Applied Beef Cattle Breeding and Selection Inbreeding and Heterosis in Beef Cattle Larry V. Cundiff ARS-USDA-U.S. Meat Animal Research Center 2008 Beef Cattle Production Management Series-Module IV Great Plains Veterinary Education Center University of Nebraska, Clay Center August 1, 2008

Homework Participants Module 2 Module 3 Anderson Castleberry Davidson X Fox Frese Furman Jones Langon Linhart Matlick Van Boening Werhman Ondrack

Email homework to larry.cundiff@ars.usda.gov

Degrees of inbreeding according to relationship of mates (Lush, 1945) Species crosses Outbreeding within a breed First cousin Full sib Self Fertili- zation Half sib Random Mating In a pure breed Cross breeding

Zygotic Frequency with Self Fertilzation of a Heterozygote (Aa) Female gamete Male gamete .5 A .5 a .25 AA .25 Aa .25 aa

Change in genotypic frequency with self fertilization Generation AA Aa aa 100 1 25 50 2 37.5 3 43.75 12.5 4 46.875 6.25 5 48.4375 3.125 … Various but many

Effects of different degrees of dominance on phenotypic value (additive) Partial dominance Complete dominance

Effects of inbreeding on heterozygosity/homozygosity Zygous line Inbred Line F = .5 Sire Daughter Or Full sib Pure Breed Random mated Cross breeding ? 100 80 60 40 20 H O M Z Y G S I T (%) AA aa E R Aa Effects of inbreeding on heterozygosity/homozygosity (Cundiff and Gregory, 1977) ?

Average expected performance of crossbred, purebred, and inbred lines with additive and non additive gene effects. Frequency (%) per /genotype Addi-tive Partal Dom. Com-plete AA Aa aa Crossbred 100 0.5 0.75 1.0 Purebred 10 80 0.70 0.9 Sire-daughter 20 60 0.65 0.8 Inbred line F=.5 30 40 0.60 0.7 Homozygous line 50 0.50

Effects of inbreeding in cattle (Brinks et al., 1975. Western Regional Project W-1, Tech. Bulletin 123) Fertility (percentage of cows pregnant declined 2% and 1.3% with each 10% increase in inbreeding of the dam and calf, respectively. Percentage calf crop weaned declined 1.6% and 1.1% with each 10 percent inbreeding of the dam and calf, respectively. Inbreeding also depressed growth and maternal weaning weight.

Estimating Heterosis for a specific two breed cross Sire breed Dam breed Calf breed Weaning wt H A HA 430 AH 416 AA 405 HH 395 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

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[( C X AB) + (C X BA)] – .5[(C X A) + (C X B)] = hMAB

Crossbred calves (individual heterosis) HETEROSIS EFFECTS IN CROSSES OF BOS TAURUS X BOS TAURUS BREEDS AND IN CROSSES OF BOS INDICUS X BOS TAURUS BREEDS FROM DIALLEL CROSSING EXPERIMENTS Bos taurus X Bos indicus X No. Bos taurus No. Bos taurus Trait Est. Units % Est. Units % Crossbred calves (individual heterosis) Calving rate, % 11 3.2 4.4 Survival to weaning, % 16 1.4 1.9 Birth weight, kg 16 .8 2.4 4 3.3 11.1 Weaning weight, kg 16 7.3 3.9 10 21.7 12.6 Postweaning ADG, g/d 19 34 2.6 6 116 16.2 Yearling weight, kg 27 13.2 3.8 Cutability, % 24 -.3 -.6 Quality grade, 1/3 gr. 24 .12 --- 6 .3 ---

Bos taurus X Bos indicus X HETEROSIS EFFECTS IN CROSSES OF BOS TAURUS X BOS TAURUS BREEDS AND IN CROSSES OF BOS INDICUS X BOS TAURUS BREEDS FROM DIALLEL CROSSING EXPERIMENTS Bos taurus X Bos indicus X No. Bos taurus No. Bos taurus Trait Est. Units % Est. Units % Crossbred cows (maternal heterosis) Calving rate, % 13 3.5 3.7 7 9.9 13.4 Survival to weaning 13 .8 1.5 7 4.7 5.1 Birth weight, kg 13 .7 1.8 6 1.9 5.8 Weaning weight, kg 13 8.2 3.9 12 31.1 16.0 Longevity, yrs 3 1.36 16.2 Lifetime prod. No. Calves 3 .97 17.0 Cum. wn. wt., kg 3 272 25.3

