E-189 01/11

Texas Adapted Genetic Strategies for Beef Cattle IV: Breeding Systems

Angus cow in a straightbred system. F1 Brahman-Hereford cow in a terminal system.

Stephen P. Hammack*

logical genetic strategy for a beef cow herd the breed, straightbreds generally have more uniform visi- should include four steps. First, determine your ble characteristics than most crossbreds. Straightbreeding production conditions (including climatic, for- is the simplest system to operate. Aage and marketing) and the levels of animal performance Inbreeding occurs over time in any breed, particularly that fit those conditions. Second, choose a breeding sys- in breeds closed to outside breeding stock. This can reduce tem. Third, identify the biological types and breeds within performance (called inbreeding depression), especially in those types that are compatible with the first two consid- traits such as fertility, livability, and longevity. One type of erations. And fourth, select for breeding the most useful inbreeding is linebreeding, which can, through carefully individuals within those breeds. planned matings, elevate the influence of a genetic line or There are about 75 breeds of cattle in the United States, individual while minimizing inbreeding over all. with 15 or so most common. Commercial cow/calf pro- *Professor and Extension Beef Cattle Specialist Emeritus, ducers who confine themselves to one breed have straight- The Texas A&M System. bred herds. If more than one breed is used, the herd is crossbred. Straightbreeding Straightbreeding simply means using the same breed for both sires and dams. Depending on the background of Crossbreeding If two F1s of the same cross are mated, the progeny, called F2, should have about half the Crossbreeding begins with the mating of heterosis of the F1. However, if F2s and subse- two purebreds of different breeds. This results quent generations of this cross are intermated, in first-cross progeny, termedF 1. There are three their progeny average no additional loss of het- potential benefits of crossbreeding—heterosis, erosis except for any inbreeding that might favorable breed combinations, and complemen- develop over time. This is a factor in creating tarity. combination breeds or using a composite breed- Heterosis ing system as discussed later. Heterosis, also called hybrid vigor, occurs Characteristics express heterosis differently. when the performance of crossbred progeny Heterosis tends to be highest in fertility, livabil- is different (usually better) than the average of ity, and longevity; intermediate in milk produc- their parent types, as shown in the example in tion, weight gain, feed efficiency, and body size; Figure 1. This example illustratesdirect heter- and lowest in carcass traits. osis, the effect of a crossbred individual’s gene Even with the benefit of heterosis the crosses combinations on its performance. There can from mediocre parents usually do not perform also be maternal heterosis, or the indirect effect as well as superior purebreds. So, the most pro- of a crossbred dam’s gene combinations that ductive crossbreds come from genetically supe- influence her calf’s performance through the rior parents. maternal environment she provides. Favorable Breed Combinations Even without heterosis there can be bene- fits merely from combining breeds. For exam- Breed A Average Breed B ple, breeds with high carcass quality are gen- 500 lb 525 lb 550 lb erally not well adapted to tropical conditions, and those that do have good tropical adaptabil- ity usually have relatively low carcass quality. Progeny Crossing breeds of these two types can produce 545 lb progeny with an acceptable intermediate level of (545 – 525 = 20 lb heterosis both traits. Such favorable breed combinations 20 ÷ 525 = 3.8% heterosis) can be the most important benefit of crossbreed- ing. They are the primary motivation for creat- Figure 1. Heterosis. ing new breeds by combining existing breeds, as discussed in the Combination Breeds section.

