Milk quality issues: Causes and how to reduce the risk

There has been a steady stream of farmers with milk quality issues, especially those with block-calving herds in late pregnancy and early lactation, and herds at grass, according to Andrew Bradley, professor of dairy herd health and production at the University of Nottingham and director of Quality Milk Management Services (QMMS).

Bugs in milk may come from the environment through poor teat preparation, from inadequate plant cleaning, or from intramammary infection, and may be exacerbated by problems with milk cooling.

See also: 3 steps to reduce mastitis risk in dairy cows at housing

Any one or a number of these will result in a dip in milk quality, and each combination can be characterised by a different pattern of somatic cell counts and Bactosan results.

But a significant issue, says Prof Bradley, can be poor or sub-optimal water quality in the parlour.

Reasons for poor water quality

There are many reasons why water quality may fall short of what’s needed to avoid milk quality problems.

Even using mains water is not a guarantee of good quality, as pseudomonas species of bacteria – which typically grow at low temperatures – can be present in low numbers in drinking water, and multiply if water is poorly stored.

While the presence of low numbers of pseudomonads alone is not usually enough to cause a problem, it can when combined with other factors affecting water quality. These include:

• Uncovered or poorly maintained header tanks
• Using water for the volume washer that has been used previously to cool milk through the plate cooler
• Using poor-quality volume washer water to clean dirty clusters – any water used in the parlour must be of drinking-water quality
• Failing to monitor water quality from a borehole where this is used instead of mains water
• Using mainly mains water, but topping up, from time to time, from a borehole that isn’t being monitored for quality.

“The classic case is where a borehole has been installed, but regular testing for quality, two or three times a year, is not in place,” says Prof Bradley.

“Or, where a borehole is used and an ultraviolet [UV] lamp has been installed to kill bacteria, the bulb has blown, or scaled, and not been replaced.

“You have to have clear, clean water for a UV lamp to work, and professional advice is needed [when it’s installed] so it can be tailored to the rate of flow.

“[Working out what the problem is] is challenging and a detailed investigation is needed to know what’s going on. It’s very easy to go in the wrong direction.”

Analysing bacteria counts

Tests on milk samples from the bulk tank are targeted at assessing the relative importance of thermoduric bacteria (those that survive the pasteurisation process and impact the keeping quality of milk), coliform bacteria, and the psychrotrophic bugs (those that can grow at low temperatures).

As a general rule:

• An inflated thermoduric count indicates a plant cleaning issue
• High coliform and psychrotrophic counts point to a teat-preparation or environmental problem
• A rise in psychrotrophic bacteria alone suggests a milk cooling issue or poor-quality water
• Combined high psychrotrophic and thermoduric counts are often the result of poor plant hygiene and bulk tank cleaning
• A high total bacteria count with low thermoduric, coliform and psychrotrophic counts indicates the presence of bugs from an intramammary infection with Streptococcus species, particularly Streptococcus uberis.

Impact of one infection

Just one cow in a 200-cow herd with a quarter infected can cause a spike in Bactosan results, shedding billions of bugs into each millilitre of milk, says Prof Bradley.

Early lactation is often associated with high somatic cell counts, so autumn-calving herds may be experiencing this now.

Cows become infected in the latter part of their dry period by picking up bugs through their teats from their environment, but don’t show clinical signs before calving.

Teat sealants reduce, but don’t eliminate, the risk of cows picking up infection, so it’s still important to manage their environment to reduce the risk further.

“If you are calving a lot of cows at once, particularly outdoors, managing their environment is crucial to achieving low cell counts and Bactosan in early lactation,” he says.

“For example, if cows in a block-calving herd are gathering outdoors around ring feeders, they run the risk of acquiring infection.”