Composition of free and adherent ruminal bacteria: inaccuracyof the microbial nutrient supply estimates obtained using freebacteria as reference samples and 15N as the marker

Previous studies have indicated that 15N enrichment of solid-associated bacteria (SAB) may be predicted from the same value in liquid-associated bacteria (LAB). The aims of this study were to confirm this and to measure the error in the nutrient supply from SAB, when LAB are used as the reference sample. For this purpose, the chemical and amino acid (AA) compositions of both the bacterial populations were studied in four experiments carried out on different groups of three rumen cannulated wethers. Diets (one in Experiments 1 and 4 and three in Experiments 2 and 3) had forage-to-concentrate ratios (dry matter (DM) basis) between 2 : 1 and 40 : 60, and were consumed at intake levels between 40 and 75 g DM/kg (BW) 0.75. The bacteria samples were isolated after continuous infusion of ( 15NH 4) 2SO 4 (40, 18, 30 and 25 mg 15N/day, in Experiments 1 to 4, respectively) for at least 14 days. In all experiments, SAB had consistently higher concentrations of organic matter (826 v. 716 g/kg DM, as average) and total lipids (192 v. 95 g/kg DM, as average) than LAB. Similar CP concentrations of both populations were observed, except a higher concentration in SAB than in LAB in Experiment 3. A consistent (in Experiment 4 only as tendency) higher AA-N/total N ratio (on average 17.5%) was observed in SAB than in LAB. The 15N enrichment in SAB was systematically lower than in LAB. On the basis of the results of all studies a close relationship was found between the 15N enrichment in SAB and LAB, which was shown irrespective of experiments. This relationship was established from Experiments 1 and 2 and the above cited previous results (n = 20; P < 0.001; R 2 = 0.996), and then confirmed from the results of Experiments 3 and 4. These relationships between SAB and LAB demonstrate that CP supply from SAB is underevaluated by, on average, 21.2% when LAB are used as the reference. This underevaluation was higher for true protein and even higher for the lipid supply (32.5% and 59.6%, respectively, as an average of the four experiments). Large differences in AA profile were observed between SAB and LAB. The prediction equation obtained using 15N as the marker may be used to correct the errors associated with the traditional use of LAB as the reference sample, and therefore to obtain more accurate estimates of the microbial nutrient supply to the ruminants. © Copyright The Animal Consortium 2011.Financial support was provided by the CICYT funded Projects AGL 2001-3662, AGL 2005-01712 and AGL 2006-08300. Analyses of 15N isotope ratios were performed at the Servicio Interdepartamental de Investigacio´ n, Universidad Auto´ noma de Madrid, Spain.González, J.; Arroyo, J.; Ouarti, M.; Guevara-González, J.; Rodríguez, C.; Alvir, M.; Moya Salvador, VJ.... (2012). Composition of free and adherent ruminal bacteria: inaccuracyof the microbial nutrient supply estimates obtained using freebacteria as reference samples and 15N as the marker. Animal. 6(3):468-475. https://doi.org/10.1017/S17517311110018074684756

Malic acid or orthophosphoric acid-heat treatments for protecting sunflower (Helianthus annuus) meal proteins against ruminal degradation and increasing intestinal amino acid supply

The protection of sunflower meal (SFM) proteins by treatments with solutions of malic acid (1 M) or orthophosphoric acid (0.67 M) and heat was studied in a 3 × 3 Latin-square design using three diets and three rumen and duodenum cannulated wethers. Acid solutions were applied to SFM at a rate of 400 ml/kg under continuous mixing. Subsequently, treated meals were dried in an oven at 150C for 6 h. Diets (ingested at 75 g/kg BW0.75) were isoproteic and included 40% Italian ryegrass hay and 60% concentrate. The ratio of untreated to treated SFM in the concentrate was 100 : 0 in the control diet and around 40 : 60 in diets including acid-Treated meals. The use of acid-Treated meals did not alter either ruminal fermentation or composition of rumen contents and led to moderate reductions of the rumen outflow rates of untreated SFM particles, whereas it did not affect their comminution and mixing rate. In situ effective estimates of by-pass (BP) and its intestinal effective digestibility (IED) of dry matter (DM), CP and amino acids (AAs) were obtained considering both rates and correcting the particle microbial contamination in the rumen using 15N infusion techniques. Estimates of BP and IED decreased applying microbial correction, but these variations were low in agreement with the small contamination level. Protective treatments increased on average the BP of DM (48.5%) and CP (267%), mainly decreasing both the soluble fraction and the degradation rate but also increasing the undegradable fraction, which was higher using orthophosphoric acid. Protective treatments increased the IED of DM (108%) and CP, but this increase was lower using orthophosphoric acid (11.8%) than malic acid (20.7%). Concentrations of AA were similar among all meals, except for a reduction in lysine concentrations using malic acid (16.3%) or orthophosphoric acid (20.5%). Protective treatments also increased on average the BP of all AA, as well as the IED of most of them. Evidence of higher increases for those AA showing a high resistance to degradation in the untreated meal were also observed. The total supply of metabolisable AA was increased by 3.87 times for sulphur-containing AA, whereas that of lysine was increased by 2.5 times, mainly because of lysine losses with heat treatments. These treatments and especially that with malic acid would be useful to increase the protein value of these meals but their combined use with lysine-rich protein concentrates would improve the metabolisable protein profile. © The Animal Consortium 2012.Peer Reviewe

Protein value for ruminants of a sample of whole cottonseed

The effective ruminal degradability (ED) of dry matter (DM), crude protein (CP) and amino acids, and the effective intestinal digestibility (IED) of DM and CP of a sample of whole cottonseed was measured using in situ and rumen outflow rate techniques in three wethers cannulated in the rumen and duodenum. The microbial contamination of rumen incubated residues was corrected by a continuous rumen infusion of 15NH3 as microbial marker and rumen solid associated bacteria as reference sample. Microbial contamination resulted in an overestimation of the undegradable fraction of DM (0.291 v. 0.275; P< 0.05) and CP (0.071 v. 0.037; P< 0.01) and a small underestimation of ED of DM (0.500 v. 0.512; P= 0.09) and CP (0.755 v. 0.779; P = 0.052). A proportion of 0.1 of the ruminal undegraded CP was of microbial origin and for essential amino acids this proportion varied from 0.042 to 0.150. Differences in ED between amino acids modified the amino acid profile, with an important reduction (0.2; P< 0.01) in the proportion of lysine. Apparent intestinal digestibility of the insoluble fraction of this food, measured with the mobile nylon bag technique, showed large reductions (P< 0.001) with the increase of the ruminal incubation time between 0 and 72h: from 0.392 to 0.026 for DM and from 0.851 to 0.099 for CP. These evolutions fitted an exponential function with a previous lag. The IED was estimated either by integration of these equations and those describing the ruminal degradation and rumen outflow or by incubation through the intestines of a sample pooled to be representative of rumen flow of the undegraded food. The two methods gave similar values for both DM (0.222 v. 0.203) and CP (0.659 v. 0.658).Peer Reviewe