Heterosis is the opposite of inbreeding Complementarity depression, so it is greatest in the progeny of Complementarity requires dissimilar sires least related parents. For instance, there is and dams. Complementarity results not only greater heterosis in crossing the less related from the favorable combination of different breeds Hereford (created in the British Isles) types but also from the manner in which they and Brahman (created from cattle originating are combined. As stated, the progeny of a breed in south central Asia) than in crossing the more with high carcass quality crossed with a breed closely related breeds Hereford and Angus (both with tropical adaptability have a blend of those originating in the British Isles). traits. But the most productive and efficient way Heterosis is reduced when both parents con- to conduct this cross is to use sires with high tain the same breed. There is no loss of heter- carcass quality and dams that are adapted to osis if the parents share no breed in common, tropical conditions. The reverse is not as effec- whether the parents are purebreds or crossbreds. tive because the dams are not well adapted and If an F1 is bred to either of its parent breeds it is the dams that must perform year-round (called a backcross), heterosis in its progeny is under prevailing conditions. about half of that expressed in the F1. If the F1 is Another example of complementarity is the not backcrossed but is bred to a third breed, or use of large sires on smaller dams. The result an unrelated crossbred, there should be no loss of is that dams produce a higher percentage of heterosis in its progeny because the sire and dam their weight, and do it more efficiently, than have no breed in common as in a backcross. if they were bred to sires of similar size. This 2 type of complementarity also can be realized does not guarantee complementarity; sires and in straightbreeding by using genetic variation dams must be different and they must possess within a breed. But it is done more effectively complementary traits. Specialized types can with crossbreeding. be used in terminal systems to take maximum advantage of complementarity by exploiting Types of Breeding Systems their strong points while minimizing or elimi- There are two basic breeding systems in nating weak points. Terminal systems are usu- commercial production. If replacement females ally crossbred but can be straightbred. are produced in the herd the system is continu- ous. If heifers are not put back in the herd, but Continuous Crossbreeding Systems are brought in from outside, the system is ter- True Rotations minal. True rotation systems use two or more Calves from continuous systems have two breeds and the same number of breeding functions: Some heifers are saved for replace- groups. The simplest true rotation uses two ments and go back into the herd, while the rest breeds and is sometimes called a crisscross (Fig. of the calves are grown and/or finished to pro- 2). A different breed of sire is used in each of duce beef. But all calves from terminal systems two breeding groups. Replacement heifers are have only one use—the production of beef. (A moved (rotated) from the group where they small segment of producers specialize in pro- were produced to the other group, where they ducing replacement females to be marketed to are mated to the breed that is not their breed of other producers.) sire to minimize loss of heterosis in the system. There can be combinations of continuous Females remain in that breeding group, with the and terminal systems. Producers should under- same breed of sire, for all of their lifetime mat- stand the differences in these systems to avoid ings. Over time, females in the two groups grav- inefficient and costly mistakes. itate toward a composition of two-thirds of the breed of their sire and one-third of the other Continuous breed. If a rotation has three or more breeds, Since a continuous system produces its a heifer is moved to the breeding group with replacement females, it requires only external the breed of sire to which she is least related to sires to avoid inbreeding. Because replacement ensure minimal loss of heterosis. females are retained, the cow herd has genetics from both sires and dams. If sires have genet- ics for traits that are undesirable in brood cows, Breed B ♂ those traits are perpetuated in the cow herd. Therefore, both sires and dams should have a A - sired ♀ group similar level of expression of important traits, (Replacement heifers moved to other group where they without any undesirable characteristics. Genetic remain for all matings.) extremes generally do not fit. Continuous sys- tems can be either straightbred or crossbred. B - sired ♀ group (System stabilizes with Terminal Breed A ♂ two groups of ⁄ sire breed In a terminal system, replacement females and ⁄ other breed.) come from outside the terminal-cross herd. Figure 2. True 2-breed rotation. Replacements can be either purchased or pro- duced in another herd. Since heifers are not retained for breeding there is more flexibility in Because they require multiple breeding choosing types of sires and dams. Genetics for groups, true rotations increase the complexity maternal ability are irrelevant in terminal-cross of a breeding program. (Artificial insemination sires because their female progeny are not saved can simplify the mechanics, but not the man- for replacements. However, genetics for mater- agement, of some crossbreeding systems.) Also, nal ability are important in sires that produce a compromise must be made between comple- the females used for a terminal cross. mentary matings and uniformity among groups. Terminal crossing is the only system in Because of these complexities and limitations, which complementarity can be realized. How- true rotations are uncommon, especially those ever, merely implementing a terminal system involving more than two breeds. 