Dr. Arshad begins by reviewing the inclusion criteria in the meta-analysis he conducted. He wished only to look at studies where lysine was supplemented in a rumen-protected form. The meta-analysis did not include studies that infused lysine into the abomasum or intestine. In addition, only completely randomized design or randomized complete block design studies were included. Feed ingredients and chemical composition of diets for each experiment were run through NASEM to predict the metabolizable lysine content using the same model so all studies were on the same scale. (6:04)

The bioavailability of the different rumen-protected lysine products used in the studies ranged from 22 to 90 percent. If the paper's authors reported bioavailability values, they were used in the meta-analysis. If the paper did not provide bioavailability values, Dr. Arshad contacted authors or lysine product manufacturers to offer them. (13:53)

Dr. Arshad discusses the percentage of lysine as a percent of metabolizable protein in the diets as well as differences among the prediction of the flow of amino acids to the small intestine from NASEM, NRC, and CNCPS models. (16:45)

Around 40% of the meta-analysis dataset was from early lactation cows where rumen-protected lysine was supplemented starting from 20 days in milk. The rest of the dataset came from mid-lactation cows. The duration of lysine supplementation also varied. Cows supplemented with rumen-protected lysine for more than 70 days In early lactation produced 1.5 kilograms more milk than control cows. Mid-lactation cows supplemented for less than 70 days produced 0.8 kilograms more milk than control cows. Increasing lysine as a percentage of metabolizable protein linearly increased milk and component yield. (20:11)

During the transition period, cows not only experience negative energy balance but also negative protein balance, estimated at one kilogram of protein loss from skeletal muscle during that time. Plasma lysine starts to decrease around 21 days before calving but bounces back after seven days in milk. This suggests that lysine utilization by the mammary gland and other tissues is high during the prepartum period. Supplementing lysine before calving and during early lactation should improve the efficiency of protein synthesis and may explain the difference between early and mid-lactation responses observed in the meta-analysis. (24:10)

Lysine supplementation improved feed efficiency. Dr. Arshad discusses potential reasons for this and also points out that somatic cell counts were lower for lysine-supplemented cows, suggesting that this amino acid may be important for mammary gland health. He also discusses some of the interactions with methionine found in the meta-analysis. Dr. Zimmerman and Dr. Arshad also hypothesize about the mechanism of action of supplemental lysine increasing milk fat percentage. (30:44)

Dr. Arshad describes how he would design the next rumen-protected lysine study given what he learned from the different studies in the meta-analysis. In particular, he would like to see more work with primiparous cows, and dose-titration studies to pinpoint the optimal amount of lysine to supplement and to further explore the impact of lysine on immune function. (42:42)

The base diet and bioavailability of the rumen-protected lysine product are critical components to determine the supplementation rate for a particular group of cows. Dr. Arshad details the differences between this meta-analysis and previous meta-analyses regarding lysine supplementation. (46:40)

In closing, Dr. Zimmerman was excited to see this meta-analysis and it validated observations from the field. Dr. Weiss underlines the strict inclusion criteria and regression analysis as particularly strong points in the paper. Finally, Dr. Arshad reminds the audience that creating a balanced ration should include essential and non-essential amino acids. He again emphasizes the importance of having an understanding of the bioavailability of rumen-protected products before conducting research projects with them. Lastly, he identifies a research gap regarding lysine supplementation of primiparous cows, which make up 30-35% of herd dynamics. (52:43)

You can find this episode’s journal club paper from the Journal of Dairy Science here: https://www.journalofdairyscience.org/article/S0022-0302(24)00499-5/fulltext

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