Previous studies showed that diets with more than 15% field peas (FP; DM basis) resulted in reduced milk and milk protein yield in dairy cows. We hypothesize that decreased yields were caused by limited supplies of MP-Lys and MP-Met due to extensive degradation of FP RDP in the rumen. The objective of this study was to evaluate diets with 25% of FP supplemented with rumen-protected (RP) Lys (AjiPro-L) and Met (Smartamine-M) as a substitute for corn meal (CM) and soybean meal (SBM). Twelve multiparous and 4 primiparous lactating Holstein cows were blocked by DIM, milk yield and parity, and randomly assigned to 1 of 4 diets in a replicated 4 × 4 Latin square design. Diets were 35.5% corn silage, 15.5% grass-legume haylage, 5.9% roasted soybean, and: (1) 36% CM and 1.3% urea (3.59:1 MPLys:MPMet ratio; negative control: NC), (2) 29.7% CM, 9.8% SBM, and RPLys-Met (3.07:1 MPLys:MPMet ratio; positive control: PC), (3) 25% FP, 12.3% CM, and 2.4% SBM (3.88:1 MPLys:MPMet ratio; PEAS), and (4) 25% FP, 12.2% CM, 2.4% SBM, and RPLys-Met (3.13:1 MPLys:MPMet ratio; PEASAA). Data were analyzed using the MIXED procedure of SAS and Tukey adjustment for means separation (α = 0.05). All dietary treatments had 15.1% CP and 1.58 Mcal/kg. As expected, cows fed NC had decreased DMI, milk protein yield and total concentration of ruminal VFA and increased excretion of MUN. Cows fed NC and PEAS had decreased plasma concentration of Met. Feeding cows PC, and PEASAA mitigated these negative responses. Results showed that plasma Lys was higher for diets fed FP, suggesting that Met is the first limiting AA in FP-based diets. Table 1. Feeding field peas to dairy cows

Item	Diet				SEM	P-value
NC	PC	PEAS	PEASAA
DMI, kg/d	23.30b	24.96a	24.63a	25.00a	0.39	<0.01
Milk, kg/d	41.79	42.93	42.69	42.71	1.04	0.53
Milk fat, kg/d	1.40	1.41	1.45	1.49	0.04	0.09
Milk protein, kg/d	1.15b	1.25a	1.21ab	1.24a	0.03	<0.01
MUN, mg/dL	9.85c	7.93a	9.09b	8.77b	0.27	<0.01
Ruminal total VFA, mM	103.08c	113.23b	111.92b	120.92a	1.84	<0.01
Plasma Lys, mM	67.20b	69.94b	77.21a	76.97a	3.96	0.03
Plasma Met, mM	19.92c	27.71b	19.63c	31.89a	1.06	<0.01