What is a crossbreed or a composite?
Because of the advantages of hybrid vigor (heterosis) gained when utilizing crossbreeding in a beef production program, almost every major breed has jumped on the bandwagon to get in on the action by creating and promoting composites that utilize their breed as one of the components. They come up with fancy names for these composites--Amerifax, Limflex, SimGenetics, Stabilizers, Rangemakers, Balancers, Southern Balancers, Chiangus, Equalizersand it's like trying to choose between brand names at the grocery store.
So what exactly is a crossbred or a composite animal? Technically, a crossbred is an animal produced by breeding two purebred parents of different breeds. The term can also refer to an animal produced by breeding a crossbred animal to a cow or bull of a third breed, or might even refer to the result of mating two crossbred animals with each other. The term crossbred generally refers, however, to the first generation produced by mating animals of different breeds.
By contrast, a composite is an animal produced after several generations of selective crossing with two or more breeds, to come up with a uniform group of animals that have a fixed percentage of each of those breeds. Examples of composites that have been around a long time include Beefmaster, Brangus, Santa Gertrudis, Red Brangus, Braford, and so on. These composites have now become accepted as uniform types of cattle that combine some of the advantages of the parent breeds and still retain a certain amount of heterosis.
Some composites have their own breed associations, with herdbook and registration of association members' cattle. Many of the original composites in the U.S.--like Brangus and Santa Gertrudis--were formed with a specific goal in mind. The purpose was to create beef animals that combined beef-production qualities of British breeds with the heat tolerance and insect resistance of Brahman (Bos indicus) cattle so these hybrid animals could thrive and be more productive in our southern climates.
Some of the newer composites have been created to simply produce a type of cattle with more hardiness and better performance in a variety of environments, taking advantage of the feed efficiency/gainability and increased fertility of the hybrid animal and seeking to blend the best (most desired) features of two or more breeds.
Hybrid vigor, also called heterosis, is a phenomenon associated with crossing two breeds or species. A well-known example of the latter would be the crossing of a horse and a donkey to create a mule, or crossing bison and cattle to create a hybrid animal that some people have called beefalo. By crossing two different breeds or species (or sub-species), we are able to create traits in the offspring that are superior to or stronger than those of the parents.
For instance, crossbred cows tend to be more fertile (reaching puberty sooner and breeding back quicker after calving) and to have a longer life of productivity, producing more calves in their lifetime, than purebred cows of either parent breed. Crossbred bulls are more fertile and tend to be more active and vigorous than bulls of the parent breeds. Crossbred calves are hardier and have a higher survival rate due to their stronger immune systems. They tend to gain weight faster and more efficiently, and adapt more readily to harsh environments.
Research has shown that part of the reason crossbred animals are hardier than purebreds is because of a stronger immune system. Animals that embody heterosis tend to develop better immunity when vaccinated or exposed to disease, and crossbred cows supply their calves with more antibodies in their colostrums--which in turn keeps the calves healthier through the risky days of early calfhood. After the passive immunity wears off, a crossbred calf builds strong immunity of his own. This all adds up to higher survival rate in calves.
Heterosis beneficially influences traits like feed efficiency and longevity, which are important to beef production. In general, the more diverse the breeds being crossed, the greater the heterosis we see in the calves--as when crossing Brahman or other zebu-based breeds (Bos indicus) with British breeds or European breeds (both of which are Bos taurus). Greater heterosis response is also gained when crossing British breeds with European breeds than when crossing them among themselves, since the British breeds are more closely related to one another than they are to most European breeds.
All "breeds" were originally created with some degree of inbreeding and linebreeding to "fix" certain desired traits that were seen in the foundation animals. A breed is essentially a closed group of cattle, to maximize uniformity and to exclude infusion of any other traits. Keeping a breed "pure" always limits the genetic potential of these animals, Livestock breeding and tends to accumulate inbred traits over time. These traits include lack of hardiness, less immune response, less vigor.
Inbreeding has the potential to double up recessive genes in the limited gene pool, or undesirable traits that result from mutations. Mutations occur in humans and animals all the time, but rarely cause problems unless doubled up by breeding related individuals that both carry the mutated gene from the common ancestor. Inbreeding limits variety and increases the probability that inherited defects will crop up.
By inbreeding during the early history of a breed to establish uniformity and "fix" certain desired traits, some degree of beef production potential (the opportunity for maximum growth and vigor) was sacrificed. Thus crossbreeding is the opposite of inbreeding. It opens the door for wider genetic variation and results in heterosis, which in simplest terms is essentially the recovery of lost potential--the reversal of accumulated inbreeding's depression of traits. In just one generation, the crossbred offspring exhibit the greatest degree of what was lost (in growth and vigor) through many generations of pure breeding within a closed gene pool.
True composites take many gears to create
A true composite is not easy to develop because it requires several generations and a large population of cattle. A composite animal is produced by mating crossbred animals of similar breeding; the breed mix in both the sire and dam is the same, and has been standardized into a predictable blend over several generations of breeding crossbred to crossbred. The animals all have the same percentage of specific breeds-whether half-and-half, or 3/8 and 5/8, or some other fixed percentage of two breeds, or a specific mix of three or more breeds.
