Effects of ensiling on ruminal degradability and intestinal digestibility of Italian rye-grass

Abstract

The effective degradability (ED) and the intestinal effective digestibility (IED) of dry matter (DM) and crude protein (CP) of a green Italian rye-grass (GRG) crop and its silage (ERG) were determined using in situ and particle passage techniques on three wethers, cannulated in rumen and duodenum. Two rumen incubations with duplicate bags filled with 3 g of freeze-dried samples were performed for each feed at times of 0, 2, 4, 8, 16, 24, 48 and 72 h. On each incubation, one series of bags was used to determine rumen degradation and the other was freeze-dried and pooled for each incubation time. Then two sub-samples (0.2 g) were incubated into mobile nylon bags through the entire intestine of each animal. The microbial contamination of rumen incubated residues (determined with 15 N techniques) was fitted to an exponential function. The asymptotic values (m) for DM contamination showed that silage particle reached a greater colonisation (P=0.006) but with a slower rate of microbe accumulation (P=0.03). Values of m for CP also showed that the undegradable CP fraction was mainly of microbial Abbreviations: a, soluble fraction; ADF, acid detergent fibre; ADIN, acid detergent insoluble N; b, non-soluble degradable fraction; CP, crude protein; DM, dry matter; ED, effective degradability; ED p , effective degradability calculated using k p ; ED c,p , effective degradability calculated using k c and k p ; ERG, ensiled rye-grass; GRG, green rye-grass; IED, intestinal effective digestibility; k c , rate of particle comminution; k p , outflow rate from the rumen; NDF, neutral detergent fibre; NDIN, neutral detergent insoluble N; r, undegradable fraction; SAB, solid adherent bacteria; TAA, total analysed amino acids

Ruminal protein degradability of a range of tropical pastures

“…Such high Edg values have been reported previously for ryegrass varieties (e.g. González et al 2007). However, there are few reported Edg values for tropical forages of low CP content with which to compare our measurements.…”

In situ ruminal amino acid degradability of green and ensiled Italian rye-grass according to particle transit model and microbial contamination correction

“…Values of effective degradability were estimated considering only k p (ED p ), in accordance with Ørskov and McDonald (1979), or both k c and k p (ED cp ) as indicated by McDonald (cited by the Agricultural Research Council, 1984). These rates were determined in this experiment for the ensiled Italian ryegrass included in the diet labelled with europium and their values (mean ± SEM) were k p = 0.0497 ± 0.0113 and k c = 0.181 ± 0.0165 (per h; González et al, 2007). The corrected results of degradability were also used to establish the AA profile of the undegraded protein.…”

“…The microbial content of each individual AA in the incubated residues was calculated as the product of the microbial DM content of the residue and the AA concentration (on a DM basis) in SAB. Additional details on bag characteristics and management as well as on microbial contamination correction are shown in González et al (2007). The evolution with time of the non corrected and corrected disappearance values of AA from the incubated bags was described for each animal using the model exposed by Ørskov and McDonald (1979).…”

“…In addition, effective degradability estimates commonly consider only the fractional outflow rate of Livestock Science 123 (2009) 209-214 small particles from the rumen (k p ) but not that derived from the process of density increase and comminution of particles (k c ), which is necessary for them to reach the reticulum. A previous paper from this experiment (González et al, 2007) showed that jointly both limitations lead to a large error on the estimates of the undegraded protein, which increases with ensiling. In the present study, a sample of Italian rye-grass was used as a model of temperate grass to determine: i) the errors on the AA degradability estimates induced by not correcting for microbial contamination and by not using the k c rate and ii) the effects of ensiling on the AA degradability values as well as on the AA profile of the undegraded protein.…”

“…The animals were fed at 40 g DM/kg BW 0.75 with a mixed diet of ERG, corn silage and concentrate (1:1:1 on DM), distributed in six equal meals. The chemical composition and characteristics of both forages and the diet as well as the details of animal management are shown in a previous paper (González et al, 2007).…”