If a cow produces forty-five litres of milk per day and its production suddenly drops to ‘a mere’ thirty-five litres, what is wrong with that cow? She is not ill, but also not in top condition. And if more cows show a milk production decrease of over 20% then there is an operating problem on the farm.

Holstein-Friesian
Up until the seventies (20th century), the cows served a dual purpose: both their milk and their meat was of economic interest. The Friesian cow was top notch in that respect for a long time and was exported to all corners of the world. But since then, separate milk and beef stocks were bred. Today, Holstein-Friesians are mainly used for the production of milk. These were bred in the States from the originally Friesian cows and exported throughout the world, including back to the Netherlands. The present dairy farms in the Netherlands also mainly use Holstein-Friesians. That is one reason why the milk production per cow has increased from an average of 5000 litres per year in 1984 to 8200 litres in 2015. And now, five years later in the year 2020, the national average of the production per cow in the Netherlands, is further increasing to approx. 9500 litres of milk per year (31 litres per day as an average). In addition to the hereditary qualities, it is mainly the feed of the dairy cows that has highly improved in those years, making it possible to increase the milk production that much.

Feeding
Up until the seventies, cows were in the pasture day and night from April until October. They were kept indoors in the winter and fed silage or hay, supplemented with mangel-wurzel (fodder beets). Nowadays, in the 21st century, only young cattle are kept at pasture day and night in the summer; cows are not outdoors anymore, or only a few hours a day. Because it is not possible to achieve a daily milk production of forty to fifty litres of milk with pasture grass alone. It requires a sophisticated diet. Corn silage and ensilage make up the basis. A laboratory analysis of the corn silage and ensilage determines which products are to be added to that, for example soy, potatoes or rapeseed; brewery spent grain, sugar beet pulp or palm kernel scraps. A mineral mixture is also added. All these components are thoroughly mixed and this so-called roughage must be available to the dairy cattle day and night and changed twice a day. The remnants are fed to the youngsters and the dry dairy cows. In addition, each dairy cow is individually fed two or three types of concentrate that are geared to its daily production and the percentages of fat and protein in the animal’s milk. To that end, a number of computer-controlled feeding boxes have been installed in the barn. Each cow is recognised by the transponder around its neck or one of its legs. And so feeding dairy cattle has become pure workmanship.

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feeding alley with tractor

Milking
Most farmers milk their cows twice a day. More often if milking robots are used because each cow can offer herself around the clock to the robot to be milked. On average, this happens over three times per 24 hour period. Milking more often increases the milk production. But milking robots are expensive and two robots are needed for a hundred cows. The rotary milking platform is a less expensive alternative. Twenty-eight or more cows stand on a ring-shaped platform that slowly rotates as the cows are milked. The farmer stands in the ‘milk pit’ with the udders of the cows at eye level. The production of each individual cow is measured and any deviations to the normal amount are detected. Once the milking of a cow is finished, the animal steps off the platform and another cow takes her place.

rotary milking platform

During the milking process more characteristics are monitored. For example the conductivity of the milk as an indicator for an udder infection. If the conductivity deviates, then the milk of that cow is tapped off so that it does not enter the milk tank. This ensures quality control of the milk that is to be supplied. Nowadays, milking cows on a modern dairy farm involves high-tech equipment and requires major investments.

Decrease in production
A dairy farmer called the practice because the milk production of a number of cows has been too low for a few days; this had been detected by the milking machine. Other than that, they seem perfectly healthy. What is going on here?
There are many reasons that may explain the situation. Most of the time the cows concerned do not eat enough for all sorts of reasons: they are agitated during draughtiness and do not eat enough. Or the roughage is not quite tasty; or it is badly mixed so that some animals take in insufficient amounts of minerals, for example. The claw trimming may have been delayed too long, as a result of which some cows are suffering from painful feet, are inclined to lay down and thus eat less at the feeding railing. The supply of concentrate to the feeding boxes may be stagnated if the feed computer malfunctions or if a jackscrew used for the transport from the silo to the feeding boxes is defective. Perhaps a silo was supplemented with the wrong type of concentrate. It sounds far-fetched, but all of these examples are from actual practice and most occurred more than once.

Examination
A few of the ‘evildoers’ are standing at the feeding railing when I arrive. They were milked a half hour ago. The search for the reason of lowered productions starts with the clinical testing of these animals. They have no fever, nor pathologic murmurs from the lungs or the heart and the rumen too is functioning normally. Internal examination, via the rectum, shows no deviations in the uterus or the ovaries. The manure is normal, so the food seems well digested. The udders are flexible, but the lymph nodes in the groin are swollen. And the orifices of the teats are callous-like. I squeeze a spout of milk from each quarter onto a black CMT dish. It looks normal. However, adding some teepol (a soap solution) makes the milk from both rear quarters of these cows slimy, meaning that the cell count in the milk is too high. That is the result of inflammation. But fever, swelling and pain are lacking. That's why this is called a subclinical mastitis. I take milk samples from the affected quarters for bacteriological testing.

