In vivo and in situ measurements of forage protein degradation in beef cattle.

Abstract

In vivo and in situ protein degradation measurements were compared using alfalfa (2.62% N) and prairie hay (.88% N) fed to six cannulated cows in a two-period crossover experiment. Additionally, two in situ procedures were evaluated: in P1 samples were ruminally incubated in cows fed the same forage as incubated; in P2 samples were incubated in the rumens of two steers fed a "standard" brome hay (1.38% N). Duplicate bags were incubated for 0, 2, 6, 10, 16, 24, 48, and 72 h. Protein degradability was estimated using residual N from all incubation times fit to a nonlinear, least squares model (full time-series), from the 16-h incubation alone (single-point) and from a combination of the 0-h and 16-h values (double-point). Protein degradability estimates from in vivo, in situ P1, in situ P2, single-point P1 and P2, and double-point P1 and P2 were 83.4 +/- 4.3, 91.5 +/- .6, 87.2 +/- .6, 94.0 +/- .2, 92.4 +/- .8, 90.4 +/- .4, and 88.3 +/- .5, respectively, for alfalfa, and 55.5 +/- 3.5, 58.3 +/- 1.3, 57.2 +/- .4, 50.0 +/- 1.7, 52.0 +/- 2.2, 55.5 +/- 2.1, and 60.0 +/- 2.3, respectively, for prairie hay. Although relatively large differences in rates of degradation and sizes of protein fractions were measured between P1 and P2, differences between procedures for protein degradability estimates were small relative to errors of in vivo measurement. Furthermore, differences in protein degradation using single-point values as compared with full time-series analysis were overcome with the double-point approach.

In situ rumen degradation kinetics as affected by type of pasture and date of harvest

“…Dacron bags (n: 144) were incubated in the rumen for 2, 4, 8, 12, 24 and 48 h using a "gradual in/ all out" sequence, with duplicate bags at each time for each forage sample. All bags were placed within three polyester laundry bags (30 × 40 cm) to ensure similar location within the rumen and to facilitate location for removal (Vanzant et al, 1996). After removal from the rumen, dacron bags containing forage residues were washed under running cold water until no further color appeared, frozen at -20 ºC for 24 h to stop fermentative activity and rinsed in a domestic washing machine with cold tap water for 30 minutes.…”

Effects of spontaneous heating on fiber composition, fiber digestibility, and in situ disappearance kinetics of neutral detergent fiber for alfalfa-orchardgrass hays

“…For all selected hays, additional bags were preincubated and rinsed without ruminal incubation, creating a 0-h incubation time. After machine rinsing, residues were dried at 50°C, equilibrated with the atmosphere in the laboratory (Vanzant et al, 1996), and then weighed to determine residual DM. To determine NDF disappearance kinetics, 0.5-g subsamples of the air-equilibrated residues from each Dacron bag were digested in NDF solution using the Ankom procedures described previously; no heat-stable α-amylase or sodium sulfite were included in the neutral-detergent solution.…”

In vitro determination of ruminal dry matter and cell wall degradation, and production of fermentation end-products of various by-products

“…The prediction of the extent of degradability using an in situ method has advantages and is now widely used and reported [16,38]. This technique proposed by Ørskov et al [26] can be used for the prediction of dry matter intake, digestible dry matter intake and animal performance.…”