Dairy Farmers are committed to improving milk quality and cow health. More effective management practices to accomplish this mission is evident from the annual declines in SCC values and other data related to udder health. Comparing lactation data from 2013 with 2018 on approximately 3,000 Holstein herds reflects average weighted SCC declined from 237,000 to 211,000, and the top 20% of Holstein herds lowered SCC from 147,000 to 128,000. While improvements in milking routines, as well as housing and management practices have made a significant impact in lowering SCC, mastitis continues to be a costly disease, posing various threats to the cow. Production losses and increased treatment costs are typically the first things we associate with mastitis, but impacts can vary and data has shown that secondary impacts can express themselves as reduced conception rates following the time of infection. Managing udder health is an ongoing challenge, however during the summer months, as heat and humidity increase, mastitis cases typically increase as well. By monitoring udder health, especially during summer months, you can avoid a nasty surprise case of mastitis and its associated costs.

What did 2018 tell us?

In addition to individual cow data, it is effective to monitor overall herd metrics for weighted SCC, new infections, fresh cow infections, chronic infections, cure rates and dry-cow cure rates. We summarized 2018 test data from 650,000 cows to evaluate the impact of last summer’s weather on herds. Figures 1 and 2 show the overall trend in weighted SCC and management level milk (MLM) by month for Holstein and Jersey cows respectively. MLM refers to converting milk production to a common base, in this case a second lactation cow 150 days in milk producing 4.0% fat and 3.3% protein. Figure 1 shows that cows dropped 5 lbs. in MLM May through July and August to September last year. Although many factors such as heat stress impact milk production, increases in SCC will contribute significantly to any production losses.

Figure 1: Holstein Weighted SCC and MLM Trend by Month
Figure 2: Jersey Weighted SCC and MLM Trend by Month

Although 2018 wasn’t an exceptionally hot summer throughout the Midwest, the summer months did show an increase in cases of new cow infections. Figures 3 and 4, respectively, show the percent of new infections, overall percent of cows with high SCC (>200,000) and fresh cow infections in 2018 for Holsteins and Jerseys. The percent of cows with high SCC in the winter months averaged 18% and peaked at 21% in July, remaining there through September. 

Figure 3: 2018 Holstein Infection Trends
Figure 3: 2018 Jersey Infection Trends

A more significant difference can be observed in fresh cow infection, reaching a high of 20% in July and a low of 14% in April and October. 

Figures 5 and 6 show the average SCC for Holstein and Jersey cows, respectively, broken down by lactation and month. When you break down the herds into lactation groups and analyze the trends in SCC throughout the year, older lactation cows are impacted far more during the summer than 1st lactation cows.

Figure 5: 2018 Holstein Weighted SCC Trend by Lactation Group
Figure 6: 2018 Jersey Weighted SCC Trend by Lactation Group

Older lactation Holstein cows averaged an SCC value of 278,000 in March and saw a peak of 343,000 in August. Holstein first and second lactation cows also experienced the highest values in July through September but did not show the same increase as older lactation cows. Older lactation Jersey cows respond similarly to summer heat, peaking in August and September, while first and second lactation cows tended to peak in May and June during 2018.

Figure 7: 2018 Holstein Dry Cow Cure Rates

Dry cow management is a critical component of udder health and if not properly managed can lead to many transition cow problems. Cure rates in addition to SCC and fresh cow infection rates are key measures to monitor the effectiveness of your dry cow program. Figure 7 shows the cure rates for Holstein cows in 2018. Similar to infection rates, the lowest cure rates are observed in the summer. Failure to cure rates reached a low in April at 25% and maxed out at 35% during July and August. Failure to cure cows are cows that had an SCC value greater than 200,000 and started the subsequent lactation with an SCC still above 200,000 during the prior lactation. This high SCC count then leads to potentially negative impacts during the transition into the new lactation.

Economic Impact

The economic impact of higher SCC and increased number of infected cows shows up first and foremost in the bulk tank. Cows that experience higher SCC values show a reduction in milk production when expressed on a linear scale. First lactation cows show a loss of 275 pounds of milk, while older lactation cows lose 585 lbs. of milk per linear score increase. Using the 2018 numbers from Figure 5 above, Table 1 shows the average production impact higher SCC values have.

Table 1: 2018 Milk Production Losses Based on Linear SCC Comparison from March to August

Aside from production losses, other impacts can be lower premium, increased treatment expenses and secondary impacts such as reduced conception rates causing increases in days open and higher number of services per conception. A prior AgSource Dairy study measured the impact of different types of infection on pregnancy rates. Table 2 shows the difference in pregnancy rates based on the udder health status around the time of breeding.

Cows that were newly infected around time of breeding showed almost a 6% reduction in pregnancy rates when compared to cows not infected.

How to avoid future problems

The dairy industry continues to lower the number of cases of mastitis resulting in lower SCC values every year, yet the fact remains that the summer months are a time to stay vigilant. Closely monitoring key measures is important so immediate action can be taken to address the cause, minimizing the future impact of subclinical and clinical mastitis. AgSource Dairy provides multiple decision tools that allow producers to monitor the udder health status of the herd and perform follow-up milk analysis tests to define the best course of action when determining a treatment protocol.

The AgSource Dairy Udder Health Management summary, developed with input from the University of Wisconsin School of Veterinary Medicine, provides key measures to monitor new infections, cure rates, and more.  Picture 1 shows an example of the overall herd Risk Group Analysis. Additional analyses provide data by lactation group, or stage of lactation, to pinpoint specific areas of concern. To dig further into the data, MyAgSource provides producers with a cloud-based tool to view their data and compare it against dynamic benchmarks that are based on all herds.  Cows of interest can be selected, and the cow’s full history can be reviewed before making a decision.

Picture 1: Udder Health Summary Risk Group Analysis

In addition to the Udder Health Summary, AgSource offers PCR milk analysis testing and milk cultures to determine the actual pathogens that are causing mastitis. As concerns about the use of antibiotics continue to be voiced by the consumer, PCR analysis can pinpoint which pathogens should be treated allowing the dairy producer, together with the veterinarian, to plot the appropriate course of action.