embryo in half mechanically to produce __________
embryos, which are then transferred to recipient females. This is possible because the young embryonic
cells   are   ___________________.       At   this    stage,   the   cells   have   not   yet   begun   to
_______________________ into specialized cells; they still have the potential to become any type of
cell in the adult animal. Because this method only produces two identical twins, it is designed to
increase the efficiency of the embryo transfer rather than producing multiple _____________.

The process of nuclear transplantation transfers the complete genetic material (i.e., the DNA contained
in a ___________ nucleus) from a mature donor cell into an immature recipient egg cell, one whose own
nucleus was removed. (The transplanted nucleus contains the ______________ information from which
an organism may develop, while the recipient egg cell does not.)




                                                     -7-
Advantages of cloning
     Individuals with outstanding genetics can be ___________________.
     Cloning allows for __________ production of outstanding animals.
     Sex selection of an animal can be _______________________.
     Records of evaluation become more ________________.

Disadvantages of cloning
     The rate of ______________ is lower.
     More ___________ and other expenses are required.
     The potential for ______________ variation is decreased.
     Selection of outstanding animals from a cloned herd becomes more _________________.
     A highly-skilled technician and specialized equipment is needed to perform the procedures.

FACTORS TO CONSIDER WHEN SELECTING A METHOD OF ANIMAL BREEDING

Selecting a Breeding Season

After the systems and methods of breeding have been established, a ________________ season must be
selected. The time and duration of the breeding season affects the birthing season and the uniformity of
the offspring. While some producers may choose to have a year-long breeding season, many producers
prefer to have offspring born in the spring or fall and have offspring that are similar in age and
_____________. So ideally, offspring for a given livestock enterprise should be born within a specified
number of days; for example, _______ to 60 days is a common time frame for cattle.

Factors to consider include the following:
     Climatic conditions will affect the amount of equipment, __________, and housing needed.
     The availability of ___________ should determine the system of mating to use, as well as the time
      of year the offspring will be born.
     Usually, prices for market animals are better during certain times of the year than others, so
      “target” dates for _________________ need to be set.
     In certain areas, availability of _________________ and housing are factors that affect choice of
      breeding season. For example, some species of livestock will have to be placed in a barn and
      provided __________ during the winter months.
     If the females and offspring are to be provided ______________, then its availability may be of
      great importance. Usually, grazing is best during late _____________ and early summer.

                                                 -8-
     Livestock show rules may require that animals be classed based on their __________. Frequently,
      animals that are the maximum allowable age for a particular class have a ____________________
      advantage.
     The purpose for which livestock are produced determines the ________________ season. For
      example, the birth of offspring for replacement purposes determines the season in which they will
      reach a desirable breeding age and thus the _____________ of time required to bring them into
      production.

Age of Puberty and Breeding Ages of Livestock

Season of birth, temperature, nutrition, rate of ________________, and heredity affect the age at which
animals reach puberty. It should be emphasized that age of puberty and breeding age are two distinct
___________________ of physical development. Because an animal has reached puberty does not
always mean that it is capable of reproducing ____________________. For example, recent research
reveals that frequently stage of __________ development is more important than age in determining
when animals will reach puberty. Usually, it is advisable to allow animals to continue to develop and
_____________ after reaching puberty.

Moreover, proper breeding age may vary widely depending upon __________ growth and development
of individual animals within a breed and species. The livestock producer must determine the minimum
________________ age of the particular species to be bred. Often, it may appear to be advantageous to
breed at an early age to reduce ___________________ expenses. However, sometimes it is to the
producer's advantage to ___________ breeding to avoid the possibility of physical injury occurring and
to reduce the incidence of birthing problems associated with physically underdeveloped females.

Suggested breeding ages for some species of livestock are also listed in the following table.

                                                Puberty Age
                            Puberty Age Ranges (Months)               Breeding Age Ranges (Months)
       Species
                             Males                Females               Males               Females
        Cattle            6 - _______              4 - 14               18 - 24                 15 - 24
        Horses              12 - 24            15 - _______             24 - 48                 24 - 36
        Swine                 3-8                  3-8                 8 - _____                8 - 10
        Sheep                4 - 10                4 - 10               12 - 20           14 - _______
        Goats                 4-8                  4-8               _______ - 20               12 - 18
        Rabbits             4.5 - 12             _____ - 12             6 - 12                  6 - 12
       Chickens            _____ - 6               5-6                   5-6                     5-6
       Turkeys              6.5 - 7.5          6.5 - ________          6.5 - 7.5            6.5 - 7.5

                                                   -9-
Breeding Ages of Females

Mating females, for the first time, at a _____________ breeding age offers certain advantages to the
producer. For example, breeding heifers at two years of age offers a physiological advantage, and it
frequently increases the heifer’s rate of __________ production upon calving. On the other hand, early
breeding can potentially increase the lifetime production of the female. Supplemental feeding of heifers
or providing them with good pastures can cause heifers to develop and _____________ faster and thus
breed earlier.

