Jocelyne Aufrere

Comparison of methods for predicting digestibility of feeds

Abstract Five techniques were investigated to find a laboratory method for the prediction of the in vivo digestibility of feeds and mixed feeds: two chemical techniques (Weende crude fibre and van Soest methods), one biological technique (in vitro digestibility) and two enzymatic techniques (digestion by pepsin-cellulase, normal or modified (HCl 0.1 N instead of 1 N)). The enzymatic degradability (Method B, HCl 0.1 N) allowed a more accurate prediction of the in vivo organic matter digestibility (OMD) of 24 feeds than the separate data of crude fibre, neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL) contents or in vitro digestibility. The selected equation obtained with the cellulase method could also be used for feed mixtures.

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.

In vivo and in situ measurements of the digestive characteristics of sainfoin in comparison with lucerne fed to sheep as fresh forages at two growth stages and as hay.

In vivo and in situ digestive characteristics of sainfoin (Onobrychis viciifolia L., a tannin-rich forage) and lucerne (Medicago sativa L., a tannin-free forage) were compared to evaluate the effects of condensed tannins (CT) and growth stage (vegetative v. early flowering) in experiment 1. In experiment 2, the hays of the two forages, harvested at early flowering, were compared. Ingestibility, organic matter digestibility (OMD) and nitrogen (N) retention were measured in sheep fed sainfoin and lucerne fresh forages and hays. The loss of dry matter (DM) and N from polyester bags suspended in the rumen, abomasum and small intestine was also measured using rumen fistulated sheep and other intestine fistulated sheep. Nitrogen content was lower in sainfoin than in lucerne. Content of CT in sainfoin decreased with growth stage (3.5 to 2.5 g CT/kg DM) and was lower for sainfoin hay (0.6 g CT/kg DM). Ingestibility and OMD did not differ between fresh-fed forage species. Total N tract digestibility in vivo was much lower for sainfoin than for lucerne fresh forages (mean value 0.540 v. 0.721, P < 0.001) and for sainfoin hay than lucerne hay (0.464 v. 0.683, P < 0.001). In both species, N digestibility was not altered by growth stage. The rumen degradation of N was lower in sainfoin than in lucerne, resulting in a lower proportion of N intake excreted in urine. The intestinal digestibility of sainfoin was also lower than that of lucerne, resulting in a higher N excretion in faeces. Hence the efficiency of N utilisation by sheep (ENr) was similar (mean value 0.205 and 0.199 g N retained/g N intake for fresh sainfoin and lucerne, respectively). The coefficient of N retention by the animal was higher for sainfoin at the vegetative stage than for all the other forages. Nitrogen degradability in the rumen determined by the nylon bag technique (DegN) was lower for sainfoin than for lucerne when forages were studied both fresh (mean value 0.608 and 0.818, respectively) and as hays (0.631 and 0.767). The efficiency of forage N digestion (ENd) was higher for sainfoin at the vegetative stage. Compared with lucerne, sainfoin greatly increased the in situ estimate of forage N escaping the rumen but decreased its intestinal digestibility.

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.

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.

Effects of condensed tannins in wrapped silage bales of sainfoin ( Onobrychis viciifolia ) on in vivo and in situ digestion in sheep

The objective of this study was to characterize the condensed tannins (CTs) in wrapped silage bales of sainfoin (Onobrychis viciifolia) and examine their potential action on in vivo and in situ digestive characteristics in sheep. Silage was made from sainfoin, cut at two phenological stages. The first phenological stage, at which silage was made, was from the first vegetation cycle at the end of flowering and the second stage silage was made from regrowth, 5 weeks after the first cut, but before flowering. The silages made from the two phenological stages were fed to 12 rumen-fistulated sheep in a crossover design. Of the 12 sheep, six received polyethylene glycol (PEG) to bind with and remove the effects of CT, whereas the other six were dosed with water. Organic matter digestibility, total-tract N digestibility and N (N) balance were measured over 6 days. Kinetic studies were performed on total N, ammonia N (NH3-N) and volatile fatty acids (VFAs) in rumen fluid before and 1.5, 3 and 6 h after feeding. The kinetics of degradation of dry matter and N from Dacron bags suspended in the rumen were also determined. Biological activity of CT (protein-binding capacity) and CT concentration were greater for the silage made from sainfoin at the early flowering stage. Total-tract N digestibility was increased by the addition of PEG (P < 0.001) to the sainfoin silage before flowering (P < 0.001). CTs decreased N excretion in urine (P < 0.05) and increased faecal N excretion (P < 0.001), but had no effect on body N retention, which is beneficial for the animal. Ruminal N degradability was smaller in the presence of active CT (P < 0.001) at both phenological stages; however, soluble N (P = 0.2060) and NH3-N (P = 0.5225) concentrations in rumen fluid remained unchanged. The results of this experiment indicate that CT in the sainfoin retain their ability to affect the nutritive value of preserved forage legumes.

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.

Mixing sainfoin and lucerne to improve the feed value of legumes fed to sheep by the effect of condensed tannins.

The aim of this study was to investigate whether the use of sainfoin-based condensed tannins (CT) enhances feed value when given with tannin-free legumes (lucerne) to sheep. The experiments were conducted with fresh sainfoin and lucerne harvested at two stages (vegetative stage as compared with early flowering) in the first growth cycle. Fresh sainfoin and lucerne forages were combined in ratios of 100 : 0, 75 : 25, 25 : 75 and 0 : 100 (denoted S100, S75, S25 and S0, respectively). Voluntary intake, organic matter digestibility (OMD) and nitrogen (N) retention were measured in sheep fed the different sainfoin and lucerne mixtures. Loss of dry matter (DM) and N from polyester bags suspended in the rumen, abomasum and small intestine (SI) was also measured using rumen-fistulated sheep and intestinally fistulated sheep. The CT content in sainfoin (S100) decreased with increasing percentage of lucerne in the mixture (mean value from 58 g/kg DM for S100 to 18 g/kg DM for S25) and with growth stage (S100: 64 to 52 g/kg DM). OMD did not differ between different sainfoin/lucerne mixture ratios. Sainfoin and lucerne had an associative effect (significant quadratic contrast) on voluntary intake, N intake, total-tract N digestibility, N in faeces and urine (g/g N intake) and N retained (g/g N intake). Compared with lucerne mixtures (S0 and S25), high-sainfoin-content mixtures (S100 and S75) increased the in situ estimates of forage N escaping from the rumen (from 0.162, 0.188 for S0 and S25 to 0.257, 0.287 for S75 and S100) but decreased forage N intestinal digestibility (from 0.496, 0.446 for S0 and S25 to 0.469, 0.335 for S75 and S100). The amount of forage N disappearing from the bags in the SI (per g forage N) was the highest for high-sainfoin mixtures (from 0.082, 0.108 for S100 and S75 to 0.056, 0.058 for S25 and S0, P < 0.001). Rumen juice total N (tN) and ammonia N (NH3-N) values were the lowest in the high-sainfoin diet (mean tN 0.166 mg/g in S100 as compared with 0.514 mg/g in S0; mean NH3-N 0.104 mg/g in S100 as compared with 0.333 mg/g in S0, P < 0.001).