Rumen degradability and microbial contamination of fish meal and meat meal measured by the in situ technique

Abstract

Rumen degradation characteristics and effective degradability of six fish meals (FM) and five meat meals (MM) were measured in two trials by using nylon bag and rumen outflow rate techniques in rumen cannulated sheep. In trial 1, apparent degradation of crude protein (CP) of five FM and four MM samples from different processing plants were studied with three animals. In trial 2, microbial contamination in the incubated residues of one additional FM and MM sample was determined by continuous ${}^{15}\text{N}$ intraruminal infusion and using isolated solid associated bacteria as reference sample, with four animals. These values were used to correct the estimates of apparent degradation of dry matter (DM) and CP. During both trials, animals were fed at the same intake level (40 g DM Kg⁻¹ LW^−0.75) with 2:1 hay to concentrate diets. Crude protein content (on DM) and buffer CP solubility of the samples ranged from 61.5% to 68.2% and 5.4% to 14.3% for FM and from 52.3% to 66.7% and 9.9% to 22.7% for MM, respectively. Apparent CP degradability ranged from 18.2% to 34.9% and 41.1% to 60.4% in FM and MM, respectively. Degradability values of CP in FM were conditioned by a lag phase (range 3.5–20.7 h) which was inversely correlated with the in situ (r=−0.76) and buffer (r=−0.52) CP solubilities. Buffer CP solubility explained 81% of the CP degradability variation and can be used as a predictor of it. Changes of microbial contamination with incubation time of residues, expressed as percentages of DM and N, fitted well to a simple mono-exponential model. Contamination levels were always very low, with higher values for MM than for FM. The fractional rate of microbial accumulation was markedly higher in the MM than in the FM sample. No correction for microbial contamination decreases CP degradability estimates (P<0.001), but this error (0.82% and 1.11% for FM and MM) can be considered of low nutritional significance in both meals.

Introduction

The use of fish meal and meat meal in diets for ruminants with high production levels is based on their high contents of rumen escape protein and essential amino acids. However, the use of protein concentrates of animal origin could be limited by a possible reduction in the ruminal synthesis of microbial protein (Rooke and Armstrong, 1987; Zerbini et al., 1988; Titgemeyer et al., 1989; Hussein et al., 1991).

Information on rumen protein degradability of both meals shows large variations (Madsen and Hvelplund, 1985; Verité et al., 1987; Howie et al., 1996; Yoon et al., 1996), probably, because of differences in raw materials and processing. Therefore, the ability to predict degradability is very important.

Suitable predictions of protein degradability had been obtained for fish meal from protein solubility measures (Madsen and Hvelplund, 1985; Yoon et al., 1996), however, information concerning meat meal is more limited. Also, the knowledge about the colonization of these meals in situ by ruminal microorganisms, which could confound their degradative characteristics, is very limited (Mathers and Aitchison, 1981; Beckers et al., 1995).

The aims of this study were: (1) to extend the base of information concerning protein degradability and its prediction for fish meals and meat meals and (2) to measure the pattern of the microbial colonization of these feeds incubated in the rumen and its associated effect on the effective degradability.