🥛 Udder Health and Mastitis Control

Mastitis is inflammation of the udder, and it is almost always caused by bacteria getting into the mammary gland. That is the whole definition. What makes it the central health topic of a dairy business is not how dramatic it is, but how quiet it usually is.

Mastitis comes in two forms, and they behave completely differently.

Clinical mastitis is the form everybody recognises. You see clots or flakes in the milk, or the milk goes watery or discoloured. The quarter is hot, hard and swollen. In a severe case the cow herself is sick - off her feed, dull, sometimes with a fever. You cannot miss it, and you will act on it, because it is in front of you.

Subclinical mastitis is the form that takes your money. There is nothing to see. The milk looks normal in the pail. The udder feels normal in your hands. The cow eats normally. But the gland is infected and inflamed, and the yield from that quarter is falling, day after day, without any signal at all. The only way to find it is to test for it - by somatic cell count in a laboratory, or by the California Mastitis Test at the cow's side, which you will learn to do in Lesson 4.

Here is what the veterinary literature reports on how widespread it is. In dairy herds generally, the prevalence of infected cows ranges from 5 percent to 75 percent, and infected quarters from 2 percent to 40 percent. That is an enormous range, and it should be read as exactly what it is: herds differ hugely, depending on their hygiene, their housing and their management. But essentially all dairy herds carry some subclinically infected cows. Not most. Essentially all.

So the correct starting assumption for your own herd is not "my cows look fine, so they are fine." It is "some proportion of my quarters are probably infected, and I do not know which ones until I test."

There is a second finding that changes how you should think about diagnosis. Of milk samples collected from actual clinical mastitis cases and sent for culture, 30 to 40 percent yield no organism at all on culture. Between three and four cases in every ten come back from the laboratory saying nothing grew.

That does not mean those cows did not have mastitis. They clearly did - the samples came from clinical cases. It means the organism was present in numbers too low to grow, or had already been cleared by the cow's own immune system while the inflammation continued, or did not survive the journey to the laboratory. The practical lesson is blunt: a negative culture result does not rule out mastitis. Your own clinical judgement and the cow-side tests in this module remain essential, and you must not let a laboratory report talk you out of what you can see and feel.

Why does subclinical mastitis matter more commercially than the clinical kind? Three reasons.

First, it is far more common. Clinical cases are the visible tip of the problem.

Second, it goes on for a long time. A clinical case forces a decision within a day. A subclinical case can run for an entire lactation, taking a share of that quarter's milk every single day, and you will never notice, because you have no record of what that cow should have been giving.

Third, it is a reservoir. A subclinically infected cow is shedding organisms into the milk at every milking, and if the organism is one of the contagious types you will meet in the next lesson, she is infecting your other cows through your hands, your cloth and your equipment. She looks like your healthiest animal and she is your source of infection.

That is why udder health is a testing problem before it is a treatment problem. You cannot manage what you cannot see, and the whole point of the California Mastitis Test is that it makes the invisible visible for the cost of a paddle and a bottle of reagent.

One last framing to carry into the rest of this module. Mastitis is not bad luck. It is the outcome of a chain: bacteria are present in the environment or on another cow, they reach the teat end, they get through the teat canal, and the gland becomes infected. Every control measure in the rest of this module breaks that chain at one specific point - the housing breaks it at the environment, the milking routine breaks it at the transfer between cows, the post-milking teat dip breaks it at the open teat canal, and dry cow management breaks it during the weeks when the canal is at its most vulnerable.

There is one question you must answer before you spend a shilling on mastitis control: is your problem contagious or environmental? Get it wrong and you will work hard, spend money and see no improvement at all, because the two problems come from completely different places and are fixed by completely different actions.

Contagious mastitis spreads from cow to cow. The organisms live in the infected udder, and they move to the next cow mainly at milking time. The named contagious pathogens in the veterinary literature are Staphylococcus aureus, Streptococcus agalactiae, and Corynebacterium bovis.

How do they travel? On your hands. On a shared washing cloth dipped in a communal bucket and used on one cow after another. On the milking machine cluster or the bucket unit if you have one. The route is short, direct and entirely under your control.

