By Steve Cranefield, BSc BVSc
The ultimate aim of mastitis control is to limit the number of bacteria on the cow’s teats and to reduce the risk of bacteria entering the udder through the teat canal. Although this sounds simple, mastitis is the end result of complex interactions between the cow, bacteria, environment, milking machine and the farmer. The relative importance of these factors varies from farm to farm so it is important that your plan is specific to your farm.
Our understanding of mastitis management is always evolving, there is increasing pressure on the farming community to reduce the use of antibiotics and we are learning more about the value of efficient milking routines to reduce mastitis.
There are two key elements to reducing mastitis
Eliminate existing infections
Infected cows are the source of infection for other cows during lactation.
- Cull long term infected cows.
We need to make more use of historic records to identify and cull chronically infected cows. Too often clinical mastitis records are incomplete and/or poor use is made of historic herd test information so it is only the recent high SCC cows that are culled. Also, mandatory culls (e.g. a high empty rate) often take precedence over culling for mastitis.
- Drying off strategies.
We should all aim to achieve consistently low SCC throughout the season to reduce the need for antibiotic dry cow therapy at dry-off. Cows with an ISCC of <150,000 cells/ml and heifers with a ISCC of < 120,000 cells/ml can be regarded as uninfected and new infection can be prevented with teat sealants although strict hygiene is critical when these are administered.
2. Prevent new infections
There are 3 key areas of importance during milking that will reduce the mastitis risk:
- Identify and treat mastitis cows early.
Routine stripping of the herd (e.g. a quarter at every milking) will identify infected cows quicker to minimise the spread of infection.
- Ensure your cows have good teat skin condition all year round.
Teat spraying is still the most important single thing you can do to reduce the spread of mastitis. The reason for this is that every time you apply cups to a cow you are passing bacteria to the teats of the next cow to be milked. These bacteria can then enter the teat canal and cause mastitis
Bacteria from milking an infected cow will contaminate the cluster for the next five cows that are milked by that cluster. Teat spray trials in New Zealand and overseas all show a 50% reduction in the new infection rate if teat spray is mixed and applied correctly. Healthy teat skin has a fatty acid layer that slows bacterial growth reducing the mastitis risk. If teat skin is dry the fatty acid layer is lost and bacteria will multiply in the cracked skin. It is critical to achieve good teat condition in your herd all year round. This requires addition of sufficient emollient and ensuring full coverage of all teat surfaces at every milking all season. This should be a key focus and constantly assessed throughout the season. Pre-milking teat spraying the colostrum cows will assist to improve milk let down, improve teat condition and reduce bacteria on the teats.
Adopt efficient milking routines to minimise teat end damage
All bacteria that cause mastitis have to enter through the teat canal. Having a normal intact teat end is the best defence against entry of mastitis bacteria. The teat skin should be smooth and supple and the teat canal should just be visible as a pin point hole about 1mm in diameter.
Teat ends can be damaged from the physical action of the milking machine allowing bacteria to grow and enter the teat canal. Teats may be examined and classified as normal, rough or very rough / cracked.
Adopting efficient milking routines will help reduce the mastitis risk from teat end damage caused by over-milking.
MaxT (maximum milking time) is a strategy which defers residual milk to the next milking, where it can be harvested more efficiently. Cows are milked to a pre-determined end-point — either to a fixed time point, or to a set milk flow rate threshold, whichever comes first.
Using the fixed time point, the idea is to estimate when about 80 per cent of cows would have completed milking and remove the cup clusters from the remaining 20 per cent.
Research shows the implementation of MaxT can increase the number of cows milked each hour in many New Zealand dairies, with no loss of milk yield and no increase in mastitis or somatic cell count (SCC). MaxT's principles are based on harnessing basic cow physiology.
How the udder works
Milk is held in two compartments of the udder: the cistern (a bag above the teat) holds around 20 per cent of the milk, and the alveoli (the udder tissue cells where the milk is made) holds the remaining 80 per cent.
When clusters are attached, the milk harvested in the first few minutes is from the cistern; then the milk ejection or let-down reflex is triggered. This causes the remaining milk to move from the alveoli into the cistern, where the machine can harvest it.
Cows whose clusters are removed early show a greater milk flow rate during the first few minutes of the next milking compared with fully milked-out cows. So, there's more milk being held in the cistern from the previous milking (residual milk) which can be harvested immediately and more efficiently at the next milking, without waiting for milk let-down.
There is no net loss in milk production nor any increase in SCC.
If you have automated cup removers adjust the low-flow threshold — usually from a default of 0.2 kilograms per minute (kg/minute) or equivalent — to 0.4 kg/minute and if possible, set a fixed time end-point.
For manual cup removal in a herringbone: Get the cups onto cows as soon as they are at the front gate and change cups and teat-spray as you go (using a 'leapfrog' routine if there is more than one-person milking). Take cups off as you go - don't wait for slow-milking cows to 'milk out'. Open the gate early so cows leave the shed while you're changing the last few cups over.
For manual cup removal in a Rotary shed; Don't let cows go around twice. The platform speed should be as fast as practical, so cows get milked out about three-quarters of the way round — without rushing staff. Once cows reach the exit, out they go.
The cows will tell you why they have mastitis!
If you assess your cow’s teats once a month you can learn why there is mastitis in the herd and monitor the results of change. Farmers are encouraged to assess 50 cows for teat skin condition and teat end damage once a month through the season as an early indicator of problems. The targets are:
Teat skin condition - target > 95% supple.
Teat end damage - target > 90% normal.
If any of these risk factors are lower than the target then farmers should look for rectify possible causes or seek expert advice to avoid mastitis.