Our objective was to access effects of dietary forage and rumen undegradable protein (RUP) on intake and performance of growing heifers. Holstein heifers with mean 6.5 mo of age and 166 kg of body weight were randomly assigned to 4 groups of 8 and fed diets with 2 forages and 2 RUP levels in a 2 × 2 factorial design. Forage sources were cowpea (Vigna sinensis) or pangola grass (Digitaria decumbens) hay added at 250 g/kg dietary dry matter (DM). Diets contained 260 (RUP260) or 360 (RUP360) g RUP/kg crude protein (CP). Heifers were housed in individual metabolism cages. The trial lasted 10 wk: 2 wk for adaptation and 8 wk for data collection. Diets were formulated for 175-kg heifers at 0.8 kg/d of average daily gain (ADG). In wk 10, microbial protein synthesis (MPS) was estimated from urinary purine derivative excretion; apparent digestibility was estimated by total fecal collection. Fish meal or urea were fed to equalize dietary N and to produce contrasting RUP concentrations. Data were analyzed as a 2x2 factorial using the mixed methods of SAS; results are in Table 1. Replacing dietary pangola hay with cowpea hay increased (P < 0.05) intake of DM and CP, apparent digestibility of OM and NDF, and ADG. There were trends (P = 0.06) for increased NDF digestibility, ADG and feed conversion efficiency (FCE; g ADG/kg DMI) with increased dietary RUP; however, increasing RUP reduced MPS. No forage by RUP interactions were detected. Replacing dietary pangola hay with cowpea hay increased intake and digestibility and improved performance of growing Holstein heifers. Table 1 (Abstr. 233). Effect of dietary forage and RUP on intake and performance of dairy heifers

Item	Pangola hay			Cowpea hay		SEM	P-value
RUP260	RUP360	RUP260	RUP360	Forage	RUP	Forage × RUP
DMI, kg/d	6.88b	7.00b		7.39a	7.36a	0.073	<0.01	0.54	0.33
CP intake, kg/d	0.89b	0.90b		0.95a	0.95a	0.007	<0.01	0.20	0.71
OM digestibility, %	65.5c	67.6bc		70.6a	69.7ab	0.97	<0.01	0.56	0.13
NDF digestibility, %	54.2b	57.6ab		58.7a	60.8a	1.37	0.01	0.06	0.64
MPS, g/d	568ab	476bc		615a	445c	41.3	0.84	<0.01	0.36
ADG, g/d	785b	831b		845ab	956a	39.2	0.03	0.06	0.41
FCE, g/kg DM	114b	118ab		115b	130a	5.0	0.26	0.06	0.29

^abcMeans with different superscripts differ (P < 0.05).