So the control for contagious mastitis is milking hygiene and milking order:

• Wash your hands before you handle any udder, and between cows.
• Use an individual cloth or paper towel per cow, never one cloth dipped back into a shared bucket. That shared wet cloth is a direct transmission route from an infected cow to a clean one.
• Disinfect equipment between cows if you use any.
• Milk known-infected and suspect cows last, or with separate equipment and separately washed hands, so infection is never carried forward to a clean cow in the same session.

Environmental mastitis is different. Those organisms are not living in another cow's udder waiting for a lift. They are living in the cow's surroundings. Bedding is named as the primary reservoir, with contaminated water, teat dips and mud also implicated.

That list is a housing list, not a milking list. Every item on it comes from the previous module: wet bedding, a flat platform where urine pools, a mud yard that needed 40 to 60 square metres per animal and got five, dirty drinking water, a teat dip container that has been standing open collecting dirt.

So the control for environmental mastitis is cleanliness between milkings, not at milking:

• Dry, clean bedding, changed often enough to stay dry.
• A lying platform that drains, at the 2 to 4 percent slope from the housing module.
• A well-drained yard, paved if it cannot be given the space an earth yard needs.
• Clean drinking water.
• Clean, uncontaminated teat dip, made up fresh as directed.

Now put the two together and see why the diagnosis matters so much. Milking hygiene fixes a contagious problem and does very little for an environmental one. A farmer with a wet, dirty lying area can wash his hands between every cow, use a fresh towel per cow, and disinfect everything he owns - and the cows will keep getting infected, because they lie down in the source every night. The reverse is equally true. A farmer with beautifully dry bedding who uses one wet cloth on six cows in a row is running a transmission line straight from his worst cow to his best.

So how do you tell which one you have? You will not get certainty without laboratory culture, and remember from Lesson 1 that 30 to 40 percent of clinical samples culture negative anyway. But the pattern tells you a great deal, and pattern is free.

A contagious problem tends to spread. Test your cows, and test them again a week or a month later, and you see infection appearing in animals that were clear before, moving through the herd in the order you milk them. It tends to persist in the same cows and quarters over long periods, because organisms like Staph aureus establish themselves deep in the gland.

An environmental problem tends to be scattered rather than spreading. Cases appear without following your milking order. They often cluster in time - after heavy rain, when the yard is worst, or when the bedding has not been changed. New cases appear in cows that were previously clean and clear up, then appear in others.

The honest position is that many herds have both, in different proportions, and the right answer is usually to work out which one is dominant and attack that first while doing the cheap basics of the other. But you must decide. A control plan that says "improve everything" is a plan that improves nothing, because your time and money run out before the actual source is touched.

Write your answer down, with the evidence you based it on. Then re-test in a month and see whether the pattern moved the way your diagnosis predicted. If it did not, your diagnosis was wrong and you have just learned something more useful than any amount of general advice.

Somatic cell count, usually written SCC, is the laboratory standard for measuring udder health. The name sounds technical but the idea is simple. Somatic cells are body cells - mostly white blood cells - and they appear in milk when the udder is fighting infection. The cow sends white cells into the gland to deal with bacteria, and some of them end up in the milk. Count them, and you have a direct measure of how much fighting is going on.

SCC is counted in cells per millilitre of milk, and the numbers are large, so they are usually written in thousands.

Here are the sourced figures.

An individual cow's SCC, whether from one quarter or from her composite milk, of 200,000 cells per millilitre or higher indicates a high likelihood of infection. That is the working threshold for saying this cow probably has something.

But inflammatory changes can begin at levels as low as 100,000 cells per millilitre. So 200,000 is not a wall with health on one side and disease on the other. It is a decision point on a rising scale, and a cow moving from 80,000 to 150,000 is already telling you something even though she is under the threshold.

For a whole herd, a bulk-tank SCC below 200,000 cells per millilitre is described as a desirable herd target. Bulk tank means the pooled milk from all the cows, which is what a cooperative or processor actually receives, and it is an average weighted by how much milk each cow contributes. That has an important consequence: a high-cell-count cow giving very little milk gets diluted in the tank, while a high-cell-count cow giving a lot of milk moves the whole tank figure. A bulk tank result tells you the herd is in trouble, but it never tells you which cow.

Now the regulatory point, and it is important that you hear it clearly. Bulk-tank SCC limits for the legal sale of milk are set by national and regional authorities and differ by country. This course does not know your limit and will not print one. The 200,000 figure above is a management target described in the veterinary literature, not a legal maximum anywhere in particular.

