Abstract T19

1. Impact of selection for increased daughter fertility on productive life and culling for reproduction H. D. Norman, J. R. Wright*, R. H. Miller Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350 Abstract T19 2008 http://aipl.arsusda.gov/ RESULTS (cont.) • Least-squares differences for PL (mo) INTRODUCTION • Improving reproductive traits through genetic selection was usually considered futile because of low heritability (<5%). • Pregnancy rate declined by 7% and days open increased by 39 days from 1960 To 2000. • AIPL began calculating genetic evaluations for daughter pregnancy rate (DPR) in 2003. DATA & METHODS (cont.) Analysis: • Examine least-squares differences between cow groups on a within-herd basis with cow birth year in the model. RESULTS (cont.) • Mean of cow PL by ancestor PTA DPR group Max. MGS differ-ence MGS quintile Sire quintile RESULTS • Number of cows by ancestor PTA DPR group PL (mo) MGS quintile Max. sire difference OBJECTIVE • Determine how effective emphasis on DPR for two generations was in changing fertility and productive life (PL). • PL was over 4 mo longer for cows with sires and MGS from the highest group than those from the lowest group. • Sire quintile had a larger effect on increasing length of PL (2.8 to 3.3 mo) than MGS quintile (0.8 to 1.4 mo). Sire quintile • Overall productive life mean was 27.0 months. • Cows in the lowest PTA DPR ancestor group (1,1) had a mean PL of 25.0 while the highest group averaged 28.7 months. • The increase in PL was similar to the increase seen in first parity pregnancy rate. • First parity mature-equivalent milk mean was 1,230 kg lower in the highest PTA DPR group (5,5) than in the lowest (1,1). DATA & METHODS Data edits: • Holstein AI bulls with January 2008 PTA DPR based on 35 daughters. • Holstein cows with birth dates from 1988 through 1999 and calving dates from 1990 through 2005. • Cows excluded if they changed herds, had missing lactation records within first 5 parities, or were in herds with <10 cows. • Final data set of 4,380,300 cows in 31,759 herds. • Bulls assigned to 5 groups (quintiles) based on their PTA DPR. • Cows divided into 25 groups based on their sire and maternal grandsire (MGS) quintile for PTA DPR. Examples: • Cows in group 1,1 had both sires and MGS in the lowest 20% of AI bulls for PTA DPR • Cows in group 5,5 had both sires and MGS in the highest 20% of AI bulls for PTA DPR • Least-squares differences for percent culled for reproduction • Distribution of cows by group ranged from 2.6% to 6.5%, most likely due to heavy use of certain bulls. • Sire and MGS PTA DPR mean by group (not shown) varied by over 4% (from -2.1 in group 1,1 to 2.1 in group 5,5). Max. MGS differ-ence MGS quintile Sire quintile • Mean 1st parity pregnancy rate by ancestor PTA DPR group • Percent cows reported culled for reproduction by ancestor PTA DPR group Max. sire difference • Cows with low ancestor PTA DPR were culled for reproduction at a 2% higher rate than those with high ancestor PTA DPR. • Sire quintile and MGS quintile effect were nearly linear across groups. Pregnancy rate (%) % culled CONCLUSIONS • Emphasis on DPR for 2 generations increased PL and decreased culling for reproduction. • Selection for PTA DPR can be effective in improving fertility. • First parity pregnancy rate rose from 20.0% for cows sired by the lowest PTA DPR ancestor group (1,1) to 27.3% for cows sired by highest (5,5). • Frequency of culling for reproductive reasons decreased over 3% from 13.1% (group 1,1) to 10.0% group (5,5).