Animal breeding systems

The design of a breeding programme is a never-ending process – markets change, livestock change, technologies change, and humans change. There are however some proven breeding programmed that have withstood the test of time.

It is important to first understand animal breeding systems before attempting to re-design the wheel in planning your own breeding system.

A breed is a group of domestic animals with a homogenous appearance, behaviour and other characteristics that distinguish it from other animals.

Animal breeding is a segment of animal science that addresses the evaluation of the genetic value of domestic livestock.

What is the purpose of breeding systems?

The purpose of breeding is summarised as follows:

If you don’t know, you cannot measure
What you don’t measure, you cannot manage
Desirable traits are what you select for
Negative traits are what you select against/li>
Breeding is done towards a specific goal or target

The big debate in breeding animals is captured in the concepts of a system of straight breeding, versus a system of cross breeding

Straight breeding vs. Cross Breeding

Straight breeding

Straight breeding with commercial cows/ ewes can be relatively straightforward using the selection principles you have already learned and the goals you have set for your operation. You would select breeding stock out of one breed and continue to use that same breed of bull / ram to breed progeny. A breeder would only have to be familiar with the traits and selection tools of one breed.

Cross Breeding

Crossbreeding creates the ability to take advantage of the strengths of two or more breeds to produce offspring that have optimum levels of performance in several traits. There are several factors and challenges that need to be considered when evaluating choice of crossbreeding system, including:

Number of cows / ewes in the herd
Number of available breeding pastures
Labour and management
Amount and quality of feed available
Production and marketing system
- Availability of high-quality bulls of the various breeds

As an example, European breeds (Bos Taurus such as Charolais, Limousine, and Simmental) are typically superior for cutability (red meat yield), whereas Zebu breeds (Bos Indicus such as the Brahman) through centuries of exposure to inadequate food supplies, insect pests, parasites, diseases and the weather extremes of Africa, have developed some remarkable adaptations for survival. Combining the breed types results in offspring that have desirable levels of both qualities.

Pure breeding

Pure-breeding (or Purebred breeding) is the mating of males and females of the same (particular) breed (breeding line) for many generations that always produce progeny of the same phenotype. A purebred flock can be managed as a single flock because all animals are of the same breed.

(A breeding line is a group of identical pure-breeding diploid or polyploid organisms, distinguished from other individuals of the same species by some unique phenotype and genotype.)

(Purebred (True breeding) refers to the offspring of 2 parents that are genetically the same. In terms of Mendelian genetics, this type of breeding requires that the organism is homozygous, which means a single trait stems from having identical alleles.

The exception is found in plant genetics and includes two types of asexual reproduction, including parthenogenesis (reproduction from an ovum without fertilization) and apomixis (replacement of the normal sexual reproduction by asexual reproduction), because their reproduction can also result in pure breeding.)

The goal of purebred production is to provide superior genetics to the commercial livestock industry. Therefore, it is important to note that purebred animals are not in the sense “better” than crossbreed animals. Pure- breeding is a specialised industry whereby breed standards are prescribed by a stud breeders association that also administrates the evaluation and registration of specific breeds. Due to the homozygous genetic characteristics of purebred animals, undesirable recessive characteristics may appear, and careful selection is needed to avoid this.

Pure-breeding is a very expensive breeding exercise. The following pure-breeds are affiliated to the South African Stud Book Association (SA Stud Book).

Beef cattle

Afrigus Club
Afrikaner Cattle Breeder’s Society of South Africa
Angus Society of South Africa
Beefmaster Cattle Breeders’ Society of South Africa
Bonsmara Cattle Breeders’ Society of Namibia
Bonsmara Cattle Breeders’ Society of South Africa
Boran Cattle Breeders’ Society of South Africa
Braunvieh South Africa
Charolais Cattle Breeders’ Society of South Africa
Dexter Cattle Breeders’ Society of South Africa
Drakensberger Cattle Breeders’ Society of South Africa
Gelbvieh Cattle Breeders’ Society of South Africa
Hugenoot South Africa
Nguni Cattle Breeders’ Society of South Africa
Pinzgauer& PinZ²yl Cattle Breeders’ Society of South Africa
Red Poll Cattle Breeders’ Society of South Africa
Romagnola Cattle Breeders’ Society of South Africa
Senepol Cattle Breeders’ Society of South Africa
South Africa Hereford Breeders’ Society
South Devon Cattle Breeders’ Society of South Africa
Sussex Cattle Breeders’ Society of South Africa
Tuli Cattle Breeders’ Society of South Africa