The figures for the actual limit that binds you must come from your own dairy regulator - in Kenya that would be the Kenya Dairy Board and the Kenya Bureau of Standards, and every country has an equivalent dairy board or bureau of standards. If you sell to a cooperative or a processor, they will also have their own acceptance standard, which may be tighter than the legal one. Ask both. Write the answers down with the date, because standards get revised.

What should you do with an SCC result when you get one? Three things.

First, treat it as a screening signal, not a diagnosis. A high count says there is inflammation. It does not say which organism, or whether the cause is contagious or environmental. That still needs the pattern reasoning from Lesson 2 and, where you can get it, culture.

Second, track it over time rather than reading single results. One high result could be a cow at the very end of lactation, or a sample taken badly. Two or three high results a week or a month apart is a persistent infection, and persistent infections are the ones eating your yield all lactation.

Third, if you can get quarter-level results rather than composite, do. Infection lives in individual quarters. A cow with three excellent quarters and one badly infected one has a moderate composite count that hides a serious problem, and only quarter-level testing shows you where to act.

Here is the practical difficulty for most smallholders, stated honestly. Laboratory SCC testing needs a laboratory. If there is no milk-recording service, no cooperative laboratory and no veterinary laboratory within reach of you, you will not get an SCC number, and no amount of wanting one will produce it.

That is exactly why the next lesson exists. The California Mastitis Test does the same job at the cow's side, with a plastic paddle and a bottle of reagent, in about twenty to thirty seconds per cow. It gives you a score rather than a precise count, and the correspondence between the score and an SCC number is approximate. But it is available, it is cheap, it needs no electricity and no laboratory, and it turns the invisible disease of Lesson 1 into something you can act on this morning.

So learn what SCC means, ask your buyer and your regulator what limit applies to your milk, and then get a CMT paddle, because that is the tool you will actually hold in your hand.

This is the practical skill at the centre of udder health for a smallholder. It costs a paddle and a bottle of reagent, it takes twenty to thirty seconds per cow, and it converts the invisible disease of Lesson 1 into a score you can write in a notebook.

What you need: a CMT paddle, which is a plastic tray with four shallow round wells, one for each quarter, and CMT reagent, which is a detergent solution usually with a purple dye in it. Nothing else. No power, no laboratory, no thermometer.

How it works: the reagent breaks open the somatic cells in the milk and releases their DNA, which is a long, sticky molecule. The more cells there are, the more DNA is released, and the thicker and more gel-like the mixture becomes. So thickness equals cell count equals inflammation. You are literally seeing the cow's immune response in a plastic tray.

The procedure, step by step:

1. Discard the first streams of foremilk from each quarter. Do not put these in the paddle. Foremilk sitting in the teat cistern is not representative and will mislead you.
2. Draw about a teaspoon, roughly 2 millilitres, of milk from each quarter into its own well of the paddle. Keep track of which well is which quarter. Front left in the front left well, and so on, every time, so your records mean something.
3. Add an equal volume of CMT reagent to each well. Equal volumes matter - this is why the wells have a marked level.
4. Rotate the paddle gently in a circular motion to mix, for no more than about 10 seconds.
5. Read the reaction within about 20 seconds.

Those two timings are not decoration. They are the test. The gel reaction forms and then breaks down again quickly, so a paddle rotated too long or read too late will show you a weak reaction from a badly infected quarter. If you rotate for thirty seconds while chatting and then read it, you have not done the test, you have wasted the reagent.

Now the scoring, and the approximate somatic cell counts each score corresponds to:

• N, negative: no thickening. Approximately 0 to 200,000 cells/mL. Healthy quarter.
• T, trace: slight thickening that fades if you keep rotating. Approximately 200,000 to 400,000. Early or subclinical.
• 1: distinct thickening but no gel forms. Approximately 400,000 to 1,200,000. Subclinical mastitis.
• 2: immediate thickening with a slight gel. Approximately 1,200,000 to 5,000,000. Serious infection.
• 3: a firm gel, and the surface rises in the middle of the well as you rotate. Over 5,000,000. Serious infection.

Be honest about what those SCC bands are. They are described as approximate in the source material, and they come from general and North American extension teaching resources. A locally validated African CMT-to-SCC correspondence table was not available for this course, and this module will not invent one. So do not treat a score of 1 as proof of a count of exactly 800,000.

