The Bulk Milk SCC (BMSCC) is an indirect way of estimating the level of subclinical mastitis in the herd. For herds with a BMSCC of 300,000 cells/mL or less, each 100,000 cells/mL indicates approximately 15% of cows are infected.
A series of BMSCCs should be reviewed to see both the level and trend for a herd.
In all herds, a sudden increase, of 50,000 cells/mL or more, may indicate that one or more clinical cases have been missed.
The impact will be more pronounced for smaller herds, or when there are fewer animals in the herd, such as at the start or end of the season.
Herds with a higher BMSCC may have more fluctuations of the BMSCC on a day-to-day basis because there will be many more infected quarters.
11.1 - Check bulk milk SCC, using up to date data
Bulk milk SCC data is usually available within 24 h of a tanker pickup, through the dairy company websites. Paper printouts or “tanker dockets” are delivered at the next tanker pickup.
Check the results for sudden daily rises (Figure 1), which often indicate one or more missed clinical cases. This is particularly common in herds running high cell counts. With experience, you will identify a daily increase for your herd e.g. 50,000 cells/ml that indicates a missed clinical.
Use graphing functions on the dairy company website to track trends on daily, 10 day, or monthly averages.
Reviewing bulk milk SCC
Most milk processors provide online SCC data. Contact your milk supply company to set up a login.
Figure 1. Check bulk milk SCC for: A: Sharp spikes that indicate undetected clinicals; B. Increasing trend that indicates spread of contagious mastitis; and C. SCC reaching crisis levels and high SCC cows need to be excluded from supply.
Compare your monthly averages with the example curves in Figure 2. These are equivalent to seasonal averages of 125,000, 150,000 and 200,000 cells/ml.
Use these curves to work out target curves for your herd. An example is shown in Figure 3. Take action if your monthly figures are consistently “off target”.
Figure 2. Examples of monthly bulk milk SCC that relate to seasonal averages of 125,000 cells/mL (dotted line), 150,000 cells/mL (full line) and 200,000 cells/mL (dashed line).
Figure 3. The monthly bulk milk SCC curves can be used to create target, monitor and "take action" zones to help reach a season target, of 150,000 cells/mL.
11.2 - Consult your advisor if consistently above trigger or close to grading
Advice is readily available from dairy companies and veterinarians to help solve a high SCC problem. Some private consultants specialise in mastitis control.
Demerit relief (redirection of financial penalties) may be available from your dairy company to offset the cost of professional advice.
The trigger points for seeking advice will vary from farm to farm. A full investigation may be required if:
- One or more BMSCCs are above the penalty threshold
- Two or more BMSCC warnings are received
- Spikes in BMSCC are regular
- BMSCC trend upwards is steeper than your target curve
- BMSCC monthly averages are “off target” for past 3 months.
Bulk milk SCC at peak production
As a general rule of thumb, the bulk milk SCC at the end of the season is double the SCC at the peak of production, generally in the 3rd or 4th month of supply. See Figure 2 in Guideline 11.1.
11.3 - Check for clinical cases or exclude cows from supply
Check for clinical cases in the milking herd when bulk milk SCC rises above your trigger or is at risk of grading.
If no clinical cases are found, individual cows may need to be excluded from the milk supply to reduce the SCC and reduce the risk of grading.
Use recent herd test information or RMT (Rapid Mastitis Test) scores to identify high SCC cows to be excluded from supply.
See Healthy Udder - Find 2 for tips on testing cows with RMT. See Guideline 5.2 for more on stripping the herd to find clinical cases.
See Guideline 12.1 for options for cows excluded from supply.