Dairy cattle

Ayrshire Cattle Breeders’ Society of South Africa
Jersey South Africa
Shorthorn Cattle Breeders’ Society of South Africa
South Africa Dairy Swiss
South Africa Guernsey Cattle Breeders’ Society
South African Holstein Frieslands

Sheep

Afrino Sheep Breeders’ Society of South Africa
Bapedi Sheep Breeders’ Society of South Africa
Damara Sheep Breeders’ Society of South Africa
Dohne Merino Sheep Breeders’ Society of South Africa
Dormer Sheep Breeders’ Society of South Africa
Dorper Sheep Breeders’ Society of South Africa
Ile de France Sheep Breeders’ Society of South Africa
Karakoel Club
Meatmaster Sheep Breeders’ Society of South Africa
Merino Landskaap
Merino Sheep Breeders’ Society of South Africa
SA Mutton Merino Breeders’ Society
Suffolk Sheep Breeders’ Society of South Africa
Van Rooy Sheep Breeders’ Society of South Africa

Goats

Kalahari Red Club
SA Boer Goat Breeders’ Association
Savannah Boer Goat Breeders’ Society of South Africa
South Africa Milch Goat Breeders’ Society

Inbreeding

Inbreeding is the reproduction from the mating of two genetically related parents, for example a parent with offspring, full brother and sister, or half brother and sister. In other words, it is mating between individuals that are genetically related.

Inbreeding = the mating of two animals that are genetically related

All pure breeds of animals can be traced back to a relatively limited number of foundation ancestors. Therefore, pure breeding is a system of inbreeding, although the term is not generally used to refer to mating where a common ancestor does not occur within a five-generation pedigree.

Linebreeding (or close breeding) is a term developed and used by pure breeders (stud breeders) to cover the milder forms of inbreeding.

What does inbreeding do?

What does inbreeding (in the genetic sense) do? Basically, it increases the probability that two copies of any given gene will be identical and derived from the same ancestor. Technically, the animal is homozygous for that gene. The heterozygous animal has some differences in two copies of the gene. Remember that each animal (and plant) has two copies of any given gene (two alleles at each locus), one derived from the mother and one from the father. If the parents are related, there is a chance that the two genes in the offspring are identical copies contributed by the common ancestor. This is neither good nor bad in itself. Unfortunately, we cannot breed animals based on a single gene – the genes come as a package. Inbreeding tends to make all genes more homozygous

Inbreeding is measured through the inbreeding coefficient. This is related to the probability that both copies of any given gene are derived from the same ancestor. The degree of inbreeding is denoted with Wright’s inbreeding coefficient, indicated with the letter “F”. The coefficient of inbreeding (F), indicates the percentage (%) with which heterozygosity decreases.

The continued mating of brother and sister will give the following “inbreeding coefficient”, which expresses the genetic percentage of progeny in the table below:

The above coefficient shows that heterozygosity (Aa) decreases in further generation inbreeding of siblings, and that homozygosity increases (AA) (aa). This increases the chances of offspring being affected by recessive negative traits (aa).

The Inbreeding coefficient “F” for some inbreeding matings are:

Father X Daughter = 25%
Mother X Son = 25%
Brother X Sister = 25%
Half Brother X Half Sister = 12.5%
Cousin X Cousin = 6.25%

This generally leads to the decreased fitness of a population, which is called inbreeding depression (also called an inbred animal). Breeders also use this technique to show recessive gene characteristics to enable them to eliminate these characteristics through culling.

On the other hand, the increased heterozygosis for the dominant traits (AA) leads to the use of selection techniques to establish new and desirable traits in livestock. This leads to the creation of hybrid animals.

With inbreeding, it is possible to develop highly productive inbred lines of animals. Although occasionally high-performance animals are produced, inbreeding generally results in an overall reduction of performance, and this reduction is manifested in many ways.

