Non-forage fiber feeds are generally highly digestible, however, most calculations of undegradability are made from static calculations based on Chandler et al. (1980) or Weiss et al. (1992). The objective of this study was to analyze the extent of aNDFom degradation in non-forage fiber feeds, to obtain the undegradable aNDFom (uNDF). Samples of 12 feeds (citrus pulp, beet pulp, wheat middlings, soy hulls, corn gluten meal, corn gluten feed, wheat distillers, corn ethanol distillers, flaked corn, rice hulls, soybean meal, and canola meal) were collected, each from 2 providers, and analyzed in duplicate in 3 separate batches for the extent of NDF digestion using the in vitro technique. Samples, 0.5 g, were weighed into Erlenmeyer flasks and 40 ml of Goering and Van Soest (1970) buffer was added to each flask under continuous CO2, and incubated in a water bath at 39°C. After 2 h of incubation, 10 mL of mixed rumen fluid from 2 lactating cattle were added to each flask and continuous CO2 was maintained throughout the fermentation. Fermentations were conducted for 96, 120, and 240 h consistent with previous data from Raffrenato (2011). Residues were filtered on a glass microfiber filter (934-AH, Whataman) with a 1.5 µm pore size to enhance residue recovery. To analyze changes in uNDF the residues were compared with a t-test in JMP. For non-forage aNDFom the uNDF was obtained at 120h with the exception of citrus pulp where residues continued to digest out to 240 h compared with 120 h residues (P-value = 0.002). Table 1. The aNDFom (%NDF) residues of feeds after 96, 120, and 240 h of fermentation

Item	Time (h)			SEM	P-value
96	120	240
Beet Pulp	22a	19b	17b	0.01	0.004
Canola Meal	40	41	41	0.01	0.79
Citrus Pulp	21a	20a	16b	0.01	0.002
Corn Gluten Feed	16a	14ab	13b	0.01	0.028
Corn Distiller	16	16	14	0.01	0.50
Corn Germ	34	29	27	0.03	0.74
Flaked Corn	14	14	12	0.02	0.73
Rice Hulls	94	93	93	0.01	0.61
Soybean Meal	11	9	9	0.01	0.95
Soy Hulls	10a	9ab	8b	0.01	0.022
Wheat Distiller	28	26	25	0.01	0.20
Wheat Middling	36a	31b	30b	0.01	0.001

^a,bValues with different letters are statistically different.