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heart examination

Milking machine
Why didn’t the milking machine spot this?
The milking equipment measures the conductivity of the milk. Acute mastitis increases conductivity because the milk contains more salt. But the salt content scarcely changes in the case of chronic mastitis. However, the number of white blood cells in the milk (the cell count) is vigorously increased by chronic udder inflammations. But that is not (yet) monitored by the milking equipment. Despite a high cell count, the colour, scent and taste of the milk are often unchanged during chronic mastitis. So the milk looks normal. Which is why this is referred to as ‘invisible' mastitis. Nevertheless, the amount of milk produced is decreased. This invisible type of mastitis is usually caused by the milking machine. For example, if the machine sucks the teats too roughly. Which may have various causes: when (false) air is sucked into the teat cups during the milking because they do not correctly fit the teats. Older cups are often too wide for the smaller teats of modern heifers and cows. False air may be sucked when the cups hang in a crooked position to the udder, or because they have cracked inner linings. In such cases the vacuum of the milking machine is often magnified to suck the milk out of the udders despite those defects. But this rough sucking leads the orifices of the teats to become irritated and callus is formed after some time so that the orifices don't properly close anymore after milking. This enables bacteria from the skin or from the cow cubicles to penetrate the udder and cause mastitis. These things frequently happened during the stormy developments on dairy farms in the thirty-one years of the super levy. During that time, every dairy farmer encountered a thorough renovation of his milking stable sooner or later.

milk tank

Treatment
The laboratory cultures of the milk samples from the affected cows showed the presence of staphylococci (S. aureus). These bacteria are often present on normal skin, but after invading the udder they cause mastitis. Which is often subclinical in nature but still results in high cell counts in the milk. In the antibiogram this bacterium appeared to be very sensitive to neomycin. That antibiotic was part of the former udder injector Ubrocelan® which also contained penicillin and a propellant. Both antibiotics were driven deep into the milk ducts of the udder up to the mammary glands to kill the bacteria. However, these injectors have meanwhile been withdrawn from the market. The same antibiotics (neomycin and penicillin) are in Neopen®. Which is a suspension that may be injected into the cow’s muscles. It is not primarily about how much (in fact how little) of the injected suspension is secreted into the udder. But it's essential (in my opinion) that the same antibiotics are administered in both the muscles and in the udder. In that way the concentration differences between the antibiotic levels in the udder and in the circulating blood shrink. Thus, the drain away of these medicines by the blood takes more time so that their inhibiting concentrations in the udder remain high for a longer period of time. Because the cows in question were in full lactation, it was no option to dry them off and administer a long-acting antibiotic in the udders (dry cow antibiotic). Instead they were injected with Neopen in the muscles of the neck during three consecutive days and with Ubrocelan in the affected udder quarters in addition to the evening milking. The milk of these cows was not delivered for consumption during the treatment and five consecutive days.

Prevention
A specialist of the Health Service for Animals tested the milking machine during the milking (a so called wet testing). It appeared that pressure fluctuations at the top of the teats (inside the teat cups) were too great. This somewhat older milking machine could no longer handle the ever increasing amounts of milk that are produced by modern cows in an increasingly shorter amount of time. The outlet for the milk into the milk tank was no longer fast enough because the content of the milk claws and the diameter of the outlet tubes were too small. The milk congested in the claws as a result and because of that, the vacuum in the teat cups (almost) disappeared during milking. To prevent the cups from falling off the teats, the vacuum of the machine had been magnified. This caused major fluctuations in pressure on the teats, hurting the cows. So they were not at ease during milking and the orifices of their teats became horny in the long run, resulting in subclinical mastitis. Bigger claws and double sized outlet tubes were installed the next time that the milking equipment underwent its regular maintenance. Such to prevent invisible mastitis.

Support
Dairy farmers require assistance to keep their cows in top condition. The veterinary surgeon, the dairy factory (milk inspections), the installer of the milking machine (maintenance), the feed supplier (ration calculation), and the claw trimmer, they all should visit the farm with some regularity to support the production process. However, if the milk production is wavering, a thorough veterinary examination of the cow (or several cows) is the key to the solution. Which is a huge challenge for the craftsmanship of a veterinary physician. At least, that was my experience.