Can You Breed a “Good Breeder”

Kristi M. CammackDepartment of Animal

ScienceUniversity of Wyoming

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?

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

Fertilization

Gestation / Fetal Development

Parturition

Postnatal survival / growth

And an in

finite #

of s

teps

in b

etw

een!

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 h2.

h2 of Common Female Reproduction Measures

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.

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 h2 estimates:

h2 # Estimates< 0.10 1

0.10 to < 0.20 30.40 to < 0.50 4

> 0.60 3

From: Laster et al., 1972

Age at Puberty (days)Purebred H 389.5Purebred A 372.2Purebred mean (A or H) 380.9Crossbred mean (HxA or AxH) 360.9H = Hereford; A = Angus

Age at Puberty

• Correlated Trait - Weight at Puberty– h2: 0.40 to 0.70

Weight at Puberty (lb)Purebred H 593.5Purebred A 603.4Purebred mean (A or H) 598.3Crossbred mean (HxA or AxH) 590.4H = Hereford; A = Angus

From: Laster et al., 1972

Weight of Heifers Reaching Puberty by 15 Months of Age (lb)Yes No Difference

H x H 606.9 543.9 63.1A x A 640.9 552.9 88.0H x A 662.9 567.9 95.0A x H 631.0 586.0 45.0

From: Laster et al., 1972

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.

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.

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:– 1st breeders versus multiple breeders.

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.

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.

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.

Pregnancy Rate

• Not generally affected by breed.– Typically used breed types.

• ↑ conception rates when inseminations made prior to end of standing estrus.

Pregnancy Rate

Correlations of Conception Rate with Other Reproductive Traits of InterestCorrelation

Weight at start of breeding period -0.02Weight change from weaning to breeding 0.12Date of estrus -0.02Number of estrus events before breeding -0.12

From: Laster et al., 1972

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.

Calving Rate

• # Calves produced by a cow / # of potential calves.

• h2: 0.02 to 0.17

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).

Dystocia

• Calving difficulty.• “Risk” factor.– Increased in heifers.

• h2: 0.22 to 0.42• Scaled:

1 No difficulty; no assistance2 Minor difficulty; no assistance3 Major difficulty; usually mechanical assistance4 Caesarian section or other surgery5 Abnormal presentation

BIF Calving Ease Scores

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.

– h2: 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 h2!h2 # Estimates

0.20 to < 0.40 60.40 to < 0.50 50.50 to < 0.80 3

**Highest estimate: 0.78 (Coulter and Foote, 1979)

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 h2.• 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 h2 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 h2.

• Some reproductive traits are themselves moderately h2.

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

Acknowledgements

• Milt Thomas (New Mexico State University)

• Mark Enns (Colorado State University)• WERA-1 (Beef Cattle Breeding

Committee)