That caveat costs you nothing in practice, because the CMT's real power is as a relative tool. Test all four quarters of all your cows at the same milking, with the same reagent, by the same hands. Then any quarter reacting more strongly than her herdmates is worth closer attention, and where you can get laboratory SCC or culture, that is the quarter to send. You do not need a validated conversion table to see that three quarters are watery and the fourth is a gel.

How to use it well:

Test every quarter, not one quarter per cow. Infection lives in individual quarters and a cow with one bad quarter and three good ones is common.

Test repeatedly and write it down. One test is a snapshot. Two tests a week apart separate a passing irritation from a persistent infection, and it is the persistent ones that eat your lactation.

Record the quarter by name. "Cow 2, front left, score 2" is a record you can act on next month. "Cow 2 had a problem" is not.

Test before drying off. This matters enormously for the next lesson, because knowing which quarters are infected before the dry period is what allows a treatment decision to be made on evidence instead of guesswork.

And one thing the CMT does not do, which you must never forget. It measures inflammation. It does not detect brucellosis, bovine tuberculosis, or antibiotic residues. A CMT-negative cow can still be shedding organisms that are dangerous to the person drinking her raw milk. That is a completely separate subject, and it is coming later in this course.

The dry period is the deliberate rest between the end of one lactation and the next calving. The udder tissue regresses, then rebuilds, ready for the lactation to come. Skip it or shorten it and the next lactation suffers.

The recommended dry period length is 45 to 60 days. Be clear where that figure comes from: it is temperate dairy-system extension guidance. A specific African smallholder recommendation, and any evidence on outcomes from shorter or longer dry periods in African crossbred or zebu cows, was not available for this course. Use 45 to 60 days as the standard target while knowing exactly what it is and is not.

Now plan it. Gestation in a cow is about 283 days. If you want the dry period to start 45 to 60 days before calving, then drying off should begin at roughly day 223 to 238 of pregnancy, which is about seven and a half months into gestation.

Work the arithmetic yourself so you trust it:

1. Gestation length: 283 days.
2. Take off 60 days for the longer dry period: 283 minus 60 equals 223.
3. Take off 45 days for the shorter: 283 minus 45 equals 238.
4. So dry-off falls between day 223 and day 238 after the successful service.

The practical consequence is one of the best habits in this whole course: the day you confirm a cow is pregnant, count forward and write the dry-off date on your calendar. Do not wait to "notice" her yield dropping. Yield drops for a dozen reasons and by the time it is obvious you may already be inside the window.

Now the reason this lesson sits inside an udder health module. The transition into the dry period is one of the highest-risk windows in the whole year for a cow to pick up a new mastitis infection.

Two things happen at once. The udder stops being emptied regularly, so any bacteria that get in are no longer being flushed out twice a day. And the teat canal - the narrow channel that is the physical barrier keeping bacteria out of the gland - takes time to seal after the last milking. For that period the door is neither being cleaned nor closed.

That is why dry cow management is a subject at all, and why standard commercial practice exists around it. In commercial systems, dry cow therapy means infusing an antibiotic product formulated for intramammary use into each quarter immediately after the final milking before drying off, one tube per quarter. The products commonly contain penicillin, cloxacillin, a cephalosporin or novobiocin. Internal teat sealants, used either alongside an antibiotic or instead of it in lower-risk cows, are described as reducing new infections during the dry period.

Whether to treat every quarter of every cow with antibiotic at drying off, or to reserve antibiotic treatment for cows and quarters with a diagnosed infection and use a non-antibiotic teat sealant for the rest, is an active question in dairy practice. That second approach is called selective dry cow therapy.

This course does not recommend blanket antibiotic dry cow therapy as a universal practice. That decision interacts directly with antimicrobial use policy and milk quality regulation in your country, and it is a decision to make with a veterinary officer, not to apply automatically because a book said so. Whatever product is used carries a milk withholding period that must be observed once the cow calves down and rejoins the milking string - and that withholding period is set by the product label and your national authority, never by this course. The next lesson deals with that in full.

Here is what you can do at no cost and with no drug at all, and it applies to every cow whether or not she is treated.

Keep the bedding clean and dry through the whole dry period. Remember from Lesson 2 that bedding is the named primary reservoir for environmental organisms, and this is the window when the teat canal is open and unflushed. A dry cow lying in wet bedding is being challenged at exactly the wrong moment.