The most obvious effects of inbreeding are:

Poorer reproductive efficiency
Higher mortality rates
Lower growth rates
Higher frequency of hereditary abnormalities

Advantages of inbreeding

The breeder produces pure breeding groups with uniform families and blood lines
The relationship with a specific ancestor can be kept at a high level
Recessive harmful traits can be made homozygous and identifiable for elimination
Separate uniform families can be formed and selection between groups can be performed effectively
Advantageous pre- potency can be fixed in offspring because individuals contain a greater number of advantageous traits, due to being homozygous

Disadvantages of Inbreeding

Physical strength and good health (vigour) of animals decrease
Undesirable genes become homozygous fast and all animals with weaknesses are not all eliminated, although undesirable genes can be fixed in the progeny
Inbreeding decline can soon appear in a flock
Genetic variation becomes less, and selection of successful variants become difficult
Deformed animals in flocks will become common
To eliminate deformed animals through breeding is expensive. The reason is that genetic outstanding animals must be used waisted in a breeding programme to achieve this.
Beneficial inbreeding requires expert knowledge
Fertility is lowered
Production is lowered
Inbred animals are less adaptable
Inbred animals are less resistant to diseases

Outcrossing

In the opposite of inbreeding, out crossing refers to the mating of two parents who are totally unrelated to each other.

Outcrossing = the mating of animals that are members of the same breed, but which show no relationship close-up in the pedigree.

As an example, if you take a look at the diagram of a cattle family tree, you can see why.

Outcrossing is also referred to as cross breeding, but in the sense of using the term “outcrossing ” it is easier to understand that it refers to the selection of a trait in a breeding programme by crossing two animals from different families ( unrelated) who reflect the same traits in phenotype. Outcrossing is the safest way to add new blood to an inbreeding programme, whilst causing the least amount of retrogression in what has been accomplished in the line breeding programme.

Using outcrossing in a line breeding programme, the unrelated outcross minimises the chance of intensifying undesirable traits. Unfortunately, due to the heterozygous, or dissimilar, genetic nature of a group of unrelated stock, the chance of intensifying desirable traits is likewise diminished.

In theory, the product (progeny) of outcrossing programs may be more heterozygous than that off inbred stock. Outcrosses might be outstanding performers, but as breeding stock, they will not pass on their desirable characteristics consistently. Often the most consistent results in an outcrossing program are obtained when the pure strain individual used in the cross is also from another strong linebred individual (from an unrelated stud breeder).

After making use of an outcross, a breeder should breed right back into the original strain, as explained in the diagram above. This is the only safe procedure to continue with an inbreeding programme, after the desired trait has been obtained and the purpose of the outcross has been achieved.

There is no genetic reference or prescription as to when it is necessary to bring in a new bloodline through an outcross in an inbreeding programme. After too many generations of linebreeding, there is sometimes a risk of producing non-desirable traits. Not all breeders agree that these risks occur, but many have experienced problems which they have attributed to linebreeding. A rule of thumb between in-breeders is to do an outcrossing after each 3^rd generation inbreed.

An outcross does have the risk of bringing in a “loose type”, resulting in the loss of a specific trait selected for over a long period of time in an inbreeding programme. The breeder needs to introduce new genetic material only if the animal used (strange bloodline) can bring something needed into the programme and if the linebred and/or inbred programme have been repeated already several times. The breeder needs to know and research the origin and ancestors of the “external” animal well, as well as the traits that those ancestors can add to the existing inbred line. In many cases, the level of danger inherent in inbreeding, linebreeding, and outcrossing can be equal when these breeding methods are practiced by a careless or inexperienced breeder.

After making use of outcrossing, the breeder must continue immediately with linebreeding of the progeny to ensure that the “good genes” brought into that line by the outcross is transferred to the original inbreeding programme. An outcross can also help a breeder to achieve “missing traits” not produced before. This is normally achieved through outcrossing with a superior animal or a very rare and proven pedigree which is not yet in his programme. This system can bring the qualities needed or correct / eliminate some trait faults.

Outcrossing can bring vigour(robustness, healthiness, good health, hardiness, strength, stamina, sturdiness, fitness, good shape, good trim, good condition, fine fettle, toughness, ruggedness, muscle, power) into a linebreeding programme, but a pure linebreeding programme as such, when very carefully planned, should have the same result because vigour is a desirable trait which a breeder should line breed for.

