Milkability

The dairy industry is swiftly changing. Dairies are becoming larger, more productive, and more intensively managed. High-quality labour may be difficult to attract and retain. The recent low milk prices have presented an all too obvious challenge. Consumers are increasingly demanding higher quality and safer products. Legitimate somatic cell count levels will likely be reduced in the next few years.

 

 

These changes require technical advances in milking systems to milk cows efficiently in a manner consistent with highest product quality and animal health. On most commercial dairies, the parlour is a major capital investment. It is also where the primary income source is reaped, where much of the labour is employed, and where the quality of the product is largely determined. For these reasons, parlour performance and efficiency discussions are common in today’s dairy industry. The goal of most dairies is to milk as many high-producing cows during each milking while still allowing time for adequate cleaning of the equipment. Several studies have shown teat condition and teat sanitation prior to unit attachment are key factors in reducing the new mastitis infection rate. Poor teat skin condition decreases the primary protective mechanism from mastitis. Roughened teat end conditions can cause difficulty in cleaning teat ends effectively. These factors can lead to higher new infection rates. Many herds in the United Kingdom have problems with good “milk ability”. Cows may be more reluctant to enter the parlour in these herds. In a parlour, poor milk ability can be spotted early in the milking process when cows move and step excessively during udder preparation practices. Stepping may also be seen soon after the units are attached and/or near the end of milking, often leading to a significant number of units being kicked off during milking. Excellent milk ability is present when cows have excellent milk flow as soon as the last teat cup is attached to the cow, with a steady, visible increase in flow until peak levels are reached. Peak flow should last 60 to 120 seconds, depending on the production of the cow. With excellent milk ability, milk flow will drop off rather quickly after peak milk flow is over. As the end of milking nears, milk flow should suddenly drop to very low levels. If equipment settings are proper, the unit will then be promptly removed. There should be minimal stepping and kicking throughout the entire milking process. Good milk ability requires adequate oxytocin prior to units being attached to cows. However, this creates a major dilemma in the industry. To achieve better performance from a parlour, the goal often becomes focused only on milking more cows. When more cows are milked, there may not be enough time allowed to properly prep cows for effective cleanliness and maximum oxytocin let-down. Unit on time (duration) is a key factor of parlour performance that has been largely ignored until recently. Unit on time is dependent on the amount of milk and the average claw vacuum under peak milk flow conditions. Adjusting systems to achieve average claw vacuum levels between 40 to 42 kpa under peak milk flow conditions will decrease the unit on time. Adjusting take off settings to remove units promptly upon completion of the milking will also significantly reduce the unit on time.

 

Research in both Europe and the United States has shown the key factor to reducing teat end hyperkeratosis is unit on time. To appreciate how unit on time contributes to reduced teat end hyperkeratosis, it is important to understand the normal pattern of milk flow from cattle during each milking. Immediately after the unit is attached to properly stimulated cows, milk flow increases rather rapidly until it reaches a peak milk flow rate. This peak flow rate is variable and depends to a great extent on the amount of milk actually given during a milking. After a period of peak milk flow, milk flow drops rather quickly. Depending on how the milking equipment is set, there can be a long period of extremely low flow and relatively higher vacuum exposure of the cows’ teats. The longer the period of relatively low flow, the longer high vacuum and increased pulsation cycles will be applied to the teat ends. This will lead to increased hyperkeratosis and a reduction in skin condition teat scores. Adjusting take-offs to remove units sooner will simply shorten the low flow/high vacuum phase at the end of milking. Removing units sooner and at a more appropriate time is important to improve teat end condition and teat end scores. However, earlier removal of units is in opposition to one of the oldest doctrines of the dairy industry: Under-milking the cow
Will cause new mastitis infections. This urban myth in fact is not true, but this perception is very difficult to overcome on some dairies… Proper udder preparation allows cows to milk quickly, completely and evenly, all of which are key factors to improving milk ability in the herd. Improved milk ability will improve the attitude of operators because fewer units will require readjustment or reattachment. Clearly, reducing unit on time offers distinct advantages to any dairy farm.

Will milk quality after Brexit have an impact on the future of your dairy?

How will milk quality after Brexit have an impact on the future of your dairy?

