Can You Breed a “Good Breeder”

1. Can You Breed a “Good Breeder” Kristi M. Cammack Department of Animal Science University of Wyoming

2. Question of the Day:What is Fertility? • Female: • Pregnancy rate? • Heifer pregnancy? • Calving rate? • 1st service conception rate? • Longevity? • Male: • Scrotal circumference? • Breeding soundness? • Libido/service capacity?

3. What is Fertility? • In short, there is no single trait that defines fertility! • Too many inputs! • “Successful reproduction is dependent on many factors that require sires and dams capable of carrying out each critical stage of reproductive development.”

4. Mating Fertilization And an infinite # of steps in between! Gestation / Fetal Development Parturition Postnatal survival / growth

5. Factors Affecting Reproduction • Species • Bostaurusvs. Bosindicus • Breed • Purebred • Crossbred • Location • Sex • Animal class • Environment • Management • Production setting • Etc.!

6. Reproduction Trait Evaluation • National evaluations historically focuses on production traits. • Growth traits. • Carcass traits. • Why? • Limited data available for reproduction traits. • Lack of total-herd reporting. • Difficulty in analyses procedures. • Especially binary traits. • Ex: Pregnancy (Yes, No) • Generally lowly h2.

7. h2 of Common Female Reproduction Measures

8. Reproduction Trait Evaluation • Why the low h2? • A large part of the observed variation is unexplainable. • Unknown environmental effects. • Yet unexplained genetic effects. • Additive, non-additive • Reproductive traits largely influenced by management practices.

9. Female Reproduction • Beef cattle not reproductively efficient. • Per service calving rate ~50-60%. • AI or natural service. • Function of underlying endocrine and physiological factors. • ↑ Efficiency of cow-calf herd requires: • Improved cow fertility. • Improved yearling heifer fertility. • Replacement heifer development program.

10. Female Reproduction • The crux of the situation… Selection has not been practiced to improve fertility…but instead to minimize infertility.

11. Age at Puberty • Measure of heifer fertility. • Subsequent reproductive performance. • Other predictors of heifer fertility: • Age at first estrous. • Age at first breeding. • In general… • Reproductively efficient heifers reach puberty sooner, and therefore conceive earlier.

12. Age at Puberty • Measured as first observed standing heat. • Affected by: • Body weight. • Nutrition. • Hormones. • Breed!

13. Age at Puberty • Variable h2 estimates:

14. From: Laster et al., 1972

15. Age at Puberty • Correlated Trait - Weight at Puberty • h2: 0.40 to 0.70 From: Laster et al., 1972

16. From: Laster et al., 1972

17. Age at First Calving • Routinely recorded. • h2: 0.01 to 0.37 • Genetically correlated with: • Age at subsequent calvings. • Interval between subsequent calvings. • Used to evaluate heifer fertility. • Later age at first calving: • Associated with ↓ lifetime productivity.

18. Calving Date • Routinely recorded. • h2: 0.03 to 0.21 • Reflection of: • Initiation of calving by calf. • Initiation of estrous cycles by dam. • Semen quality of sire. • Libido / service of sire.

19. Calving Date • Generally, earlier is better: • Calves have ↑weaning weights. • Predetermined calendar date versus weight- or age-constant weaning date. • Dams have ↑ postpartum interval. • Sufficient time to return to estrus.

20. First Service Conception Rate • Economically driven: • Cost of semen. • Labor for estrus detection. • Labor for breeding. • AI versus Natural Service. • Calf differences. • Age. • Performance. • Management tool: • 1st breeders versus multiple breeders.

21. First Service Conception Rate • h2: 0.03 to 0.22 • Other traits that take AI versus Natural Service into account: • Calving to 1st insemination. • Conceptions per estrous cycle. • Conceptions per service.

22. Pregnancy Rate • Binary trait. • 1 = pregnant; 0 = not pregnant. • h2: 0.14 to 0.21 • Heifers: • Sexual maturity. • Probability of exposed heifer becoming pregnant, and remaining pregnant. • Become pubertal and pregnant by 12 to 15 months of age. • Calve by 24 months of age.

23. Pregnancy Rate • For economic viability: • Replacement heifers must calve by 2 years. • And must remain in productive herd. • Lifetime Pregnancy Rate: • # pregnancies / # mating years • h2: 0.04 to 0.12 • Affected by number of factors, especially length of breeding season. • Longer breeding season = ↑ Pregnancy Rates • But also ↓ weaning weights and↓ postpartum period potentially.

24. Pregnancy Rate • Not generally affected by breed. • Typically used breed types. • ↑ conception rates when inseminations made prior to end of standing estrus.

