Evaluating the TMR stability of rumen protected lysine products.

The TMR stability of rumen-protected lysine (RPL) products has been previously investigated, albeit without a positive control, potentially introducing bias. The objective of this experiment was to evaluate the TMR stability of 6 RPL products using a modified technique that used an unprotected Lys treatment as a positive control. Triplicate Ziploc bags containing RPL (equivalent of 1 g of Lys), no RPL (negative control) or unprotected Lys-HCl (positive control; 1 g of Lys) mixed with 200 g of TMR (36% DM) were incubated from 0 to 24 h. At each time point, bag contents were transferred to strainer bags and soaked in 1 L of distilled water for 1 min to solubilize any free Lys released from the products. A sample of solution was filtered (0.45 μm) and stored frozen (−20°C) until analysis for free Lys content via cation exchange HPLC. The Lys content for samples containing RPL or unprotected Lys were corrected for background Lys measured in the negative control samples. Recovery of unprotected Lys was influenced by TMR exposure time and was not complete (85%, 54%, 50%, and 44% at 0, 6, 12, and 24 h, respectively). Thus, a correction factor was applied to samples containing RPL to account for unrecoverable Lys released from the products. Total Lys release was calculated for RPL. Data were analyzed using PROC MIXED of SAS. Means within an incubation time were separated using the Tukey adjustment. Products B and E were the least stable from 6 to 24 h of incubation. Products D and F lost the least amount of Lys at 6 and 12 h of exposure. Product F was the most stable at 24 h (Table 1). These findings highlight significant differences in TMR stability among RPL products and underscores the importance of using unprotected lysine as a positive control to account for incomplete recovery of released lysine.

Key Words: rumen-protected lysine, TMR, lysine