Mastitis – Culling Decisions

Culling is a key strategy in managing mastitis on farm as it is the only way to eliminate some infections.  It is, however, expensive so it is important that culling decisions are made wisely and that other measures are taken to prevent new infections occurring, in order to achieve good mastitis control.

When making culling decisions we want to choose infected cows that have a low chance of curing over the dry period.

Antibiotic dry cow therapies do not cure all infections.  The following factors reduce the chance of an infected cow curing over the dry period:

  • Cows that have had repeated clinical cases of mastitis in one season. Cure rates are approximately 75% for first cases of mastitis, 45% for second cases and 12% for third cases (consider culling immediately after the third case or drying off the quarter if the same quarter is being affected).
  • Infections of long duration. Cows that had a high SCC on the last herd test last season and the first this season despite being treated with antibiotic DCT are likely to be chronically infected and have a low chance of curing.  Cows that have had high SCC only in this season are candidates for Antibiotic Dry Cow Therapy.
  • Staph aureus infection
  • Older cows

Subclinically infected cows have a bacterial infection (and usually a high SCC) but no clinical signs of mastitis.  A higher proportion of subclinical infections are contagious bacteria (as opposed to environmental) and pose a significant risk for the spread of infection within the herd.

Somatic cell count data from herd tests and clinical mastitis records are the main sources of information used to make culling decisions.  There are various options available for culturing milk samples from individual cows to identify the bacteria involved and/or sensitivity to different antibiotics.  These include laboratory testing through your vet, Mastatest on farm testing, DairySmart and Staph aureus testing via your herd test.  Taking sterile milk samples for bacterial culture can help justify a culling or treatment decision.  However, some Staph aureus infections do not reliably yield a positive culture result as the bacteria are good at hiding inside cells and emerging intermittently into the milk.  Conversely, a positive Staph aureus culture may still have a good chance of cure in a young animal with a relatively recent infection. 

SCC, clinical mastitis history and age should be considered alongside culture results.  Beware of making decisions from a single piece of information.  Without a comprehensive approach to mastitis control (including strict hygiene at teatseal/DCT insertion, milking management, early detection of mastitis and culling decisions) new cows will always be waiting to jump into the millionaire’s club.

Culling 1-2% of the herd each year for mastitis reasons is a realistic benchmark.  Whether it is economic to cull more than this will depend on the impact individual cows are having on the BTSCC, the consequent penalties or loss of incentives, the risk of mastitis spreading to other cows and the cost of replacements.

Talk to your vet if you would like help with making culling decisions for your herd.  Dairy Vets can provide expertise in all areas of mastitis management including investigating somatic cell count and clinical mastitis problems, milking management assessments, teat scoring, data analysis, milk culture, treatment decisions and staff training.

Johne’s Testing

Request a Johne’s test on your next herd test if you have not already done so!

It is that time in the season that is the most opportune moment to perform a whole herd screen Johne’s test to find positive cows.  Removing these cows now saves on the costs of wintering them and reduces the chances of infection in the biggest risk period during calving.

Cows infected with Johne’s generally do not perform well over the challenge of transition and calving, and it is often enough to tip them over the edge and they deteriorate clinically.  In one case study performed by LIC, a third of cows testing high positive had died on farm during the calving period.  Cows testing positive are more likely to leave the herd by dying on farm than going to the works, compared with cows testing negative.

Any cows which test positive, should be retested with a blood test to confirm the identity of that cow.  In a season where reproductive results have been strong, there may be more flexibility to remove cows from the herd which test positive.  It may well aid culling decisions, looking at SCC, udder conformation and mobility, if Johne’s status is known also.  It is also becoming common practice for buyers to request a Johnes test before purchasing cows.

LIC Johne’s Dashboard Development

LIC are currently developing a dashboard, via MINDA, to better display and manage Johne’s positive cows within the herd, based on historic and current Johne’s results on farm.  It is currently in a trial period at the moment, but from what we have seen it is looking to be useful tool to help visualise the extent of a JD problem on each farm. Particularly interesting is showing which cohorts have been most at risk to infection, and benchmarking compared with national average.


It is still in a prototype phase, but may well prove to be an important tool in seasons to come. Watch this space.

Below is a extract, taken from LIC’s website, about the importance of testing and showing how missing a year’s testing can cause Johne’s prevalence to resurge.

Prevalence of JD positive and high positive results in herds testing with LIC 2013-2023

* Note this is industry median data so may not predict what may happen on individual farms.

