Heterosis – The Forgotten Tool?

1. Heterosis – The Forgotten Tool? Dr. Tom Field Colorado State University Dr. Andy Herring Texas A&M University Cattlemen’s College 2005 NCBA Meeting, San Antonio

2. General Comments The seedstock cattle industry exists as a business only because of the demands of the commercial cattle industry. Without purebred animals, F1 crossbred animals cannot be produced.

3. Basics of Quantitative Genetics Performance = Genetics + Environment Genetic aspects are: 1. Additive (breeding value – gene content) 2. Non-additive (hybrid vigor – gene combinations) Alleles at a gene locus can act additively (or not). Genotypes across gene loci can act additively (or not).

4. Breeding Systems • It is important to know breed characteristics to fully take advantage of breeding systems • It is important to know characteristics of different types of breeding systems

5. Properly designed beef cattle crossbreeding programs have the potential of substantially improving production efficiency over commercial straightbreeding programs.

6. The improved efficiency from crossbreeding can result from: • Heterosis (hybrid vigor) • Blending, in the offspring, of characteristics from different breeds and/or, • Characteristics of the dams and sires as these characteristics, themselves, affect the efficiency of the system.

7. Heterosis Hybrid vigor (also called heterosis) is the higher performance of crossbred animals as compared to purebred animals. For a particular pair of breeds, the hybrid vigor for a particular character is the average amount that the average of the F1 exceeds the average of the two pure breeds.

8. Heterosis Example: Weaning weight information Brahman average = 500 lb Hereford average = 460 lb B x H average = 516 lb H x B average = 540 lb HV =((516 + 540)/2) - ((500 +460)/2) = 528 - 480 = 48 lb = 48/480 = 10%

9. Heterosis -most important for reproduction and survival traits -tends to be higher between breeds that are more genetically different from each other (2 to 3 times higher in Bos indicus/Bos taurus crosses than in Bos taurus/Bos taurus crosses) -highest in F1, and tends to be proportional to degree of heterozygosity -especially important for female productivity (reproduction and maternal ability)

10. Crossbred Cows Because of heterosis for female productivity (fertility, calf weaning weight, longevity), much of the advantage from crossbreeding systems comes from the use of crossbred cow.

11. Maternally Influence Characters Performance for a maternally influenced character (such as weaning weight) is a function of 1. breed composition of the calf 2. heterosis in the calf (direct) 3. breed composition of the dam 4. heterosis in the dam (maternal)

12. How to Estimate Heterosis • There are two major considerations here: • The actual amount of increased performance in units of the trait in F1 animals. • The expected fraction (or percentage) of the F1 advantage in other types of crosses.

13. How to Estimate Heterosis F1 animals will exhibit 100% heterosis between the two breeds involved, but this is 100% of some actual advantage in performance. For example: In some F1 crosses, this may be 100% of a 25 lb advantage, and in other F1 crosses this may be 100% of a 40 lb advantage.

14. How to Estimate Percent Heterosis Heterosis percent (fraction) is based on the fraction of gene loci in animals that are expected to have two alleles from two different breeds. Angus bulls x Hereford cows => F1 calves These calves are ½ Angus, ½ Hereford, but 100% of their gene loci are heterozygous.

15. How to Estimate Percent Heterosis If we take F1 bulls and F1 heifers and mate them: F1 bulls (½ A ½ H) x F1 heifers (½ A ½ H) => F2 calves (½ A ½ H) The F2 calves are expected to have ½ heterosis themselves (50% direct), but also benefit from heterosis in cows (100% maternal).

16. How to Estimate Percent Heterosis If you know the fractions of the breeds in the parents, you can estimate the fraction of heterosis in progeny (based on chance of inheritance). ½ A ½ H bulls x ½ A ½ Gelbvieh cows => ½ A ¼ H ¼ G calves Heterosis in calves can come from A-G, H-G, H-A combinations, each has ¼ chance of occurrence. We would say these calves have 75% heterosis.

17. Heterosis • 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.

18. Cumulative Effects Of Heterosis For Weight Of Calf Weaned Per Cow Exposed To Breeding 23.3 14.8 Percent 8.5 8.5 Straightbred cows straightbred calves Straightbred cows X-bred calves X-bred cows X-bred calves

19. Heterosis Utilization is Critical for Commercial Producers • Consider pounds of calf weaned per cow exposed to breeding • Cow-calf System Productivity* lb calf • Straightbred cows producing • straightbred calves 100 450 • 2. Straightbred cows producing • crossbred calves 108.5 488 • Crossbred cows producing • crossbred calves 123.3 555 *Based on data from USDA MARC involving Bos taurus crosses and purebreds.

