This is another of these topics that would seem relatively simple to answer yet there is not many published studies... 🤦♀️
I have managed to find a handful of studies that compared feeding calves warmed milk or cold milk, although there are a few considerations to take on board when reading through these studies... I will explain further as we go!
Key Points
One study compared warm and cold milk fed to calves but only fed one group for 21 days but the other group were fed for 42 days making it difficult to tell what impact the temperature of the milk had on the calves.
A second study reported that calves that were fed warm milk consumed more milk than those fed cold milk.
Both of these studies were completed in Northern hemisphere systems and published approx. 50 years ago. Definitely need some more recent studies done to see if we should be warming more milk for young calves!
The first study was completed by researchers in Nebraska and was published in 1982 using Holstein calves.
Calves were kept with their dams until 2 days of age then moved to individual pens.
Once in their individual pen they were either fed according to the "Conventional" program (39 calves) or the "Simplified" program (41 calves). The details of the two feeding strategies are given in the table below.
Basically the only similarities between the 2 programs was the amount of milk fed and the abruptness of weaning.
Calves in the simplified program were weaned abruptly at 21 days of age. Calves in the conventional program were weaned abruptly at 42 days of age, so they had twice the amount of time on milk (3 weeks longer) than the calves fed the simplified program.
Calves fed the conventional program were fed 1.59 kg of milk per feed (3.18 kg per day) and the calves fed the simplified program were fed 3.18 kg once per day.
The 'colostrum' fed was what we in NZ would (should!) call colostrum and transition milk. Colostrum is the first milking stuff and everything after that until after the 8th milking should be called transition milk.
The colostrum (and transition milk) was collected from cows for the first 6 milkings after calving and stored frozen. Before being fed to calves it was defrosted, which was why it was so cold!
All calves had access to water and a starter ration of mostly corn, oats and soybean meal.
After 60 days of age, the calves were grouped together (based on age) and were followed until after their first lactation.
The figure below shows the average weight of the calves at birth, 21 days, 42 days and 57 days. Both treatment programs had similar weights at 21 days, but by 42 days the calves fed on the conventional program were heavier (by approx. 3 kg). This small weight advantage continued to 57 days.
By the time the calves were 6 months of age, there were no differences in weight between the two feeding programs.
There were also no differences in reproductive performance (measured as number of services per conception) or milk production.
The conclusions from the authors were that there were no detrimental effects of using a more restrictive program compared with a conventional program.
Putting our science hats on here, we are interested in comparing feeding warm milk vs cold milk. This study has MANY factors that were different between the two feeding treatments other than the temperature of the milk.
There was a difference in weaning age (21 vs 42 days), temperature of milk (cold vs warm), type of milk (colostrum vs milk) and feeding frequency (once vs twice). By having so many variables with only 2 treatments, it becomes difficult (if not impossible) to tell why there were differences between the two.
As there were no significant differences between the two at 21 days of age, but there were differences at 42 days of age it is likely that what is causing the main differences is mostly from weaning age rather than the temperature of the milk.
But again, difficult to tell! Let's move onto the next study!
The second study was based in Berkshire (South East England) using Hereford x Friesian male calves and was published in 1969. Similar to the first study, these calves were reared individually indoors.
This study investigated similar things as the first study but instead of two feeding treatments, this study had eight!
These were combinations of warm vs cold milk, full-cream milk replacer vs substitute, or drinking water available vs not available. As this research summary is trying to investigate milk temperature we will be focusing on these results, but if you want to read more, the link to the full paper is at the end of the page.
Are you enjoying this summary? Have a read of one of these while you're here!
The average milk temperature was 38 degrees celsius for the warm milk and 8 degrees celsius for the cold milk. Milk was offered ad libitum to the calves in all treatments and topped up twice daily.
On average, calves fed warm milk consumed more kg DM overall and more from milk than calves fed cold milk. There were no differences in consumption of grass or water between calves fed warm or cold milk.
Over the eight weeks from treatment start, calves fed warm milk grew faster than those that were fed cold milk.
As can be seen in the figure below, the four treatments that included warm milk were in general heavier than those fed cold milk (solid black compared with white).
However... there were only 4-5 calves in each treatment group which makes it difficult to draw concrete conclusions from the study.
Now I have searched and searched online and I can only find one NZ study on the topic of the temperature of milk. This study was published in 1971 by Colin Holmes and was conducted on 3 Jersey calves. I have decided not to summarise it here as firstly there was only 3 calves and secondly the aim of the study was to look at oxygen consumption of calves fed warmed or cooled milk. I will link the study here if you would like to read more on it (Holmes 1971).
Overall, these studies show that we don't really know enough about the temperature of milk fed to calves and how this affects them! If anyone knows of any other studies we haven't mentioned here please let us know, especially if they have relevance to our NZ system of rearing calves.
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Full Papers:
Study 1:
Owen, F.G., Larson, L.L., 1982. A Simplified Liquid Feeding Program for Calves. Journal of Dairy Science. 65:1350-1356
Study 2: