C. Demarquilly

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.

Effect of ammonia and urea treatments on digestibility and nitrogen content of dehydrated lucerne

Dehydrated lucerne of low (L: 0.53), normal (N: 0.55) and high (H: 0.73) in vivo dry matter (DM) digestibility were treated with ammonia or urea to study the effects on in situ and pepsin-cellulase DM digestibilities, water solubility and nitrogen content (Experiments 1, 2, 4) and on cell wall composition and degradability (Experiment 3). (1) N lucerne was treated with 30 g NH3 kg−1 DM for 1 to 12 weeks at 30°C and 2 to 6 days at 80°C; (2) L, N and H lucerne were treated with increasing ammonia levels: 15 to 100 g kg−1 DM for 3 weeks at 30°C and 4 days at 80°C; (3) L, N and H lucerne were treated with 60 g NH3 kg−1 DM for 3 weeks at 30°C and 4 days at 80°C; (4) L, N and H lucerne were treated with 60 g urea kg−1 DM without addition of urease for 3 and 6 weeks at 30°C. All treatments were carried out at 40% humidity. In situ and pepsin-cellulase DM digestibilities increased significantly (P < 0.05) with the duration of treatment (up to 3 weeks at 30°C and 4 days at 80°C) and with the level of ammonia (P < 0.01) (up to 30 g kg−1 DM). The greatest improvements (similar at both temperatures) were for L, N and H of 7.3, 7.2 and 3.9 points for in situ and of 10.6, 11.3 and 6.3 points for cellulase digestibilities, respectively. Water solubility also increased with duration of treatment and level of ammonia (P < 0.01) and was greater at 80°C than at 30°C. Urea treatment significantly improved (P < 0.01) digestibilities and water solubility but the doubling of treatment duration had no influence. The degree of ureolysis was only 50 to 60%. Ammonia and urea treatments considerably increased (P < 0.01) nitrogen content. Treatment with 60 g NH3 kg−1 DM induced a decrease in ethanol insoluble residue content, which was significant (P < 0.01 for L and N, P < 0.05 for H) at 80°C but not at 30°C, and was greater for L and N than for H (about 12 and 5 points, respectively). This decrease was essentially due to solubilisation of hemicelluloses (− 15%) and uronic acids (− 26%). Thus, at 30°C, the chemical solubility of the cell wall was lower than at 80°C for the same total increase in microbial degradation. This result indicates that other phenomena are involved, such as an increase in cell wall porosity and consequently improved accessibility of cell wall polysaccharides to glycolytic enzymes.

Prediction of the energy values of compound feeds for ruminants

Abstract Estimation of the net energy value of compound feeds for ruminants is important for both the feed compounder and the farmer. It is thus necessary to predict these values with good accuracy and at a low cost. This study concerned 83 compound feeds which are as representative as possible of the variety generally in use. The range of their organic matter digestibility was 65–90%. Samples of the feeds were studied in vivo in France by INRA Theix (17) and Paris (18), in The Netherlands by IVVO at Lelystad (24) and in the UK by the Rowett Research Institute at Aberdeen (24). All laboratories measured organic matter (OM) and energy digestibility. In addition, urinary energy losses and methane losses were measured at Theix and the Rowett Institute. Cell wall (crude fibre and neutral detergent fibre), lignocellulose (acid detergent fibre), acid detergent lignin (ADL) and Christian lignin contents were determined as well as enzymatic degradability. The net energy value of compound feeds was calculated by a stepwise analytical procedure. At each step, the maximum amount of in vivo data was used, after their reliability had been checked. This approach led to the formulation of equations predicting the net energy content expressed in net energy value for milk (NE 1 ) or for meat production (NE mf ) with respective residual standard deviations varying from 0.350–0.446 MJ NE 1 kg −1 OM and from 0.455–0.547 MJ NE mf kg −1 OM according to the analytical criteria considered. The major interest of this study lies in the fact that numerous in vivo measurements were performed, that a large number of laboratory methods were used and that the compound feeds were representative of the variability generally in use at the present time.

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.

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.