Milk quality means something different for every farmer in the dairy industry

Not only does quality mean something different for every producer, the way it’s measured or observed also differs,

If you’re a dairy farmer, the first thing you go to with milk quality is somatic cell count [SCC]. If you’re a buyer, bacteria counts are critical for lots of different reasons, like product safety, product quality and yield.

The key party of the dairy farm chain we often forget about is the consumer.
To the consumer, milk quality is something completely different in what we think about.
The consumer want to know how the cows are treated are they looked after well
This is why it is vital to please the consumer, and milk buyers want to produce an outstanding product, the milk quality “premium” to the dairy producer is not generated at the consumer level but at the processor level. Is that premium changing?
After Brexit, quality premiums may be a thing of the past we have to transition from producing quality milk because it makes you more money.

Will milk be picked up if you consistently make a 300,000 to 400,000 SCC or high bacteria count?

So why the change?
We will be on the world markets to keep ahead of the game we need to shift to better milk quality.

Every dairy farmer has the skill to produce high-quality milk and, in the future, it’s not going to be an option dairy processors are going to have to produce a higher -quality product.
Your milk might go to the same plant every day, but the components of that milk they produce – like the whey protein concentrate and all those other pieces – go in different directions, and quality impacts all of those.
Don’t accept high cell counts and  bacteria counts,

These are based on views on other developing countries that have reacted to world trends.

host-defence of the teat canal and resistance of cows to mastitis.

A REVIEW of the latest scientific literature indicates that there is a marked difference in teat end closure after milking dependent on the condition of the teat end score.

Not all cows are the same!

The teat cistern and the gland cistern are connected by the annular ring. The teat canal is surrounded by muscle in the form of a sphincter which has the function of closing teat canal.

The teat end is the first barrier against invading pathogens. The structural and physical features of the teat canal determine the regeneration rate of teat canal keratin to inhibit penetration of udder pathogens. It is theorised that up 40% of the keratin lining is removed at each milking and, therefore, it requires constant regeneration. Consequently, it is important to ensure that the Teat canal is closed post milking.

It is assumed that as milk production increases, more keratin is lost during milking.

This is the reason why it is recommended that cows should stand for at least 30 minutes post milking in a clean manure free area before returning to the cow housing.

During the post milking period cows close the teat with a keratin plug, some cows never form a complete keratin plug post milking.

After bacteria breach the teat end, they are taken up and destroyed by the cow’s immune defence.
Cows with ketosis have a lower defence and immune response.

Ketosis is a metabolic disorder that occurs in cattle when energy demands (e.g. high milk production) exceed energy intake and result in a negative energy balance. Ketosis cows often have low blood glucose (blood sugar) concentrations.

When large amounts of body fat are utilised as an energy source to support production, fat is sometimes mobilised faster than the liver can properly metabolise it. If this situation occurs, ketone production exceeds ketone utilisation by the cow, and ketosis results.

This also varies dependant on the cows, Clinical ketosis has been shown to increase in the risk of clinical mastitis and ketotic cows can experience more severe clinical mastitis.

These findings provide new insights into understanding host-defence of the teat canal and resistance of cows to mastitis.

What are your aims for the coming year?

Is your  aim  to reach the top 25% of the current milk market for all milk quality measurements.
A low cell count along with low bactoscan and thermoduric counts reduced mastitis incidence and overall improve general health of your herd.

You have to look at the cost of a case of mastitis for your farm, track the cost in your herd.

Many dairy producers do not believe mastitis costs as much as studies suggests. Many producers think of mastitis costs as the price of intramammary antibiotic tubes. Dumped milk is valued at zero because waste milk is fed to calves. The financial losses based on the grade of mastitis, stage of lactation, reduced peaks, lower conception rates and damaged lactation curves do not show up on your financial report so money lost is unseen. But mastitis affects your bottom line every day.

The economic impact of mastitis is typically much larger than many dairy farmers think; much work has been done to estimate losses at the cow level, the herd level, and the industry level. Understanding the economic effects of mastitis, including partial budgeting for mastitis will highlight the cost, it is time dairy farmers budgeted for mastitis costs?

Education is the key looking forward and introducing mastitis control plans and implementing them with your team.
This belief of negative cost can be transmitted to your employees.
If you have 40% of clinical cases as is suggested its 40 cows per 100.
Highlighting the number of cases in the view of your team can be an eye opener and an education many workers are not privy to this information.
Is your challenge to improve herd health ?

