Table 3.

Effects of rumen-protected L-Arg (RP-Arg) supplementation or injected L-Arg-HCl on N intake and site of digestion and microbial efficiency in forage-fed steers

	Treatmentsa
Item	CON	Arg-INJ	Arg-RP180	Arg-RP360	SEM	P-value
Total N intake, g/d	94b	95b	106b	144c	18	0.009
N intake from hay	94.1	94.6	86.5	105.2	18.2	0.36
N intake from RP-Arg	0.0b	0.0b	19.6c	38.7d	0.2	<0.001
Duodenal N flow, g/d	90.9b	91.8b	95.7b	117.8c	11.7	0.02
Bacterial N flow	43.5	40.4	41.4	48.0	4.7	0.39
Apparent feed N flow	46.7b	51.9b	53.6b	69.6c	7.3	0.009
Ileal N flow, g/d	54.6b	59.0b,c	65.3c	78.3d	7.0	0.01
Fecal N output, g/d	36.2b	41.0b,c	38.9b,c	47.3c	4.7	0.09
N digestibility, % of intake
Apparent ruminal	−4.20b	1.35b	3.98b,c	16.44c	8.07	0.08
True ruminale	46.5	44.0	45.0	51.1	5.5	0.72
Apparent small intestinal	39.0	35.0	31.1	31.5	6.2	0.16
Apparent large intestinal	22.5	20.3	25.5	18.1	9.3	0.43
Apparent total tract	58.2b	56.7b	61.4c	65.5d	3.0	0.003
Microbial efficiency, g microbial N/kg OM truly fermentedf	10.5	8.6	12.3	10.4	1.0	0.10

^aTreatments included: ad libitum grass hay (CON), CON hay with 27-mg L-Arg-HCl/kg BW injected twice daily (54 mg/kg BW daily; Arg-INJ), CON hay with 90-mg rumen-protected L-Arg/kg BW supplemented twice daily (180 mg/kg BW daily; Arg-RP180), and CON hay with 180-mg rumen-protected L-Arg/kg BW supplemented twice daily (360 mg/kg BW daily; Arg-RP360).

^b,c,dMeans within a row without a common letter superscript differ (P < 0.05).

^eCorrected for N of bacterial origin.

^fCorrected for OM of bacterial origin.