Although early breeding may offer some advantages, more often than not, it is __________ development
that determines when producers will mate females for the first time.

Breeding Ages of Males

Breeding ages of males are not as important as for females. The principle consideration is the number
and ______________ of offspring that a male can sire in a given season. The total number of services
possible will vary according to a male’s age, physical development, health, ____________________,
and condition, as well as the breeding system used (hand or pasture mating) and the distribution of
services. The following table provides a mating guide for males for both __________ mating and
pasture mating systems.




                                                 - 10 -
                                                Mating Guide
      Animal                  Age of Sires                     Hand Mating              Pasture Mating
                                                            (Number of Females)      (Number of Females)
        Bull                  1 - _____ yrs.                      10 - 12                  8 - 10

                                2 - 3 yrs.                     25 - _______                20 - 25

                             3 yrs. and older                     40 - 50               25 - _______



       Boar                   8 - 12 months                  ______________                  12

                             1 yr. and older                 ______________                35 - 40



      Stallion                2 - _____ yrs.                      10 - 15             Not recommended

                                3 - 4 yrs.                     20 - _______           Not recommended

                                4 - 5 yrs.                        30 - 60          _____________________
                                                                                   _____________________
                                                                                             _

                               5 - 18 yrs.                     _______ - 100          Not recommended



       Ram                     Under 1 yr.                     20 - _______           Not recommended

                             1 yr. and older                      50 - 75               _______ - 60


If pasture mating is practiced, several other important factors such as range carrying capacity, size of
______________, and herd size will influence the number of females that can be serviced by one male.
For example, one bull to about _______ cows is the standard ratio for cattle under range conditions. A
ratio of one ram to 25 to _______ ewes is recommended for sheep under range conditions.

Most stallions are not allowed to ______________ mate because of the possibility of injury. As a
general rule, mature males of all species are capable of breeding considerably more females than are
___________ males.

Reproductive Cycles of Livestock

Factors that control reproductive cycles of females of various species of livestock include estrus, estrous,
time of _________________ within the estrus or heat period, and gestation period for pregnant females

The heat interval (estrous) includes the internal reproductive and hormonal changes a female undergoes
on a “scheduled-basis” after reaching ______________. The heat period (estrus) is that portion of the

                                                   - 11 -
heat interval during which the hormones estrogen and progesterone are secreted by the female’s ovaries.
These hormones, especially estrogen, cause outward signs of ____________________ to mating to
which males of that species may respond. _________________ is the expelling of an egg (ovum) from
the ovary, which occurs during the heat period. Following expulsion, the egg is ready to be
___________________ by a sperm cell. Once an egg is successfully fertilized, the female's body
undergoes physical changes as the ___________ develops. The period of time required for fetal
development is referred to as the _________________ period. Gestation tables indicating the
approximate date of birth in relation to the date of breeding are available and may assist a producer in
determining the probable date an offspring will be born. (See also the Animal Breeding Calendar found
in your SAEP _____________ Book.)

                                        Reproductive Cycles of Livestock
                                                                                      Time of
    Species             Estrous Cycle                         Estrus                 Ovulation          Gestation

                  RANGE          AVERAGE           RANGE           AVERAGE            RANGE             AVERAGE
                  (DAYS)          (DAYS)                                                                 (DAYS)

     Cow        18 - _______            21        10-26 hrs.           18 hrs.      10 - 12 hrs.           283
                                                                                    postestrus

     Sow          16 - 25       ____________      1 - 4 days           2 days     16 – 48 hrs. from        114
                                                                                 beginning of estrus

     Ewe          15 - 18               17        1 - _____            30 hrs.    24 - 36 hrs. from        150
                                                     days                        beginning of estrus

     Goat         15 - 24               21        2 - 3 days       ________      Near end of estrus        151
                                                                     days

     Mare         15 - 24               21        4 - 9 days           5 days     1 - 2 days before    ___________
                                                                                    end of estrus


Preparing Animals for Breeding

The percentage of females giving ___________ greatly affects the success of a livestock enterprise. In
fact, the fastest means of increasing profits is to ________________ the number of females giving birth.
This has a tremendous impact on the ___________________ cost per pound for the animal being
produced. Therefore, to ensure a high conception rate, males and females of most species of livestock
must be ________________ for breeding.

Elements that influence when female livestock will begin a heat period are age, post-birthing interval,
_________________, physical condition, and disease. Age mainly refers to those females that are too



                                                     - 12 -
___________ for breeding. The _______________________ interval is the period of time when the
female reproductive tract is returning to its original shape and tone following parturition.