E. coli mastitis

Escherichia coli or known as E. coli is a gram-negative, rod-shaped, a common kind bacterium that lives originally in the intestines of animals (such as sheep and cattle, etc.), usually in the lower guts of warm-blooded ruminant animals and can be found in the guts of humans as well. A large group of bacteria called coliform bacteria is where E. coli part of and this group plays a helpful role in the animals’ nutrition, but the waste or feces of these animals are saturated with the high content of bacteria.

Please don’t assume that they don’t spread during milking. Just like with contagious bacteria, infected cows can contaminate the cluster and spread infection to other cows during milking. However, unlike contagious bacteria, preventing cow-to-cow spread during milking will not eliminate environmental mastitis. This is because parlour routine does not tackle spread from the environment to the cow. To control environmental mastitis, you should assess environmental hygiene as well as parlour routine. Parlour routine, alongside dry cow antibiotics, has been effective in reducing contagious mastitis but the  control of environmental mastitis has been much less effective, so that environmental mastitis now accounts for more than 50% of mastitis cases in UK cattle. All farms need to include environmental milking management in their mastitis control plan.


The two most important bacteria in this group are E. coli and Strep uberis. Of the two bacteria, Strep uberis is the one that spreads more rapidly during milking, while E. coli is the one that is most commonly linked with severe toxic mastitis. However, some strains of E. coli can also be spread  during milking and the majority of mastitis caused by E. coli is mild in nature.

A soiled environment! E. coli comes from the gut, so anywhere where cow faeces can come into contact with the udder, will provide a potential source of coliform mastitis. Bedding is the most important source, particularly organic bedding where the bacteria can grow and multiply. However areas around feeding or water troughs are also risk areas as slurry around these can get splashed onto the udder. Outside of the udder, Strep uberis is also found in the intestines but, compared to E. coli; it is much more commonly found elsewhere on the cow, particularly the skin. Strep uberis has a fantastic ability to develop outside of the cow, particularly in straw. Both E. coli and Strep uberis, particularly the latter, can also cause environmental mastitis in cows on pasture as they can survive for months in contaminated wet mud.
Non-organic bedding, such as sand, doesn’t support the growth of either E. coli or Strep uberis, so the use of such beds can reduce the risk of mastitis. However, these beds need to be kept clean as there is more -than enough organic material in a single faecal pat to support exuberant bacterial growth.
The peak time for infection with new environmental mastitis-causing bacteria is the dry period. Infection during the dry period is often unseen until the cow develops mastitis after calving. In order to control environmental mastitis, we have to focus on environmental management throughout the cow’s lactation cycle. Preventing environmental contamination in the dry cow is just as, if not more than, important as it is in the milking cow.
The latest research from the USA has pinpointed a lack of clean water or contaminated water troughs can be a source of e coli

E. coli can leech into your  water where in fact they can increase in numbers  E. coli can often be found in mud ,small ponds even in bore water.

Ensure mastitis records with good bacteriology are essential to tackling an environmental mastitis problem. Always take a milk sample from cows with mastitis before treating them for the first time, freeze it and when you have a problem you have a selection of samples available to test. Without good information, individualised targeted control programmes cannot be developed for your farm.

This past summer has been a big issue of increased infection of dairy cows due to strep uberis

This past summer has been a big issue of increased infection of dairy cows due to strep uberis

How to avoid Strep uberis?

What the experts say about preventing strep uberis mastitis in dairy cows.

Prevention
Hygiene in Husbandry Conditions
An intramammary infection is initially preceded by contamination of the teats or the udder surface, whereby in indoor housing the risk of contamination during the housed period is determined by the design of the lying surfaces, the space per cow, the bedding material, the regularity of bedding addition, cleaning and disinfecting as well as the cows´ length of stay in the cubicles.
The fact that the rate of infection with environmental bovine mastitis is highest during the summer months accounts for increased bacterial counts in the bedding material. The indicator for the optimization effort in hygiene of the resting area is the cleanliness of the teats.
The objective should be for more than 90% of the animals to have only a few coarse dirt particles on the teats, which can be removed by simply wiping with a disposable towel or something similar. Feeding imbalances as well as fluctuations in the dry matter intake of the animals seem to affect the rate of clinical Strep. Uberis mastitis in dairy cows.

