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item CLAY, J - DRMS
item Norman, H

Submitted to: American Dairy Science Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/24/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Dairy Herd Improvement data from 284,450 Holstein and Jersey cows in 37 states were examined to determine relationships of test-day somatic cell score (SCS), herd, calving year, parity, lactation stage, and calving ease score with fertility [rate of nonreturn to estrus by 70 d after first service, days to first service (D1), and days open(DO)]. Relationship of elevated SCS prior to first insemination with nonreturn rate was of interest, but factors other than SCS were examined to ensure estimation of SCS effect was independent of other variables. Nonreturn rates differed by month. Rates were highest during April and May and lowest during June (difference of 8 to 9% for Holsteins and 12% for Jerseys). Nonreturn rate was affected by parity (6 to 7% higher nonreturn for first parity than for sixth parity and later), lactation stage at first service (increase in nonreturn rate of 8 to 13% from early to late lactation), and calving ease [a 7% decline in nonreturn rate from score 1 (no birth difficulty) to score 5 (extreme birth difficulty)]. For Holsteins, linear regression of nonreturn rate on preceding test-day SCS was significant (P < 0.01), particularly for SCS recorded within 2 to 3 wk prior to insemination; however, regression coefficients were small (0.004 to 0.005). A similar relationship was not found for Jerseys. Quadratic regression of D1 on SCS was significant for Holsteins (P < 0.05) and Jerseys (P < 0.01); linear regression of DO on SCS was significant (P < 0.01) for Holsteins. The magnitude of SCS effect on fertility traits does not warrant postponement of first service because of elevated SCS on previous test day. However, additional emphasis on mastitis control and a slight increase in the economic weight for SCS in genetic selection may be justified.