Line Breeding

Line breeding refers to an inbreeding programme, where closely related animals are bred to keep the offspring closely related to some highly admired ancestor, such as male offspring to mother, male to female sibling, half-siblings and other lines of related male and female animals.

Linebreeding = inbreeding programme to keep the progeny closely related to a superior ancestor

An outstanding or highly admired parent is usually male, because of better evaluation and better offspring achieved through bringing a superior male (or seed) into the breeding programme. Linebreeding increases homozygosity and makes it possible that the progeny will contain the same desirable genes as the superior ancestor.

Explain Line Breeding

Ancestor No. 5 is responsible for the relationship between Father B and Mother K of Individual N. The stud book diagram shows that N received 50% of its genetic material from ancestor 5, which is also equal to the 50% of genetic material that comes from each parent.

Line breeding is used in highly rated pure-bred herds such as the Santa Gertrudis and Pinzgauer beef breeds.

Grading up

Upgrading breeding refers to the use of pure bred males on inferior females, to genetically improve the progeny.

Upgrading = Use of purebred males to genetically improve inferior females

Take cattle as an example:

A rural farmer with inferior and mixed bred cows, can obtain purebred Bonsmara bull for upgrading of his flock.

Advantages of Upgrading

It is economically a cheap method of herd improvement
One good quality male is obtained instead of a whole flock of females
It is a fast and effective method of improvement
No expert knowledge is needed

Weak recessive genes (aa) are dominated by heterozygous (Aa) result using dominant (AA) male genes, for example

Disadvantages of upgrading

Male progeny is not suitable for breeding and causes low income potential
Improvement decreases after 3^rd mating
100% pure animals cannot be bred

Crossbreeding

Crossbreeding is the mating of animals of different kinds and breeds. The product of crossbreeding is the so-called hybrid that has increased ability in terms of fertility, hardiness and general efficiency. The improved production ability is known as hybrid vigour. This improvement is measured in terms of the increased production of a certain trait (or variety of traits) above the average of the two parent populations.

Crossbreeding = mating of animals of different breeds to obtain increased production traits

In South Africa, one of the best examples of a cross breeding program to obtain a hybrid breed, is found in the crossbreeding programme developed by Prof. Jan Bonsma in breeding the Bonsmara. The Bonsmara is the only beef breed in the world created through a well-documented crossbreeding programme, with the aid of objectively recorded performance data.

The modern Bonsmara is a crossbreed composite of 5/8 Afrikaner (Bos Taurus) x 3/16 Hereford and 3/16 Shorthorn.

The Bonsmara is referred to as a composite breed, which means that the breed is a result of multiple (4 – 5 breed rotation), and as a composite breed will be used as a new purebred, not to be crossed again.

Improvements resulting from cross breeding should be measured in terms of the best parent of the cross. If there is no improvement it is not worthwhile to practice crossbreeding. Why should one crossbreed when there is already a better parent breed?

Hybrid vigour, or heterosis, cannot be fully explained, but there are various theories as to its cause. However, the result is that the efficiency of the animal is increased. It has the same influence on the animal as if the environmental conditions were much improved, with the result that an increase in mass gain, reproductive ability and general vitality is measured.

Hybrid vigour is the increased production of certain traits from the crossing of genetically different individuals. The offspring exceed the average performance of their parents for traits for which hybrid vigour is expressed.

For example:

Breed A averages 610 pounds at weaning
Breed B averages 590 pounds at weaning
When crossed, the A x B calves average 625 pounds at weaning

The hybrid vigour from this mating can be calculated with the following equation:

The hybrid vigour for this cross is 4 percent above the average of the parent breeds for weaning weights. This is known as individual heterosis. Individual heterosis is the increase in production seen in the crossbred offspring. This type of heterosis is generally seen in growth traits of the crossbred offspring. Throughout this publication, % heterosis will be in reference to an F1 (first-generation cross) with 100 percent heterosis.

It has also been found that the greater the difference between two crossed breeds, the more heterosis occurs. It is also important that the parents used for crossbreeding should be as pure as possible.

The characteristics influenced most by cross-breeding are those with a low heritability for example fertility, milk production and growth. These are the traits influenced most by environmental conditions and are difficult to improve through breeding.

