Animal Health

An unintended consequence

By Rod Dyson

CAMERON* WAS feeling comfortable.

The expansion plan for the family farm had gone well. He had secured a long term lease on the block next door, added another 50 cows (with plans for more), extended the dairy shed, and employed a labour unit to assist the family on the farm.

The new season had started well. It had been a wet spring, but there had been very little clinical mastitis during calving and the spring, and the farm’s Bulk Milk Cell Count (BMCC) had sat comfortably below 150 000 cells/ml all that time.

But as they moved into summer, things started to come unstuck.

The new labour unit left at Christmas, and with a poor outlook for milk prices, the family decided to continue on without hired help. They seemed to be coping with the workload, although it meant there was often only one person in the dairy for milking.

Then the number of clinical cases of mastitis began to steadily increase, although the BMCC had not changed.

Cameron had taken the dairy from a 16-a-side swingover herringbone out to 28 units, and until now, it had seemed to be going well.

He recognised that now, if there was only one person in the dairy at milking, there was likely to be considerable overmilking. During the upgrade, he had baulked at the cost of Automatic Cup Removers (ACRs), so he arranged to have them fitted as quickly as possible.

Confident that this would solve the problem, Cameron was frustrated that the number of clinical cases did not decrease. In fact, nothing changed — they continued to occur at the same rate!

Fortunately, Cameron had milk samples from some new clinical cases of mastitis in the freezer, so the first step was to get those sent off to the laboratory.

The lab reported most samples to be Strep uberis, which is an environmental bacteria that is also capable of spreading in the dairy during the milking process. Also, some quick data analysis showed that Cameron’s clinical mastitis case rate was now well above the Countdown trigger point of 2 cases per 100 cows per month during lactation!

Armed with this information, we started our farm visit with a look at the environment, and as Cameron had assured us, things were now pretty dry in the summer, with little in the way of risky contaminated areas in either lanes or paddocks.

At the afternoon milking, a Dairy Focus Mastitis Risk Assessment of the dairy resulted in a Total Mastitis Risk Score for Cameron’s milking process of 22 points — enough to put him in the “Medium Risk” category.

The good news for Cameron was that the milking plant was performing well, the cows had excellent teat condition and were very comfortable during the milking process.

But 11 points of Cameron’s 22 point risk score arose from significant issues with teat disinfection.

Due to the milking routine with only one operator, the delay after cups off until teats were disinfected was a minimum of 10 minutes, and often considerably more.

The workload of a single person in the dairy also meant the application of teat disinfectant was rushed. We measured the delivery of the teat spray wands and found it would take 3 — 4 seconds to deliver the 20 ml of disinfectant that is usually required to get good coverage.

The result was that coverage of teats with the teat spray disinfectant was reasonable, but definitely not great.

This meant that after milking, our discussion would centre on a few key items.

The 3 – 4 seconds delivery time for teat spray is really not negotiable. Countdown has taught us that unless we are using 20 ml per cow per milking, we are very unlikely to be getting good coverage. Also, if we have 3– 4 seconds, it allows a slower, careful spray technique, which is always better than a “quick squirt” or a “jiggle” beneath the teats!!

Solving the delay issue was an interesting discussion. Eventually the agreed solution was to adapt the routine to operate the dairy as if it was two distinct sheds.

The rushed routine also meant there was no consistent method for detection of clinical cases, meaning a significant risk of spread from cases not being discovered for a few days. It was decided to ensure an extra person in the dairy on regular basis to enable a herd strip for earlier detection of clinical cases.

Implementing these changes would result in a Total Mastitis Risk Score below 15 points, and a “Low Risk” rating.

A month later, things had improved dramatically. The BMCC was actually a bit lower, clinical cases of mastitis had “dried up”, now occurring at a rate well below the Countdown trigger point.

The lessons here are firstly, whilst overmilking is often blamed for an outbreak of mastitis, in fact it is never the only issue, and ACR’s alone are unlikely to solve a mastitis issue.

Secondly, teat disinfection is a cornerstone of mastitis control, and good application of teat disinfectant is a function of both timing and coverage of teats.

* Names have been changed for this article

• Rod Dyson is a Director of www.dairyfocus.com.au