María Remedios Alvir

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

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.

Protection of sunflower seed and sunflower meal protein with malic acid and heat: effects on in vitro ruminal fermentation and methane production

BACKGROUND Combined malic acid-heat treatments of protein supplements have been shown to reduce ruminal protein degradation, but there is no information on their possible influence on ruminal fermentation and methane emissions. This study aimed to investigate the effects of the treatment of sunflower meal (SM) and sunflower seed (SS) with malic acid and subsequent drying at 150°C for 1 (MAL1) or 3 h (MAL3) on in vitro rumen fermentation and methane emission using ruminal fluid from sheep as inoculum. RESULTS Compared with untreated samples, the MAL3 treatment reduced (P < 0.05) the dry matter effective degradability (DMED) by 78% and 46% for SS and SM, respectively, indicating heat damage. The MAL1 treatment reduced the DMED of SS by 22%, but did not affect (P > 0.05) total volatile fatty acid production for any feed. This treatment also increased (P < 0.05) the propionate proportion (by 17.7% and 15.6% for SS and SM, respectively) and decreased (P < 0.05) methane production (by 15.5% and 11.3%, respectively) and ammonia-N concentrations (by 26.5% and 14.5%, respectively). CONCLUSION The MAL1 treatment was effective in reducing both ammonia-N concentrations and methane emissions without depressing SS and SM fermentation, but more research is needed to formulate environmentally cleaner diets for ruminants.