photo by tim mccabe courtesy of usda natural resources conservation service. methods of animal...

Photo by Tim McCabe courtesy of USDA Natural Resources Conservation Service.

METHODS OF ANIMAL

BREEDINGAgriscience 332

Animal Science

#8407

TEKS: (c)(4)(C)


IntroductionNearly 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 methods of breeding.


Producers must be prepared to successfully breed livestock by using the appropriate technology and by applying a thorough working knowledge of animal nutrition, as well as, animal reproduction and physiology.


Breeding Systems

Breeding systems are a set of management 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 all producers.

Some systems may include grading-up, crossbreeding, purebred breeding, line-breeding, and inbreeding.


Factors to consider when determining which breeding system to use:

1. Climatic conditions,

2. Types of markets,

3. Knowledge of genetics,

4. Size of operation,


5. Personal preferences,

6. Available resources, and

7. Goals of the breeder.


Crossbreeding

Crossbreeding involves the mating of two animals of different breeds.

Usually, both animals are purebreds.


However, commercial breeders will often mate purebred sires to females that are considered grade animals (animal having non-purebred ancestors) with the resulting offspring also considered “crossbreds” or F1s.

This system may be referred to as indiscriminate crossbreeding.


Crossbreeding is done to improve the overall performance of offspring that result from mating individuals with different, but complementary, breed values.

Another reason for crossbreeding is to produce hybrid vigor or heterosis for traits such as fertility and survivability.


Advantages of crossbreeding are

1. Weaknesses can be improved upon or eliminated by breeding an animal “strong” in a particular trait to an animal that is considered to be lacking or “weak” in that trait;


2. The average productivity of the offspring is increased over either parent;

3. Crossbreds are more fertile than their purebred parents;


4. Crossbreds wean heavier offspring than purebreds; and

5. Crossbreds are more vigorous than purebreds.


With several crossbreeding methods in use, crossbreeding is the most popular breeding system practiced by commercial livestock operations.

However, some methods work better for certain species than others.


Three types of crossbreeding 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 commercial females, with the ultimate goal of eventually creating a purebred herd or flock.


The purpose of grading-up is to improve quality, develop uniformity, and increase performance in the offspring.

Breeding replacement females from within a commercial herd back to purebred sires results in offspring that are more genetically similar to the purebred sire.


A noticeable improvement through the fourth generation can be expected; however, progress is much slower for proceeding generations.

The purebred sires should be products of different production-tested herds.


Backcrossing

Backcrossing is the mating of an individual to any other individual with which it has one or more ancestral breeds or lines in common.

The backcross method is popular in commercial cattle operations.


With the backcrossing method, two purebreds are crossed and then the resulting offspring is bred back to one of the original parental breeds, but not the same parent animal.


This method of breeding productive female offspring to related breeds of superior males can be continued for several generations.


Repeated backcrossing is used to incorporate a specific trait found in one population into a different population, while maintaining selective traits found in the second population.

However, when using this system, the breeder may risk losing some hybrid vigor in later generations.


Three-breed Rotational CrossingThe three-breed rotational cross method is a type of crossbreeding that is popular with swine breeders.

This system involves breeding crossbred females to purebred males.


The rotation of purebred males from three breeds on subsequent generations of selected crossbred females can be continued for several generations.


InbreedingInbreeding is the mating of individuals over several generations that are more closely related than average for the population they represent.

Inbreeding is used more in purebred operations than in commercial operations.


When inbreeding is practiced for several generations it is called intensive breeding.

When “overused,” this form of breeding gives inbreeding a negative connotation.


When used appropriately, the purposes for inbreeding are to concentrate the inheritance of desirable traits and eliminate undesirable traits for a given group of animals.

If starting with a desirable group of animals, a breeder can make further improvements by inbreeding.


Ways inbreeding can improve livestock are:

• to develop outstanding herds,

• to form families,

• to produce breeding stock,

• to develop lines for crossing, and


• to determine the genetic value of an individual.

Some potential disadvantages of inbreeding may be decreases in reproductive efficiency, vigor, survival rate, and growth rate.


Line-breeding

Line-breeding is a “milder” form of inbreeding designed to maintain a degree of relationship to highly regarded ancestors, without resulting in a level of inbreeding that is harmful.


Similar to inbreeding, line-breeding is more often used in purebred operations.

Animals are never mated that are closer than half-brothers or half-sisters.


A breeder using the line-breeding system should recognize its potential and limitations.

Line-breeding is only successful in herds that have a high degree of excellence and possess outstanding individuals as indicated by progeny tests.


Purebred Breeding

Inbred lines are established breeds.

Rather than referring to the process 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 registered in a breed association or are eligible for registry.

A purebred animal’s lineage 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 superior.

