There are about 100 organisms that can cause infections in the udders of dairy cows. Selecting the best path of management for an individual case of mastitis starts with knowing what type of bacteria is causing the problem. Milk culturing, when a milk sample is placed on culture media, allows dairy producers to determine the origin of the infection.

According to Cornell University’s Mike Zurakowski, D.V.M., the most important questions that can be answered through milk cultures are, “Are we dealing with contagious or environmental organisms?” and “Are organisms even present or are we dealing with inflammation associated with mastitis rather than an active infection?” Zurakowski, a senior extension veterinarian with Cornell’s Quality Milk Production Services Animal Health Diagnostic Laboratory, discussed milk cultures and mastitis prevention during the October Hoard’s Dairyman webinar.

For contagious pathogens, the udder is their main breeding ground. Once the pathogen is in an animal, it can be transmitted through the milking machine or milkers’ hands.

“These pathogens are transmitted mostly during milking,” he said. “When dealing with contagious pathogens, the most important thing is to identify which animals have them and which animals do not, so that we can protect those animals that are not infected.”

This can be done by segregating infected animals, milking them last, or perhaps milking them with a separate milking unit. Zurakowski said some cows with contagious mastitis can be treated, but for others, the best scenario may be to cull them.

Environmental mastitis pathogens, as the name suggests, are found in the environment, and a dairy barn has all the components — nutrition, warmth, moisture, and the appropriate pH — that bacteria need to survive.

Zurakowski said this kind of mastitis can be picked up during milking or after. Milk culturing can be used to identify the type of organism, and with this information, a farm can then pinpoint where it is coming from and methods of prevention.

Culturing milk can also determine if the case is an active infection or inflammation associated with mastitis. Twenty to 30% of all clinical mastitis cases are culture negative due to the animal’s immune system attacking and killing the organism causing mastitis. When we collect milk with typical signs of mastitis (flakes, clots, abnormal milk, and so forth), the organisms responsible may already be dead. There is no need to treat these cases if no live bacteria are present.

Risk factors causing infections include milking equipment, milking routines, the dairy barn environment, cow cleanliness, and teat end condition. Farmers have more control over some of these areas than others.

More people-side factors

Considering all factors that contribute to mastitis risk, Zurakowski said cow factors only account for 20% of cases. The other 80% of infections are caused by humans, and more specifically, how the farm is managed.

“When we have mastitis issues, we can’t really blame the cow,” he stated. “We have to look at ourselves first.”

One factor in our control is routine milking equipment maintenance. “We recommend your system is gone through twice a year,” he said, noting that on some farms, the milking equipment is running nearly 24 hours a day. Areas to evaluate are average claw vacuum at peak flow, pulsation under load, and milk line vacuum during milking.

For many farms, Zurakowski said maintenance may not happen until the equipment breaks. “We have control over our milking system and milking equipment. We want to make sure our animals are happy being milked,” he noted.

Another factor is the milking routine and the milkers themselves. Whoever is milking cows on the farm has a very important job. “We need to spend time making sure people know what they are doing, why they are doing it, and that they are doing a good job with milking procedure and stall maintenance,” Zurakowski said.

A problem that can affect a milker’s ability to do a good job is dirty cows and dirty udders. Dirt on the udder elevates the risk of mastitis, and it also increases milking length due to more prep time.

“Udder hygiene is really key,” he said. Zurakowski recommended having a fresh set of eyes look at your animals to evaluate cleanliness. “Over time, what you are used to seeing becomes normal,” he said.

Take note of how much dirt or manure is on the skin of the udder, evaluating 20% of the herd or 80 cows, whichever is greater. He said to look at different groups, including dry cows and heifers, as well.

“It’s pretty easy, but it’s something you need to stop and do,” he said. “With poor udder hygiene, it makes it harder to achieve clean and dry teats prior to unit attachment.”

There are various udder hygiene scoring charts available. Zurakowski said less than 10% of cows should fall in the moderately dirty or dirty category. If your herd has more dirty cows than that, take a closer look at where animals are gathering when they are not being milked, stall grooming, how they lie in stalls, alleyway cleanliness, and so forth.

“Udder surfaces are never sterile. There’s always bacteria on teat ends, but our job is to reduce that bacteria load as much as possible before the milking process,” he noted.

To evaluate teat end cleanliness, use an alcohol swab after udder prep right before the milking unit is placed to see how well milkers are getting teats cleaned. Assess cows prepped by different milkers across all groups to determine if teat end cleanliness is related to a specific individual or if it is a systemic milking procedure issue. If the teat end is still dirty, this in an opportunity for organisms to enter the udder. A farm should have fewer than 10% of cows in the slightly dirty or dirty category.

Zurakowski said he is often asked if it is better to dip a teat or strip a teat first. He said it doesn’t matter, as long as both are being done. “In terms of removing organisms from the teat end and reducing bacteria numbers, both predipping and prestripping are important,” he explained. “You want to do both so that we have well-sanitized teats and good stimulation for milk let-down.”

A farm must also monitor the condition of teat ends. Teat end condition is influenced by a multitude of factors, including milking equipment, overmilking, and weather.

A strip yield test can be used to measure how much milk is left in the udder after milking. To do this, strip each quarter for 15 seconds into a measuring cup after milking.

“The goal is that 80% of cows should have at least 1/2 cup to 1 cup remaining from the combined four quarters,” he said. If cows have less milk than that in their udder, or if they kick while being stripped, it could be a sign of equipment malfunction or overmilking, which can lead to discomfort and teat damage.

“We don’t want damage to teat ends,” he said. “Let’s leave some milk in there; we’ll get it the next milking.”

To evaluate teat end conditions, look at 80 cows or 20% of the herd. Check cows of all lactations.

“If you are seeing greater than 20% of animals with abnormalities, this is a big concern we need to jump into and try to find the reason why,” Zurakowski said. “When we have damage to the teat, it takes longer for the teat canal to close, and this opens the door for infections to occur.”

Come up with a plan

Zurakowski said farms should aim for a mastitis rate under 5% of all cows in the herd. When rates go above 10% and up toward 20%, there is reason for concern.

He encouraged dairy producers to create a mastitis management plan with input from farm staff and the herd’s veterinarian. By evaluating the areas listed in this article, a farm can identify specific risks on the dairy. In addition, the use of milk culturing will identify the pathogens that are present in the herd. This data can help minimize the people-side factors that contribute to mastitis in dairy cows.