Presentation on theme: "Can You Breed a “Good Breeder” Kristi M. Cammack Department of Animal Science University of Wyoming."— Presentation transcript:
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 Fertilization Gestation / Fetal Development Parturition Postnatal survival / growth And an infinite # of steps in between!
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
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.
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 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 !
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 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)