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Relationship of somatic cell score with fertility measures Poster 1390 ADSA 2001, Indiannapolis

Relationship of somatic cell score with fertility measures Poster 1390 ADSA 2001, Indiannapolis. R. H. Miller 1 , J. S. Clay 2 , and H. D. Norman 1 1 Animal Improvement Programs Laboratory, USDA, Beltsville, MD 2 Dairy Records Management Systems, Raleigh, NC dnorman@aipl.arsusda.gov.

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Relationship of somatic cell score with fertility measures Poster 1390 ADSA 2001, Indiannapolis

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  1. Relationship of somatic cell score with fertility measuresPoster 1390ADSA 2001, Indiannapolis R. H. Miller1, J. S. Clay2, and H. D. Norman1 1 Animal Improvement Programs Laboratory, USDA, Beltsville, MD 2 Dairy Records Management Systems, Raleigh, NC dnorman@aipl.arsusda.gov

  2. Abstract Dairy Herd Improvement (DHI) data from 284,450 Holstein and Jersey cows in 37 states were used to examine relationship of test-day somatic cell score (SCS), herd, calving year, parity, lactation stage, and calving ease score with fertility measures: nonreturn rate (NRR) by 70 d after first service, days to first service (D1), and days open (DO). Factors other than SCS were examined to ensure estimated SCS effect was independent of other effects. NRR were highest during April and May and lowest during June. Parity had a large effect on NRR, which was 6 to 7% higher for first parity than for sixth and later. Effect of lactation stage at first service on NRR was large; NRR increased by 8 to 13% from early to late lactation. Effect of calving ease score on NRR also was large: a 7% decline from score 1 to 5. A small linear regression was found for NRR on preceding test-day SCS for Holsteins, but this relationship was not significant for Jerseys. The magnitude of SCS effect on fertility traits does not warrant postponing first service when SCS is high.

  3. Introduction • Mastitis infections thought to affect reproduction negatively. • Practical importance of mastitis in open cows lies in possible delay of breeding until clinical symptoms disappear. • Confirmation of a relationship between SCS and reproduction would justify increasing economic weight on mastitis resistance (SCS) because reproduction has no direct economic weight in current selection indexes.

  4. Objectives • Determine magnitude of possible effect of elevated SCS prior to first service on NRR, D1, and DO . • Examine effect of herd, calving year, month, parity, lactation stage, and calving ease score on NRR, D1, and DO.

  5. Data • Records from Dairy Records Management Systems (Raleigh, NC) for 2.7 million Jersey and Holstein lactations from 37 states and calving years 1995-98. • Two data subsets for Holsteins, each with ~10% of original data. • Records included SCS for first 3 test days; service sire, cow, and parent identification; DIM at first service; and parity. • Calving ease scores available for ~8% of original Holstein data.

  6. Data • Records limited to AI first services, cows bred at 15-365 DIM, <150 DIM on third test day, daily milk yield of 4.5-109 kg, test-day component percentages of 2.0-8.0, and component sampling for at least 2 of first 3 test days. • Record excluded if >56 d between last test day and first service, virgin heifer or cow left herd within 70 d after first service, or breeding was second within 4 d.

  7. Data • Records with DO of >329 set to 329 d. • First breeding successful if cow not rebred within 70 d. • Herds required to have >9 AI matings annually and mean NRR of 62.5%.

  8. Analysis • Model to relate SCS on test-day prior to first service to NRR: y = h + p + s + m + c + t + b(SCS) + e where y = NRR, h = random herd effect, p = fixed effect of parity (1, 2, ..., 6), s = fixed effect of lactation stage (DIM <50, 50-59, ..., 130-139, >139), m = fixed effect of calendar month, c = fixed effect of calving year, t = fixed effect of interval from prior test day to first service, b = regression coefficient, and e = random residual effect.

  9. Analysis • Difference between effect of elevated SCS just prior to first service and several weeks prior determined using 6 interval classes (<8, 8-14, 15-21, 22-28, 29-42, 43-56 d). • Similar models for D1 and DO. • For Holstein cows with calving ease data, additional analyses of NRR, D1, and DO.

  10. Results • Large effect by parity; decrease of 6-7% in NRR from first parity to sixth and later. **P  0.01

  11. Results • Seasonal effect of first service:

  12. Results • Large effect by lactation stage; increase of 8-13% in NRR from early to late lactation. • Significant effect by calving ease score; decline in NRR of 7% from score 1 (easy calving) to score 5 (difficult calving). • Regression of D1 on SCS significant and quadratic for Holsteins and Jerseys. • Regression of DO on SCS significant for Holsteins.

  13. Conclusions • Significant (but very small) linear regression of NRR on test-day SCS prior to first service for Holsteins, but no relationship for Jerseys. • Possible causes for seasonal effect on NRR: temperature, humidity, pasturing patterns, competition from crop management activities. • Delaying breeding solely because of high SCS on prior test day unwarranted. • Additional emphasis on mastitis control and a slight increase in economic weight for SCS in genetic selection warranted.

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