After the first herd test
Spend some time looking at the first herd test (HT) results. The list of cows with the highest somatic cell count (SCC) identifies animals that are infected and either sub-clinical (most on the list), or clinical but not detected as such by the day of test.
The target at the first HT is less than 15% of cows with an individual SCC (ISCC) above 150,000. Nationally the best 25% of herds will have 9% or less above 150,000 at the first HT. How do you compare?
The list can look a bit daunting, however, it is the cows above an ISCC of 500,000 that you need to be concerned with. The cows above 500,000 significantly increase the bulk tank SCC (BTSCC) and also carry the greatest risk of causing new infections in the herd.
Cows above 500,000 should be singled out for a rapid mastitis test (RMT) and the following actions taken.
- Any that have clinical evidence of infection i.e. clots in the milk, should be treated as per usual.
- Cows with a sub-clinical infection (high ISCC but normal milk) should be managed according to their age and previous history:
- Cows that have been treated in the 30 days before the HT are probably still recovering and can be left. Recently treated cows should be approaching 500,000 or less by 30 days after detection for a cure to be considered as the probable outcome
- Heifers positive to the RMT should have the appropriate quarter/s treated
- For cows three years and older check their previous history:
- No previous history then RMT and treat affected quarters
- High ISCC in a HT from a previous season but returned to a low ISCC before the most recent HT, then paddle test and treat
- History of repeated high ISCC, then leave and drycow at the end of the season
- History of repeated high ISCC and has previously been treated with drycow add to the cull list at the end of the season
Where the daily consignment BTSCC is high, there is the temptation to treat as many high ISCC cows as possible. Unfortunately the cure rate is poor for mixed age cows with a previous history of high ISCC and clinical infections. At best there is a temporary improvement and the BTSCC is highly likely to return to the previous high levels within six weeks.
The best approach is to select candidates as outlined above for treatment and hold the remaining worst offenders out of the supply if the risk of grading is high. As the season progresses, the BTSCC will most likely improve to more manageable levels, allowing cows to be returned to the supply.
Chronically infected cows are responsible for spreading infection within the herd. This risk can be minimised by consistent teat spraying (every milking for the whole of the season) and by ensuring rubberware is in good condition. Effective teat spraying requires that the barrel and the teat end are covered with spray. If you are not using 1.5-2.0L of diluted teat spray per 100 cows at each milking then you are not spraying the cows well enough. In, around and out is the recommended approach.
Finally, rubberware should be changed at least twice per season. If the recommended 2500 milkings is followed then rubberware is past its best after approximately 125 days or four months.