Random mating is the mating of individuals without consideration of either pedigree or performance. In its purist form random mating amounts to allowing the cattle to "run the ranch." Unfortunately, this is essentially what results in many purebred herds which use several unrelated bulls each season and base the selection of those sires on their show ring record at Denver and Louisville or the prediction of a livestock magazine representative as to which bulls will be "hot" next year. Breeders must have a goal and develop a sound, factual plan to achieve it or herd improvement will not occur.
Inbreeding has a negative connotation with most people. The mating of close relatives in the pedigree of cattle, horses, dogs or people frequently causes alarm. However, inbreeding can be an effective tool in livestock breeding programs when understood and properly used. Defined, inbreeding is simply the mating of animals more closely related than the average of the breed or population from which they come. This definition implies that all animals within a breed are somewhat related and therefore carry a degree of inbreeding, which is true. Breeds are created by inbreeding. However, such inbreeding is rather mild and after a breed is formed the term "inbreeding" usually refers to closely related matings such as full brother/sister or sire/daughter matings. Genes occur in pairs. If each gene of a pair is identical an animal is said to be "homozygous" for that gene and if the genes of the pair are different an animal is termed "heterozygous". In a gene pair of "A" and "a" only three genotypes are possible - AA, Aa or aa. Each new individual receives only one gene of each pair from each parent so the results for each type of mating is as follows:
When inbreeding is initiated in a heterozygous herd and closely related animals are mated the offspring tend to become more homozygous in thier genotype. This explains why inbred animals are more uniform than outbred individuals. Note that in the case of matings 1 and 6 above, when animals of the same genotype are mated the offspring are all alike.
Unfortunately, which gene of a pair become homzygous is at random and so inbred animals can be homozygous for either desirable or undesirable genes. Many of the undesirable ones can not only reduce performance but can drastically reduce fertility or even be lethal. This has caused inbreeding’s bad reputation and explains the fact that “random inbreeding” tends to reduce average performance with a reduction in growth rate, mature size, fertility and overall thriftiness. Particularly disturbing is the uncovering of recessive lethals such as dwarfism and syndactoly (mule foot) resulting from this increased homozygosity. Remember, the inbreeding does not create the lethal genes. If the herd caries no genetic trash none will result from inbreeding.
True, “random inbreeding” is almost always negative. However, “inbreeding with selection” can be a powerful tool for her and/or breed improvement. Inbreeding with accurate selection for reproductive efficiency, growth rate and carcass excellence can yield superior breeding stock. Outstanding inbred individuals are productive, predictable, prepotent and the most valuable breeding animals of all. Unfortunately, the problems with such an inbreeding program are many. First, cattle carry thousands of gene pairs. This requires large numbers of animals, the time to turn many generations, accurate selection, and extensive culling of the many inferior animals produced. Obviously, the maintenance of a large herd for a long period of time with a major portion of each calf crop selling for commercial prices or less demands some additional financial support and perhaps a bit of good luck.
The classic example is found in the USDA’s inbreeding experiment at the Miles City, Montana station. This project involved the establishment of 11 lines of Hereford cattle each of which were very closely “inbred with selection” for many generations. Only two of those lines survived with others eliminating themselves through the undesirable genes uncovered. One of the surviving lines was ordinary in performance and only the now famous Line 1 Herefords was superior and made a major contribution to the breed.
Conclusion – If one has the knowledge, the time and wherewithal the development of a superior inbred line is a possibility and can be personally satisfying and financially rewarding. If someone else has already created such a train buy them if you can. They are the best and therefore the best investment as well.
Linebreeding is simply inbreeding designed to increase relationship of a herd or strain to a single individual. This is done to maintain the superior traits of an outstanding individual among its descendants thereby increasing the number of animals which possess these same outstanding traits. As in any inbreeding program, linebreeding increases homozygosity which increases uniformity. However, keep in mind that which gene of a pair becomes homozygous is at random so inbred animals may become homozygous for either desirable or undesirable genes. This fact dictates that complete and accurate performance records be maintained and used in order to acquire and maintain genetic superiority.
Outbreeding is the mating of individuals less closely related than the average of the breed or population from which they come. Most breeders practice outbreeding because of the widespread fear of inbreeding. Outbreeding with accurate selection can result in improvement. However, most herds using an outbreeding system of mating tend to remain near the breed average. This istrue since every new, unrelated herd sire brought into the herd risks on half the merit of his calf crop. A breeder must be very lucky to select a bull every two years that results in improvement in his herd. Therefore, the breeder who practices outbreeding should expect the average excellence of his herd to periodically regress downward toward the average of the breed due to a mistake in selecting a new unrelated sire. In an inbred or linebred herd the genetic uniformity insures against a serious mistake in sire selection. The progress may be slow but it is constantly upward while the excellence of the outbred herd goes up and down.
If the goal is uniformity and predictability, outbreeding is not the answer.
Crossbreeding has been presented to the beef industry as a panacea. Crossbreeding is a useful tool in beef production but, as with any tool, it must be used intelligently. Likewise, as with any tool, it must be designed for a specific purpose in order to function effectively.
