ARTICLE 70 FEED & ADDITIVE MAGAZINE October 2025 cow, but if we are using heat treated sources to get the protein to bypass the rumen, lysine digestibility may be compromised. Additionally, lysine is very hygroscopic, meaning it attracts water. For this reason, lysine is difficult to encapsulate to make it rumen protected and is particularly unstable in moist environments such as a total mixed ration (TMR). It is critical that any encapsulated lysine is well protected and stable in TMR. An analysis of TMR stability of different encapsulated lysine products (Figure 1) revealed substantial loss of stability in some encapsulated lysine products, meaning the encapsulation is not sufficient in TMR and lysine is released from the encapsulation and will be free lysine in the TMR. When the cow consumes this, any free lysine will be immediately degraded by the microbes in the rumen and will not be available for the cow herself. The most stable encapsulated lysine product was AminoShure™-XL, with 98% TMR stability at 12 hours and it was still 91% TMR stable at 24 hours in the TMR. For this reason, including a portion of the metabolizable lysine supply as RPL, such as AminoShure™-L (24.3% metabolizable lysine) or AminoShure™-XL (34.6% metabolizable lysine) is recommended. This provides a consistent and reliable source of metabolizable lysine. CONCLUSIONS Lysine has not had as much attention as methionine in dairy diets, but that does not mean it is less important when balancing rations. Based on all of these data, feeding RPL to dairy cows can be beneficial for increasing milk yield and milk fat yield, especially if started in early lactation. When reviewing rations in herds, it is important to not just look at methionine supply, but also lysine since these amino acids interact. Just balancing for one amino acid can cause the dairy to miss out on some production, especially milk fat and protein, and cause the cows to be less efficient. When trying to balance for lysine and methionine, keep in mind that the most consistent way to deliver metabolizable amino acids is in a rumen-protected form but this is not always the most cost-effective way. Feeding a combination of bypass proteins and RPAA is more economical for the dairy and ensures that lysine and methionine needs are met. It is also very important to take into account the TMR stability when choosing the RPL product that is best for your herd. About Dr. Laura Niehues Having obtained her Bachelor’s degree in Animal Science from University of Florida, Dr. Laura Niehues then went on to complete a Masters in Equine Nutrition from Kansas State University and a PhD in Dairy Cow Nutrition from University of Illinois. During her PhD, Niehues focused on amino acids during the transition period of dairy cows, specifically rumen-protected lysine. After completing her PhD, she worked as a Technical Services Manager for Novita, working specifically with bypass protein for dairy cows, and for Native Microbials working with rumen microbes and on farm technical support. Currently, Dr. Niehues is the Technical Services Specialist for the Eastern United States and Canada at Balchem. She greatly enjoys providing technical support for balancing for amino acids in modern dairy cow rations. Dr. Laura Niehues resides in the United States in Florida. TMR Stability of RP-Lys Products 100 90 80 70 60 50 40 30 20 10 0 TMR Incubation Time (hr) Lys Stability (%) AminoShure-XL A B C D E 0 6 12 18 24 Figure 1. Stability of encapsulated lysine products in TMR Source: Estes et al., 2024 C M Y CM MY CY CMY K
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