The ________________ condition of the female is very important at breeding time. For this reason, all
livestock species should be provided with supplemental nutrients during pregnancy and lactation.
Moreover, females that are either too thin or too fat will frequently be infertile. Further, animals that
have ________________ that affect fertility or pregnancy should be eliminated.

Cattle

The ultimate goal of most cattle producers is to achieve a ________% calf crop. If producers want their
cows to calve annually, then they must plan for them to calve at least _______ days before the beginning
of the next breeding season, so they may be rebred in a timely fashion. The ________ of the cow
influences the number of days after calving that will pass before she will come into heat. Usually, older
cows come into __________ sooner than younger cows. Moreover, first-calf heifers have to perform all
the bodily functions of a mature cow, while at the same time continuing to __________. Also, the stress
related to producing milk affects the rate of _________________ of first-calf heifers. However, research
has shown that a _______% conception rate for first-calf heifers can be achieved, if they are handled
properly following the birth of their first calf.

The most common problem affecting early breeding is a retained ________________. If attention is not
given to this problem, the cow’s _____________ may become infected and delay her next estrous cycle.
Further, post-calving interval influences recycling and ___________________ rate. For example, cows
should not be rebred until approximately _______ days after calving; about one-third of cows with a
shorter post-calving rest will experience serious reproductive problems.

A female’s genetic capability is another factor that influences breeding performance. Selection based on
regularity of breeding is an effective means of increasing overall ________________ efficiency. This
may be determined by examining (palpating) the females for pregnancy about _______ days after the
bulls were removed. At this time, any nonpregnant females should be _____________ from the herd and
sold.

_________________ is the most important environmental factor affecting reproduction. Most breeding
failures and late ______________ incidents can be related to a lack of adequate nutrition. Nutrition is
important for gestation, lactation, and rebreeding. If extra feed or grazing is not provided, the cow will

                                                    - 13 -
mobilize body __________ to compensate for the deficiency and will suffer a weight loss. This weight
loss may prevent her from cycling and rebreeding in a timely fashion

It has often been said that a bull is ________________ of the cow herd. Factors such as general health,
condition of feet and legs, age, teeth, and abnormalities of ______________________ organs should be
checked during a bull’s breeding soundness evaluation. Bulls should be fertility-tested prior to the
breeding season to determine ___________ quality. Another indication of a bull's reproductive ability is
his libido (sex drive), which is controlled by the hormone testosterone. This factor can be evaluated
when the bull is placed with cows that are in __________; at this time, a bull should become sexually
aroused and eager to mate.

Sheep

For most sheep producers, the goal set for their lambing crop is not 100%, but instead ________%.
Because most ewes are physically capable of giving birth to __________ lambs, producers tend to select
and keep ewes that consistently deliver healthy twins. Also, the practice of ________________
increases the rate of conception and influences the occurrence of twinning. For this reason, four to eight
weeks before breeding ewes, they should be flushed with good high-quality green pasture or fed
additional ______________________. In addition, every ________ should be fertility-tested prior to
each breeding season.

Similar to cattle, factors such as quality and quantity of feed nutrients are very important at time of
breeding, during gestation, and while _________________. Also, since most ewes go through a period
of _________________, they tend to only lamb in the late winter and spring. Therefore, the post-
birthing interval is not as critical as with cattle, because sheep have more time before rebreeding. Most
breeds of sheep will experience 17-day estrous cycles beginning in mid-fall and ending in early
_____________.

Swine

Most swine producers want their breeding stock to produce from eight to ______________ pigs per
litter. Female swine are selected based on the number of pigs born and weaned as well as their overall
_________________ ability. As with sheep and cattle, female swine productivity is affected by nutrition
prior to breeding (flushing), during gestation, and during lactation.



                                                   - 14 -
Boars exposed to stress or __________ temperature conditions may stop producing sperm. So, boars
should be kept in a __________, well-ventilated area. A boar’s feed intake should be increased during
times of active breeding. Ideally, boars should be purchased several months prior to the breeding season
so they can become accustomed to their new ____________________. Also, boars should be
_________________ tested once they are established.

Horses

Most authorities agree that mares are the most difficult of all livestock species to “settle” or to
________________. Before breeding, mares should be checked for signs of ________________ disease,
general sickness, and other types of unsoundness. Plenty of exercise and adequate __________ should
be provided during the mating season.

If possible, the mare should be taken to the stallion for ______________. Allow the mare to become
quiet and _____________ prior to breeding. Permit the stallion to mount the mare only when he is
___________ for service. After mating, return the stallion to his ___________ or pen. Allow the mare to
remain ___________ for a short period of time after service, then return her to her quarters. During
gestation, a mare should receive the __________ ration as before breeding.




                                                 - 15 -

				
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