Protein Sources from Dairy
The composition of a milk product must always be tailored to the animal’s needs and digestive capacity. In this context, the quality and level of protein are crucial. Protein in milk products provides the essential amino acids needed to build body proteins, such as those found in organs and muscles. The crude protein content in most rearing milk for calves ranges between 19% and 24%. However, this percentage alone does not provide much information about the protein quality. How well the animal can utilize this protein depends on its digestibility, amino acid profile, and the available energy from fats and carbohydrates. The apparent digestibility of the protein in a well-formulated milk product is over 90%. For decades, Denkavit has been studying the digestibility of both dairy and plant-based raw materials for calves and lambs. But what protein sources are we talking about? Figure 1 illustrates the most important dairy raw materials and their relationships to each other.
Depending on the quality, digestibility, and level of non-protein nitrogen (NPN), a raw material may be more or less suitable for a high-grade milk product. Ingredients such as skimmed milk powder (SMP) and whey protein concentrate (WPC) are high-quality protein sources with a similar amino acid profile and low NPN content. Both are often used in products like infant formula and are also highly suitable for milk products for young animals.
Whey Ingredients
In the whey ingredient segment, there are far more dairy options than just WPC. These ingredients vary significantly in protein, ash, and NPN content, and even more so in quality and digestibility. Due to this wide variation in raw material streams, knowledge of the different production processes and their effects on the animal is crucial.
Whey permeate is a byproduct of WPC production. Compared to whey permeate, WPC contains more protein and relatively less NPN. When using whey permeate as a raw material for ruminants, it’s important to balance the nutrient levels with other ingredients. Due to its higher ash content, whey permeate has a less appealing taste. This is especially important when used for young lambs and calves right after colostrum. It’s difficult to determine from a label whether a milk product contains high-quality ingredients or cheaper whey types, as whey ingredients are often all listed as whey powder. However, there can be significant differences in the type of whey ingredient used, affecting both digestion and quality. Ultimately, the animals themselves will indicate whether a milk product is good or not—something that cannot be determined just by reading a label.
SMP Ingredients
There are also different streams available within the SMP segment, which vary in origin and quality. One of the most important quality characteristics of SMP is its coagulation quality. The majority of the protein in SMP, casein, can only be properly digested in the duodenum after coagulation in the abomasum. When milk is consumed, it bypasses the fore-stomachs and goes directly into the abomasum. Coagulation occurs almost immediately due to the influence of acid and proteases.
One of these proteases is rennin, which is active at a pH between 5 and 6 and is crucial for the formation of the “cheese” (Figure 2). This enzymatic process cleaves glycomacropeptide from the casein molecules, causing them to precipitate as curd instead of remaining in solution as micellar protein. If the SMP does not coagulate properly in the abomasum, intact, undigested casein may reach the small intestines.
This situation increases the risk of nutrition-related digestive disturbances, particularly in the animal’s first few weeks of life. Whether the SMP coagulates properly depends on its quality and production process. Before SMP can be used in milk products, it must first be tested for coagulation in our laboratory (Figure 3).
Coagulation Process
There are, of course, several factors that influence the coagulation process in the animal’s abomasum. The percentage of SMP in the product, milk concentration, and infection pressure in the barn also play significant roles. Therefore, it’s essential to always use a high-quality product with the correct preparation procedure and maintain proper management of your animals to prevent issues, such as poor coagulation.
In addition to dairy ingredients for protein, plant-based raw materials are also used in milk products as protein sources. In a subsequent article, we invite you to learn more about this interesting group of ingredients.
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