NDF degradability of hays measured in situ and in vitro

• Published in: Animal feed science and technology Vol. 104; no. 1; pp. 201 - 208
• Main Authors: Spanghero, M, Boccalon, S, Gracco, L, Gruber, L
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 20-02-2003; Elsevier
• Subjects: Biological and medical sciences; Degradability; Fundamental and applied biological sciences. Psychology; Hays; In situ; In vitro; Intestine. Mesentery; NDF; Vertebrates: digestive system; NDF; Hays; Degradability; d NDF; In vitro; In situ; Animal feeding; Ruminant animal; Digestive system; Fodder; Rumen; Digestion; Fermentation; Straw; Dietary fiber; Comparative study; Digestibility
• ISSN: 0377-8401; 1873-2216
• DOI: 10.1016/S0377-8401(02)00327-9

The NDF degradability (
d
NDF) of hays measured by an in situ method (nylon bag technique) was compared with in vitro fermentation, using the Daisy
II incubator (Ankom
®, Tech. Co., Fairport, NY, USA). Eighteen hays were produced from mountain areas (about 700 m.s.l.) from plots subjected to different cutting frequencies (two to four cuts per season) and types of N fertilisation (slurry and slurry plus mineral). Hay samples from each cut were incubated (in situ) in the rumens of three cows (incubation times: 2, 4, 8, 16, 24, 48 and 72
h; sample weight: 15
mg/cm
2 of free bag area) or inserted (in vitro) into three different digestion jars (jar volume: 2
l; bag size
5
cm×3
cm; sample weight: 250
mg per bag) that were placed into the Daisy
II incubator for 48
h.
The forages showed large variation in effective
d
NDF (assumed rumen turn over rate: 3% per hour) which ranged from 38 to 43% for hays with two cuts to 58–65% for the hays with four cuts per season. The
d
NDF obtained in situ (
Y, effective) and in vitro (
X, after 48
h of incubation) were highly correlated (
P<0.01) and the regression equation was
Y=0.74(±0.05)X+6.39(±2.90),
n=18,
S.D.=±1.96,
r
2=0.94.
The variability (coefficient of variation, CV) of the in vitro measurements (among jar repeatability) was 2.8%, which is close to that generally found for some chemical analyses of feedstuffs and lower than that obtained for the in situ measures (among cow repeatability, CV: 3.7%). The Daisy
II incubator produces repeatable in vitro
d
NDF data which are highly related to those obtainable with the reference in situ procedure.