Dairy producers conducting monthly Dairy Herd Improvement (DHI) testing, are able to monitor changes in milk production and components over time, and detect deviations needing to be addressed by management. Monthly monitoring of somatic cell count (SCC) enables producers to identify spikes and trends on an individual cow and herd level.  Remember we cannot manage what we do not measure! When a herd is enrolled in DHI testing, various DHI reports are available. This article will cover one of the reports available from Dairy Records Management Systems (www.DRMS.org) to help producers manage and detect high SCC trends from a herd level.

DHI 202- Herd Summary

The DHI 202 Herd Summary is a summary of the performance of all the cows in the herd. It evaluates milk production, SCC, reproduction, culling, and calving results. The information is broken down into convenient, easy to read tables. When using the DHI 202 to evaluate somatic cell counts trends and effectiveness of mastitis prevention programs, specific sections to review include those highlighted in this article.

Yearly Production and Mastitis Summary

On the bottom of the back page of the DHI 202-Herd Summary report, a table displays the last 12 months of test day data (for those using PCDART see standard report 802). (The figure to the right has been edited to save space.) This table provides information regarding current trends or seasonality in SCC for the herd. For each test date, the percentage of cows within each SCC category is calculated. By adding the first 2 columns (0,1,2,3 and 4) together, the percentage of cows below 283,000 can be calculated. The goal for each test date is at least 75 to 85% of the cows at or below a SCC of 283,000 with the highest percentage in the first category. In this example for the 9-25 test date, 73% (56+17) of cows had SCC under 283,000 cells and 56% were under 142,000. This indicates an opportunity for improvement if the goal is for at least 75% of cows to have SCC under 283,000. However, when evaluating the yearly average, 77% (59+18) of cows are on target for 75% to 85% of cows under 283,000 cells. This table also provides the weighted average of the actual SCC for each test day period. Producers should ask themselves the following questions to evaluate trends:

  • Is there a larger percent of cows with high SCC in the summer or the winter?
  • What months have been the worst for high SCC?
  • What months have been the best?
  • When does SCC start to increase or decrease?  Where any changes noted at this time frame regarding management for the herd?

Somatic Cell Summary

After evaluating the monthly and annual trends, the next step is to evaluate SCC by lactation number. The DHI 202 Somatic Cell Summary section (PCDART standard report 802) displays the percentage of cows that fall within each SCC category by lactation number. This table allows a producer or consultant to evaluate SCC by lactation number. The National Mastitis Council goal for the percentage of cows under 283,000 cells for each lactation is still at least 75% to 85%. On average, first lactation cows should have a lower SCC than mature cows. In this example herd, the first lactation cows are not meeting this goal (58%+11%= 69% of 1st lactation cows). However, the second lactation (62% +15%=77% of 2nd lactation cows) cows have met this goal. Conversely, the third plus lactation cows (52%+22%= 74% 3rd + lactation cows) are not meeting this goal. The biggest bottleneck is with the first lactation cows.  The key is to investigate why they have higher SCC and change management practices to lower the SCC of these young cows or cows entering the herd in the future. This summary also includes the pounds of milk production and the money lost for the current test period due to high SCC cows.

Stage of Lactation Profile

After evaluating the percentage of cows in each SCC category by lactation, the next step is to review each lactation group by stage of lactation for the current test day. The Stage of Lactation Profile found in the upper left hand corner on the back of the DHI 202 report (PCDART standard report 802) breaks down the lactating cows into their different lactation numbers and by stage of lactation.

When evaluating a herd for mastitis, the key areas to examine are the SCC ACT and SCC ACT >= 200 (outlined in black). If the default option for the herd is somatic cell score, it will display SCC Score and SCCS >=3.9. (To change the SCC option from score to actual, notify your DHI technician.) The SCC ACT row displays the weighted average SCC for each lactation number and stage of lactation and by lactation number. Values are listed as the number of cells/mL/1,000. The SCC ACT >= 200 category is the number of cows with a SCC higher than 200,000 indicating an immune response to a mastitis pathogen. (To calculate the percent of cows under 200,000 cells, subtract the number from 100.) A herd goal would be to have a less than 15% of cows above a SCC of 200,000 cells or 85% under 200,000.

For this example herd, 30% of cows have actual SCC equal or greater than 200,000 cells for this test, thus suggesting an opportunity for improvement. Keep in mind, low numbers of cows in a stage of lactation leads to a larger impact on the total percentage of cows over 200,000 cells. Producers should ask themselves the following questions when looking for trends:

  • Overall, are you achieving a target of 85% of your cows with a SCC less than 200,000 cells?
  • Are first lactation and older cows calving in with high SCC?
  • Are 3+ lactation cows doing better or worse than other lactations for SCC?
  • Which stage of lactation has more cows with high SCC (>= 200 SCC)? If the cows are housed by stage of lactation, problem pens can be quickly identified.

Take Home Message:

DHI testing provides standardized, accurate milk production and milk component information for every cow for each test date. Producers using DHI testing and DHI reports can track high SCC trends in order to improve their milk quality. Identifying trends and deviations in monthly SCC can aid in making management decisions. Remember we cannot manage what we do not measure!

To sign up for DHI testing or the reports discussed in this article contact www.mydhia.org or www.drms.org.

Authors:  Michele Jones and Donna M. Amaral-Phillips, Ph.D.

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