H. D. Norman *,1 , J. L. Edwards, and J. R. Wright

1. Accuracy of reported births and calving dates of dairy cattle in the United StatesPoster 1705ADSA 2001, Indiannapolis H. D. Norman*,1, J. L. Edwards, and J. R. Wright 1 Animal Improvement Programs Laboratory, USDA, Beltsville, MD dnorman@aipl.arsusda.gov

2. Abstract Frequencies of births that were reported for specific days of the month were documented for US dairy cattle born since 1987 by birth year, herd size, and registry status and compared with calving frequencies for those dates. Because birth dates are expected to be random and uniformly distributed throughout each month, percentages of births on individual dates were expected to be equal (3.3% for d 1 through d 28, 3.2% for d 29, 3.0% for d 30, and 1.9% for d 31). However, percentages of reported birth dates for d 1, 2, 10, 15, and 20 were higher than expected. Percentage of reported births for d 1 was highest (5.3%) of all days of the month regardless of herd size or registry status. The nonuniform distribution of birth dates within month indicated that a substantial number of birth dates were unknown and that estimated birth dates had been reported. CONTINUED

3. Abstract About one-third of the birth dates recorded on d 1 appeared to have been estimated, or altered to gain an advantage in cattle shows. The highest frequencies for birth dates on d 1 (5.9 to 7.4%) were found for registered cows during months that initiated age groupings for dairy shows (March, June, September, and December). Birth dates for some registered cows were intentionally misreported as confirmed by comparison of birth dates of individual cows with calving dates of their dams. Reported calving dates appeared to be more accurate than reported births; the inflated frequency of recorded calvings on d 1 was only about 30% as large as the inflated frequency of recorded births. Because cow age is determined by birth date, proper reporting of birth dates is important to ensure the accuracy of standardized yield and fitness records and the genetic evaluations that are based on those records. When animals’ recorded birth dates and their dams’ calving dates differ, more credence should be given to the latter to improve accuracy.

4. Introduction • Correct birth dates are essential because they impact standardized milk yield and fitness traits though age adjustment. • Birth dates and calving dates are assumed to occur randomly throughout a given month. • Expected percentage of births and calvings should be 3.3% on d 1-28 and 3.2, 3.0, and 1.9% on d 29, 30, and 31, respectively. • Because size has a positive impact on show ring placing of calves and yearling heifers, animals born as early as possible within the 3-mo age group have an advantage.

5. Objectives • To determine accuracy of recorded birth dates through examination of the percentage of births reported for each day within month. • To assess whether year, herd size, and registry status are related to the recording of birth and calving dates.

6. Data • 9.6 million lactation records of registered and grade cows born after 1986 from all over US. • Herd size groups: • Small (<50). • Medium (50-150). • Large (>150). • Subset of 497,832 cows born in 1997 matched with dam's recorded calving date for further examination (embryo transfer animals excluded).

7. Frequency of recorded birth dates by birth year and day of month

8. Results • Highest birth date frequency within month over all years was 5.3% on d 1, which was higher than expected (3.3%). • Data from recent years slightly more accurate for d 1 within month. • Little variation between small, medium, and large herds in frequency of recorded birth dates. • Highest calving date frequency within month also on d 1 over all years (3.9%).

9. Results • Calving date frequencies (3.1-3.6% for d 2-28) varied little from expected. • Exact matches between animal birth date and dam calving date for animals born during 1997: • 95% of grade animals. • 92% of registered animals.

10. Percentage of recorded births on d 1 of month for small herds (<50 cows):

11. Results • For registered cows, significantly more birth dates on d 1 of March, June, September, and December (beginning of show classes) than on d 1 of other months. • For grades, higher frequency of birth dates on d 1 than expected but more consistent across months (more real birth dates may have been unknown than for registered cows).

12. Conclusions • Approximately 1/3 of recorded birth dates for d 1 were estimated or altered, possibly to gain advantage at cattle shows. • Substantial number of unknown birth dates not coded as estimated. • Frequencies of birth dates on d 1 of month higher than expected for all herd sizes and for both registered and grade cows. • Use of estimated birth date code should be more widely used to differentiate between cows with known and estimated birth dates.