Can You Breed a Good Breeder Kristi M

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

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

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. ”

Mating tw e ps d n A an i in f n ite # t s of in be e ! n e Fertilization Gestation / Fetal Development Parturition Postnatal survival / growth

Factors Affecting Reproduction • Species – Bos taurus vs. Bos indicus • Breed – Purebred – Crossbred • • Location Sex Animal class Environment – Management – Production setting – Etc. !

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 h 2.

h 2 of Common Female Reproduction Measures

Reproduction Trait Evaluation • Why the low h 2? – 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.

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.

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

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.

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

Age at Puberty • Variable h 2 estimates:

From: Laster et al. , 1972

Age at Puberty • Correlated Trait - Weight at Puberty – h 2: 0. 40 to 0. 70 From: Laster et al. , 1972

From: Laster et al. , 1972

Age at First Calving • Routinely recorded. • h 2: 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.

Calving Date • Routinely recorded. • h 2: 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.

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.

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: – 1 st breeders versus multiple breeders.

First Service Conception Rate • h 2: 0. 03 to 0. 22 • Other traits that take AI versus Natural Service into account: – Calving to 1 st insemination. – Conceptions per estrous cycle. – Conceptions per service.

Pregnancy Rate • Binary trait. – 1 = pregnant; 0 = not pregnant. • h 2: 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.

Pregnancy Rate • For economic viability: – Replacement heifers must calve by 2 years. – And must remain in productive herd. • Lifetime Pregnancy Rate: – # pregnancies / # mating years – h 2: 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.

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

Pregnancy Rate From: Laster et al. , 1972

Net Calf Crop • % Calves weaned per cow exposed. • “Gross” measure of herd reproductive ability. • h 2: assumed low • < 100% calf crop: – Non-pregnant females. – Fetal deaths during gestation. – Peri-natal deaths. – Post-natal deaths.

Calving Rate • # Calves produced by a cow / # of potential calves. • h 2: 0. 02 to 0. 17

Calving Interval • Routinely recorded. • # days between successive calvings. • h 2: 0. 13 • Challenges: • Selection for ↓ calving interval = Indirect selection for later age at puberty. – 1 st calf born late. • Biases. • How to handle those with no record(s).

Dystocia • Calving difficulty. • “Risk” factor. – Increased in heifers. • h 2: 0. 22 to 0. 42 • Scaled:

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

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

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. – h 2: 0. 02 to -0. 23 • Dependent upon “given age” selected.

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

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

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

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

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

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…

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.

Obstacles - Female Reproduction • Numerous “fertility” traits recorded. • Long time required to record many such traits. – ↓ data reported. • Low h 2. • Limited data collection in pasture mating systems.

Obstacles – Male Reproduction • Variable assessments. – Serving capacity versus libido. • Many bull “fertility” traits recorded in the female. – Pregnancy rate, etc. • Few h 2 estimates. – None available for breeding soundness, serving capacity, or libido. • Difficult to identify lowly “fertile” bulls in natural mating situations.

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?

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 h 2. • Some reproductive traits are themselves moderately h 2.

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 nonadditive genetic improvements: – Earlier puberty – Increased pregnancy rate – Decreased dystocia – Increased longevity – Decreased calving interval

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