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

Abstract

Previous studies have indicated that (15)N 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 ((15)NH(4))(2)SO(4) (40, 18, 30 and 25 mg (15)N/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 (15)N 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 (15)N 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 (15)N 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.

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

“…Bacteria isolates were lyophilised and analysed for DM, N, 15 N/N and AA. Bacteria isolation and results are described in Gonzá lez et al (2012).…”

Potenciación de la respuesta productiva en rumiantes mediante el empleo de proteínas protegidas

“…Considering current mean diet contents of OM and total lipids of both bacteria types together with those of The equation derived from current and previous data of this team is also supported by that obtained (Figure 2) using mean diet values (n = 41) of 15 N enrichment in LAB and SAB obtained in cows (Martin et al 1994;Yang et al 2001;Ahvenjärvi et al 2002; Reynal et al 2005; Brito et al 2006, Ipharraguerre et al 2007), steers (Firkins et al 1987;Beckers et al 1995; Kamoun et al 2014), sheep (Chicunya and Miller 1999, Martín-Urúe et al 1998, Ramos et al 2009González et al 2012), and in vitro (Ranilla et al …”

“…However, for many years the microbial population usually used as reference to determine this supply has been bacteria harvested from the ruminal liquid fraction (liquid-associated bacteria; LAB), in spite that they are only a minor fraction of the rumen bacterial populations, as solid-associated bacteria (SAB) are largely predominant (Faichney 1980; Legay-Carmier and Bauchart 1989; Volden 1999; Rodriguez et al 2003). On the other hand, it is well known that for the most usual microbial markers, such as diamino pimelic acid, nucleic acids or its derivatives as well as nitrogen or phosphorus isotopes, the marker/N ratio is higher in LAB than in SAB and as a consequence, the use of LAB as reference underestimates the postruminal microbial flow (González et al 2012). Mixed bacterial samples (LAB + SAB) isolated from mixed liquid and solid digesta contents have been used as reference in some studies to avoid the formerly cited problem.…”

“…Although there are numerous works comparing both populations of bacteria, the effects of using LAB as reference on nutrient supply estimates on ruminants are poorly defined. The magnitude of the errors in the SAB-nutrient supply using LAB as reference can be directly established from the marker/N ratios and the contents of the examined fraction in both bacterial populations (González et al 2012). This last work points to a close relationship between the 15 N enrichments of both bacterial populations which may simplify these estimations.…”

“…As the animals were adult maintained in a controlled environment, the period effect was assumed to be negligible. shown by González et al, (2012) was determined through the mean prediction error (absolute and relative) as indicated by Montgomery and Peck (1982). Effects of the factors were declared significant at p < 0.05.…”