25. Pregnancy Rate From: Laster et al., 1972

26. Net Calf Crop • % Calves weaned per cow exposed. • “Gross” measure of herd reproductive ability. • h2: assumed low • < 100% calf crop: • Non-pregnant females. • Fetal deaths during gestation. • Peri-natal deaths. • Post-natal deaths.

27. Calving Rate • # Calves produced by a cow / # of potential calves. • h2: 0.02 to 0.17

28. Calving Interval • Routinely recorded. • # days between successive calvings. • h2: 0.13 • Challenges: • Selection for ↓ calving interval = Indirect selection for later age at puberty. • 1st calf born late. • Biases. • How to handle those with no record(s).

29. Dystocia • Calving difficulty. • “Risk” factor. • Increased in heifers. • h2: 0.22 to 0.42 • Scaled:

30. Dystocia • ↓ Calf survival at birth. • ↓ Subsequent milk production. • ↓ Calf survival to weaning. • ↑ Risk of culling. • ↓ subsequent reproductive success.

31. Dystocia • Why? • Feto-pelvic incompatibility. • Oversized calf. • Higher BW. • Longer gestation period. • Undersized pelvic area. • Structural. • More “permanent” cause? • Both.

32. Longevity / Stayability • Longevity: • Length of time in breeding herd. • Meaning… • Fewer replacement heifers. • ↑ # high producing cows. • ↓ # culled cows. • However, not measured until late in life. • Stayability: • Probability of cow staying in herd until a given age. • Predicted earlier in life. • h2: 0.02 to -0.23 • Dependent upon “given age” selected.

33. Male Reproduction • AI versus Natural Service • Bull “fertility” affected by: • Number of females expected to service. • Length of mating period. • Serving capacity

34. Male Reproduction • Other considerations: • Bull:cow ratio • Behavior • Temperment • Management

35. Scrotal Circumference • 1. Predict quality and quantity of spermatozoa. • 2. Predict age at puberty of daughters. • Indicator trait. • Why? • Easy to measure. • Highly h2!

36. Scrotal Circumference • ↑ SC associated with: • ↑Sperm production. • ↓Semen quality. • ↓Age at puberty. • Growth traits???

37. Breeding Soundness • Most practical means of male “fertility” assessment. • Includes: • Physical examination. • SC measurement. • Semen evaluation. • Not sex drive / mating ability.

38. Breeding Soundness • Improved reproductive efficiency: • Identification of subfertile bulls. • Recurring assessment of “fertile” bulls. • Reasons for unsatisfactory scores: • Inadequate SC. • ≥30 cm by 1 year of age. • Inadequate sperm motility. • Abnormal sperm morphology. • Many more…

39. Libido and Serving Capacity • Libido – Sex drive of a bull. • Single bull + restrained female. • # Mating attempts. • Vigor of mating attempts. • Subjective assessment of sexual interest. • Serving Capacity – Number of times a bull mounts and copulates. • Steroid-treated or non-estrous females + small group of bulls. • # Services within specified time frame. • Subjective score. • ↑ Scoring bulls = ↑ Pregnancy rates.

40. Obstacles - Female Reproduction • Numerous “fertility” traits recorded. • Long time required to record many such traits. • ↓ data reported. • Low h2. • Limited data collection in pasture mating systems.

41. Obstacles – Male Reproduction • Variable assessments. • Serving capacity versus libido. • Many bull “fertility” traits recorded in the female. • Pregnancy rate, etc. • Few h2 estimates. • None available for breeding soundness, serving capacity, or libido. • Difficult to identify lowly “fertile” bulls in natural mating situations.

42. Obstacles - Genetic Analysis • Lack of whole-herd reporting. • Recently implemented in most U.S. breeds. • Binary nature of reproductive traits. • Yes, no • 0, 1 • Time required to collect data necessary for reproductive traits. • Uniformity of reproductive traits. • Many similar traits with slight variations. • BIF guidelines needed?

43. But there is hope… • A number of U.S. breed associations now recording reproductive performance traits. • SC, heifer pregnancy, and stayability included in some evaluations. • American Angus Association, Red Angus Association, American Hereford Association. • Genetic correlations with other traits (e.g. production traits) that are more highly h2. • Some reproductive traits are themselves moderately h2.

44. But there is hope… • Some reproductive traits show evidence of genetic influence. • a.k.a. “Yet unexplained genetic effects” • Crossbreeding can be used to make non-additive genetic improvements: • Earlier puberty • Increased pregnancy rate • Decreased dystocia • Increased longevity • Decreased calving interval

45. Acknowledgements • Milt Thomas (New Mexico State University) • Mark Enns (Colorado State University) • WERA-1 (Beef Cattle Breeding Committee)