Table 5.

Effect of supplementing ruminally protected lysine (LYS), arginine (ARG), or their combination on serum amino acid concentration of feedlot steers at 87 d

	Treatment1,2					P-value
Amino acids, mg/mL	CON	ARG	LYS	LYS +ARG	SEM3	ARG	LYS	LYS × ARG
Alanine	30.43	32.05	32.61	29.74	1.183	0.60	0.96	0.29
Arginine	58.36	56.59	57.14	53.69	2.717	0.34	0.45	0.66
Asparagine	0.51	0.42	0.42	0.42	0.054	0.43	0.37	0.52
Aspartate	2.95	2.51	4.95	2.90	0.863	0.16	0.17	0.20
Cystine	6.34	6.37	6.08	6.99	0.782	0.55	0.82	0.87
Glutamine	13.22	12.65	12.36	12.28	0.683	0.65	0.38	0.77
Glutamate	8.81	5.83	8.17	6.52	0.755	0.09	0.18	0.19
Glycine	14.41	13.65	14.07	14.98	0.996	0.94	0.62	0.81
Histidine	18.06	18.66	17.64	17.15	0.833	0.94	0.25	0.62
Isoleucine	16.10	14.98	15.65	15.58	0.725	0.42	0.92	0.75
Leucine	39.76	39.69	39.62	39.53	2.175	0.97	0.95	0.99
Lysine	15.05	13.66	17.19	12.88	1.519	0.07	0.66	0.22
Methionine	4.53	4.60	4.77	4.44	0.234	0.58	0.85	0.79
Phenylalanine	19.55	18.87	20.38	19.04	1.176	0.40	0.67	0.80
Proline	18.78	20.07	21.31	19.10	1.019	0.88	0.30	0.18
Serine	12.52	12.52	11.48	12.46	0.770	0.53	0.48	0.73
Threonine	2.05	1.84	1.64	1.99	0.115	0.55	0.27	0.07
Tryptophan	11.90	12.13	13.61	12.87	0.807	0.76	0.14	0.45
Tyrosine	40.92	37.59	38.89	37.33	1.967	0.22	0.57	0.56
Valine	67.59	70.42	67.04	71.07	3.711	0.36	0.99	0.83

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.