The aim of crossbreeding

To utilise heterosis in obtaining a more productive slaughter animal
To combine the favourable properties of two (or more) breeds for a specific purpose and so to obtain animals that are better adapted and mature faster, with higher fertility and better milk production

The purpose of crossbreeding

A breeder must set himself a specific goal with crossbreeding. Crossbreeding without a goal can lead to chaotic results.

Goal 1. To attain of a more productive slaughter animal

This aspect is clearly illustrated by the crossbreeding work performed at Vaalharts many years ago with Jerseys. It is generally known that the Jersey does not produce the ideal slaughter animal, since it was bred for milk production. Jersey cows were then crossed with Afrikaner, Charolaise and Hereford bulls.

Some of the offspring were slaughtered at an age of 18 months after a finishing period of 118 days. Carcass mass in the Afrikaner, Charolaise and Hereford crosses were 206,4kg, 227kg, and 210kg respectively. Carcass masses in the three crosses were good, and much better than would be expected in a pure Jersey. The Charolaise crosses produced the highest carcass mass with a good meat conformation.

The desired carcass type will therefore determine what sire breed should be used in the cross. Thus, if fat covering is a prerequisite for good grading, the Hereford will be the obvious choice as the sire breed. This is also the reason for the British beef breeds being so popular for crossbreeding in South Africa.

However, grading requirements are in the process of changing in favour of more muscle and relatively less fat. As a result of this, large-frame lean meat breeds and the dual-purpose breeds are becoming more popular. Since less fat is produced these breeds and their crosses are usually also more efficient as regards feed utilisation.

Similar results were obtained with Afrikaner cows crossed with different beef and dual-purpose breeds. Brahman-Afrikaner crosses also performed very well under veld conditions. Under these conditions they maintained an excellent growth rate and produced a carcass of above-average quality. However, under feedlot conditions these crossbred oxen did not perform better than pure Afrikaners. It is clear that the ultimate aim of crossbreeding must be clearly defined.

Goal 2. To attain more productive breeding animals

The characteristics that derive most advantage from crossbreeding are those with a low heritability, i.e. those traits which are difficult to improve by breeding. Milk productions and notably fertility are two such traits. The F1 heifers can thus gain much with regard to these traits.

It is known that generally the Hereford is characterised by low milk production. Crossbreeding with the Hereford cow will have as a result that female offspring will show considerable improvement as regards this trait. When the sire is a dual-purpose animal, it can be expected that milk production will be much improved.

Generally, milk production in the Afrikaner cow is not sufficient to maintain a high growth rate in her calf. Crossing of Afrikaner cows with a dual-purpose bull such as the Simmentaler has also had good results. The F1 heifers attain sexual maturity at an earlier age as a result of their faster growth and are capable of maintaining a high reproductive rate. These animals also produce large quantities of milk and consequently their calves grow fast. In addition, the contribution of the Afrikaner ensures that the heifers are hardier and better adapted to extensive conditions than the pure Simmentaler. On the other hand, the Simmentaler contributes to the growth potential and the conformation of the offspring.

The question is often asked whether the use of F1 bulls also holds advantage. Most results prove that the use of F1 bulls exert a negative influence on the offspring. The explanation for this phenomenon is that the advantage of F1 females is not so much associated with their breeding ability, but with their ability to make better use of the environmental conditions. This ability is not very heritable and thus cannot be transmitted to the offspring by the bull. The recommendation therefore is not to use crossbred bulls. Earlier in the chapter mention was made of the fact that maximum heterosis is obtained when parents used in cross-breeding are as pure-bred as possible. Fertility, milk production and growth of F1 heifers is thus the expression of the heterosis caused by mating of pure animals and must not be confused with the above-mentioned statement.

The choice of Suitable breeds for Crossbreeding

The purpose of crossbreeding will to a large extent determine which breeds are chosen. In South Africa there is little justification for crossing exotic breeds, except when grading up animals to a specific breed. The reason for this is that the most exotic breeds are efficient producers under favourable conditions and in addition their numbers are relatively small. It is thus difficult to obtain sufficient good mothers for crossbreeding. The crossing for example of the Hereford with the Friesland is applied in dairy herds where offspring are not retained or where young heifers are mated with a beef bull so that their potential can first be gauged.

