Dominique Graviou

Predicting in situ degradability of feed proteins in the rumen by two laboratory methods (solubility and enzymatic degradation)

Abstract Two techniques were investigated to find a laboratory method for the prediction of the in situ nitrogen degradation of concentrated feeds: a method using solubility in a buffer (phosphate buffer at pH 6.9) and an enzymatic technique (hydrolysis after 1 h ( DE 1 ) and after 24 h ( DE 24 ) by a protease extracted from Streptomyces griseus in a borate-phosphate buffer at pH 8). Ninety-seven samples of concentrated feeds, representing 26 single feeds and 49 commercial feed mixtures, were studied. Both methods allowed the same precision (residual standard deviation (RSD) ∼ 0.030) if the 26 single feeds were grouped in classes. In contrast, for feed mixtures, the prediction was very precise and much better with the enzymatic method (RSD = 0.025) than with the solubility method (RSD = 0.049). In the French digestible proteins in the intestine (PDI) system, the enzymatic method is used as a laboratory method for nitrogen evaluation.

Near infrared reflectance spectroscopy to predict energy value of compound feeds for swine and ruminants

Abstract Near infrared reflectance spectroscopy (NIRS) was compared with analytical methods for predicting chemical composition, digestibility and energy content of compound feeds for swine and ruminants. The study investigated numerous widely diversified feeds with known in vivo measurements (87 swine and 80 ruminant feeds). Accuracy of prediction of the energy values of swine and ruminant feeds using NIRS was slightly better than using empirical models from chemical composition or enzymatic methods. The two populations had to be modelled individually. Despite the need of a large number of samples for calibration, NIRS measurements are non-destructive, non-polluting and can be carried out during a short period of time. The most significant wavelengths selected by the step-up model for in vivo digestibility of swine and ruminant feeds lay in the range 1600–1700 nm and 2200 nm, respectively.

Characterisation of in situ degradation of lucerne proteins according to forage type (green forage, hay and silage) using gel electrophoresis

Abstract We compared the degradation of lucerne proteins in the rumen according to forage type (green forage, hay, silage) and to plant organ (stems and leaves). Four ruminally fistulated sheep were used. They were fed the same forage as that placed in the nylon bags. Forages were incubated in nylon bags at eight different times (0–48 h) in the rumen. Proteins were extracted, and separated by sodium dodecylsulphate-polyacrylamide gel electrophoresis. The theoretical nitrogen degradabilities (Deg) were similar between forages (83.5 for hay to 89.3 for silage treated with formic acid). The main forage protein, ribulose 1-5-diphosphate carboxylase (rubisco), was degraded rapidly in the rumen for fresh forage and hay. Little rubisco was found in stems and degradation apparently was already complete in the silo for silages. Proteins of chloroplast membranes resisted breakdown during early fermentation and completely disappeared at 48 h for all the forages.

Comparison between the mechanism of protein degradation of two cereals by enzymatic and in situ methods, using gel electrophoresis

Abstract Protein degradation of two cereals (wheat and maize) was studied by two different methods, a laboratory method using a proteolytic bacterial enzyme extracted from Streptomyces griseus and an in situ method. Results were very similar: 73% and 76% degradation for wheat and 38% and 41% degradation for maize with enzymatic and in situ incubation, respectively. Two separation procedures, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and fractionation procedures by precipitation/redissolution techniques were used to study the degradation of protein components after enzymatic and in situ incubation. Wheat storage proteins (gliadins, glutenins) were degraded more rapidly than those of maize (zein and glutelins). The electrophoretic profiles showed that protein components were less degraded after enzymatic than in situ incubation. Wheat protein components (glutelins) were not completely degraded 24 h after enzymatic incubation but were completely degraded after in situ incubation; in contrast, maize protein components were not degraded completely at 24 h neither after enzymatic nor in situ degradation. These observations agree with the results of separation procedures. Among the solubilized forms of nitrogen in the supernatant after enzymatic hydrolysis (ammonia, α amino nitrogen, protein, peptides), protein and peptides were in large concentration, and after 8 h of incubation, proteins were degraded more to peptides than to ammonia or α amino nitrogen.

Degradation in the rumen of proteins of 2 legumes: soybean meal and field pea

Ruminal protein degradation of soybean meal and field pea were compared using 2 analytical methods: in situ and a laboratory analysis with a proteolytic enzyme extracted from Streptomyces griseus. The degradation of total nitrogen in nylon bags of the feeds was measured between 0 and 48 h in the rumen of 2 cows (theoretical degradability: 70.0% for soybean meal and 94.7% for field pea). Electrophoresis of proteins of feeds and in situ residues, in sodium dodecyl sulfate-polyacrylamide gel (SDS-PAGE) showed that both species have the same type of proteins (7S and 11S) which were degraded in a similar manner in the rumen. The 7S fraction was degraded rapidly whereas the 11S fraction was more resistant. The electrophoretic profiles showed that protein components were less degraded after enzymatic than in situ degradation. In the supernatant after enzymatic hydrolysis, protein and peptides were found in large concentrations and alpha-amino nitrogen and ammonia in low concentrations. It was difficult to simulate the in vitro activity of enzyme complexes in the rumen and the results must be confirmed by direct measurement of the rumen liquid.

Estimation of organic matter digestibility of whole maize plants by laboratory methods

Abstract Relationships between organic matter digestibility (OMD, %) and a range of laboratory measurements have been developed on 43 samples of whole maize plants in trial 1, in 1967 and 1968 and on 118 samples in trial 2, in 1987 and 1988 from three locations in France. Laboratory measurements included two chemical techniques (Weende crude fibre and van Soest methods), one biological technique (in vitro digestibility) and one enzymatic technique (pepsin-cellulase method). Age after flowering and dry matter content were the two parameters best correlated with OMD. The residual standard deviation (RSD) of the prediction was 1.54, taking into account a significant interaction of location on the slope for age and a location of year effect on the interception of the Y axis. As age is not always known in laboratory analysis, it was not included in the predicting equation. All the laboratory techniques allowed the same prediction (RSD about 2 points for 118 samples) but the relationships were significantly affected by year and location. In contrast, OMD is closely correlated with indigestible cell wall content (RSD = 0.53 for 55 samples studied at Clermont-Ferrand). It is concluded that OMD could be better predicted by methods based on in vitro digestibility or pepsin-cellulase digestibility for traditional forages than for whole plant maize.