Weight of Calf Weaned Per Cow Heterosis Weight of Calf Weaned Per Cow Exposed To Breeding 23.3 Heterosis increases production per cow 20 to 25% in Bos taurus x Bos taurus crosses and at least 50% in Bos indicus x Bos taurus crosses in subtropical regions. More than half of this effect is dependent on use of crossbred cows. 14.8 Percent 8.5 8.5 This slide summarizes results from a longterm heterosis project completed in the 1970’s comparing production of straightbreds and crosses in all combinations among the Hereford, Angus, and Shorthorn breeds. Weaning wt per cow exposed was increased 8.5 % by raising cross bred calves. However the greatest advantages of crossbreeding depended on use of crossbred cows. Weaning wt per cow exposed was increased 23 % in crossbred cows raising three way cross progeny. More than half of total heterosis effect was dependent on use of crossbred cow to take advantage of their improved reproduction rate and milk production. In addition, longevity was increased, herd life was 1.9 yr longer for F1 cows than for straightbred cows. Break even cost so production were reduced 10%, these are savings that as essential today as ever, if the beef industry is to remain competitive with other meat products. X-bred cows calves Straightbred cows straightbred calves Straightbred cows X-bred calves

ANGUS (HA) AND ANGUS X HEREFORD (AH) COWS LONGEVITY AND LIFETIME PRODUCTION OF STRAIGHTBRED HEREFORD (H), ANGUS (A), HEREFORD X ANGUS (HA) AND ANGUS X HEREFORD (AH) COWS Breed group Trait H A HA AH Heterosis Longevity, yrs. 8.4 9.4 11.0 10.6 1.9* Lifetime production No. calves 5.9 6.6 7.6 7.6 1.3* Wt of calves weaned, lb. 2405 2837 3259 3515 766* HA and AH were superior to either parent breed bred straight 1.9 extra years (21%) 1.3 extra calves (20%) 766 extra pounds = 1.8 extra calves with straightbred dams. Heterosis in Bos indicus X Bos taurus crosses about 2 X this magnitude *P < .05

Conclusions Heterosis Effects are greatest for lowly heritable traits: Reproduction Survival Longevity Heterosis effects are moderate for moderately heritable traits: Direct and maternal weaning weight Postweaning gain Heterosis effects are small for highly heritable traits: Feed efficiency Carcass traits Retail product % Fat thickness Marbling

Static Three-breed Cross System Offspring marketed Pounds of calf/cow increased about19% 45-50% of Cows 25-30% 25%   A B C A AB

Rotational Crossbreeding Systems Sig heterosis maintained in rotational systems (H, A, S) 68% of max heterosis, or 15% increase in lbs calf weaned 86% or 19% increase in wn wt per cow exp in 3 breed rotational system

Heterosis for Production Per Cow in Hereford, Angus, and Shorthorn Rotational Crosses First Generation Observed (%) 16 24 Expected (%)a 19 23 Second Generation Observed (%) 24 35 Expected (%)a 14 21 aBased on individual and maternal heterosis observed in F1 generation and assumes that retained heterosis is proportional to retained heterozygosity. Two breed Three breed rotation rotation

Genetic Composition and Heterosis Expected in a Two-Breed Rotation Heteroz. of Est. Additive genetic progeny in wt. comp. of progeny relative to F1 wnd/cowa Sire A B Generation breed % % % % 1 A 50 50 100 8.5 2 B 25 75 50 19.0 3 A 63 37 75 13.8 4 B 31 69 63 16.4 5 A 66 34 69 15.2 6 B 33 67 66 15.8 7 A 67 33 67 15.5 aBased on heterosis effects of 8.5% for individual traits and 14.8% for maternal traits, when loss of heterosis in proportional to loss of heterozygosity

Genetic Composition and Heterosis Expected in a Three-Breed Rotation Additive Genetic Heteroz. of Est. increase Comp. of Progeny progeny in wt. Sire A B C relative to F1 wnd/cowa Generation breed % % % % % 1 A 50 0 50 100 8.5 2 B 25 50 25 100 23.3 3 C 12 25 62 75 21.2 4 A 56 12 31 88 18.6 5 B 28 56 16 88 20.5 6 C 14 28 58 84 20.2 7 A 57 14 29 86 19.7 8 B 29 57 14 86 20.0 aBased on heterosis effects of 8.5% for individual traits and 14.8% for maternal traits when loss of heterosis is prportional to loss of heterozygosity.

Rotational Crossbreeding Systems Sig heterosis maintained in rotational systems (H, A, S) 68% of max heterosis, or 15% increase in lbs calf weaned 86% or 19% increase in wn wt per cow exp in 3 breed rotational system

Rotational crossing systems maintain heterosis proportional to heterozygosity

Next time : Composite Populations and alternative crossbreeding systems.