3 Sire Rotations a complete three-breed static terminal system. Sire rotations are sometimes called rota- In the complete system, about one-fourth of the tions in time. Instead of rotating heifers out of dams must be straightbred, about one-fourth the breeding group where they were produced are needed to produce the F1, and only about to another breeding group, as in true rotations, one-half are available for the terminal cross. sire breeds are rotated periodically in a single breeding group. The number of years a sire breed should be used depends partly on how often Breed A Breed B heifers are put back in the herd. As is true with all breeding systems, severe inbreeding should Breed C A x B be avoided; therefore, sires should be changed at ♂ ♀ least when necessary to avoid breeding them to their daughters. There is less heterosis in sire rotations than in C x A – B Terminal-cross market calves true rotations, though the reduction is slight in (save no heifers) well-planned systems. Loss of heterosis is mini- mized by: 1) keeping replacement heifers out of Figure 3. 3-breed terminal cross. dams least related to the heifer’s breed of sire, and 2) minimizing breeding to the breed of sire. Static terminal crossing is the only system Instead of using known breed composition, that can have maximum heterosis in both cows some producers use visible breed characteristics and calves, favorable breed combinations, and and other visible features to determine whether the bonus of complementarity. However, these to keep a heifer for a replacement; this can reduce advantages are tempered by the necessity of pur- phenotypic variability, but also reduces heterosis. chasing replacement females or producing them Sire rotations are easier to conduct than outside the terminal cross. true rotations because there is only one breed- ing group. This is a common way to crossbreed. Rotation-Terminal Unfortunately, many sire rotations can not really A rotation-terminal combines continuous be called systems because they are implemented and terminal systems. It is one way to provide haphazardly with no logical plan for changing crossbred replacement females for static termi- sires. nals. A rotation system, either true rotation or sire rotation, produces replacement females both Terminal Crossbreeding Systems to keep itself going and to use in a separate ter- Static Terminal minal herd. Middle-aged dams (4 to 6 years old) In a static terminal system, replacement are moved out of the rotation to the terminal females are either purchased or produced in because they are less prone to calving problems another herd. Purchasing females simplifies the if terminal sires are relatively large. operation of this system because the only breed- You must have multiple breeding groups for ing group needed is for the terminal cross. A rotation-terminal systems—one or more for the straightbred terminal is possible, but there usu- rotation, depending on whether it is a true rota- ally is no good reason to do so (unless a pro- tion or sire rotation, and one for the terminal ducer does not want to save and manage heif- cross. (A rotation-terminal system can be approx- ers in a continuous straightbred system) because imated in one breeding group by using a multiple- the benefits of crossbreeding are absent. sire-breed system, discussed below.) About half A two-breed static system, using purebred of the dams are needed in the rotation to pro- sires and dams of different breeds, produces vide enough replacements for the entire system, direct heterosis in crossbred calves. However, leaving about half of them for terminal crossing. this system forfeits the considerable advantages Approximately two-thirds to three-fourths of sale of maternal heterosis from crossbred dams. calves come from the terminal, with most of the A three-breed terminal is more productive rest being male calves from the rotation. and efficient. Two breeds with desirable mater- Heterosis is relatively high in rotation-ter- nal traits are crossed to produce adapted and minals because all progeny and dams are cross- bred. However, since a high percentage of productive F1 dams, which are bred to sires of a third breed in a terminal cross. Figure 3 shows females from the rotation must be retained to 4 provide replacements for both the rotation and Multiple-sire-breed systems have shortcom- the terminal, there is little opportunity to select ings. There is less heterosis than in similar but individual females for breeding. more controlled systems. If large terminal sires are used there is no way to prevent their matings Combination Breeds of some of the younger females, so calving dif- Existing breeds are sometimes blended to ficulty may