In South Africa, the Brahman is usually used as the dam breed in view of their large numbers and the hardiness and mothering ability of the cow.

The following crosses can be considered for specific conditions and purposes: (Dam breeds are used as heading)

a. Zebu breeds (Afrikaner and/or Brahman) crossed with:

Zebu for breeding animals or store oxen under extensive production conditions.
New breeds (Bonsmara, etc.) for grading up to these new breeds.
Small-frame beef breeds (Hereford, Sussex, etc.) for slaughter animals under both intensive and extensive conditions.
Small-frame dual purpose breeds (South Devon) for breeding animals and slaughter animals.
Large-frame dual purpose breeds (Simmentaler, Pinzgauer, etc.) for breeding animals – watch out for calving problems in certain breeds.
Crossing with large-frame beef breeds is not recommended because of calving problems.

b. New breeds (Bonsmara) crossed with:

Small-frame beef breeds for slaughter animals under intensive and extensive conditions.
Other crosses are not recommended.
- Large frame dual purpose (Simmentaler etc.) with:
Zebu breeds for breeding animals in any system
New breeds for slaughter animals and breeding animals in any system.
Small-frame beef breeds for slaughter animals under intensive conditions.

Small-frame beef and small-frame dual purpose breeds can be crossed with Zebu and new breed bulls for slaughter and breeding animals in any system, but this is not strongly advocated.
Large-frame beef breeds (Charolaise etc) are not recommended for cross-breeding purposes since the smaller bull breeds will not be able to maintain the production potential of the pure breeds.
Dairy breeds are often crossed with bulls of Zebu breeds, small-frame beef breeds, and sometimes also new breeds. Good slaughter animals can be obtained. Where Zebu blood is brought in, the female offspring can also be used as breeding animals in any system.
- Problems encountered with crossbreeding

The best result with crossbreeding is obtained when well-bred animals representing two divergent pure breeds are mated with each other. The cowherd used for crossbreeding must either be bred by the breeder himself or brought in. A herd of purebred animals must thus be available to produce a sufficient number of good purebreds breeding animals for crossbreeding purposes, and to supply replacement heifers. However, depending on the standard of the pure herds, it is difficult, or even impossible to do this. Under favourable conditions only 10% good pure heifers are available for cross breeding. It would be sufficient to keep the crossbreeding herd constant, but not to increase the size of the herd, or to improve the herd. best replacement heifers are used for the pure herd.
Cross-bred animals are usually much more productive than their dams and require sufficient feed to fully express their potential. More and better-quality grazing is thus a prerequisite for efficient production with this type of animal. It can easily be stated that 20% more grazing per animal will be required since these bigger animals eat more. If the same number of crossbred animals is kept on the same limited area of land as their pure-bred mothers, the veld will undergo damage and retrogression. The advantages of hybrid vigour will then be changed to a disadvantage.
The heterotic effect is maximised when first-crosses are produced. In the course of time this effect will become diluted when second- and third-crosses are produced. Nothing permanent is built up for posterity. With the correct attitude towards pure-breeding, animals can be bred over a course of time that will maintain optimal and stable production in a specific environment.
Crossbreeding with small cow breeds and large bull breeds often results in calving problems because of the birth of large calves. It was established that for every 0.45 kg increase I birth mass the percentage of difficult calving increased by 3, 2% in 2-year-old Hereford and Angus heifers.
The F1 generation often has a livelier nature than their parents. The crossing of two temperamental breeds and consequent handling problems make this type of farming challenging.
Results obtained with crossbreeding in one location and with one herd are not necessarily repeatable in another herd, since the foundation material can vary to a large extent. Results of trails conducted at Mara Research Station, showed that half Hereford and half Afrikaner animals had a hybrid vigour of + 28% at 24 months of age, whereas at Neudamm Research Station a hybrid vigour of + 9,8% was recorded. The hybrid vigour of a half Aberdeen Angus half Afrikaner at 24 months of age was – 45%, and at Neudamm + 3,5% at 20 months of age. These results are probably extreme but serve to indicate that figures for hybrid vigour must be interpreted with care. Both of these previous examples were for growth on veld. The hybrid vigour for other traits does not necessarily follow the same pattern.

Crossbreeding Systems

Two breed terminals

The two-breed terminal system is the most basic crossbreeding system.

