Table 6.

Nitrogen partitioning of dairy cows grazing grass, forb, and legume-based pastures in period 1 (April 29 to May 19) and period 2 (May 19 to June 6)

							P-values*
	Grass	Forb	Legume	Period 1	Period 2	SEM	Pas	Per	P × P
N intake, g/d	420c	467b	578a	460b	517a	20.9	0.01	0.01	0.21
Urine
N, %	0.33b	0.23c	0.39a	0.27b	0.36a	0.028	0.01	0.01	0.80
NH3, mM	2.34a	3.21b	3.10ab	2.47b	3.30a	0.18	0.01	0.01	0.23
Urea, mM	56.2bc	30.9c	116.3a	57.4	78.2	13.8	0.01	0.09	0.60
Creatinine, mM	2.43a	1.81b	1.80b	2.01	2.02	0.09	0.01	0.89	0.02
Urea:creatinine	24.5b	18.0b	67.0a	31.1	41.9	6.59	0.01	0.06	0.65
Allantoin, mM	14.7a	11.2b	11.6b	12.2	12.8	0.87	0.03	0.56	0.36
Uric acid, mM	1.39a	1.07b	1.22b	1.14b	1.31a	0.08	0.01	0.02	0.02
PD1, mM	15.9a	12.2b	12.9b	13.4	14.0	0.88	0.02	0.52	0.24
Allantoin:creatinine	6.17	6.62	6.66	6.27	6.70	0.24	0.31	0.14	0.40
PD:creatinine	6.69	7.25	7.36	6.83	7.37	0.25	0.17	0.09	0.52
N output2, g/d	154.3b	134.2b	228.8a	141.8b	203.0a	21.77	0.01	0.01	0.82
N output3, g/d	187.6b	131.5c	271.8a	178.5b	215.4a	11.90	0.01	0.01	0.28
Feces
N, %	2.1c	2.8a	2.6b	2.6a	2.5b	0.05	0.01	0.01	0.39
Ash, %	19.8a	20.6a	18.0b	19.9	19.0	0.66	0.01	0.14	0.49
DM, %	10.6b	10.8b	11.6a	11.0	11.0	0.24	0.01	0.88	0.01
Milk
MUN, mg/dL	11.5b	7.50c	17.4a	10.8b	13.4a	0.56	0.01	0.01	0.28
N output, g/d	111.2b	120.8a	123.4a	118.2	118.6	2.94	0.01	0.84	0.49
Blood plasma
Urea-N, mM	4.5b	2.8c	6.9a	4.4b	5.0a	0.32	0.01	0.05	0.12
N efficiency3, %	29.6b	32.5a	25.3c	30.1a	28.2b	0.62	0.01	0.01	0.28
N efficiency4, %	27.3a	25.9a	21.6b	26.3a	23.5b	1.43	0.01	0.05	0.17

²Estimated using urine creatinine concentration according to Pacheco et al. (2007).

³Estimated according to Nousiainen et al. (2004).

⁴Milk N efficiency was calculated as milk N ÷ N intake × 100.

^a–cMeans within a row and category with different superscripts differ (P < 0.05).

*Pas, pasture type; Per, period; P × P, pasture type and period interaction; SEM: standard error for interaction.