increase. Genetic variability among form combination breeds, with new packages individuals is greater, but phenotypic variability of traits. Because these breeds are formed by may not be greater if close attention is paid to the crossbreeding, there is some residual hetero- selection of replacement females. The number of sis; how much depends on how many breeds are calves born relative to the ratio of sire breeds can included, in what portions they are included, and vary from year to year, so the supply of potential how much inbreeding occurs as the breed devel- replacement heifers also can vary. Large, exten- ops. So with these combination breeds it may be sively managed herds might be most likely to possible to obtain some heterosis using a single implement multiple-sire-breed systems. breed in a straightbred system. Hybrid Sires and Composites The first of these combination breeds in the Just as there is heterosis for reproductive U.S. was the American Brahman, created by traits in females, there is also heterosis in males combining several Bos indicus (humped) breeds for semen quality and quantity, mating capacity, imported from India or Brazil. A number of and longevity. Using hybrid sires can be a rela- breeds have been created in the southern U.S., tively simple way to create combinations of traits especially in Texas, by combining different bio- not available in established breeds. Some seed- logical types. Most of these contain Brahman and stock producers specialize in producing hybrid British or, in a few cases, Brahman and Conti- bulls. For the most part these combine differ- nental European breeds; they are generally called ent types, such as British-Continental or British- American breeds. More recently, some British and American. Several breed associations have regis- Continental combinations have been made; these tries for hybrids. are less common but are increasing in number. Finding a reliable source of suitable hybrid bulls can be difficult. There is a general feeling that Other Systems hybrid bulls produce more variable progeny, but The breeding systems discussed so far all use some research (particularly at the U.S. Meat Ani- a single breed of sire in a breeding group. There mal Research Center in Clay Center, Nebraska) are alternatives. has challenged this impression, at least for quan- titative characteristics such as body weight. There Multiple Sire Breed usually is not as much reliable genetic evaluation More than one sire breed can be used concur- available for hybrid bulls, although some breed rently in a single breeding group. For example, associations include hybrids. sires of two British breeds could be used in a con- In recent years there has been some interest tinuous system. To reduce loss of heterosis and in a breeding system called composites, which decrease phenotypic variability, retained replace- is often confused with creating combination ment heifers should be intermediate in appear- breeds. As originally conceived by the U.S. Meat ance, as much as possible. Or, British-breed and Animal Research Center, the composite system American-breed sires could be used. If so, heifers involved creating hybrids and then intermating with a more American-breed appearance should them specifically to maintain as much heterosis be retained if that type is better adapted to the as possible in succeeding generations. The intent prevailing production conditions. These systems was not to create a new breed. For a more com- are similar to two-breed rotations. plete discussion of combination breeds and com- A sire breed with desirable maternal charac- posites, see another publication in this series, teristics and a terminal-sire breed could be used E-180, Texas Adapted Genetic Strategies for Beef with heifers retained from the maternal-type sires, Cattle—VI: Creating Breeds. if they can be visually identified. More than one Distinctions between combination breeds, maternal-type sire breed could be used, either con- hybrids, and composites are often blurred. In currently or in rotation over the years, to gain many ways they can be used in the same manner some maternal heterosis. These plans are similar to in planning and implementing a breeding system. static terminal or rotation-terminal crossing. Table 1 compares the features of breeding systems. 5 Table 1. Features of breeding systems. Breeding system Calf Cow Complementarity No. breeds / Calf heterosis heterosis breeding uniformity groups (11) Straightbred (1) None None None 1 / 1 Very high Straightbred (2) Low Low None 1 / 1 High Rotation Med-High Med-High None 2-3 / 1-3 (9) Low-Med Terminal only (3) Very high None-Low High 2 / 1 High Terminal only (4) Very high Very high High 3 / 1 Med-High Complete terminal (5) Medium None-Low Medium 2 / 2 Low-Med (12) Complete terminal (6) High Medium Medium 3 / 3 Low (12) Rotation + terminal High Med-High High 3 / 2 or 3 (10) Medium Multiple sire-breed (7) Low-Med Low-Med None 2 / 1 Low-Med Multiple sire-breed (8) Med-High Low-Med Medium 3 / 1 Low Composite Med-High Med-High None 2-4 / 1 Med-High (1) Breeds with no retained heterosis (2) Combination breeds, containing some retained heterosis (3) Using straightbred females purchased or produced in another herd (cow heterosis is Low if females are a combination breed containing some retained heterosis)

