A study using 4 ruminally cannulated Holstein cows was conducted to evaluate the degradability of maize silage and alfalfa haylage by different ruminal incubation orders. Maize silage and alfalfa haylage samples were dried and ground to pass through a 2.5-mm screen. All nylon bags containing feed samples for each cow were either placed in rumen simultaneously (OI) or removed from rumen simultaneously (OII). Samples were incubated in the rumen for 2, 6, 12, 24, 36, 48, and 72 h. For maize silage, OI had higher neutral detergent fiber (NDF) and acid detergent fiber (ADF) degradability at 6 h and 12 h (P < 0.05) compared with OII. Contrarily, slowly degraded fraction (b) of OI was significantly lower than that of OII (P < 0.05). For alfalfa haylage, different ruminal incubation orders had significant effect (P < 0.05) on the NDF degradability at 6 h and 12 h, constant rate of slowly NDF degraded fraction (K_d), and rapidly ADF degraded fraction (a) (Table 1). Overall, the effects of different ruminal incubation orders concentrated during first 12 h of incubation period, but did not affect ruminally degradable part. Table 1. Degradability and degradation variations of NDF and ADF of maize silage and alfalfa haylage incubated in situ in different ruminal incubation orders¹

Item	Maize silage					Alfalfa haylage
OI	OII	t	P-value	OI	OII	t	P-value
NDF
2 h	7.14	5.59	0.98	0.39		3.70	5.59	−0.53	0.19
6 h	1.41a	6.23b	4.01	0.01		11.62b	7.75b	0.20	<0.01
12 h	17.92a	8.38b	4.03	0.01		21.31a	15.76b	0.10	0.05
a	1.84	−1.33	2.25	0.07		−0.52	0.96	−1.19	0.28
b	59.91b	81.87a	−4.16	0.01		38.20	51.02	−1.34	0.27
Kd	3.14	1.86	2.76	0.07		6.70a	3.70b	2.58	0.04
RDNDF	31.10	29.33	1.20	0.31		25.40	25.39	0.01	0.99
ADF
2 h	4.02	4.18	−0.12	0.91		0.61	2.63	−1.36	0.25
6 h	7.15a	3.65b	2.49	0.05		7.73	4.74	0.65	0.15
12 h	14.14a	7.34b	2.77	0.03		17.60	13.03	1.71	0.14
a	−1.49	−3.30	1.05	0.34		−5.04a	−1.94b	−3.65	0.02
b	65.25b	81.54a	−3.15	0.03		42.35	44.43	−1.23	0.27
Kd	2.84	2.00	2.00	0.14		6.21	4.17	1.82	0.13
RDADF	28.85	28.45	0.28	0.79		22.84	23.09	−0.16	0.88

^a,bMeans with different superscript letters with the same row represent a significant difference between treatments (P < 0.05). ¹OI = placed simultaneously, OII = removed simultaneously, t = t-test, a = soluble fraction, b = slowly degradable fraction, Kd = rate of slowly degradability fraction, RDNDF/RDADF = ruminally degradable NDF/ADF.