Milking
Machine milking can lead to the proliferation of Strep. Uberis into the glands, which can be avoided by carefully cleaning the teats prior to milking. This can, but does not have to, be carried out by means of disinfecting measures before milking.
A crucial point is that about 95% of the teats leave no or only slightly coloured residues on the disinfecting cloth with which they have had contact before the milking clusters are attached.
All the evidence points to cleaning the actual teat end.
If you’re using too much water, look at the housing and bedding.

The most evidential success of reducing strep uberis is to treat at the dry period

Mastitis is Mastitis

So I turned up on a farm with a very high cell count “the farmer said I am being penalised by the dairy for having a high cell count, but I don’t have any mastitis “

Categorizing mastitis
Once it is identified, it is important to identify the severity of mastitis as this is crucial in determining what treatment to give.

Subclinical mastitis: while appearing unaffected by the illness, may experience a reduction in yield potential due to the high SCC, and certainly represents a possible source of infection for other cows, who can become subclinical sufferers themselves, or may go on to show clinical signs of the illness, due to differences in immune status between cows.

Any milk that has a somatic cell count of more than 1,000 000 cells per millilitre is not fit for human consumption.

Mild mastitis: Abnormality of the milk is the main sign with little evidence of change in the udder and no systemic signs such as dullness and loss of appetite.

Moderate mastitis: Changes in the udder are detectable as well as changes in the milk. These changes can occur slowly or rapidly. There may be small systemic changes such as reduction in feed intake.
Over a long period of time both of these types of mastitis can persist, leading to chronic inflammation and damage in the udder (chronic mastitis).

Severe mastitis: Marked changes in the udder and milk are combined with major systemic effects in the cow such as fever, loss of appetite, depression, shock, dehydration, and collapse. These cows need urgent veterinary attention.

Whether we like it or not all the above are mastitis which occur in every UK dairy herd to varying degrees. And while it is easy and often routine to supply cows showing clinical disease with antibiotics, is the pain of the disease ever taken in to consideration?
“Its only Sub clinical mastitis doesn’t mean there is no pain”.

Antibiotics are undoubtedly important in the fight against mastitis infection, but if you were to ask any human female having experienced mastitis they would likely describe the pain as excruciating,

Sub Clinical mastitis can present itself in a wide degree of severity of symptoms which can range from low to high cells. The degree of illness and the symptoms present will depend on many factors, such as the nutritional or immune status of the cow, which pathogen is responsible for the inflammation, and a range of environmental factors such as cleanliness, humidity and ambient temperature. Moderate to severe clinical cases can be very painful and unpleasant for the cow

So what are you aiming for?
The generally-quoted aims for mastitis control and milk quality on UK dairy farms are:
A mastitis frequency rate of no more than 30 cases per 100 cows per year.
A mastitis persistence rate of no more than 20% of the herd affected per year.
A mastitis re-occurrence rate of less than 10% of the total number of cases.
A herd-average Somatic Cell Count below 150,000 cells/ml.

Maintaining a low bulk tank somatic cell count has always been a good dairy management strategy. Low somatic cell counts are associated with improved milk quality, increased shelf life and cheese yield after the milk leaves the farm, increased milk production, and reduced veterinary and drug costs.

Bulk tank somatic cell count (BTSCC) is the most commonly used measure of udder health on most dairy farms.
There are many reasons that BTSCC is used. High BTSCC is a good indicator of udder health problems on the farm. BTSCC is also readily available.

So, how do you know if you have an udder health problem despite a low BTSCC? The only way to know is to keep good records. Records can be kept on paper.

With regards to somatic cell counts in dairy cattle, the lower they are, the healthier your cows are, which in turn, means that the environment they are in, is good.
The inflammation of the udder causes large numbers of white blood cells (leucocytes) and epithelial cells to be released into the milk. It is these cells that are collectively known as somatic or body cells.

However, there is also other form of mastitis, called Subclinical Mastitis, where there is inflammation to the udder, but it isn’t noticeable. Everything looks normal, but when the milk is tested you have a high somatic cell count. This type of mastitis is common in 60-80% of all cases, and far more common than Clinical Mastitis.

Mastitis is basically an environmental disease, because the germs that cause it are everywhere. There is no magical way of controlling it, but as I said, you can reduce it by making sure that bedding is regularly replaced, and water sources are clean. Keep your fly population down. Any dairy equipment used should be clean, and udders totally dry when milking begins.

