Animal Health

When old becomes new

By Rod Dyson

Split calving and long lactations have become the norm in much of our industry now, so it was a bit of a surprise when we were contacted recently by a farm in Gippsland that is strictly seasonal, meaning the whole herd is dried-off and milking ceases completely over the dry period until calving starts.

As part of our normal process, a history of Bulk Milk Cell Counts (BMCC) for the last two years was obtained for this herd and then charted with a trend line included.

Typically, a chart of a fully seasonal herd’s BMCC would show a trend of starting a little higher as the fresh cows come into the herd, then falling quickly in early lactation, followed by a gradual increase over the season.

Sometimes there can be a steep rise right at the end of the lactation as cows are being dried off.

In this herd, the rise in BMCC during the season was considerably more than what we would like to have seen.

Despite starting in the 70 000–90 000 cells/ml range, the BMCC then steadily rose to above 250 000 cells/ml towards the end of the season.

The rise throughout the lactation was remarkably consistent, almost a straight line, and was actually no worse during the wet winter of 2016.

Naturally, when looking to understand a herd’s situation, we like to get some milk cultures to ascertain the cause and likely method of spread of new infections.

In this case, the farm had already been pro-active and had obtained several batches of milk cultures during the previous lactation, and a batch early in this lactation, thereby giving themselves a considerable head start in dealing with the problem.

The milk cultures revealed an interesting pattern with most cultures around calving and in early lactation being Strep uberis, whilst in mid to late lactation, Staph aureus became prominent.

These culture results correlated nicely with the history of clinical cases in this herd. A Countdown Mastitis Focus report showed a high level of clinical cases of mastitis around calving, and much lower levels in cows that have been calved more than 14 days.

This was beginning to look like herd with a problem due to Strep uberis around calving, and then Staph aureus during lactation.

Calving has already finished for this year, so little can be done about that at the moment, but can we prevent the rise in BMCC this year?

If, as seems likely, the rise in BMCC is due to the spread of Staph infections, then knowing that Staph aureus is a cow associated (or contagious) mastitis infection and virtually all the spread of infection will be occurring during the milking process, we can confidently plan our approach.

A milking time visit and mastitis risk assessment is now the priority for this herd. A full appraisal of all the potential risks for spread of mastitis associated with the milking process will allow us to draw up a list of corrective actions and a control program for the remainder of this season.

The good news is that because it is only early in the lactation, there is an excellent chance of success if the control actions can be implemented reasonably quickly.

Once these changes have been implemented, a re-assessment of the effect of those changes will be critical to ensure they have achieved their goals — if not, further revised action will be needed ASAP!

Ongoing monitoring will involve tracking the herd’s BMCC and regular analysis of herd test results and clinical case records, including regular Countdown Mastitis Focus Reports.

But we also must not forget about the issues around calving!

Control of mastitis infections at calving begins at drying-off, so even though the herd has used a blanket approach to dry cow therapy with both an antibiotic dry cow therapy and a teat sealant used in every quarter of every cow at dry-off, a comprehensive review of the dry-off protocols and procedures will be critical.

This will need to be followed by a pro-active plan to managing the calving & fresh cows during the next calving season.

There are some important key lessons to learn from this herd

  • Mastitis control on a farm is often complex and dynamic, especially in split and year-round calving herds.

  • Good records make analysis much quicker and more reliable.

  • The Countdown Mastitis Focus report can be a great tool for helping define the situation on a farm, and then monitoring progress.

  • Milk cultures have yet again proved their value.

• Rod Dyson is a veterinary surgeon and mastitis adviser at www.dairyfocus.com.au