Key takeouts from this graph:

  • Farms that had six consecutive annual tests made the most progress in terms of reducing prevalence (3.3% to 1.3% over the five years since their first test).
  • Herds that missed two annual tests within this same period tended to have a rebound in prevalence (from their initial starting point, a median of 2.80% to their lowest median prevalence of 1.71% after three years to 1.96% after five years).
  • Median prevalence rebounded in herds that missed four annual tests to levels close to those identified when testing started (2.94% at year 0 to 2.04% after three years to 3.07% after five years).


Interpreting the results

The Johne’s ELISA is a very specific test – which means if a cow tests positive we know she is positive.  However, sensitivity is poor, which means if a cows tests negative, it does not necessarily mean she isn’t infected with Johne’s disease.  In any case, culling positive cows is the best way to make big leaps in managing Johne’s.

Below is a summary table explaining what each individual result means.

Testing and culling cows is of course only part of the solution. Management of the disease on farm will help mitigate spread. Below are some good resources available discussing management options, and further information on testing.



Dairy NZ Johne’s Disease Management –

Dairy NZ Johne’s Laboratory Testing –

LIC Johne’s Herd Test –

Managing Calf Scours

Towards the end of August scouring calves become more common. It is likely that this is because the pathogen load in the calf pens has risen at the same time that colostral antibodies are declining.

There is a risk period between about 1 and 4 weeks of age when antibodies from colostrum ingested in the first day (passive immunity) has declined but that from exposure to pathogens (active immunity) is not yet optimal.


If only a few calves are scouring, it is worth isolating these in a sick pen. If more become sick, it is best to leave the calves where they are. One teaspoon of rotavirus scour can infect thousands of calves so if the cause is infectious, it is likely all calves in the pen have already been exposed. It is still a good idea to put calves that are worse affected in a small pen together as they can be treated and monitored better than in a big group. If left together ad lib electrolytes will often be drunken by the healthy calves with the ones that need it more missing out.

Avoid overcrowding pens. If pens must be reused, consider replacing or topping up the bedding. Keep hay feeders high so hay stays clean and calves are not eating off the ground. Clean water troughs daily. This will help reduce the spread of disease and encourage water intake.


Electrolytes and feeding:

. Scours cause loss of fluids and body salts leading to dehydration. Electrolytes are the main treatment for scouring calves. Below is a treatment protocol for calves with mild to moderate scours.

Scouring calves should continue to be fed milk if they are willing to drink it. Weight loss will be less than if fed electrolytes alone and recovery faster.

Warm milk will encourage sick calves to drink.

It is recommended that scouring calves are fed milk twice a day with electrolytes in between.

Unwell, scouring calves are less likely to want to drink one larger feed and will receive more nutrition if fed twice.

It is best not to tube milk to scouring calves – if a calf refuses to drink milk, replace that milk feed with an extra electrolyte one. If they are still refusing to drink after 48 hours, consult your vet.

Tubing electrolytes is fine, and often necessary.

Use a high quality electrolyte such as Enerlect.



Scouring calves often feel miserable. Rheumocam (1ml/40kg under the skin) reduces fever and inflammation and will help get the calf back drinking again.

Talk to your vet if you are having scours in your calves. They can provide further advice on managing the outbreak and test samples to see what pathogen/s are involved. This will help determine if additional treatments are needed and will help with strategies for prevention in the future.

The risk period makes preventing scours challenging, however colostrum management in the first 12 hours of life is still the number one factor in preventing scours or reducing the severity of illness.

Calves that have a higher initial peak in colostral antibodies will take longer to decline and will be less severely affected if infected. Ensure every calf receives 4-6L of 22% + brix tested colostrum within 6-12 hours of birth. Organise calf blood testing with your vet annually to check that colostrum managements is working on your farm.


Multimin has New Zealand data to show that calves injected with 1ml at birth have a 50% reduction in the risk of disease and death until weaning. Optiguard is a pathogen binder that may help prevent and minimize the severity of scours. Vaccinating with Rotavec or Scourguard will boost antibody levels to Rotavirus, Coronavirus and E.coli in colostrum. Continuing to feed fresh or preserved transition milk for as long as possible, especially from vaccinated cows will help ‘mop up’ pathogens in the gut as it passes through.

Preparation of Dairy Cows for Transport

The end of another season is approaching and with that comes the movement of cows. MPI have informed us that they have been seeing a significant number of down cows arriving at meat processing plants. This article has some useful information to help you prepare cattle for transport to ensure that their welfare is protected. This is particularly important for lactating cows. Contact Dairy Vet Services if you need further advice.

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Calf Series: Hygiene

Calf Hygiene Dairy Vets

Hopefully you have all had some time to recharge the batteries before the mayhem of calving …here are some common tips to aim for when collecting calves and getting them to their calf pens this calving period:

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