One example would be the MARC (Meat Animal Research Center) composites, such as the MARC II, which is a blend of breeds that produce individuals that are half British and half European breeds. Leachman Rangemaker is a composite that is 3/4 British (a certain blend of Red Angus and Black Angus), and 1/4 European (a blend of Terentaise, South Devon, and Salers). Another composite example would be the Leachman Stabilizer that is 1/4 Red Angus, 1/4 Hereford, 1/4 Gelbveih and 1/4 Simmental. Another example is the Noble Line, in which the genetic components are approximately equal amounts of Gelbveih, Angus and Brahman blood. Many popular composites are in use today, including blends of Angus-Gelbvieh, Angus-Salers, Angus-Chianina, and many other combinations of British and continental breeds.
The key to creating a reliable composite that retains a certain percentage of heterosis (and not losing it to inbreeding) is to maintain a large enough foundation herd size to adequately represent the genetics of each breed used--without doubling up those genetics. Inbreeding linebreeding has to be avoided in future generations to maintain high levels of heterozygous genetics and heterosis.
Whenever a composite is formed, there is always some loss of heterosis when the crossbreds are mated to one another, but once the composite is established and the herd is closed (just mating the composites--animals that all have similar breed blends--with one another) the resulting heterosis will be consistent and constant. Unless the population of animals in the composite groups is very large, however, inbreeding will eventually reduce the effect of heterosis.
If the composite was formed with foresight, a complementary blend of breeds, planning, and adequate numbers, use of a composite can simplify the goal of producing cattle utilizing heterosis. It can be a feasible, low-management alternative to traditional crossbreeding schemes.
Advantages of composites include the ability to take advantages of desired traits in several breeds, offsetting the weaknesses of one breed with the strengths of another, and targeting a specific environment with cattle that can do well in that environment- along with some retention of heterosis over time and subsequent generations. For instance, a four-breed composite tends to maintain 75 percent of the hybrid vigor you'd see in a first-generation cross, and will retain it indefinitely if the composite population is large enough to avoid inbreeding.
Livestock breeding terminology and definitions
Crossbreeding: The mating of two or more breeds,
Crossbred: An animal created bg mating two purebred or straight bred animals of different breeds, or mating a crossbred with an animal of a third breed.
Purebred: an animal with parents of the same breed--which has been pure since the beginning of that breed, a purebred may be registered or unregistered.
Straightbred: an animal of just one known breed, though not necessarily purebred or registered,
Composite: A uniform group of cattle created by selectively crossing two or more breeds for several generations and establishing a certain fixed percentage of each breed (such as the Santa Gertrudis that carries 5/8 Shorthorn genetics and 3/8 Brahmon, or the Brangus that carries 8/8 Angus genetics and 3/8 Brahman, or the Beefmaster that carries approximately 1/2 Brahman genetics and the other half a blend of Hereford and Shorthorn in roughly equal percentage), In essence a composite is a new "breed" designed to retain a certain amount of heterosis in future generations without crossbreeding, and can thus be maintained as a "pure" breed without further infusions of other breeds.
Synthetic: This term is used to describe a new Line of cattle from an open breeding program where new breeds can be added at any time, No fixed percentage of certain breeds is required, Butts used might be crossbred or purebred, to add another breed to the mix, Many producers use crossbred bulls to good advantage in this type of breeding program, creating whatever mix in the calves might be desired, For instance, a crossbred bull can be used on crossbred cows of the same two breeds, to keep the mix the same in the calves, Or a crossbred bull, can be used on cows of different crosses, to add another set of desired traits to the mix, In this wag the producer can often gain the most benefit from crossbreeding (the biggest "shot" of hybrid vigor) and also avoid some of the [imitations associated with traditional crossbreeding schemes.
Hybrid vigor (heterosis): The degree to which a crossbred or composite animal outperforms the straightbred/purebred parents in any specific trait (such as growth, health and immune responses, fertility, longevity, milking ability, etc,)
Inbreeding: The mating of closely related individuals such as father daughter, brother-sister, half brother-half sister, grandfather-granddaughter, etc, to try to double up desired traits, The downside of this breeding program is a decrease in genetic variations and also more possibility of doubling up undesirable traits, some of which may result in genetic defects.
Linebreeding: 4, form of inbreeding that concentrates the genetics of a certain ancestor', the mating of relatives to try to "fix" and retain the desired traits of that ancestor or bloodline, Like inbreeding, this type of breeding program must be done carefully to avoid doubting up of undesirable traits that were hidden in the original animals.
Outbreeding/outcrossing: The mating of unrelated individuals within a breed to produce superior offspring by obtaining "new" genetics. Selective outbreeding is the best wag to improve certain traits and retain vigor when staging within a certain breed, though the results are slower and tress dramatic than with crossbreeding.
BY HEATHER SMITH THOMAS
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|Title Annotation:||The cow barn|
|Author:||Smith Thomas, Heather|
|Publication:||Countryside & Small Stock Journal|
|Date:||Jan 1, 2013|
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