(4) Using F1 females purchased or produced in another herd (5) Producing straightbred females in one group for terminal cross in another group (cow heterosis is Low if females are a combination breed containing some retained heterosis)

(6) Producing straightbred females in one group to create F1 females in another group for terminal cross in another group (7) Using two general-purpose sire breeds concurrently (8) Using two general-purpose sire breeds, concurrently or rotated over time, and one terminal sire breed (9) One group if sire rotation; two or three groups (depending on number of breeds) if true rotation (10) Two groups if sire rotation; three groups if true two-breed rotation (11) Across all breeding groups in the system (12) Uniformity within breeding groups is High to Very High

Breeding Systems • straightbreeding (of traditional or com- and Breeding Groups bination breeds) in one group to produce females for a two-breed terminal cross in The choice of a breeding system depends another group partly on the number of separate breeding • sire rotation, multiple-sire-breed, or com- groups a producer can or will maintain. If feasi- posite in one group to produce replace- ble, regardless of the breeding system, the devel- ment females for a terminal cross in opment, breeding and calving of heifers should another group be conducted in a separate management group • purchase of straightbred females for cre- using easy-calving sires. ation of F1 replacements in one group to be One Breeding Group used in a terminal cross in another group One-breeding-group herds, ranging from Three Breeding Groups those needing only one bull to large herds Three groups can be used in these systems: that require multiple bulls, have the following • true three-breed rotation choices of breeding systems: • true two-breed rotation (or rotation of • straightbreeding with either a traditional two composites or hybrids) in two groups or combination breed to produce replacement females for a ter- • static terminal cross with purchased minal cross in a third group straightbred or crossbred females • complete terminal, with straightbred • sire rotation females produced in one group to be used • multiple-sire-breed for creating F1 females in a second group • composite to be used for terminal crossing in a third Two Breeding Groups group Multiple breeding groups are more complex Two groups can be used in these systems: to manage. And, each group in a multi-group • true two-breed rotation (or rotation of two crossbreeding system has a different breed com- 6 composites or hybrids) position, which can reduce marketing flexibil- Production efficiency and financial return are ity because fewer like calves are produced. Also, usually greatest when these factors are balanced, some breed combinations may be less valuable and not when one factor dominates to the exclu- than others. Weigh these possible disadvantages sion of the others. against any expected economic benefit before implementing systems that require multiple Summary breeding groups. After choosing a breeding system, produc- ers should determine what breeds and individ- Efficiencies of Breeding Systems uals within breeds fit their climate, forage, gen- A standard measure of efficiency of cow-calf eral management practices, and market. For a production is pounds of calf weaned per bred discussion of breeds, see E-190, Texas Adapted cow, which combines fertility, livability, and calf Genetic Strategies for Beef Cattle—V: Type and weaning weight. Using this measure, the U.S. Breed Characteristics and Uses and E-191, Texas Meat Animal Research Center compared breed- Adapted Genetic Strategies for Beef Cattle—VII: ing systems. The basis for comparison was the Sire Types for Commercial Herds. For information straightbreeding of traditional breeds, which do on selecting individual animals, see E-164, Texas not have any retained heterosis. Adapted Genetic Strategies for Beef Cattle—VIII: Continuous crossbreeding systems requiring Expected Progeny Difference (EPD). only a single breeding group can increase effi- Regardless of the size of the cow herd, the use ciency by 10 to 15 percent. Crossbreeding sys- of single breeding groups is by far the most com- tems using multiple breeding groups, or three- mon practice in Texas. Therefore, the prevailing breed terminal crossing in one group using breeding systems are straightbreeding (of both introduced females, can increase efficiency by traditional and combination breeds) and pur- 15 to 30 percent. These estimates are for systems chasing replacement females for a terminal cross, using British and Continental breeds in tem- with some implementation of sire rotations or perate environments. In harsh tropical or sub- concurrent use of multiple breeds of sire. tropical environments, including types native to When choosing a breeding system, give careful these locales, especially Bos indicus, can be even thought to the entire process. Do not embark on more efficient because animals have more heter- the first stage of a system without understanding osis and greater adaptability. These are signifi- and planning for subsequent stages. A system that cant advantages. works well for one producer or one set of produc- In choosing a breeding system for commer- tion and market conditions might be unsuitable cial beef cow herds, consider the major factors for another producer or different conditions. that affect production efficiency and financial For Further Information return, including: • number of animals available to market, To obtain other publications in this Texas • average pounds per animal marketed, Adapted Genetics Strategies for Beef Cattle • average price per pound, and series, contact your county Extension office • total cost of production. or visit http://AgriLifeBookstore.org or the Texas A&M Animal Science Extension website http://beef.tamu.edu.

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Educational programs of the Texas AgriLife Extension Service are open to all people without regard to socioeconomic level, race, color, sex, disability, religion, age, or national origin. Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with the United States Department of Agriculture. Edward G. Smith, Director, Texas AgriLife Extension Service, The Texas A&M System. Revision 7