Table 6.

Effect of supplementing ruminally protected lysine (LYS), arginine (ARG), or their combination on serum amino acid concentration of feedlot steers at slaughter

	Treatment1,2					P-value
Amino acids, mg/mL	CON	ARG	LYS	LYS + ARG	SEM3	ARG	LYS	LYS × ARG
Alanine	22.10	22.40	20.33	20.70	1.183	0.78	0.15	0.53
Arginine	61.02	56.72	54.58	57.28	2.717	0.77	0.29	0.42
Asparagine	0.96	1.05	0.84	0.92	0.054	0.12	0.03	0.07
Aspartate	2.00	2.22	2.94	1.81	0.863	0.60	0.76	0.80
Cystine	5.70	7.80	6.70	6.42	0.782	0.25	0.81	0.31
Glutamine	18.52	19.16	18.32	17.75	0.683	0.96	0.26	0.57
Glutamate	3.19	3.24	3.28	3.25	0.755	0.99	0.95	0.99
Glycine	15.21	14.03	13.79	14.06	0.996	0.65	0.49	0.75
Histidine	19.01	19.12	18.22	18.00	0.833	0.95	0.28	0.72
Isoleucine	14.57	14.98	13.52	14.34	0.725	0.40	0.25	0.55
Leucine	35.05	35.88	32.77	32.93	2.175	0.82	0.24	0.68
Lysine	17.15	18.40	17.43	16.29	1.519	0.97	0.55	0.80
Methionine	3.88	3.96	3.86	3.66	0.234	0.79	0.51	0.83
Phenylalanine	22.35	21.97	19.90	21.52	1.176	0.61	0.23	0.48
Proline	14.21	15.31	14.20	14.76	1.019	0.42	0.78	0.85
Serine	12.44	12.29	10.53	11.80	0.770	0.47	0.13	0.30
Threonine	2.28	2.26	2.19	2.25	0.115	0.86	0.67	0.95
Tryptophan	13.42	12.43	12.40	12.41	0.807	0.55	0.52	0.76
Tyrosine	26.47	29.11	26.40	23.66	1.967	0.98	0.17	0.30
Valine	66.80	70.85	66.86	65.25	3.711	0.74	0.46	0.74

¹Treatments were 1) a diet with no arginine or lysine supplementation (CON), 2) rumen-protected arginine (16% metabolizable arginine, Ajinomoto Heartland, Chicago, IL) top-dressed at 63 g/steer daily (ARG), 3) rumen-protected lysine (25% metabolizable lysine, AjiPro-L, Ajinomoto Heartland) top-dressed at 40 g/steer daily (LYS), and 4) a diet with both arginine and lysine top-dressed at 63 and 40 g/steer daily, respectively (ARG + LYS).

²Five pens/treatment; 4 steers/pen sampled.

³Standard error of the mean.