20. Heterosis Depends on Crossbreeding System and Breeds Type of system Example Direct Maternal Terminal F1 cross Charolais x Hereford 100 0 Terminal F1 cross Brahman x Hereford 200 0 Two breed rotation Angus, Hereford 67 67 Two breed rotation Angus, Brahman 133 133 Three breed terminal Charolais x F1 Angus-Hereford 100 100 Three breed terminal Charolais x F1 Brahman-Hereford 150 200 Three breed rotation Angus, Simmental, Gelbvieh 86 86 Three breed rotation Angus, Brahman, Charolais 143* 143* Two breed composite 50% Hereford, 50% Simmental 50 50 50% Angus, 50% Brahman 100 100 5/8 Charolais, 3/8 Red Angus 47 47 5/8 Shorthorn, 3/8 Brahman 84 84 Four Breed Composite 25% each A, H, S, C 75 75 25% A, Br, C, G 112.5 112.5 25% A, Br, L, Nellore 125 125 *Some crosses in the system will exhibit more heterosis than others.

21. Average birth weights at the McGregor Station 1992-1997 _______________________________________________________ Birth Weight (lb) Sire breed Dam breed bulls heifers average _______________________________________________________ Hereford Hereford 80 76 78 Brahman Brahman 74 71 72.5 Hereford Brahman 75 73 74 Brahman Hereford 101 87 94 ______________________________________________________

22. Crossbreeding Systems A real challenge in beef cattle breeding is to develop effective, sustainable crossbreeding systems.

23. In order for a crossbreeding system to be sustainable in a region, it should have the following characteristics: 1. It should be possible for all the breeding stock that are needed for the system to be produced in the same region where the system will be operated. 2. The system should be fairly simple to operate. 3. All cattle used in and produced by the system should be adapted to the local environment. 4. There should be no major incompatibilities between the cattle that are mated. 5. All animals that are produced in the system must be acceptable to local market conditions.

24. Example of Three Breed Composite Composite that is ½ Angus, ¼ Charolais, and ¼ Hereford 1/2A 1/4C 1/4H bulls x 1/2A 1/4C 1/4H cows => 1/2A 1/4C 1/4H calves Breed combinations in calves can be: A-C, A-H, or C-H.

25. Breed Combinations in Calves Cows ½ A ¼ C 1/4H Bulls ½ A ¼ C ¼ H Heterosis in calves = 1/8 +1/8 + 1/8 + 1/8 + 1/16 + 1/16 = 5/8 or 62.5%

26. Results From Research Projects

27. LONGEVITY AND LIFETIME PRODUCTION OFSTRAIGHTBRED 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 3518 3514 766* *P < .05

28. TAMU Diallele Project • Purebred and F1 cows of Angus, Hereford, Brahman, Holstein and Jersey were evaluated over a 14 year period. • Only production reason for culling was if cow failed to give birth to live calf every 24 months, or if cow appeared unable to raise another calf.

30. Research Project in Nebraska Angus, Hereford and Shorthorn evaluated as purebred and as F1 crossbred cows for cow productivity and longevity. Cows born 1960-1963 and were kept until they were 12 to 15 years old.

31. Survival percentage to 12 yr and longevity (kept to 12-15 yr old)

32. Mouth scores based on teeth length in aged cows Higher number indicates more tooth remaining.

33. Reasons for Nebraska cows culled

34. TAMU Riesel Project • Production of F1 calves in 1982-1985 by mating Angus, Gray Brahman, Gir, Indu-Brazil, Nellore and Red Brahman sires to Hereford cows. • All cows were kept to measure productivity and longevity. • Udder, teat and teeth soundness evaluated

35. Comparison of F1 Cows at McGregor, TX through 14 years of age % CC lb calf per % still Type of cow BWT WWT weaned cow exposed in herd Angus-H 86.6 499 83.3 416 53% Gray Brahman-H 81.6 566 88.4 500 53% Gir-H 76.6 562 91.5 514 73% Indu-Brazil-H 81.8 563 81.0 456 33% Nellore-H 81.1 566 96.1 544 80% Red Brahman-H 81.9 574 86.0 494 43%

36. Comparison of F1 Cows at McGregor, TX through 14 years of age Teats that were too large, and/or udders that were too pendulous caused increases in calf illness because it was difficult for calves to nurse on their own initially. Size of udder did not appear related to milk production within a breed. Nellore crossbred cows had smallest teats and tighest udders, and best overall production and longevity. All of Bos indicus-Hereford F1 cows had better mouths later in life than Angus-Hereford F1 cows.

37. Heterosis Retention Project at McGregor, Texas • Initiated in mid 1990s to measure heterosis retention in Bos indicus-Bos taurus crosses. • Purebred Angus, Hereford, Brahman and Nellore. • Cow reproduction and productivity major focus of project.

38. Heterosis Retention Project - McGregor, TX

39. Heterosis May Vary Across Environments • There have been several research projects in cattle where there seems to be more heterosis expressed in more challenging environments.

40. Matching Genetic Potential to the Climatic Environment (Olson et al., 1991)

41. Note that important differences in environments can be across the fence from each other.

42. Summary Because of heterosis for female productivity (fertility, calf weaning weight, longevity), much of the advantage from crossbreeding systems comes from the use of crossbred cow.

43. Bad Breeding Decisions are Costly