University of Wisconsin scientists examined DHI records for 145 herds and found that many herds had either very poor cure rates or problems with mastitis reinfection that occurred before the first DHI test after calving. In this research and many other situations, any cow with a somatic cell count (SCC) above 200,000 was considered infected. The Wisconsin herds had an average of 21% of heifers infected at first test, and the herd averages ranged from 0 to 58%. However, 95% had SCC less than 250,000 by the fourth milking, indicating many were cured spontaneously. Unfortunately, 22% of dry cows developed new mastitis infections during the dry period, while 63% of the cows infected at drying off were cured during the dry period (ranged from 20 to 100%). Dry period cure rates were 83% in top herds. It's been my experience that too many dairy producers DO NOT compare SCC after calving to SCC at drying off and thus DO NOT monitor the effectiveness of the herd's dry cow program, which is a result of both treatment and other management practices such as environment and nutrition. This Wisconsin research found that 53% of coliform mastitis that occurred during the first 100 days of lactation actually developed during the dry period, or non-lactating period in heifers, and 50% of new environmental streptococci infections also occurred during this time. SCC in first lactation cows of 274 Dutch herds ranged from 400,000 to 700,000 at time of clinical mastitis and then decreased slowly to less than 200,000, while SCC in older cows averaged 550,000 to 900,000 and tended to remain high (200,000-460,000). Get into the habit of reviewing SCC at first test after calving for all cows and compare them to SCC at drying off for older cows and identifying if your herd has too many first lactation cows that calve with high SCC.

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