Extension Bulletin E-270 New June 1999 Crossbreeding Systems for Beef Cattle Harlan Ritchie, B. Dennis Banks, Daniel Buskirk, Joel Cowley and David Hawkins Department of Animal Science sis is that expressed by the crossbred Reasons for Crossbreeding Heterosis and Its Effects calf; maternal heterosis is that Crossbreeding can increase levels of The level of heterosis tends to be expressed by the crossbred dam. production in livestock in two ways: inversely proportional to heritability. Table 1 illustrates the relationship 1. Complementarity utilizes the In moderately to highly heritable between heritability and heterosis in desirable characteristics of two or traits, such as carcass characteristics, various traits. It is important to note more breeds to achieve a higher fre­ the level of heterosis is low. On the that reproduction traits, which are low quency of desired genes among the other hand, in traits having low heri­ in heritability and for that reason can­ crossbreds than could be found within tability, such as fertility and Hvability, not be changed readily through selec­ a single breed. In other words, the heterosis is high. In general, heterosis tion within a pure breed, can be strong points of one or more breeds is expressed to a greater degree in markedly improved through the can be used to compensate for the reproduction and in traits expressed effects of heterosis. Conversely, car­ weak points of another breed. up to weaning time. cass traits exhibit little or no heterosis Geneticists refer to this as additive Heterosis is classified as either indi­ but respond well to selection within a gene effects. vidual or maternal. Individual hetero­ breed. As animals in a cross become geneticallv more divergent or unlike, 2. Heterosis (hybrid vigor) results from non-additive gene effects. It is Table 1. Heritability and heterosis estimates for defined as the percent of superiority some economically important traits. expressed in a trait by crossbred prog­ eny over the average of the parent Totol breeds in the cross. Heterosis is calcu­ Troit Heritability0 heterosis0 (%) lated by the following formula: % heterosis = Calving rate .02-.17 6 crossbred avg. - straightbred avg. ,QQ Calf survival to weaning .10 — .15 4 straightbred avg. Weaning rate .17 8 As an example, assume that the two Birth weight direct .31 6 parent breeds in a cross had weaning Weaning weight direct .24 11 weight averages of 575 and 475 Milk production .20 9 pounds and their crossbred progeny Postweaning gain .31 3 averaged 550 lb. The percent of het­ Yearling weight .33 4 erosis would be: Mature cow weight .50 1 Feed conversion (TDN/gain) .32 -2 550-525 x 100 = 4.8% Dressing % .39 0 525 Rib eye area .42 2 The basic objective of crossbreeding % cutcbility/retail product .47 0 systems is to optimize simultaneously Marbling/quality grade .38 2 the use of heterosis and breed differ­ Tenderness .29 0 ences within a given production and marketing environment. The produc­ 0 Koots efo/. (1994). tion environment includes feed b Kress and Nelsen (1998). resources as well as climatic condi­ tions. MICHICAN STATE EXTENSION heterosis is usually higher. As an example, when Bos taurus (European) Table 2. Effects of individual and maternal heterosis in crossing Herefords, Angus breeds are crossed with Bos indicus and Shorthorns in Fort Robinson Research Station study.0 (Brahman) breeds, the effects of het­ erosis are greater than those shown in Phase 1, Phase II, Total Table 1. On the other hand, when individual heterosis, maternal heterosis, heterosis, bloodlines within a breed of cattle are % % % crossed, little, if any, heterosis is Weaning % +3.0 +6.4 +9.4 expressed. Weaning wt. +4.6 +4.3 +8.9 The cumulative effects of individual Weaning wt./cow exposed +8.5 +14.8 +23.3 and maternal heterosis on calf weight weaned per cow exposed can be very ° Cundiff and Gregory (1977); Gregory and Cundiff (1980). dramatic. This is shown in Table 2, which summarizes a long-term cross­ breeding study conducted in two maternal heterosis and one-third (8.5 3. A.I. or natural service? More phases at the Fort Robinson Research percent) to individual heterosis. complex systems can be used if Station in Nebraska. Phase I mea­ Experiments involving Brahman x you are set up for A.I. sured individual heterosis by compar­ European crosses have shown even ing crossbred calves against straight- 4. Can high-quality replacements greater cumulative increases over the bred calves, both of which were be purchased at a competitive average of the straightbred parents. raised by straightbred dams. Weaning price? If so, crossbreeding is made percentage was 3 percent higher for If your goal is to maximize heterosis, easier. the following requirements should be crossbred calves because of 3 percent 5. Quantity and quality of labor: met (assuming natural service and higher livability. This, coupled with a More elaborate systems can be raising your own replacements): 4.6 percent heavier weaning weight, utilized as family or hired labor resulted in 8.5 percent more calf 1) Avoid backcrossing and subsequent becomes more plentiful and weight weaned per cow exposed in loss of heterosis by making the most skilled. favor of the crossbred calves. divergent matings possible. 