Introduction
The Calf Notes family of educational resources has grown to include the new video series “What’s Happening?” – a series of videos that describe an interesting – and educational – photo or video that Jim collected during his 40+ year career in working with young calves. This series of Calf Notes will reprise the first “season” of What’s Happening? episodes… this Note will review Episode #6 – “Colostrum in the Refrigerator: How Long Is Too Long?”.
Episode #6
On farms around the world, refrigerators are commonly used to store fresh colostrum prior to feeding. The assumption is simple:
“It’s in the fridge — so it must be safe.”
Unfortunately, refrigeration slows bacterial growth — but it does not stop it.
The problem is that colostrum is an ideal growth medium for bacteria. It contains high concentrations of protein, fat, lactose, vitamins, and minerals — everything bacteria need to multiply rapidly.
Even at refrigeration temperatures, bacterial numbers can increase dramatically in a short time.
What the Research Shows
A study conducted at the University of Minnesota examined bacterial growth in colostrum stored at room temperature and under refrigeration for up to four days. Researchers measured total plate count (TPC) — the number of bacteria per milliliter, expressed as colony-forming units (CFU/mL).
At collection (0 hours):
- Pooled colostrum samples already contained approximately 100,000 CFU/mL.
- This level is generally considered the maximum acceptable bacterial count for feeding newborn calves.
After 24 hours:
- Refrigerated samples: increased to >500,000 CFU/mL
- Room temperature samples: increased to approximately 18 million CFU/mL
At this point:
- The colostrum stored at room temperature was completely unfit to feed.
- Even the refrigerated samples had exceeded recommended bacterial limits.
- pH declined due to bacterial fermentation.
By 48 hours (2 days):
- Bacterial counts reached 1–4 million CFU/mL, depending on storage temperature.
- Significant fermentation had occurred.
- None of the samples were suitable for feeding newborn calves.
By 4 days:
- Bacterial levels were extremely high.
- All samples were microbiologically unacceptable.
The Bottom Line
Without intervention (pasteurization or preservatives), colostrum stored in a refrigerator should not be kept longer than 24 hours.
Why High Bacterial Counts Matter
High bacterial contamination in colostrum is more than a cleanliness issue. It has real biological consequences:
- Reduced IgG absorption
Bacteria bind immunoglobulins (IgG), reducing passive transfer efficiency. - Increased disease risk
Feeding contaminated colostrum introduces pathogens directly into the newborn calf. - Fermentation and nutrient loss
Bacterial growth alters pH and nutrient quality. - Increased scours risk
High bacterial loads are associated with greater enteric disease incidence.
Remember: the newborn calf’s immune system is immature. The first feeding of colostrum sets the foundation for survival and performance.
Changing Recommendations Over Time
In Calf Note #13 (1997), it was suggested that colostrum could be refrigerated for up to one week. At the time, that recommendation reflected the knowledge available.
However, research over the past two decades has clarified that such extended refrigeration allows unacceptable bacterial growth.
More recent guidance — such as Calf Note #215 (2020) — correctly recommends:
- Refrigeration for no more than 1 day
- Otherwise, freeze colostrum promptly
Science evolves. Good management evolves with it.
What Should Farms Do?
If colostrum will not be fed within a few hours:
Acceptable Options
- Refrigerate no more than 24 hours
- Freeze promptly for longer storage
- Pasteurize before storage
- Use approved preservatives (e.g., potassium sorbate) when appropriate
A Simple Rule
Colostrum should be in one of two places:
- In the calf
- In the freezer
The refrigerator is only a short-term holding area — not a storage solution.
Practical Take-Home Messages
- Refrigeration slows but does not stop bacterial growth.
- By 24 hours, bacterial counts can exceed recommended limits.
- Never store colostrum in the refrigerator for more than one day unless pasteurized or treated.
- Freezing is the safest long-term storage method.
- Clean colostrum is critical for successful passive transfer.
Calves crave clean colostrum.
That first feeding is one of the most important management decisions on the farm. Protect it.