Applied Beef Cattle Breeding and Selection Composite Populations Larry V. Cundiff ARS-USDA-U.S. Meat Animal Research Center 2008 Beef Cattle Production Management Series-Module V Great Plains Veterinary Education Center University of Nebraska, Clay Center September 18, 2008
Estimating Heterosis for a specific two breed cross HA = 430 = .5gH + .5 gA + hIha + mA AH = 416 = .5gH + .5 gA + hIha + mH AA = 405 = gA + + mA HH = 395 = gH + + mH (.5)(HA + AH) - .5 (AA + HH) = 423 – 400 = 23 = hIah
HA = 430 = .5gH + .5 gA + hIha + mA • AH = 416 = .5gH + .5 gA + hIha + mH • AA = 405 = gA + + mA • HH = 395 = gH + + mH • In the above equations, • HA denotes a crossbred calf with a Hereford sire and an Angus dam. • AH denotes a crossbred calf with an Angus sire and a Hereford dam. • HH denotes a straightbred calf with a Hereford sire and Hereford dam. • AA denotes a straightbred calf with an Angus sire and Angus dam. • gH denotes the additive breed effect for Herefords and gA the additive breed effect for Angus. • hIha denotes effect of individual hetersosis expressed by Hereford X Angus or Angus X Hereford reciprocal crosses. Note that hIha = hIha. • mA denotes the maternal (MILK) breed effect for Angus and mH the maternal breed effect for Hereford dams.
Estimating Maternal Heterosis C X A = .5gC + .5 gA + hIca + mA C X B = .5gC + .5 gB + hICB + mB C X AB = .5gC + .25 gA + .25gB + .5hIAC + .5hIBC + .5mA + .5 mB + hMAB C X BA = .5gC + .25 gB + .25gA + .5hIAC + .5hIBC + .5mA + .5 mB + hMAB .5[( C X AB) + (C X BA)] – .5[(C X A) + (C X B)] = hMAB
C X A = .5gC + .5 gA + hIca + mA C X B = .5gC + .5 gB + hICB + mB C X AB = .5gC + .25 gA + .25gB + .5hIAC + .5hIBC + .5mA + .5 mB + hMAB C X BA = .5gC + .25 gB + .25gA + .5hIAC + .5hIBC + .5mA + .5 mB + hMAB In the above equations, the gA, gB and gC denote additive breed effects for breeds A, B and C respectively. hICA, hICB and hIAC denote individual heterosis effects for C X A (or A X C) , C X B (or B X C) , and A X C (or C X A) breed crosses, respectively. mA and mB denote maternal (MILK) breed effects for breeds A and B, respectively. hMAB denotes maternal heterosis expressed by A X B (or B XA) crossbred dams.
Composite populations can be used to exploit: • HETEROSIS • COMPLEMENTARITY among breeds optimize performance levels for important traits and to match genetic potential with: • Market preferences • Feed resources • Climatic environment
MARC I ¼ Limousin, ¼ Charolais, ¼ Brown Swiss, c Angus and c Hereford MARC II ¼ Simmental, ¼ Gelbvieh, ¼ Hereford and ¼ Angus MARC III ¼ Pinzgauer, ¼ Red Poll, ¼ Hereford and ¼ Angus Limousin Simmental Pinzgauer Charolais Gelbvieh Red Poll Brown Swiss (Braunvieh) Hereford Hereford Angus Angus Angus Hereford
HETEROSIS EFFECTS AND RETAINED HETEROSISIN COMPOSITE POPULATIONS VERSUS CONTRIBUTINGPUREBREDS (Gregory et al., 1992) Composites minus purebreds Trait F1 F2 F3&4 Birth wt., lb 3.6 5.0 5.1 200 d wn. wt., lb 42.4 33.4 33.7 365 d wt., females, lb 57.3 51.4 52.0 365 d wt., males, lb 63.5 58.6 59.8 Age at puberty, females, d -21 -18 -17 Scrotal circumference, in .51 .35 .43 200 d weaning wt., (mat.), lb 33 36 Calf crop born, (mat.), % 5.4 1.7 Calf crop wnd., (mat.), % 6.3 2.1 200 d wn. wt./cow exp. (mat.), lb 55 37
Composite populations maintain heterosisproportional to heterozygosity(n-1)/n or 1 – S Pi2
MODEL FOR HETEROZYGOSITY IN A TWO BREED COMPOSITE Breed Breed of sire Dam ½ A ½ B ½ A ¼ AA ¼ AB ½ B ¼ BA ¼ BB (n-1)/n or 1 – S Pi2 = .50
MODEL FOR HETEROZYGOSITY IN A THREE BREED COMPOSITE Breed Breed of sire Dam .50 A .25 B .25 C .50 A .25 AA .125 BA .125 CA .25 B .125 BA .0625BB .0625 CB .25 C .125 AC .125 BC .0625CC 1 – S Pi2 = (1 - .375) = .625
Weaning Wt Marketed Per Cow Exposed for Alternative Crossbreeding Systems Relative to Straightbreeding (%) Wean. wt H i Hm marketed System (+ 8.5%) (+14.8%) per cow exp Straight breeding 0 0 0 2-breed rotation (A,B) .67 .67 15.5 3-breed rotation (A,B,C) .86 .86 20.0 4-breed rotation (A,B,C,D) .93 .93 21.7 2-breed composite (5/8 A, 3/8 B) .47 .47 11.0 2-breed composite (.5 A, .5 B) .5 .5 11.7 3-breed composite (.5A, .25 B, .25C) .625 .625 14.6 4 breed composite (.25A,.25B,.25C,.25D) .75 .75 17.5 F1 bull rotation (3-breed: AB, AC) .67 .67 15.5 F1 bull rotation (4-breed: AB, CD) .83 .83 19.3
Composite populationsprovide for effective use of • Heterosis • Breed differences • Uniformity and end product consistency
Genetic Variation in Alternative Mating Systems Optimum Assumes that the Two F1’s Used are of Similar Genetic Merit
Genetic potential for USDA Quality Grade and USDA Yield Grade is more precisely optimized in cattle with 50:50 ratios of Continental to British breed inheritance.
CEFFICIENTS OF VARIATION IN PUREBRED AND COMPOSITE POPULATIONS (Gregory et al., 1992) Trait Purebreds Composites Gestation length, d .01 .01 Birth wt. .11 .12 200 d wn. wt. .09 .09 365 d wt., females .08 .08 365 d wt., males .09 .09 Age at puberty (females) .08 .07 Scrotal circumference .07 .07 5 yr cow wt, lb .07 .08 5 yr height, in .02 .02 Steer carcass wt, lb .08 .08 Rib-eye area .10 .10 Retail product, % .04 .06 Retail product, lb .19 .20
COMPLEMENTARITY is maximized in terminal crossing systems Terminal Sire Breed Rapid and efficient growth Optimizes carcass composition and meat quality in slaughter progeny • Cow Herd • Small to moderate size • Adapted to climate • Optimal milk production • for feed resources Progeny Maximize high quality lean beef produced per unit feed consumed by progeny and cow herd
Rotational and Terminal Sire Crossbreeding Programs Two Breed Composite Cow Age No. 1 20 2 18 3 15 2Breed Rotation A B 1/2A - 1/2B 45% 4 13 5 12 - - - - 12 1 T x (A-B) T x (A-B) 55% Lbs. Calf/Cow 18% 21%
Weaning Wt Marketed Per Cow Exposed for Alternative Crossbreeding Systems Relative to Straightbreeding (%) Wean. wt Terminal H i Hm marketed crossa System + 8.5% +14.8% per cow exp (+5% wt/calf) Straight breeding 0 0 0 0 2-breed rotation (A,B) .67 .67 15.5 20.8 3-breed rotation (A,B,C) .86 .86 20.0 24.1 4-breed rotation (A,B,C,D) .93 .93 21.7 25.4 2-breed composite (5/8 A, 3/8 B) .47 .47 11.0 17.3 2-breed composite or F1 bulls (.5 A, .5 B) .5 .5 11.7 17.8 3-breed composite (.5A, .25 B, .25C) .625 .625 14.6 20.3 4 breed composite (.25A,.25B,.25C,.25D) .75 .75 17.5 22.2 F1 bull rotation (3-breed: AB, AC) .67 .67 15.5 20.8 F1 bull rotation (4-breed: AB, CD) .83 .83 19.3 23.6 a Assumes 66 % of calves marketed (steers and heifers) are by terminal sire breed out of more mature age dams and 33% are by maternal breeds (steers only).
General Considerations • Rotational Systems Provide for more effective use of • Heterosis • Composite populations Provide for more effective use of • Breed differences • Uniformity and end product consistency
Figure 6. Use of heterosis, additive breed effects and Complementarity with alternative crossbreeding systems.
Implications for Crossbreeding • Advantages of terminal sire crossing systems are not as great today as 30 years ago due to similarity of breeds for rate and efficiency of growth. • However, differences between British and Continental breeds in carcass traits are still significant and relatively large. • Inter generation fluctuations in mean performance for carcass traits are still large and significant. • For carcass traits, uniformity and end-product consistency can still be enhanced by use of composite populations or hybrid bulls. • Adaptation to intermediate subtropical/temperate environments can be optimized with greater precision by use of composite populations or hybrid bulls.
Module IV Applied Animal Breeding and Selection Homework questions assigned September 18 To be returned by October 23, 2008 (Email to: email@example.com) The Brangus breed has a genetic composition of 5/8 Angus and 3/8 Brahman breeding. 1) What is the expected heterozygosity or level of Brahman X Angus heterosis expected in the Brangus breed (show work)? 2) How would you expect the effect of heterosis for Brangus to compare to that in a breed with a composition of 5/8 Angus and 3/8 Shorthorn, why or why not? (In other words, would effects of heterosis be the same, or more, or less for Brahman X Angus crosses than for Angus X Shorthorn crosses, why or why not?) 3) What is the expected level of heterosis in a four breed composite founded with ¼ breed A, ¼ breed B, ¼ breed C, and ¼ breed D inheritance (show work)? 4) State the location and describe a typical production environment for cow herds where you reside or provide service. 5) If you were to develop a composite population adapted to this production environment, what foundation breeds would you select? 6) What proportions of each breed would you use in the composite population? 7) What would the expected level of heterosis be in your composite population (show work)? 8) Why would you select these breeds (Discuss the merits of each breed selected for additive direct and maternal breed effects).