To use crossbreeding productively cattlemen must understand a few basic principles of animal breeding.
Perhaps the best solution of all is an F1 cowherd resulting from crossing two breeds or strains, each of which is superior in maternal traits and adapted to range conditions. Both parent breeds used to produce the F1 cow should be medium to low medium in frame size and mature weight and have shown a propensity for marbling. Recall that as frame size increases, mature size increases, puberty is delayed, and a longer feeding period is required to put sufficient marbling in the ribeye to make the choice grade. Also, as frame size increases mature size increases raising maintenance requirement. Finally, a large framed steer carrying sufficient muscling to assure good cutability results in too much carcass weight.
Such F1 cows should be mated with bulls selected individually for rapid growth and carcass cutability. These traits are both highly heritable so the bulls must themselves have recorded rapid post weaning gains on high energy diets and be lean, trim and heavily muscled. Remember, “terminal cross” bulls must not be selected on the basis of breed but on each bull’s own growth rate and composition. The bulls, like the cows, should be medium to low-medium in frame size and for the same reasons.
The female offspring should all be fed and slaughtered along with the steers since their “terminal cross” sire will add too much growth, muscle and mature size for good mother cows. Slaughtering the heifers requires the “remaking” of the F1 cows which is the only disadvantage of the breeding program. However, such a breeding program takes advantage of maximum heterosis and results in reproductive efficiency, efficient and rapid feedlot growth and uniform carcasses of desirable weight, cutability and quality.
With this kind of breeding program a rancher should retain ownership of the calves all the way to the rail in order to take advantage of their superior growth rate and carcass value potential.
Purebred breeders should take advantage of their respective breed’sperformance record programs and develop strains of seedstock superior in specific traits. This makes available the genetic material necessary to furnish the unrelated maternal strains for producing the F1 cows as well as the terminal cross bulls.
The right crossbreeding program can be a plus in commercial beef production. Total heterosis (hybrid vigor) for the maternal traits, including weaning weight, which is largely due to milk production, is estimated at 20 to 25%. This is a sizeable amount and cannot be ignored by commercial cow/calf operators. Remember that this increase in performance is only above the average of the parents. Therefore, the excellence of the cattle crossed is the major factor in determining the level of performance of the offspring.
As stated above, the ideal crossbreeding program, and the program yielding maximum heterosis, employs first cross females (F1) resulting from the crossing of two breeds, both of which are superior in maternal traits. Such F1 cows should be mated with terminal cross bulls with superior individual performance in growth rate and body composition. However, the one disadvantage of this program is the fact that the daughters of terminal cross bulls should not be retained in the breeding herd. This requires that the F1 dams be replaced by again making the cross between two maternal breeds rather than retaining the heifers sired by terminal cross bulls.
Animal breeding specialists have suggested that the development of composite breeds is a solution to the replacement female problem. A typical composite might be constructed by combining four breeds with each breed contributing equally or 25%. For example, an F1 generation is established by crossing breeds A and B. Another F1 group is created by crossing breeds C and D. Finally, these two F1 groups are crossed which results in the foundation herd for this composite with each breed contributing 25% and with maximum heterosis. This foundation herd is then “closed” with all future replacements – both male and female – coming from within the herd.
The basis for the use of composites is the work of Sewell Wright back in 1922 working with guinea pigs. His work was confirmed by Dickerson using cattle and swine in the late 1960’s. These gentlemen offered the formula (n-1)/n which states that retention of the initial heterosis of the F1 composite foundation with random mating within the herd is proportional to the number of breeds that made up the composite. This simply means that in the case of a four-breed composite, 25% of the heterosis is lost between the F1 and F2 generations and no further loss takes place as long as no inbreeding occurs. Therefore, a breeder can maintain a composite herd indefinitely without further loss of heterosis provided all matings are random and the herd is large enough to prevent inbreeding.
To better understand how composites are supposed to work, assume that a seedstock producer creates a four-breed composite. This composite has demonstrated an adequate level of performance in a certain environment and has produced a final product that is acceptable in the market. Foundation females and bulls from this composite are sold to other breeders for commercial production, for sale as breeding stock or both. Theoretically, this composite could become the only cattle in this environmental zone. Each producer would use replacements from his own calf crop and the level of performance and heterosis would remain constant as long as all matings were at random (no inbreeding).
The author’s opinion is that composites will not take over the beef production industry for the following reasons:
Certain individuals have attempted to sell composites by stating that the swine and poultry industries are using composites successfully. This is not true. Both groups have developed strains or lines superior in certain traits which are crossed and the crosses sold to commercial breeders. For example, a swine breeder crosses two lines superior in maternal traits and sells the F1 females to commercial producers to be used as brood sows. Similarly, two lines superior in growth and carcass are crossed and the F1 males sold to be used on those sows. This provides superior performance, maximum heterosis and allows the seedstock producer to retain his purebred lines intact. This is as it should be.