Having said that, mastitis can also be caused by incomplete milking, or improper drying off when it is done too quickly.

Most mastitis is caused by germs entering the udder through the teat canal. Therefore the teats should be checked regularly for cracks, cupped teats, enlarged milk ducts, warts, cuts, scratches etc. that would allow the germ to enter.

Of course the milking machines themselves don’t do the cows any favours either for mastitis and somatic cell counts. Often the vacuum rates and fluctuations cause the teats to be irritated, which in turn encourage infection. Using the milking machine on a cow with mastitis, followed by a healthy cow during the same milking session, without any cleaning in between, will result in spreading the infection.

Mastitis occurs when the dairy cow has few defences against infection due to either injury, or the sanitary or even mechanical aspects of the milking machines used, how the udders are handled during milking, the type of housing provided and any stress that the animal may be under, can all contribute to mastitis, which, in turn will result in a high somatic cell count.

STOP! Looking at controlling the symptoms, you should be looking at the causes. Good management of your dairy cattle will always work in your favour of keeping the somatic cell count down.

Can you justify a new milking parlour ?

As cow numbers increase and parlours age milking systems might need upgrading or full replacement. That change is one of the most significant capital investments made on a dairy farm.

When considering building a new parlour, one of the biggest questions to ask is can you do what you want with what you have, Technology has changed considerably over the years and producers may be missing out on developments that could help capitalize on their bottom line.”
There are three areas that indicate the need for a parlour change, they are
Stall work: Some parlours are well beyond their intended use, metal work and stalls are worn and broken, this could lead to a monumental system failure or worse: injury to cows or workers.
Parlour is too small: When herd size increases this leads to cows spending more time in the milking process that means more time away from feed, water and relaxation.
Increase efficacies: That could be in terms of labour, time or automation. There’s a big difference between wanting and needing a new parlour.

Convincing yourself of a solid return on your investment is a first step, “Will the new investment improve returns? Will the leap in technology improve cow care, performance and efficiency? Generally it comes down to return.
Working capital, repayment capacity and overall equity position are key components of knowing whether a dairy business is secure enough financially to take on a parlour renovation. With regard to parlour type,

When it comes to incorporating technology in the parlour, how information will be used is what really matters. “Technology can improve return on investment, despite the added cost, can you demonstrate how data will be used, if you just let the information pile up and never look at it, producers should just go with simple parlours.

Full-fat Dairy Products Won’t Hurt You–But You Knew That

Enjoying full-fat milk, yogurt, cheese and butter is unlikely to send people to an early grave, according to new research by The University of Texas Health Science Center at Houston (UTHealth).
The study, published today in the American Journal of Clinical Nutrition, found no significant link between dairy fats and cause of death or, more specifically, heart disease and stroke — two of the country’s biggest killers often associated with a diet high in saturated fat. In fact, certain types of dairy fat may help guard against having a severe stroke, the researchers reported.
“Our findings not only support, but also significantly strengthen, the growing body of evidence which suggests that dairy fat, contrary to popular belief, does not increase risk of heart disease or overall mortality in older adults. In addition to not contributing to death, the results suggest that one fatty acid present in dairy may lower risk of death from cardiovascular disease, particularly from stroke,” said Marcia Otto, Ph.D., the study’s first and corresponding author and assistant professor in the Department of Epidemiology, Human Genetics and Environmental Sciences at UTHealth School of Public Health.
Dariush Mozaffarian, M.D., of the Friedman School of Nutrition Science and Policy at Tufts University, was senior author of the study, funded by the National Institutes of Health.
The study evaluated how multiple biomarkers of fatty acid present in dairy fat related to heart disease and all-cause mortality over a 22-year period. This measurement methodology, as opposed to the more commonly used self-reported consumption, gave greater and more objective insight into the impact of long-term exposure to these fatty acids, according to the report.
Nearly 3,000 adults age 65 years and older were included in the study, which measured plasma levels of three different fatty acids found in dairy products at the beginning in 1992 and again at six and 13 years later.
None of the fatty acid types were significantly associated with total mortality. In fact one type was linked to lower cardiovascular disease deaths. People with higher fatty acid levels, suggesting higher consumption of whole-fat dairy products, had a 42 percent lower risk of dying from stroke.
The 2015-2020 Dietary Guidelines for Americans currently recommend serving fat-free or low-fat dairy, including milk, cheese, yogurt, and/or fortified soy beverages. But Otto pointed out that low-fat dairy foods such as low-fat yogurt and chocolate milk often include high amounts of added sugars, which may lead to poor cardiovascular and metabolic health.
“Consistent with previous findings, our results highlight the need to revisit current dietary guidance on whole fat dairy foods, which are rich sources of nutrients such as calcium and potassium. These are essential for health not only during childhood but throughout life, particularly also in later years when undernourishment and conditions like osteoporosis are more common,” Otto said.
Evidence-based research is key to educating people about nutrition, Otto said.
“Consumers have been exposed to so much different and conflicting information about diet, particularly in relation to fats,” she said. “It’s therefore important to have robust studies, so people can make more balanced and informed choices based on scientific fact rather than hearsay,” she added.
The research was supported by the National Heart, Lung, and Blood Institute (grant R01HL085710 and R01HL085710-07S1).

