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Heterosis is maximized when breeding animals with very different genetics, such as when using animals of breeds that are completely unrelated—such as a British breed and a breed containing Bos indicus (zebu) bloodlines, like Brahman. Heterosis is also very great when breeding British breeds to continental breeds, even though all of these animals are Bos taurus. The British breeds are less closely related to most continental breeds than the British breeds are to each other (or the continental breeds to one another).

Breeding animals within the same breed always limits the genetic potential to some degree because all of our modern breeds were created by using a certain amount of inbreeding to “fix” the desired characteristics so there would be uniformity in the offspring. By definition, the gene pool in any given breed is limited. A certain amount of production potential is always sacrificed in order to gain the uniformity desired in a breed, since the most dependable way to gain the uniformity was by using inbreeding and linebreeding in the early history of the breed. A breed is essentially a closed group of cattle (not allowing any infusion of other genetics) and thus accumulates some inbreeding over time, even if it’s not done deliberately.

A crossbred animal is created by mating two straightbred animals of different breeds or a crossbred animal to an animal of a third breed, or two crossbred animals of different mixes of breeds. Crossbreeding is the opposite of inbreeding. It opens the door for much wider genetic variation, and results in heterosis. As explained by Dr. Jim Gosey (retired University of Nebraska Extension Beef Specialist), heterosis is actually the recovery of accumulated inbreeding depression. In just one generation, the offspring exhibit the maximum of what was lost through generations of “pure” breeding within a closed gene pool.

Many stockmen feel that heterosis is most easily maximized with a 3 breed crossing system, mating a crossbred cow with a bull of a third breed. It is often easier to buy (or use semen from) a purebred bull than a crossbred bull, unless the bull is a composite. Composites are gaining in popularity because they simplify the breeding program; the animals are already mixed in a desired combination.

A composite is an animal created by mating two animals that have crossbred parents of similar breeding; in other words the breed “mix” is the same in sire and dam and has been standardized into a predictable blend over several generations of breeding crossbred to crossbred. The animals are all the same percentage of certain breeds, such as half and half of two breeds, or 3/8 of one breed and 5/8 of another, or a certain blend of 3 or even 4 or more breeds. Some of the “breeds” in use today like Brangus (a stabilized percentage of Angus and Brahman), Santa Gertrudis (Shorthorn and Brahman) and Beefmaster (Brahman, Shorthorn and Hereford) were some of the first composites. There are a number of very popular composites today, such as Angus and Gelbvieh, Angus and Salers, Angus and Chianina, several combinations of British and continental breeds, etc.

Crossbred Cows Provide the Ultimate Benefit
The greatest amount of benefit gained by crossbreeding is by using crossbred cows. Even though many stockmen use crossbreeding of straightbred parents to produce exceptional market calves (calves that gain faster than straightbreds and do well in the feedlot), the crossbred cow is the key to maximum beef production and profitability in a cow-calf operation, since hybrid vigor in the cow produces phenomenal maternal advantages. Research has shown that a crossbred cow is 8 percent more efficient than a purebred cow, lives 38 percent longer and has 25 percent more lifetime production (pounds of calf weaned). This is partly due to the fact that crossbreeding has the biggest impact on traits that are not highly heritable (and hence more difficult to improve through selective breeding within a breed), such as fertility, age at puberty, and longevity.

Crossbred cows live longer and are also less apt to be culled for being late or open, due to increased fertility. Any cow that can calve at 2 years of age, never miss a year of calving, and stay in your herd another year or two beyond average culling age makes you money. When you consider all the benefits of a crossbred cow, you can see why animal scientists call this the “only free lunch” in the cattle business. As pointed out by Dr. Larry Cundiff (U.S. Meat Animal Research Center, Clay Center, Nebraska), data from their heterosis studies showed that the breakeven costs of production were reduced about 10 percent by using crossbred cows. Another study, at Montana State University compared the effects of breed and heterosis on heifer pregnancy using purebred and crossbred females of several breeds. Results showed that a higher percent of crossbred heifers calved at 2 years of age (reaching puberty and becoming pregnant earlier) than purebreds.

And if a cow is healthier, with a stronger immune system due to hybrid vigor, she develops better immunity when vaccinated, imparts better colostrum to her calf, which in turn keeps him healthier through the risky days of early calfhood. Genetics plays a big role in an animal’s immunity and immune response; the crossbred animal is hardier than a straightbred animal partly just because genes control the process of recognizing disease agents and inbreeding doubles up more of the undesirable immune-response genes. Every pure breed is inbred to some degree. Crossbreeding ensures more genetic diversity and optimal immune response. Thus a crossbred cow tends to have more optimum immune system function than a straightbred cow, and hence not only stays healthier herself but may also produce more protective colostrum.