This system crosses Breed A females with Breed T sires to produce a crossbred animal that is 50% Breed A and 50% Breed T and known as an F1.

The crossing of two well-bred pure breeds is done to attain maximum hybrid vigour in slaughter animals. The greatest advantage of this system is the complementary effect of the breeds on each other. One pure breed cow and two bull breeds, viz. one for pure-breeding and one for crossbreeding are required. All offspring are marketed.

The system is simplistic
Only one breeding herd is required or needed
Labour and management are minimised
Progeny are highly uniform and marketable
Replacement heifers are purchased (marketed?), which frees up labour, land, and other resources to be dedicated to other aspects of production
This programme is appropriate for herds of all sizes because only one sire breed is used; just one breeding pasture is needed, and replacement females are purchased

Three breed Terminal

The three-breed Terminal System is merely identical to the two-breed rotational system. The only difference is that the females are crossbreds (A x B) mated with breed T bull.

Diagram: Three-breed Terminal system

Advantages of the Three-breed Terminal system:

Only one breeding pasture is needed
Sire identification of breeding females is easily recognized.
Replacement females are purchased, and all calves are marketed
Because replacement heifers are not being produced, sires can be chosen only on growth and carcass with no attention to maternal traits
The system works for herds of all sizes
The system results in the most hybrid vigour of any crossbreeding scheme
This system results in 100 % percent of both individual and maternal heterosis over the average of the parent breeds, which results in an increase of 24 % in weight of calf weaned per cow exposed.

A reliable source of quality and the same type of replacement heifers is a necessity. The age of heifers is very important regarding their puberty and readiness to mate, when purchased. The cost of these replacement heifers is an important factor in the economy of this system.

Two breeding Rotation

Two-breed rotation is an effective and relatively simple crossbreeding system that takes advantage of individual and maternal heterosis.

In this system, females sired by Breed A are mated to sires of Breed B, and females sired by Breed B are mated to sires of Breed A. This system requires two breeding herds and identification of sire for each breeding female.

Diagram: Two-breed rotational system

Two bull breeds are used on two-crossbred cowherds as shown above. It is important to note that the cows in each herd as well as the bulls denoted to them remain in the same herd for their full productive life. Only heifers get transferred to alternative herds. This system is simple and easy to manage.

The identification of breeding animals can easily be managed with an ear-tagging system, through different colours and numbers for the breeding herds. The replacement heifers mated by Breeds A and B are retained. The hybrid vigour will stabilise at 67% of potential and direct heterosis with an expected 16% increase in weaner weight, after several generations.

Some considerations for the breeder:

Resources available to raise replacement heifers, and size of cowherd
Biological type is significant because females are being retained that are sired by both Breeds A and B
Both breeds should have maternal characteristics conducive to utilisation as commercial females
Replacement heifers are retained in this system, which requires additional land, labour, and resources
Cost and availability of these resources need to be considered.
Two-breed rotation requires at least one bull from each breed. Each bull is used to service 25 females annually and therefore a herd will need at least 50 breeding-age females for the system to be efficient
- The two-breed rotation can be used with fewer cows; however, bull expenses per cow will be greater

Three breed rotation

The three-breed rotation is very similar to the two-breed rotation, except that another breed is added. This rotation uses sires of Breeds A, B, and C.

Breed A sires are mated to females sired by Breed B, Breed B sires are mated to females sired by Breed C, and Breed C sires are mated to females sired by Breed A. Replacements are retained from within the herd, and three breeding pastures are needed.

Advantages of the three-breed rotation system

The primary benefit of a three-breed rotation over a two-breed rotation is the increase in hybrid vigour
In a three-breed rotation, hybrid vigour stabilizes at 86 % of potential individual and maternal hybrid vigour, and a 20 % increase in weight of calf weaning weight per cow exposed over the average of the parent breeds is realized.

Disadvantages of the three-breed rotation system

An additional (3rd) breeding pasture and breed of bull(s) must be maintained
Management and labour requirements increase because of the additional complexity of using three breeds over two

As in the two-breed rotation, the three breeds used should be complementary, with maternal characteristics conducive to the breeding females’ role in a commercial herd.