Avoid Overmilking: Preserve Teat Health

The recommendation to dairy producers has been to “milk ALL cows as completely at every milking.” This recommendation has been reviewed due to recent research and field experience. It is impossible to milk a cow completely dry; there will always be some milk in the udder even after “complete” milk out because she is constantly making milk.


Overmilking is a matter of concern because it may affect teat condition and udder health. In the past, it was believed that all milk needed to be removed from the udder to maximize milk yield. However, breeding for high milk yields has provided cows with a high alveolar capacity. Due to this, cows are more efficient as producers of milk.
Overmilking starts when the milk flow to the teat cistern is less than the flow out of the teat canal. Mouthpiece chamber vacuum typically increases during overmilking and fluctuations become larger. If the vacuum in the teat cistern is higher than beneath the teat end for short periods of time, the reverse pressure gradients across the teat canal may increase bacterial invasion of the teat cistern. Reverse pressure gradients occur only during milking of empty teats (Rasmussen et al., 1994), and overmilking will therefore increase the possibility of bacteria entering the teat. Teat end health is also greatly affected by overmilking. Hyperkeratosis of the teat is often experienced in herds with long unit on times.
Hyperkeratosis means excessive keratin growth. It is a thickening of the skin that lines the teat canal and the external orifice. Producers often notice a wart-like structure or rough spots at the end of the teat. This can be a result of poor milking management and long unit on times. Cows that experience these effects are often seen to have an increase in somatic cell count. This is due to the inability to thoroughly clean teat ends with hyperkeratosis, leaving bacteria behind to enter the teat canal during milking.
So, overmilking and prolonged unit attachment can greatly affect your herd’s udder health. How do you test if you are overmilking? There is a very simple way to do so that can be done by anyone on the farm. The strip yield test looks at overall completeness of milking. It can be done two different ways, by hand or with a unit. I prefer to do this evaluation by hand, but your preference may differ.
To accomplish the test, immediately after milking, hand strip each quarter for 15 seconds, collecting the milk in a container. I use a plastic measuring cup. A properly milked cow should have about one cup of milk left in the udder, if there is more or less, then a milk out problem may exist on your farm.
Performing this test with a milking unit requires a little more precision. A milking meter is required to perform the test using this method. To do so, the milking unit must be reattached within 30 seconds of automatic removal and downward pressure applied. Continue applying pressure for 15 seconds before removing the unit. Record the amount of milk that was harvested using this method. Once again, about one cup of milk should be left in the udder.
If you discover that a problem exists on your farm with over or under milking, there are a number of different factors that can attribute to this. It is important to properly maintain your milking machines to reach optimum performance. If automatic detachers are being used, adjustment for timely removal of the milking unit can be critical to help reduce unit on time. If your farm is manually detaching the unit, employees need to be aware of the issue that is occurring and be more consistent in removing the unit as soon as “end of milking” is reached for each animal. It is important to look at your overall milking routine and have timely unit attachment and proper let down, quiet cow handling and timely unit adjustment, and proper alignment.
In conclusion, a few simple steps on your farm to prevent overmilking can help decrease your overall herd somatic cell count. Routinely perform a strip yield test on your farm .

Many thanks to – Rassmussen, M. D., E. S. Frimer, and E. L. Decker. 1994. Reverse pressure gradients across the teat canal related to machine milking. J. Dairy Sci. 77:984-993