This study aimed to evaluate the releasing rate of lysine from 3 rumen-protected lysine products (RPL) during storage in 2 total mixed rations (TMR) diets or water. Three commercial PRL products in Japan (A: AjiPro-L; B: FeedtechTM Bypass Lysine; C: LysiPearlTM) were used. Each RPL (2 g) was mixed with 1 kg each of 2 types of TMR (TMR 1: corn- and grass-silage based TMR as the major forage sources, 52.9% DM content; TMR 2: fermented TMR comprising rice whole crop silage, 58.6% DM content). The treated TMRs were stored in the plastic bags (6 replicates) at 20°C for 0, 1, 3, 6, 12, 24, and 48 h. TMRs without RPL were used as control samples. At each time point, the solubilized free Lys in the treated TMR was extracted with 1 L of ion-exchanged water containing 0.5% Arg as internal standard. Additionally, as a simplified method to evaluate Lys release from RPL, 2 g of RPL was stored in 20 mL ion-exchanged water at 20°C for 0, 1, 3, 6, 12, 24, and 48 h. After filtration (0.45 µm) of the extracted solutions, free Lys content in the extract was analyzed, and Lys release rate (LR, %) during storage in the TMR or water was calculated. Data were analyzed by ANOVA with mixed model. The results (Table 1) showed that all RPL exhibited increased LR over storage time for both TMRs and water treatments (P < 0.01). However, RPL by time interaction was observed (P < 0.01), the LR of the products B and C was greater than that of the product A for both TMRs and water treatments. Our results indicate that there is greater lysine loss from some RPLs into the TMR, and a simple LR test with water can be used to evaluate the stability of RPL in TMR. Table 1. Lysine release (%) of RPL stored in TMR or water with time

Trt	RPL	Store time (h)							SEM
0	1	3	6	12	24	48
TMR1	A	0.8	2.0c	2.4c	3.3c	3.8c	5.1b	7.1c	0.43
	B	0.4	7.0b	46.3a	47.0a	53.2a	50.0a	42.9b	0.43
	C	2.0	17.7a	28.0b	37.3b	45.0b	51.9a	54.4a	0.43
TMR2	A	1.4	1.7c	2.9c	2.9c	3.4c	4.2b	6.7c	0.43
	B	1.2	9.5b	52.1a	49.4a	51.8a	48.9a	46.6b	0.43
	C	2.0	17.4a	27.2b	25.9b	40.4b	46.2a	54.4a	0.43
Water	A	1.2	2.6 c	3.7 c	4.8 c	6.6 c	8.9 c	12.3c	0.39
	B	1.0	28.1a	63.7a	67.2a	76.5a	76.9a	74.5a	0.39
	C	0.8	11.6b	17.9b	41.9b	56.8b	58.1b	67.8b	0.39

^a–cValues in the same treatment and time with different superscripts are different (P < 0.05).