Table 4.

Effect of physical form and urea treatment of rice straw on N balance, urinary purine derivatives and MCP synthesis in dairy steers

Item	RS		UTRS		SEM	Significance1
	LFR	CHR	LFR	CHR		U	P	U×P
N utilization (g/d)
N intake	43.9	43.8	71.5	73.1	1.31	**	ns	ns
N excretion
Fecal	27.4	30.1	36.4	40.0	1.24	*	ns	ns
Urinary	7.6	5.5	21.1	19.0	1.02	**	ns	ns
N balance
Absorption	16.5	13.7	35.2	33.2	0.69	**	ns	ns
Retention	8.9	11.0	14.1	14.2	0.84	*	ns	ns
Urinary purine derivatives (mmol/d)
Allantoin excretion	63.2	73.2	76.9	85.3	2.22	*	*	ns
Allantoin absorption	76.1	85.6	88.3	95.4	1.84	*	*	ns
MCP (g/d)	345.9	389.2	401.2	433.7	8.37	*	*	ns
EMNS (g/kg OMDRg)	18.9	18.4	21.9	21.6	0.30	*	ns	ns

¹U = Untreated rice straw vs urea-treated (3%) rice straw, P = long form rice straw vs chopped (4 cm) rice straw, U×P roughage source and physical form interaction.

^*p<0.05,

^**p<0.01, ns = Non-significant (p>0.05).