6. Facilities: With better facilities, The effects of maternal heterosis were 2) Two or more breeding pastures are more complex systems are consid­ measured in Phase II by comparing needed. ered feasible. crossbred against straightbred cows, both of which were raising crossbred 3) Two or more breeds of bulls are 7. Available capital: Developing a calves. Weaning percentage was 6.4 needed. well organized crossbreeding sys­ tem generally requires more capital percent greater for the crossbred cows 4) All females must be identified by outlay than a straightbreeding pro­ because of a higher conception rate; breed of sire and year of birth. there was no difference in calf livabil­ gram. Certain crossbreeding systems can ity. Because the crossbred cows 8. Region of the country: In some milked heavier, their calves weighed help mitigate some or all of the above requirements. regions of the United States, com­ 4.3 percent more at weaning time. plex systems may not be feasible. These two factors together resulted in Crossbreeding Systems For example, in the extensive 14.8 percent more calf weight weaned intermountain areas of the West, per cow exposed for the crossbred Factors to be considered when the more elaborate systems may dams. In the third column of Table 2, choosing a system: not be workable. the combined effects of individual 1. Size of herd: The smaller the herd, and maternal heterosis are summa­ 9. Willingness to maintain records: the less complex the system should Complex systems should be avoid­ rized. Crossbred cows raising cross­ be. bred calves weaned 23.3 percent more ed if the producer has a problem calf weight per cow exposed than 2. Number of breeding pastures: If with identification and records. straightbred cows raising straightbred you use natural service, the number 10. Factors associated with choice calves. About two-thirds (14.8 per­ of available breeding pastures will of breeds in the system: cent) of this advantage was due to be a factor in how elaborate the system can be. a. Feed resources - abundant, average or sparse? Table 3. Comporison of crossbreeding systems. % of % of the marketed colves % of maximum Est. % inc. in lb. Minimum no. Mating cow generated by possible caff weaned per of breeding Minimum type herd this mating heterosis0 cow exposed postures herd size Two-breed rotation at equilibrium A-B rotation 100 100 67 16 2 50 Three-breed rotation ot equilibrium A-B-C rotation 100 100 86 20 3 75 Static terminal sire system A-A 25 17 B-A 25 17 C x (B-A) 10 13 T x (B-A) 40 53 Overall 100 100 86b 20 100 Two-breed rotation and terminal sire system (rota-terminal) A-B rotation 50 33 T x (A-B) 50 67 Overall 100 100 90° 21 Terminal sire x purchased F| females T x (A-B) 100 100+ b 28 Any size Rotate sire breed every 4 years A-B rotation 100 50 12 Any size A-B-C rotation 100 67 16 Any size Composite breeds 2-breed composite d4 A, KB) 1 50 12 Any size 3-breed composite (^ A, %i,%0 1 100 63 15 Any size 4-breed composite (X A, x B, % C, K D) 1 100 75 17 Any size Rotating unrelated F| bulls A-B ^ A-B 100 100 50 12 1 Any size A-B <-* A-C 100 100 67 16 1 Any size A-B ++ C-D 100 100 83 19 1 Any size Based on heterosis effects of 8.5% for individual traits and 14.8% for maternal traits. Assumes a 10% increase in breeding value for caff weight produced per cow exposed to terminal sires. b. Climate - severe, average or d. Breed availability in your In the following sections, systems stress-free? region. that are in general use across the country will be discussed. A summa­ c. Frame size required by the e. Breed preferences in the ry of these systems is presented in market - in other words, how marketplace. Table 3. This publication does not much should the carcasses necessarily include all systems that from the progeny weigh when have been used or recommended. they reach Choice grade? 3 Two-breed Rotation (Fig. 1) The two-breed rotation is initiated by mating females of breed A to bulls of breed B, with the resulting BA replacement heifers mated to bulls of breed A for their entire lifetime. In each succeeding generation, replace­ ment heifers are bred to bulls of the opposite breed from their sire.