Yet, purebred animals may be preferable in many respects when compared to grade animals.


Methods of Breeding

Livestock species can be bred naturally or through assisted reproductive (artificial) technologies.


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,


• Facilities,

• Financial resources,

• Breed registry policies, and

• Personal preference.


Natural Breeding

As the name suggests, natural breeding allows animals to breed naturally.

However, there are ways of controlling the natural breeding process.


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 mating.


Under the hand mating system, when the female comes into heat (estrus) she is brought to the male and mated individually.

Advantages of this system are that the male can service more females, the act of mating is controlled, and accurate records (breeding dates, etc.) are easier to keep.


Hand mating requires additional labor because the female must be checked for heat twice daily during the breeding season and also brought to the male when mating is to occur.


Pasture Mating

The pasture mating system, used with most commercial herds, allows the male to be with the females throughout the breeding season or for the entire year.


If uniformity in size of offspring and time of parturition are important production factors, exposure to males must be limited to only the breeding season.


The pasture mating system may be used for all species of livestock.

It requires less labor because it involves less handling of the animals.

A disadvantage is that records are more difficult to keep, especially when more than one male is used for pasture mating.


When exact records are desired, place the recommended number of females per male and keep them in separate pastures.


Corral Mating

Corral mating is used mostly by horse breeders and involves putting the mare and stallion together in a strongly fenced corral.


There is no human assistance required, other than transporting the animals to the corral.

Both mare and stallion are returned to their respective pens after service.


Flock Mating

Flock mating, popular with poultry breeders, allows a number of males to be placed with an entire flock of females.


On average, a placement ratio of 12 to 15 males per 100 females is practiced in poultry breeding flocks.

There tends to be high fertility rates with this system and it requires less labor.


Pen Mating

Pen mating, a breeding method practiced primarily by poultry breeders, places one male with 8 to 20 females in a single pen.


The pen mating system makes it easier for a producer to know the parents of every chick and to evaluate a male’s reproductive performance.


Fertility is generally not as good in pen mating as compared to flock mating because the females cannot choose their mate, and there is no competition occurring between males for mates.


Assisted Reproductive Technology

Technology offers new approaches for the artificial breeding of animals and can assist in addressing problems of infertility.


Modern reproductive technologies include artificial insemination, semen freezing, embryo transfer, and cloning.


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 health as well.


Artificial Insemination (A.I.)Artificial insemination is a reproductive technology in which semen is collected from males and then used to breed females.

Artificial insemination is discussed in-depth in lesson 8818-A.


Advantages of Artificial Insemination

1. It allows the use of superior, performance-tested sires;

2. Records for production (such as sire identification) can be improved;


3. The number of females that can be bred to one superior male increases;

4. The chance of spreading disease is reduced; and

5. The chances of breeding-related injuries are reduced.


Disadvantages of Artificial Insemination1. A trained inseminator is

required;

2. More time and supervision of the female is required, thus more labor is needed;

3. Special handling facilities and sterile equipment are required; and


4. The cost may be a problem for some producers.


Embryo Transfer

Embryo transfer is the process of removing an embryo from a female’s reproductive tract, during the early stages of embryonic development, and transferring the embryo to another female’s reproductive tract for further development and subsequent birth.


Embryo transfer procedures are more expensive and labor intensive than other methods and are used more often in cattle than in other species of livestock.

Embryo transfer technologies are discussed in-depth in lesson # 8818-B.


However, through the use of artificial insemination and embryo transfer, there can be a greater number of offspring produced from genetically superior sires and dams.


Estrous SynchronizationEstrous synchronization is a process that uses chemically manipulated hormones to bring females into heat at or near the same time.

Estrous synchronization can be used in any breeding program.


Estrous synchronization of several females can be economical for producers.

It reduces the number of days needed to inseminate or transfer a herd, thus concentrating labor needs to specific breeding and birthing times.


Cloning

Cloning is a reproductive technology that may be used to produce genetically identical individuals.

There are several methods of cloning such as embryo splitting and nuclear transfer.


Embryo Splitting

Embryo splitting, or bisection, involves mechanically cutting an embryo in half to produce twin embryos, which are then transferred to recipient females.


Embryo splitting is possible because the young embryonic cells are totipotent; that is, the cells have not yet begun to differentiate into specialized cells and have the potential to become any type of cell.


Embryo splitting occurs naturally in the case of identical twins.

Embryo splitting is designed to increase the efficiency of the embryo transfer rather than producing multiple clones.


Nuclear Transfer

The process of nuclear transfer takes the genetic material from the nucleus of a donor cell and transfers it into an immature recipient egg cell, one whose own nuclear material was removed.

This process is discussed in-depth in lesson #8518.