Brown Swiss (Braunvieh) MARC I ¼ Limousin, ¼ Charolais, ¼ Brown Swiss, c Angus and c Hereford Limousin Charolais Angus Hereford Brown Swiss (Braunvieh) MARC II ¼ Simmental, ¼ Gelbvieh, ¼ Hereford and ¼ Angus Angus Simmental Gelbvieh Hereford MARC III ¼ Pinzgauer, ¼ Red Poll, ¼ Hereford and ¼ Angus Pinzgauer Red Poll Angus Hereford 3 composite pops. 75:25, 50:50, 25:75 Continental to British

Composites minus purebreds HETEROSIS EFFECTS AND RETAINED HETEROSIS IN COMPOSITE POPULATIONS VERSUS CONTRIBUTING PUREBREDS (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 Sig heterosis maintained in composite pops into F3 and and F4 generations ~ 75 % of F1 heterosis on average over all composites and for most traits Proportional to increased heterozygosity expected

Composite populations maintain heterosis proportional to heterozygosity (n-1)/n or 1 – S Pi2

Rotational crossing systems or composite populations maintain significant heterosis

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 .0625 BB .0625 CB .25 C .125 AC .125 BC .0625 CC 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 populations provide 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. Consistent with results in earlier cycles of the program, genetic potential for quality grade and yield grade are still more nearly optimized in cattle with 50:50 ratios of Continental to British inheritance than in cattle with higher or lower ratios of Cont. to British inheritance.

COMPLEMENTARITY is maximized in terminal crossing systems Cow Herd Small to moderate size Adapted to climate Optimal milk production for feed resources Terminal Sire Breed Rapid and efficient growth Optimizes carcass composition and meat quality in slaughter progeny Progeny Maximize high quality lean beef produced per unit feed consumed by progeny and cow herd

Rotational and Terminal Sire Crossbreeding Programs Cow Age No. 1 20 2 18 3 15 2 Breed Rotation Two Breed Composite  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 21% 18%

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).

SUMMARY

Figure 6. Use of heterosis, additive breed effects and Complementarity with alternative crossbreeding systems.

Implications for Crossbreeding Similarity in mean performance of British and Continental European breeds means they are more suited for use in rotational cross-breeding systems today than 30 years ago Performance levels are not expected to fluctuate as much with rotational crossing for growth traits and cow size . Growth rate can be stabilized by using Across-breed EPDs. Differences in birth weight are still significant and warrant use of sire breeds with lighter birth weight on first calf heifers (i.e., Angus, Red Angus, etc.). Intergeneration fluctuations in milk production still persist but they are less than half as great as 30 years ago. Milk levels can be stabilized by using Across-breed EPDs.

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.

Heterosis proportional to heterozygosity in various matings Mating type Progeny Dam Pure breed 0 0 Two breed F1 cross (A x B) 100 0 F2 (AB x AB) 50 100 F3 (AB x AB) (or F4, ..Fn) = 2 breed Composite 50 50 Backcross (A x AB) 50 100 1st backcross interse (A-AB x A-AB) 37.5 50 ¾-1/4 composite (.75A, .25B) 37.5 37.5 5/8-3/8 composite (.625 A, .375 B) 47 47 2 breed rotation 67 67 Three way cross (A x BC) 100 100 1st 3-way interse (A - BC) x (A-BC) 62.5 100 3 –breed composite (.5 A, .25 B, .25C) 62.5 62.5 3 breed rotation (A, B, C) 86 86 Rotation F1 hybrids, 1 common breed (AB -AC) 67 67 Four way cross 100 100 4- breed composite (.25 A, .25B, .25C, .25 D) 75 75 4-breed rotation (A, B, C, D) 93 93 Rotation 2 F1 hybrids (AB - CD) 83 83

Rotational and Terminal Sire Crossbreeding Programs Cow Age No. 1 20 2 18 3 15 2 Breed Rotation 3 Breed Rotation  B A B    45% A  C 4 13 5 12 - - 12 1 T x (A-B) T x (A-B-C) 55% Lbs. Calf/Cow 21% 24%

an important genetic resource BREED DIFFERENCES an important genetic resource Cross breeding of 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

Composite populations provide for effective use of Heterosis Breed differences Uniformity and end product consistency

Trait Purebreds Composites 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 Sig heterosis maintained in composite pops into F3 and and F4 generations ~ 75 % of F1 heterosis on average over all composites and for most traits Proportional to increased heterozygosity expected

COMPLEMENTARITY is maximized in terminal crossing systems Cow Herd Small to moderate size Adapted to climate Optimal milk production for feed resources Terminal Sire Breed Rapid and efficient growth Optimizes carcass composition and meat quality in slaughter progeny Progeny Maximize high quality lean beef produced per unit feed consumed by progeny and cow herd

General Considerations Rotational Systems Provide for more effective use of Heterosis Composite populations Breed differences Uniformity and end product consistency

Composite populations provide for effective use of Heterosis Breed differences Uniformity and end product consistency

Effect of Heterosis on Percentage Cows Remaining in Herd At Different Ages Relative to Those Originally Retained as Breeding Heifers Crossbred cows Straightbred cows Percentage Cows Remaining Age At Exposure to Breeding (years)

Rotational Crossbreeding Programs   A B A B    C Increase Lbs. Calf Per Cow 15% Increase Lbs. Calf Per Cow 19%

Genetic Variation in Alternative Mating Systems Optimum Assumes that the Two F1’s Used are of Similar Genetic Merit

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).