September 5, 2017 at 3:32 p.m.
By basic definition, mastitis is inflammation of the udder caused by bacteria. Determining which bacteria are causing the inflammation is the first key to prevention and control.
"[A cow's] primary defense [against bacteria] is the teat ends," Dr. John Middleton said. "In the teat end, cows have keratin, which prevents bacteria from getting in. Once that is breeched, you have an infection."
Pathogens are categorized as contagious or environmental. For contagious pathogens, the reservoir is the mammary gland. They are generally transmitted at the time of milking, Middleton said, harbored through infected milking equipment.
"Another thing we have to consider are the milkers' hands," Middleton said. "The milkers' hands are a great environment for the development of bacteria, which is why a lot of your milking protocols require that milkers wear gloves."
Staph aureus, strep ag, mycoplasma and Corynebacterium bovis are all pathogens that cause contagious mastitis.
Staph aureus is one of the most prevalent contagious mastitis-causing pathogens. It typically causes subclinical disease, contributing to high bulk tank SCC, and can cause chronic infection that survives a cow's dry period.
"So the old adage, 'Once a staph cow, always a staph cow,' has some meaning to it," Middleton said.
Strep ag has been greatly reduced since the introduction of dry cow therapy. It causes persistent high somatic cell and bacteria counts.
"The good thing is it responds well to treatment," Middleton said. "So we can treat early in lactation and get an economic benefit in reducing the number of strep ag cows in the herd. Or we can treat during the dry period and often times clear up these infections."
Because it is contagious, mycoplasma tends to spread quarter to quarter and can infect multiple quarters in one cow. It can cause clinical mastitis and can cause arthritis-like symptoms in infected cows and respiratory diseases in youngstock. This bacteria is associated with large herds, especially those that purchase a lot of cattle. It can be screened for through bulk tank samples.
"The thing about mycoplasma is it's not treatable, so these are cull cows," Middleton said. "Once you get mycoplasma in a herd, you get rid of it when you get rid of the cows."
Another pathogen that has been greatly reduced is Corynebacterium bovis, or C. bovis.
"With the advent of teat dip, we don't see as much C. bovis as we used to," he said. "When you see this in a herd, really this is a good indication that there's something wrong with the teat dip protocol on a farm."
C. bovis can be transmitted cow to cow if one udder cloth is used to clean multiple cows, so single-use cloths are important, Middleton said.
Environmental pathogens - as their name suggests - are spread through the environment. Reservoirs can include bedding, fecal matter and stagnant water. Certain pathogens are attributed to certain bedding types. Klebsiella is associated with sawdust, whereas environmental streptococci are associated with straw. Pseudomonas species are more often found in or around stagnant water.
Transmission of environmental pathogens typically happens between milking. They can cause both clinical and subclinical mastitis and can become chronic.
To further break down pathogens, they can be described as gram-negative or gram-positive. Gram-negative bacteria include e. coli, klebsiella, enterobactor and cirobactor. Gram-positive bacteria include streptococci, strep uberis and strep distolactia. Toxic mastitis is usually caused by gram negative bacteria due to the production of endotoxins and the presence of bacteria in the blood stream. These cows, Middleton said, will normally not contribute to high SCC problems.
"But if we have a lot of toxic cows in the herd, it tells us something about herd management and bedding management, and so this can be an index for suspicion of environmental pathogen control," he said.
Another large group of mastitis-causing pathogens is the coagulative negative staphs (CNS), which - though thought to be of minor threat in the past - can contribute to bulk tank SCC.
Detecting clinical mastitis can be done through viewing physical manifestations - inflammation, altered secretions - as well as through the milk itself, which will often contain clots.
"One of the reasons we forestrip is to find clots in the milk, changes in the milk quality," Middleton said.
Detecting subclinical mastitis is more challenging because the milk looks normal. The most reliable indicator of subclinical mastitis is somatic cell count, Middleton said. In general, cows should have a cell count of 200,000 or less. An increase typically means an infection, though it could also mean some sort of trauma to the udder.
"There are things that cause elevation in somatic cell count that are not bacteria, but probably 99 percent are caused by bacteria or some sort of intra-mammary infection," he said.
The California Mastitis Test (CMT) is a popular tool for screening for high somatic cell count. But while it is quick and easy to do, Middleton said there is some degree of overlap between the categories.
Looking at goals for somatic cell count, Middleton said producers should strive for a bulk tank count of 200,000 or lower, with 90 percent of the herd less than 300,000 and less than 5 percent of the herd above 800,000. There are two main areas farmers should focus on if their herd exceeds these goals: the milking parlor and the cows' environment.
In the milking parlor, check the overall hygiene of the cows as well as udders, teats and teat ends. Enforce good milking preparation procedures and make sure the units are attached and functioning properly.
"The goals of the milking procedure are efficiency and consistency in a clean, low stress environment," Middleton said.
A checklist to evaluate milking procedure included observing for physical signs of mastitis, forestripping, pre-dipping, using one towel per cow, wearing clean gloves, attaching the unit properly, avoiding over milking, post-dipping and milking contagious cows last. Keys to controlling contagious pathogens include much of the same as well as using dry cow therapy, culling chronic cows, not purchasing older cattle and screening cattle prior to purchase.
In controlling environmental pathogens, bedding management is critical, Middleton said, as well as cow cleanliness. Steps to controlling these pathogens include using pre- and post-dip, minimizing water usage in the parlor, keeping the cows standing after milking and good freestall management.
To identify problem cows, individual milk cultures or composite samples may be done.
"Random [sampling] is a good way to screen, but it doesn't identify which cows are the problem," Middleton said. "If you want to implement a strategy at the cow level, you have to have data at the cow level."
When treating subclinical cows, Middleton suggested milking these cows last and waiting to treat until their dry period. For clinical cases, cull cows with gram-negative pathogens and treat those with gram-positive.
Middleton summed up his presentation into three main points.
"Mastitis is generally cause by bacteria. Bacteria comes from two major sources, and milking procedure, freestall management and teat management are important [in preventing and controlling mastitis]," he said.
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