Whole milk versus milk replacer

Posted on August 4, 2023 in Animal health
By Lucas Mitchell, Ph.D., Vita Plus dairy calf and heifer specialist

We frequently compare whole milk and milk replacer when discussing dairy calf nutrition.  It is difficult to offer sound advice or make appropriate decisions on which liquid diet to offer calves unless we understand how they are different.  It also is critical for understanding the different challenges that may occur with each feeding program.

It’s my opinion that whole milk is as near the perfect food as we have available.  Momma cow gets it right by producing nutrient-packed milk for her calf.  That said, there can be some serious challenges to feeding whole milk and, in those situations, offering calves a high-quality milk replacer may be the best option for the producer and the calf.

Let’s start by evaluating Table 1 and noting some macro differences between whole milk and a couple milk replacer formulations.

Table 1. Average whole milk composition compared with two different milk replacers.
Whole milk Traditional 20/20 milk replacer Talon 25/25 milk replacer
Wet basis Dry basis Wet basis Wet basis
Water 87.1 0.0 3 3
Protein 3.2 24.8 20 25
Fat 4.0 31.0 20 25
Lactose 5.0 38.8 49 41
Ash 0.7 5.4 8 6
Total solids 12.9 100 97 97

To start, whole milk is usually going to be between 12.5% and 13% solids on-farm.  For this example, I’ve selected what I would expect from an average Holstein.  Lactose and ash are going to be consistent at 5% and 0.7%, respectively.  Protein should be in the 3.1% to 3.4% range and fat may be a bit more variable coming in between 3.7% and 4.4%.

To compare this to what we see in a bag of milk replacer, we need to convert those numbers from wet basis to dry basis.  To do this, simply select a component, like protein, at 3.2% and divide it by the total solids of 12.9% and then multiply by 100.

3.2/12.9 × 100 = 24.8% dry basis

While milk replacer is not completely dry coming out of the bag, it only contains 3% moisture, which allows for a fair comparison once whole milk components have been converted to dry basis.

A few key things to note with whole milk:
  • Fat is around 31% on dry basis, which is quite high compared with most milk replacers.
  • Some are concerned that elevated fat in milk replacers could negatively impact starter intake.  However, recent research indicates that concern may be overblown or counteracted by positive associations of increased fat on calf health.

One potential driver of improved health may be lower osmolality of milk replacer with increased fat content.  This directly ties into the next observation.  Lactose and ash are low in whole milk, especially when compared with more traditional milk replacers.  This is important because the primary drivers of osmolality within milk and milk replacer are lactose and ash.

Increased osmolality is associated with impaired intestinal barrier function or “leaky gut.”  The osmolality of milk is approximately 290 mOsm/L, while traditional milk replacer and Talon, mixed at 13% total solids, are approximately 420 mOsm/L and 368 mOsm/L, respectively.

Table 1 also demonstrates that not all milk replacers are created equal.  For example, Talon is close to whole milk for protein, lactose and ash content.  Most importantly, lactose and ash are reduced in Talon compared with a traditional 20/20 milk replacer.

What’s in whole milk?
  • Water constitutes 87% to 87.5% of whole milk.
  • Protein makes up approximately 24.5% to 27% of the solids in whole milk on a dry basis.  Whole milk has two primary proteins.  Casein constitutes about 80% of the protein while whey accounts for the remaining 20%.  When a calf consumes whole milk, the casein will clot in the abomasum and form a curd that will be more slowly digested.  Whey, on the other hand, will pass through with the water to the small intestine.
  • Fat makes up about 30% to 34% of the solids in whole milk on a dry basis.  The fats consist primarily of triglycerides and are packaged by the cow into milk fat globules that are well digested by the calf.
  • Lactose makes up 39% to 40% of the solids in whole milk on a dry basis.  This is the primary carbohydrate in whole milk.  Lactose is a disaccharide consisting of one glucose and one galactose.  It is a good energy source for the young calf.
  • Ash makes up 5.4% to 5.6% of the solids in whole milk on a dry basis.  Ash consists of various macro (Ca, P, K, S, Na and Mg) and micro (Zn, Cu, Mn, Fe and Se) minerals, which are critical for immune function and structural growth in the young calf.
What’s in milk replacer?
  • Protein makes up between 20% and 28% of the solids in milk replacer.
  • Whey protein concentrate (WPC) and skim milk:  The primary source of protein used in milk replacer is WPC, which is made from liquid whey, a byproduct of cheese manufacturing.  Another common protein source is skim milk.  Skim milk contains casein and whey proteins.  This should result in some amount of curd formation within a calf’s abomasum when consuming a milk replacer with this ingredient.  Research does not indicate that one of these protein sources results in superior performance over the other.  Using some blend of the two tends to be preferred so that some abomasal curd is formed and there is ingredient flexibility.  This may allow for pricing advantages if markets shake up.
  • Dried animal plasma is another excellent source of protein that may be used in milk replacer.  Outside of dairy ingredients, plasma may be the most researched milk replacer ingredient.  It is consistently shown to help combat scours, due to the small amounts of IgG that it brings into the formula.
  • Vegetable proteins from soy or wheat also may be used in some milk replacers.  These proteins help lower cost, but may be best used when fed to calves older than three weeks of age.  Calves younger than three weeks of age do not digest vegetable proteins as well as milk proteins or plasma and, as a result, tend to scour more.
  • Fat may range between 14% and 25% of the solids in milk replacer.
  • Protein-encapsulated fat (PEF):  While whole milk contains fat packaged into milk fat globules, milk replacer fat is packaged into PEF.  The primary fat sources used are lard, tallow, palm oil and coconut oil.  Lard, tallow, and palm oil are used and bring a lot of C16 and longer-chain fats to the formula.
  • Coconut oil is used in smaller amounts to bring more medium-chain fatty acids to make the fatty acid profile of milk replacer more like that of whole milk.  These fats are melted down, blended, and homogenized with small amounts of protein and emulsifiers to form the PEF, which is then spray-dried.  The medium chain fatty acids from coconut oil also have antimicrobial properties.
  • Lactose makes up between 40% and 50% of the solids in milk replacer.  While lactose is an excellent source of energy for calves, milk replacers with levels of lactose on the higher side of this range run the risk of upsetting the digestive track.  Lactose is a primary driver of osmolality.  Calves may experience more loose manure if the osmolality is too high.  Furthermore, lactose reaching the small intestine may cause disruption by being digested in the hind gut and shifting the microbial ecology to a narrower population that is more tolerant of low pH.  The negative impacts of high-lactose formulas seem to decrease as calves age.
  • Ash makes up between 6% and 10% of the solids in milk replacer.  It is higher than in whole milk due to the byproducts that are used in milk replacer manufacturing.  As with whole milk, macro and micro minerals are contained within this fraction.
  • Milk replacers also may contain various specialized additives like direct-fed microbials, yeast products, mannan oligosaccharides (MOS), essential oils, coccidia control, fly control, flavors and other functional ingredients.
What’s best for your calves?  As always, the answer is “it depends.”  While whole milk is close to nature’s perfect food, we must remember that whole milk and waste milk are not the same.  Whenever we collect and store milk to feed calves, we are introducing the risk of bacterial contamination.  If we can collect, pasteurize and feed whole milk without excessive bacterial growth, it can be a great option.  However, in situations where producers want simplicity and consistency, or when milk price is high and we want to sell as much as possible, the right milk replacer can be an equally good option.

Category: Animal health
Calf and heifer nutrition
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