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Who is this for?
This Technical Bulletin is essential reading for anyone making decisions about calf milk replacers. Whether you manage a dairy herd, rear beef calves or advise farmers on young stock nutrition, understanding the differences between skim and whey protein can help you choose the right product with confidence.
What this bulletin covers
This bulletin examines the science behind dairy protein sources used in calf Milk Replacer formulas, focusing on skim milk powder (which is high in casein) and whey protein concentrate. It draws on multiple peer-reviewed studies as well as trial work conducted at AFBI Hillsborough, Northern Ireland in 2019.
A common assumption in calf rearing is that skim-based milk replacers are superior because casein forms a clot in the abomasum. This bulletin challenges that view. The evidence reviewed here shows that the clotting effect of casein is not the fundamental factor in calf performance. What matters more is ingredient quality and how the milk replacer is processed.
Research basis: Multiple peer-reviewed studies plus a calf trial at AFBI Hillsborough, Northern Ireland (2019)
Calves studied (AFBI trial): 80 Holstein Friesian calves, birth to 10 weeks
Milk Replacer compositions tested: 66% skim, 44% skim, 22% skim and 0% skim (all whey protein concentrate)
Published: January 2020
Key takeaways
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1
Processing quality matters more than protein type. Both well-formulated skim and whey-based milk replacers deliver comparable calf growth and health. The clotting effect of casein in the abomasum is not required for optimal calf performance.
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2
Calves digest whey-based milk replacers as efficiently as skim-based ones. In the AFBI trial, body weight from birth to 70 days and daily live weight gain were not significantly different across milk replacers ranging from 66% skim to 0% skim.
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3
Not all whey is equal. Standard whey powder contains only 12.5-13% protein, while concentrated whey protein (CWP) contains around 35%. A Milk Replacer containing whey powder will not deliver the same protein level as one containing concentrated whey protein.
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4
Processing temperature is critical for whey quality. At 85°C, over 60% of whey proteins denature within 30 minutes. At 65°C, only 15% are affected. Low-temperature ultrafiltration retains valuable bioactive proteins including immunoglobulins and lactoferrin.
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5
Calf health was comparable across all skim levels. In the AFBI trial, there were no significant differences in the number of scour or respiratory episodes between groups, and average faecal scores remained below 2 throughout.
Key figures
3x
more whey protein in colostrum than whole milk, making whey the protein fraction most essential for early calf development
35%
protein content of concentrated whey protein, vs 12.5–13% in standard whey powder
60%+
of whey proteins denatured within 30 minutes at 85°C processing temperature
Frequently asked questions
- Is skim-based or whey-based milk replacer better for calves?
When properly formulated and processed, both skim and whey-based milk replacers can deliver comparable calf growth and health. The key factors are ingredient quality and processing method, not which protein source is used. Research shows that the clotting effect of casein in the abomasum is not required for optimal calf performance.
- What is the difference between whey powder and concentrated whey protein?
Standard whey powder contains only 12.5-13% protein, while concentrated whey protein (CWP) contains around 35%. This difference is significant as a Milk Replacer made with whey powder will deliver considerably less dairy protein per kilogram than one containing concentrated whey protein, even if both are described as whey-based.
- Does a calf need a clot to form in the abomasum for good digestion?
No. It was previously believed that abomasal clot formation, which occurs with casein-containing milk replacers, was necessary for good nutrient digestion. More recent research, including trials at AFBI Hillsborough, has shown that calves fed whey-only milk replacers with no clot formation achieve similar growth rates and digestibility scores to those fed skim-based products.
- Why does processing temperature matter for milk replacer quality?
High processing temperatures denature the bioactive proteins found in whey, including immunoglobulins and lactoferrin, which support calf immunity and development. At 85°C, over 60% of whey proteins are denatured within 30 minutes. Low-temperature ultrafiltration preserves a much higher proportion of these proteins in the finished milk formula.
- How can I tell if a milk replacer contains good quality whey protein?
Check how the whey is described on the label and ask your supplier about the processing method. Look for concentrated whey protein rather than standard whey powder and ask whether low-temperature processing is used. Products using high heat treatment will have lower levels of naturally occurring immunoglobulins, even if the finished protein percentage appears similar.
- Does the level of skim in a milk replacer affect clot strength?
Yes. Curd firmness decreases as the proportion of skim milk powder falls. Research has shown that at 20% skim, curd firmness drops to around 14g compared to 50g at 67% skim. However, as other research demonstrates, this weaker or absent clot does not appear to compromise calf performance when the Milk Replacer is otherwise well formulated.
Get the complete Technical Bulletin
Download the full bulletin for detailed data tables, digestibility research and guidance on evaluating milk replacer quality.
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