Do not crowd dry cows. Crowding means dirtier lying areas and more teat contact with contaminated surfaces.

Keep the teat itself clean and undamaged. A cracked, chapped or injured teat end is a broken barrier.

And test before you dry off. Run the CMT on every quarter in the days before drying off, and write the results down. That single act turns the treatment decision from a guess into evidence, gives your veterinary officer something real to work with, and tells you which quarters to watch most closely when she calves down and comes back into milk.

Every veterinary medicine you give a dairy cow has a consequence for the milk. This lesson is about that consequence, and it is the one place in this module where the correct answer is not a number in a book but a question you must go and ask.

The principle first. Any veterinary medicine given to a lactating cow, or to a cow who will soon be lactating, carries a withholding period. That means a defined number of days, or sometimes a defined number of milkings, during which milk from that cow must not be sold or consumed, because the drug or its residues can still be present in the milk.

This applies to more than antibiotics. It applies to dry cow therapy from the previous lesson. It applies to dewormers. It applies to tick treatments. It applies to any hormone product and to any other registered veterinary drug. If it went into the cow, ask about the milk.

Now the part this course will not do. The exact withholding period is set by the national veterinary and medicines regulatory authority. It is specific to the exact registered product and its formulation, not just to the active ingredient. And it differs from country to country. Two products containing the same active ingredient, registered by different manufacturers or in different countries, can carry different withholding periods.

So this course gives you no withholding period for any drug, and you should be suspicious of any book, poster or neighbour who does. If someone tells you "penicillin is three days" as a general fact, they are giving you a number that may be wrong for the exact product in your hand, in your country - and if it is too short, you will sell contaminated milk while believing you followed correct practice. That is precisely the mistake that a printed universal number causes.

What you do instead is a three-step process, and it is not complicated.

1. Read the product label and the package insert for the specific product used. The withholding period is a legal requirement and it is printed there. Keep the box or the insert until the period has passed.
2. If in doubt, or if the label is missing or unreadable, ask the veterinary officer or the agrovet who supplied or administered the drug. That is what they are for.
3. If a whole herd or a whole batch is at risk - for example after an unplanned mass treatment, or if you realise afterwards that treated milk may have gone into a can - contact your buyer or cooperative and your local veterinary authority before you deliver, not after a residue problem is found downstream.

And the standing rule when you genuinely cannot find out: withhold the milk and ask. Not the other way round. Milk withheld for an extra two days costs you two days of income from one cow. Milk sold with residues in it can cost far more, and here is why.

Even a very small volume of antibiotic-contaminated milk mixed into a much larger bulk tank or collection-centre batch can be enough to fail a residue test on the whole batch. Residue screening tests are designed to be highly sensitive, precisely so that they catch contamination.

Think about what that means at a collection point. Twenty farmers deliver into one can. Nineteen of them observed every withholding period correctly. One did not. The batch fails, and the whole can is rejected. Nineteen farmers lose their money because of one person's record-keeping.

That is why withholding-period discipline is not a private matter. In a cooperative it is a collective responsibility, and a cooperative that does not talk openly about it is carrying a risk that will eventually land on all its members at once. Specific residue-test sensitivity thresholds were not available for this course, and they are properly a matter for your buyer's own testing protocol and your national regulator - ask them what test they use and what it detects.

So how do you make this automatic instead of relying on memory? With one page in a notebook. For every treatment given, write down five things:

• The cow's name or number.
• The date the treatment was given.
• The exact product name as printed on the box, not just the active ingredient.
• The withholding period stated on that label.
• The calculated date on which that cow's milk can go back into the can.

That last line is the whole point. Do the arithmetic once, at the moment of treatment, when the box is in your hand and the label is in front of you. Write the release date down. Then you are not depending on remembering what a vet said three weeks ago at the end of a long day.

This single record is the difference between confident, legal milk sale and an accidental residue violation that you did not intend and could not have detected yourself.

One more connection to close this module. The whole reason mastitis control matters commercially is that it protects yield and it protects milk quality. But the treatment for mastitis is usually a drug, and every drug creates a withholding period. So every case of mastitis you prevent - through the housing of Module 7, the hygiene of Lesson 2, and the testing of Lesson 4 - is also a treatment you never have to give, a withholding period you never have to observe, and milk you never have to throw away.