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Genetic selection for reproduction:. Current reproductive status of the national herd;. Application of selection indexes for dairy producers. 2007. Current reproductive status of the national herd. H.D. Norman. Dairy Cattle Reproductive Council Convention ( 2 ). Bull fertility.
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Genetic selection for reproduction: Current reproductive status of the national herd; Application of selection indexes for dairy producers
2007 Current reproductive statusof the national herd H.D. Norman Dairy Cattle Reproductive Council Convention (2)
Bull fertility • Estimated Relative Conception Rate (ERCR) • 70-day nonreturn rate (NRR) • Phenotypic evaluation • Source: • DRMS (Raleigh, NC), 1986−2005 • USDA (Beltsville, MD), 2006−present • Western Bull Fertility Analysis • 75-d veterinary-confirmed conception rate • Source: AgriTech (Visalia, CA), 2003 −present
Survey of AI organizations • Does your organization rate bulls on fertility from field data? • Where do you obtain the data you use to evaluate them? • How long a time period is included in your evaluation? • What do you publish? • How many nonreturn days are in your calculation? • Is your evaluation derived from first or all services? • Do you eliminate cows sold before a specific number of days after insemination? • Do you eliminate cows in herds that go off test before a specific number of days after insemination? • Is information on services from natural service bulls that follow AI breedings available to you to document failures of those AI breedings?
Survey results • All had programs to monitor bull fertility, but few relied completely on in-house information • Most received some information from technician breedings • One purchased breeding records from a dairy records processing center • Another obtained breeding records directly from cooperating herds • Most common fertility measure was NRR • Varied from 59 to 90 days for first breeding • Some organizations used a range of days
Survey results (cont.) • Conception rate (CR) used by one because of availability of pregnancy-check records • Time period for data included in a bull’s fertility evaluation varied from 1 year to no limit • Equal number included only first services compared with all services • Data from technician breedings • Not adjusted for cow departures because of culling or when a herd discontinued production testing • No access to data that showed when natural service followed an AI mating
New USDA service sire evaluation • Based on conception rate rather than NRR • More accurate • Inseminations from most of the United States • All services (not just first) • Additional model effects included • Available early 2008 • Documentation at ftp://aipl.arsusda.gov/pub/outgoing/BullFert/
Pregnancy rate (PR) • Percentage of nonpregnant cows that become pregnant during each 21-day period • Advantages over days open (DO) • Easily defined • Information from nonpregnant cows included more easily • Larger (rather than smaller) values desirable • PR = [21/(DO − voluntary waiting period + 11)]100 • Voluntary waiting period assumed to be 60 days • Factor of +11 adjusts to middle day of 21-day cycle • Examples • Herd with average of 133 DO has PR of 25% • Herd with average of 154 DO has PR of 20%
USDA pregnancy rate • Linear approximation • PR = 0.25 (233 − DO) • 1% higher PR = 4 days fewer open
Daughter pregnancy rate (DPR) • First USDA genetic evaluations in 2003 • Same across-breed animal model as for yield traits, productive life (PL), and somatic cell score (SCS) • Heritability of 4% • Predicted transmitting abilities (PTAs) reported as percentages • Daughters of bull with PTA DPR of 1 expected to be 1% more likely to become pregnant during estrous cycle than if bull had PTA DPR of 0 • Each increase of 1% in PTA DPR equivalent to decrease of 4 days in PTA DO • PTA DO approximated by −4 × PTA DPR • Example: Bull with PTA DPR of +2.0 would have PTA DO of −8
NM$ CY$ PTI FM$ 2007 Application of selection indexesfor dairy producers H.D. Norman Dairy Cattle Reproductive Council Convention (31)
DPR benefits over productive life • Additional calves produced • Decreased units of semen needed per pregnancy • Decreased labor and supplies for heat detection, inseminations, and pregnancy checks • Higher yields because more ideal lactation lengths
Lifetime value • Factors in determining economic value • Loss of about $1.50/DO • 2.8 lactations per cow • No breedings for half of cows during final lactation • Correlation of heifer and cow fertility (0.3) • Value of extra calves • Other unmeasured health expenses • Total lifetime merit value of $21/PTA DPR unit
Total Performance Index (TPI) • Calculated by Holstein Association USA (Brattleboro, VT) • Emphasis of 19% on early breeding • 10% on PL • 8% on DPR • −1% on dairy form • 95% correlation between USDA lifetime net merit and Holstein TPI
2007 Conclusions H.D. Norman Dairy Cattle Reproductive Council Convention (41)
Service sires • Using bulls with higher conception rates returns profit fairly quickly • Premium of $2 could be paid for semen per 1% improvement in fertility • Unit of semen from bull with ERCR of +2 worth $8 more than unit from bull with ERCR of −2 • Little genetic improvement in male fertility expected over time • Use bull fertility as a secondary selection trait after production and economic indexes
Selection for cow fertility • Selection for improved fertility possible and recommended • Most benefits delayed for 2 years or more • Select service sires for overall lifetime merit that includes daughter fertility rather than for daughter fertility alone • Producers with herd fertility problems may choose to emphasize DPR extensively, which can be done with little loss in overall net merit
Benefits of improved reproduction • Lower semen cost • Improved ability to optimize lactation and lifetime yields • Reduced culling due to delayed or failed conception • More herd replacements
Fertility emphasis • Service-sire fertility and DPR important for all management systems, but most important for grazing herds with seasonal calving • Use of a few bulls that average 3.0% for PTA DPR (equivalent to a decrease of 12 DO) could recover much of genetic decline in fertility from use of high-yield bulls for 40 years • General recommendation still is to select for overall merit based on genetic-economic index appropriate for current milk market