When all factors are weighed, the crossbred cow gives you the most benefit. By contrast, the stockman who is merely trying to take advantage of hybrid vigor in the calves (using straightbred cows and bulls of another breed) gains less impact on profitability. Calf weaning weights for crossbred calves are 5 percent more (and yearling weights 4 percent more) than straightbred calves. The research study in the 1990’s that came up with these figures showed that a straightbred cow with a crossbred calf earned an average of $23.37 more than if she had a straightbred calf. But a crossbred cow with a crossbred calf netted $116.88 more than a straightbred cow with a straightbred calf. This is one reason a number of producers went to crossbred cow herds.

In the past decade, however, with the increasing popularity of “black” cattle and the drive toward more uniformity and marbling, many of America’s commercial cow herds have lost most of the heterosis they once had. Due to market pressures for beef calves, many stockmen have been using bulls of just one breed, and the replacement heifers become more and more straightbred with each generation. According to Dr. Jim Gosey (retired Beef Extension Specialist, University of Nebraska), the loss of heterosis in these herds shows up most quickly in the traits that are least heritable (and most associated with inbreeding depression), namely reproduction (fertility), hardiness and longevity. The price paid for the loss of heterosis is cumulative—as a number of very small losses add up and amount to a substantial sacrifice in lifetime productivity.

As one cattle buyer observed following a very cold and slow spring during which feed supplies were short, most of the cows in several herds he worked with were thin, and there was a high rate of open cows after the breeding season. Interesting to note, the cows that bred back the best, and on time (in spite of the tough conditions), were the old crossbred cows that were still in the herds. The younger females that were a high percentage of straight breeding didn’t do so well.

How Can You Keep the Positive Effects of Heterosis?
The maximum benefit from heterosis is in the first generation (F1), producing a crossbred animal from 2 different parent breeds. The next generation (F2) loses some of that vigor if the F1 female was bred back to a bull of one of the parent breeds. Some stockmen therefore use a bull of a third breed in order to produce calves with maximum heterosis from the crossbred cow. Maximum benefit can also be obtained by using a crossbred bull, of different breeds than the crossbred cow.

There are various degrees of hybrid vigor in the calves produced from various crossbreeding systems, such as a 2 or 3 breed rotational cross. To get an idea of the range of difference, we can assume that breeding a purebred to a purebred of the same breed produces 0 percent hybrid vigor and breeding a purebred to a purebred of a different breed (especially if the 2 breeds are very genetically different) results in 100 percent heterosis in the offspring.

In a traditional 2 breed rotational system, crossbred cows of breed A and B are bred back to bulls of breed A (creating calves that are ¾ one breed and ¼ the other breed). Then those daughters are bred to bulls of breed B. The bull breed is continually switched back and forth. After a couple of generations the heterosis obtained stabilizes at about 67 percent, according to Michael MacNeil (research geneticist at the USDA Agricultural Research Service at Miles City, Montana, in 1998). Adding another breed to the rotation (switching the sires for each generation between bulls of breed A, B, and C) extends and expands the effects, resulting in 86 percent heterosis in each generation. Adding a fourth breed to the rotation results in an increase to 93 percent heterosis, which will be continued indefinitely in each crop of calves from this mix (a sire from breed A, B, C or D bred to crossbred cows that embody the 4-way cross).

One disadvantage of any rotational crossbreeding system, however, is that the breed makeup of the calves swings heavily (slightly more than half) toward the breed of the sire in each generation. As pointed out by MacNeil, unless the breeds used are similar in certain traits and performance level, there can be a lot of variability in the calves produced, from one year to the next. Another disadvantage is that rotation systems require a stockman to have more than one breeding pasture (since there will always be 2 or more sire groups), and sorting of cows into the proper group so their calves will be sired by the proper breed of bull to make the system work. This can be difficult on some ranches that use community range pastures, or ranches that utilize intensive grazing management with rotation of pastures.

One way around this is to use crossbred bulls. Then the breed mix in the calves can be kept more consistent, without swinging so heavily toward one breed or another. If crossbred bulls of different breeds than the crossbred cows are used, heterosis is maximized once again, or if crossbred bulls of the same (or one of the same) breed are used, heterosis is somewhat reduced but the breed mix can be kept at a more acceptable level—for instance if you want to create calves that are only ¼ continental blood rather than half.

Another way some ranchers minimize the breeding pasture problems is to use bulls of one breed for about 3 years and then change to a bull of the second breed, and then to a third, or back again, and so on. The rotation of bull breeds over time will sacrifice some heterosis but this loss can be minimized if you use bulls of 3 or 4 different breeds, for only 2 years each.