Advantages of Cloning

1. Individuals with outstanding genetics can be replicated;

2. Cloning allows for mass production of outstanding animals;

3. Sex selection of an animal can be predetermined; and


4. Records of evaluation become more accurate.


Disadvantages of Cloning

1. The rate of success is lower;

2. More labor and other expenses are required;

3. The potential for genetic variation is decreased;


4. Selection of outstanding animals from a cloned herd becomes more difficult; and

5. A highly-skilled technician is needed to perform procedures.


Factors to Consider When Selecting a Method of Animal

BreedingWhen selecting a method of animal breeding, producers should consider the following factors.


• Breeding season;

• Age of puberty and breeding ages of livestock;

• Reproductive cycles of livestock; and

• Preparation of animals for breeding.


Selecting a Breeding SeasonWhen establishing breeding

systems and methods of breeding, producers must decide on a breeding season.

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 weight.


Ideally, offspring for a given livestock enterprise should be born within a specified number of days; for example, 40 to 60 days is a common time frame for cattle.


Factors to consider:

• Climatic conditions will affect the amount of equipment, feed, and housing needed;

• The availability of labor 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 marketing the offspring need to

be set;

• In certain areas, availability of equipment and housing are factors that affect the choice of breeding season. For example, …


some species of livestock will have to be placed in a barn and provided heat during the winter months.

• If the females and offspring are to be provided grazing, then its availability may be of great importance (usually grazing is best during late spring and early summer);


• Livestock show rules may require that animals be classed based on their ages (Frequently, animals that are the maximum allowable age for a particular class have a competitive advantage); and

• The purpose for which livestock are produced (For example, …


the birth of offspring for replacement purposes determines the season in which they will reach a desirable breeding age and thus the length of time required to bring them into production).


Age of Puberty and Breeding Ages of Livestock

Season of birth, temperature, nutrition, rate of maturity, and heredity affect the age at which animals reach puberty.


The age of puberty (age at which animal reaches sexual maturity and is capable of reproducing) and breeding age are two distinct benchmarks of physical development.


Because an animal has reached sexual maturity does not always mean that it is capable of reproducing efficiently.

For example, research reveals that stage of body development is frequently more important than age in determining when animals will reach puberty.


Usually, it is advisable to allow livestock to continue to develop and mature after reaching puberty.

Proper breeding age may vary widely, depending on body growth and development of individual animals, within a breed and species.


Often, it may appear advantageous to breed at an early age to reduce production expenses.

Sometimes it is to the producer’s advantage to delay breeding to avoid the possibility of physical injury occurring and to reduce the incidence of birthing problems associated with physically underdeveloped females.


Puberty Age


Breeding Ages of FemalesMating females for the first time at a mature breeding age offers certain advantages to the producer, such as a physiological advantage and increasing a heifer’s rate of milk production.


Early breeding can potentially increase the lifetime production of a female.

Supplemental feeding of heifers or providing them with good pastures can cause heifers to develop and mature faster and thus breed earlier.


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


Breeding Age of MalesThe principal consideration for the breeding age of males is the number and quality 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, temperament, and condition, as well as, the breeding system (hand or pasture mating) used and the distribution of services.


Mating Guide


If pasture mating is practiced, several other important factors, such as range carrying capacity, size of pasture, and herd size, will influence the number of females that can be serviced by one male.


One bull to about 25 cows is the standard ratio recommendation for cattle under range conditions.

A ratio of one ram to 25 – 30 ewes is recommended for sheep under range conditions.


Pasture mating is not recommended for stallions, due to the possibility of injury.

As a general rule, mature males of all species are capable of breeding considerably more females than are young males.


Reproductive Cycles of LivestockFactors that control reproductive

cycles of female livestock:

• Estrus,

• Estrous cycle,

• Time of ovulation, and

• Gestation period.


Estrous (or heat interval) – includes the reproductive and hormonal changes a female undergoes on a “scheduled-basis” after reaching puberty.


Estrus (or heat period) – is the portion of the heat interval during which hormones are secreted by female and outward signs of receptivity to mating are displayed.


Ovulation is the expelling of an egg (ovum) from the ovary.

Ovulation occurs during the heat period (estrus) and signals that the egg is ready to be fertilized by a sperm cell.


Once an egg is successfully fertilized, the female’s body undergoes physical changes as the fetus develops.

Gestation period – the period of time required for the fetus to develop.


Reproductive Cycles of Livestock


Preparing Animals for BreedingThe percentage of females

giving birth greatly affects the success of a livestock enterprise.

The fastest means of increasing profit is to increase the number of females giving birth, which impacts the production costs per pound.


To ensure a high conception rate, males and females of most species of livestock should be prepared for breeding.