Using the previous example of 25 cows per bull with three breeds of bulls, at least 75 breeding age females are needed to be efficient. The three-breed rotation can be used with fewer cows; however, bull expenses per cow will be greater. Lastly, the ability to locate three breeds that fit a given breeding scheme can be challenging and limit the ability to readily use three breeds.

Four Breed Rotation

The four-breed rotation is like the other rotation systems, only with four breeds of bulls utilised.

Breed A sires are mated to females sired by Breed B, Breed B sires are mated to females’ sire by Breed C, Breed C sires are mated to females sired by Breed D, and Breed D sires are mated to females sired by Breed A.

Replacements are retained from within the herd, four breeding pastures are used, and four breeds of sires must be maintained.

In a four-breed rotation, hybrid vigour stabilizes at 93 % of potential individual and maternal hybrid vigour, and a 22 % increase in weight of calf weaning weight per cow exposed over the average of the parent breeds is observed. This is only a slight gain from the three-breed rotation with the added cost of labour, management, and another breed of sire.

Depending upon the circumstances of the operation, the benefits may not outweigh the cost in using a four-breed rotation in place of a three-breed rotation. Also, assuming 25 breeding-age females per sire, at least 100 breeding-age females are needed for this system to be efficient.

Three Breed Roto Terminal

A three-breed roto terminal system is an extension of the two-breed rotational system. It is also known as a two-breed rotation with terminal bull system. A percentage of the breeding females are placed in the two-breed rotation, and another percentage is mated to a terminal bull C.

As example, 50 percent of herd females are in the two-breed rotation, and 50 percent are mated to a terminal sire of Breed C. The females in the two-breed rotation produce the replacement heifers, and the females in the terminal cross produce all market calves.

The roto terminal system is essentially a hybrid crossbreeding program using aspects of a terminal program and a rotational program. This system allows the breeder to produce all own replacements while making greater use of hybrid vigour in the terminal calves. Terminal sires can be selected for increased growth and carcass traits to maximize production from the cowherd. The breeds used in the two-breed rotation must still be selected for the criteria specified in the rotational programs. The downsides are that more labour, management, and breeding pastures are needed than in a two-breed rotation.

Bull rotation

Bull rotation is a common crossbreeding system. One breed of bull is used for 4 to 6 years, and then the bull breed is changed. This system can use two or more breeds depending on the goals of the producer.

This system is simple in that only one breeding pasture is used, and only one breed of bull is maintained. A relatively high level of heterosis is maintained, usually 50 % or greater depending on the number of bulls used and the sequence in which bull breeds are used. Small producers often use this programme because only one breed of sire is needed at a time.

The biggest concern when using the bull rotation is inbreeding. If a bull’s daughters are retained as replacements, action needs to be taken to prevent inbreeding. This often means replacing the herd bull or adding breeding pastures and separating females from their bulls.

Crossbreeding Systems in summary

The table below provides a summary of beef cattle crossbreeding system details and considerations. Implementing a well-designed crossbreeding system is an important management practice for improving profitability on commercial cattle operations. Such a system should be used to take advantage of breed complementarity and heterosis while also fitting the herd size and resources of the operation.

Advantages of crossbreeding
- Heterosis causes better production of the main products, meat, milk, wool, etc.
- Vigour of animals is improved
- Disease resistance is higher in offspring
- Progeny develop faster and have a bigger build
- Better feed consumption rate relate to easier and greater weight gain
- Resistance and adaptability to climate changes are better
- Crossbreeding is a basic tool in the development of new breeds
Disadvantages of crossbreeding
Heterozygosity increases and homozygosity decreases resulting in offspring that are not pure for breeding
Crossbreds are not suitable for further breeding as the progeny of cross crossbred will be weaker
- Effective crossbreeding requires expert knowledge and record keeping.

Practical Examples of Animal Crossing

Production Characteristics of selected beef breeds in Southern Africa

In southern Africa, there are 12 recognised indigenous breeds of cattle, as well as a number of related or derived breeds, all classified as Sanga types. The majority of the European beef, dual purpose and dairy breeds, in addition to the Zebu breeds, are also well represented and have been evaluated in a number of studies on pure and cross-breeding systems.

Species Crossing

Species crossing

Specie crossing is the breeding of different species. The progeny is infertile and there is very little use in this breeding practice other that of improving the strength of a donkey as draught animal, through crossing it with a horse.