Composites
A more recent answer to some of these problems has been the development of composite blends of breeds. Using a composite bull on composite cows reduces the need for separate breeding pastures or rotating breeds of sire. The composite animal embodies the desired traits from two or more breeds. If the breeds chosen complement one another, and the composite has been created with careful selective breeding and enough genetic potential to avoid inbreeding, the calves are uniform and consistent—like a “super” breed. There is not quite as much heterosis as in F1 crosses, but still a significant gain over straightbred cattle.

A composite utilizing 2 breeds that contribute equally to the mix will consistently deliver 50 percent heterosis. When 4 breeds are used equally to create the composite, heterosis is 75 percent, in each generation, continuing over time. The initial loss of heterosis in any crossbreeding program occurs between the F1 and F2 generations, but with a composite the remaining heterosis is maintained in subsequent generations of crosses—and how much is maintained depends largely on how may breeds are in the initial mix.

As pointed out by MacNeil, a composite doesn’t need to have equal genetic contribution from the breeds involved. If one breed is better in certain desired traits than another, it can be represented more extensively in the mix. For instance, one of the composites developed early on at the Fort Keogh Livestock and Range Research center is made up of 50 percent Red Angus genetics, 25 percent Charolais and 25 percent Tarentaise. With this combination of the 3 breeds, the consistent heterosis is about 63 percent, in each successive generation.

The heterosis in a composite herd is retained indefinitely unless the crossbreds are inbred again. Inbreeding in a composite can happen if the composite was originally formed by using just a few purebred bulls from each contributing breed. In the formation of a composite, animal scientists recommend that the mix be based on at least 15 to 20 sires from each contributing breed. Once the composite has been established (all of the calves are a certain percentage of each parent breed, and the cows and bulls being bred are this same percentage), the vigor of the composite can best be maintained by using at least 25 bulls per generation, to keep the rate of inbreeding very low. Thus it is easier to create a viable composite using thousands of animals than it is for a rancher with a small number of cattle to create his/her own composite. It can be done, but will necessitate more infusions of “new” genetics (in the form of unrelated crossbred bulls added to the mix) every now and then. A number of ranchers are doing this, however, using an “open” composite approach, by continually evaluating/selecting and bringing in new sires (purebred or crossbred) or using AI, choosing new bulls and sometimes new breeds. In this way, much of the heterosis is on-going in each new generation.

Combining several breeds that complement one another (one breed adding strengths where another is weak) enables the stockman to match the cow herd more perfectly to various conditions and/or produce the type of calves that best meet a target market. For instance, many stockmen feel that using a mix of British and continental genetics comes closer to meeting some market requirements than either can do alone.

Utilizing composites or crossbred bulls is often more beneficial to the cow-calf producer than using a terminal cross (breeding crossbred cows to a bull of a third breed that produces heavily muscled beef calves for market). The latter program creates super beef calves for market, but no replacement heifers. You have to buy your heifers; thus the genetic fate of your whole operation is in someone else’s hands. Many stockmen prefer to use a system in which they can retain some of their best heifers as cows, and most composite blends enable them to do this.

Some stockmen are still wary about composites, thinking that genetic variation (expressed as non-uniformity in the calves) would be greater than in a purebred herd. But Dr. Jim Gosey (retired Extension Beef Specialist, University of Nebraska) points out that a study of 3 composite blends and their parent breeds (research at USDA’s Meat Animal Research Center in Clay Center, Nebraska) found no significant difference in the coefficients of variation for certain measured traits (reproduction, weaning weight, carcass weight, retail product percent, marbling, shear force and other carcass traits). The herds of composites had as much uniformity in the end product as the purebred herds.

According to Gosey, the commercial breeder can manage a composite herd just like straightbreds (with one breeding pasture), yet composites allow each stockman to use the genetic differences among various breeds to select, achieve and maintain a high performance level for many economically important traits—in a wide range of production environments and market targets. Composites enable a stockman with any size herd to use breed differences and heterosis simultaneously to tailor a cow herd for any specific climate adaptation, creating cows with optimum mature size, fertility and milking ability, producing calves with desired growth rate and carcass traits.

In one group of composites developed by the University of Nebraska at the Gudmunsdsen Sandhills Laboratory, in which the foundation bulls were carefully selected using bulls that were better than average in calving ease, average in milk production, average or below in mature size and above average in marbling and other carcass traits, the steers produced from this composite averaged 87 percent USDA Choice or better, and 66 percent yield grade 1 and 2, which meets the beef industry’s goals for finished cattle. Thus composites can provide the commercial cattleman with a practical way to enhance management efficiency and still increase profitability.
 

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