Elements that influence when female livestock will begin a heat period are age, post-birthing interval, nutrition, physical condition, and disease.


Age – mainly refers to those females that are too young for breeding.

Post-birthing interval – refers to the period of time needed by the female reproductive tract to return to its original shape and condition following parturition.


Physical condition – refers to the body condition of the animal and is based on nutrition; females and males that are too fat or too thin frequently do not reproduce efficiently.

Diseases – affect fertility and the ability of an animal maintain pregnancy for full term.

Cattle

The ultimate goal of most cattle producers is to achieve a 100% calf crop.

Calf crop refers to the ratio of calves produced to the number of cows in the herd.

Photo by Keith Weller courtesy of USDA Agricultural Research Service.

If producers want their cows to calve annually, they must plan for them to calve at least 45 days before the beginning of the next breeding season, so they may be rebred in a timely fashion.


The age of the cow influences the number of days after calving that will pass before she will come into heat.

Usually, older cows come into heat sooner than younger cows.


First-calf heifers have to perform all the bodily functions of a mature cow, while at the same time continue to grow.

The stress related to producing milk affects the rate of recycling of first-calf heifers.


Research has shown that a 90% 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 placenta, which can cause the cow’s uterus to become infected and delay her next estrous cycle.


The post-calving interval influences recycling and conception rate.

About one-third of cows having a rest period shorter than 45 days experience serious reproductive problems.


An effective means of increasing overall breeding efficiency is to select females based on breeding performance, which is genetically influenced.

This may be done by palpating females about 45 days after bulls are removed and culling cows that are not pregnant.


The most important environmental factor affecting reproduction is nutrition.

Most breeding failures and late calving 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 mobilize body fats to compensate for the deficiency and will suffer a weight loss, which could prevent her from cycling and rebreeding in a timely fashion.


It has often been said that a bull is one-half the cow herd.

Factors such as general health, condition of feet and legs, age, teeth, and abnormalities of reproductive organs should be check during a bull’s breeding soundness evaluation.


Bulls should be fertility-tested prior to the breeding season to determine semen quality.

The bull’s libido should be evaluated when the bull is placed with cows that are in heat; at this time the bull should become sexually aroused and eager to mate.


Sheep For most sheep producers, the goal set for their lambing crop is 200%, since most ewes are physically capable of giving birth to twin lambs.

Producers tend to select and keep ewes that consistently deliver healthy twins.

Photo by Ron Nichols courtesy of USDA Natural Conservation Resource Services.

Flushing, a practice of feeding ewes good high-quality green pasture or additional concentrates four to eight weeks before breeding, increases the rate of conception and influences the rate of twinning.


Rams should be fertility-tested prior to each breeding season.

Factors such as quality and quantity of feed nutrients are very important at time of breeding, during gestation, and while lactating.


Since most ewes go through a period of anestrous, they tend to only lamb in the late winter and spring.

Most breeds of sheep will experience 17-day estrous cycles beginning in mid-fall and ending in early spring.


Swine

Most swine producers want their breeding stock to produce eight to fifteen pigs per litter.

Female swine are selected based on the number of pigs born and weaned, as well as, their overall mothering ability.

As with sheep and cattle, female swine productivity is affected by nutrition prior to breeding (flushing), during gestation, and during lactation.

Boars exposed to stress or high temperature conditions may stop producing sperm.

Boars should be kept in a cool, well-ventilated area and should have feed intake increased during times of active breeding.

Ideally, boars should be purchased several months prior to the breeding season so that they can become accustomed to their new environment.

Boars should be fertility tested once they are established.

HorsesMost authorities agree that mares are the most difficult of all livestock species to “settle” or conceive.

Before breeding, mares should be checked for signs of venereal disease, general sickness, and other types of unsoundness.

Photo courtesy of USDA Photography Center.

Plenty of exercise and adequate feed should be provided during the mating season.


If possible, a mare should be taken to the stallion for service.

Allow the mare to become quiet and cooled prior to breeding.

Permit the stallion to mount the mare only when he is ready for service, then return him to his stall. Photo courtesy of USDA Photography Center.

Allow the mare to remain quiet for a short period of time after service, then return her to her quarters.

During gestation, a mare should receive the same ration as before breeding.



SummaryProducers should carefully consider factors that affect the reproductive efficiency of livestock and use sound management practices to increase production and profitability of enterprises.


ALL RIGHTS RESERVEDReproduction or redistribution of all, or

part, of this presentation without

written permission is prohibited.

Instructional Materials Service

Texas A&M University

2588 TAMUS

College Station, Texas 77843-2588

http://www-ims.tamu.edu

2006

photo by tim mccabe courtesy of usda natural resources conservation service. methods of animal...

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