In situ neutral detergent insoluble nitrogen as a method for measuring forage protein degradability.
A method of estimating the undegraded intake protein (UIP) concentration of forages was developed and validated with a series of in situ experiments. The hypothesis was that UIP calculated from in situ neutral detergent insoluble N (NDIN) is equal to total in situ N minus the microbial N that is estimated from purines (MN). The in situ disappearance rates of total in situ N (TN), MN, and NDIN were measured for six hay samples and two range masticate samples. Hypothetical rates of passage (2 or 5%/h) were used to calculate UIP (% of DM) for each N pool. Estimates of UIP from TN were higher (P = .0001) than those from either MN or NDIN, and MN estimates of UIP were similar (P = .48) to NDIN estimates. A low-N fiber source (solka floc) was incubated in situ for 8 h. Analysis of the residue detected purines before, but not after, neutral detergent extraction. Several in situ incubation (i.e., Dacron bag size and number of Dacron bags in a mesh bag) and neutral detergent extraction conditions were tested. None of the factors tested affected in situ NDIN disappearance (P > .05). The hypothesis that NDIN is completely digestible in the rumen was tested. Estimates of the extent of NDIN digestion were made using 96-h in situ incubations, and UIP was recalculated for the test samples. Mean in situ UIP concentration decreased upon recalculation (P = .05). In situ NDIN provides estimates of forage UIP that are equal to estimates from MN. Forage UIP estimates are less when extent of N degradation is estimated and included in the calculation.
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R A
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Department of Animal Science, University of Nebraska, Lincoln 68583-0908, USA.
Lardy
G P
GP
Grant
R J
RJ
Klopfenstein
T J
TJ
D000821:Animal Feed; D000822:Animal Husbandry / Q000379:methods*; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D003902:Detergents; D004044:Dietary Proteins / Q000378:metabolism*; D004063:Digestion; D066298:In Vitro Techniques; D009584:Nitrogen / Q000032:analysis*; D012995:Solubility
D003902:Detergents; D004044:Dietary Proteins; D009584:Nitrogen