Freezing point depression

A number of factors can affect the Freezing Point of milk including:

• seasonality
• breed
• stage of lactation
• rumen protein balance
• environmental issues

However, the addition of water is the most significant factor affecting the freezing point of milk.

Added water in milk

Accidental or deliberate addition of water to the bulk milk tank will be picked up by the Freezing Point Depression Test. Dilution of milk will raise the freezing point of milk closer to 0°C.

If there is an issue with Freezing Point Depression always check first for any possibility of water contamination of milk. Any addition of water to milk will cause dilution and may result in a failed FPD test.

Thoroughly check the milking plant, including all cleaning, cooling and storage systems, are functioning correctly and there is no opportunity for water to get into the milk.

• check all wash water is completely drained from your milking plant — manually check the bulk tank before milking as water may sometimes pool there through condensation.
• check for potential leakage in plate coolers – corrosion or pinholes could result in leaks; gaskets with signs of damage or wear should be replaced.
• check if would help to increase the capacity of air-blasts, to ensure all water is excluded from milk lines, when used in conjunction with sanitiser flushing systems
• if you have an FPD problem consider running-to-waste the first milk through the lines (or feeding to youngstock).

A low FPD, when not caused by water contamination, is generally caused by a combination of different issues.

My milk regularly shows a decrease in FPD in spring, is this normal?

Seasonality does have an effect on FPD, with lower values reported during spring and summer. The seasonal effect on the FPD of milk is thought to be linked to the changes in temperature and diet: water intake in these seasons is higher, because of higher temperatures and of high intakes of fresh grass after turn-out at pasture.

This summer my FPD is very low, what is happening?

There were particular problems with FPD in 2018 with exceptionally high temperatures and water scarcity. The changes in FPD in summer are probably due to the increased water intake associated with the increased temperature and sunshine hours. Water requirements of dairy cows under heat stress are significantly higher, especially if they are kept outside. If there are not enough working water troughs in the field and cows are fed dry feed instead of grass, or if grass has a high dry matter content, they will inevitably become very thirsty and binge on water as soon as they find an available source. If this occurs close to milking time, it can lead to rapid absorption of water through the rumen, into the blood and finally into the milk. Additionally, this effect can be made worse through lack of proper mineral intake; heat-stressed cows lose potassium and sodium when they sweat. 

 What is the role of nutrition in altering FPD?

The nutritional effects on FPD are not consistent. Due to imbalances in energy and protein cows that consume low levels of dietary protein, (i.e low energy), can decrease FPD, as milk samples with low urea and protein have shown to have a lower FPD. Find out more here.

Rumen protein balance has been shown to have a significant effect on milk FP. Lower efficiency of feed protein utilisation led to higher freezing point of milk – freezing point increasing and moving closer to 0°C. Buchberger (1988) found that an increase in milk urea resulted in a decrease in the freezing point of milk.  The freezing point of the milk with low protein content was closer to zero than the freezing point of the milk with higher protein content in the study by Henno et al., 2008.

Are fresh cows more likely to have a low FPD in milk?

As previously mentioned, this study by Henno et al. reported an effect of lactation stage (Days in milk), with FPD levels closer to 0 during the first 3 months. This finding in particularly important for block calvers, especially spring block calvers, who may suffer from the effects on FPD of both lactation phase and seasonality. 

 Is there a breed effect?

Different breeds can have slightly different FPDs, probably due to the solid contents, but the difference is of no practical relevance when large changes in FPD are reported.

 TOP TIPS for FPD at critical levels

• Do not rule out water contamination of milk. Any addition of water to milk will cause dilution and decrease FPD. Thoroughly check the milking plant, including cooling and storage, to identify failures that could allow water to get into the milk
• Make sure cows have access to fresh/clean water at all times, both inside and in the field, particularly during hot weather.
• Make sure water is freely available at all times - that there are enough water troughs in the field and that all are working. Fix any leaks and check that the pressure allows for a prompt refilling of troughs, especially when several animals are drinking at the same time
• If cows are crowding around drinking troughs in collecting yards it suggests that there may be problems with access to water. (It has been reported cows can drink up to 15% of body weight in 4 minutes following dehydration).
• It is not acceptable to  restrict water intakes and if there are enough troughs at grazing it will reduce the risk cows gorge themselves with drinking water directly before milking; additional water troughs could be provided for cows after milking
• Protect cows from heat stress: this involves providing shade (or even housing them during the day in the hottest periods if feasible) and cooling down by means of fans, sprinklers or evaporative cooling
• Discuss with your nutritionist and/or farm vet the opportunity to add minerals (salt) and/or to review the diet if milk components and urea suggest there may be value in doing so.

We are thankful for the inputs received by partners, including The Dairy Group, Arla Foods, NMR and Dairy UK, in preparing this guidance