Methionine analogues HMB and HMBi increase the abundance of cellulolytic bacterial representatives in the rumen of cattle with no direct effects on fibre degradation

• Published in: Animal feed science and technology Vol. 182; no. 1-4; pp. 16 - 24
• Main Authors: Martin, C., Mirande, C., Morgavi, D.P., Forano, E., Devillard, E., Mosoni, P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 12.06.2013; Elsevier
• Subjects: Ammonia; Bacteria; bacterial colonization; Computer Science; corn; corn silage; cows; crude protein; endo-1,4-beta-glucanase; enzyme activity; fermentation; Fibre degradation; Fibrobacter succinogenes; Fibrolytic activities; Fibrolytic bacteria; hay; Holstein; Humanities and Social Sciences; Life Sciences; methionine; Methionine analogues; microbial ecology; milk composition; neutral detergent fiber; qPCR; rumen; Ruminal fermentation; Ruminantia; Ruminococcus albus; Ruminococcus flavefaciens; starch; Triticum aestivum; volatile fatty acids; wheat; xylanases; Fibre degradation; Fibrolytic activities; DM; VFAs; CMCase; CP; HMBi; Fibrolytic bacteria; NDF; Methionine analogues; Ruminal fermentation; BW; qPCR; aNDFom; HMB; Met; OM; REQUIREMENTS; PROTEIN; BLOOD-SERUM; HYDROXY ANALOG; DEGRADABILITY; LACTATING DAIRY-COWS; SUPPLEMENTATION; AMINO-ACIDS; MILK; CONTINUOUS-CULTURE
• ISSN: 0377-8401; 1873-2216
• DOI: 10.1016/j.anifeedsci.2013.03.008

Supplementation of diets for ruminants with methionine analogues such as 2-hydroxy-4-(methylthio) butanoic acid (HMB) and its isopropyl ester (HMBi) positively affect milk composition and yield, potentially partly through ruminal actions. Our objective was to investigate effects of HMB and HMBi on the rumen microbial ecosystem, with special emphasis on fibrolytic activities and fibrolytic microorganisms. Six ruminally cannulated Holstein dry cows were randomly assigned to three treatments in a 3×3 Latin square design with two cows per cell. Cows were fed twice a day at 7.5kg/d dry matter (DM) intake with a control diet based on hay and wheat (50/50 on a DM basis) supplemented or not with HMB (Rhodimet® AT88, Adisseo at 1.25g/kg DM intake) or HMBi (MetaSmart™, Adisseo, at 2.50g/kg DM intake). Substrate degradability (i.e., corn grain, corn silage) was evaluated by in sacco incubation and effective degradability measurements of DM, crude protein, starch and neutral detergent fibre. Fermentation products (i.e., volatile fatty acids (VFAs), ammonia, lactate) and fibrolytic enzyme activities (i.e., carboxymethylcellulase (CMCase), xylanase) were analyzed in rumen content samples before (−1h) and after (+3h) feeding. Protozoal populations were counted by microscopy. Abundances in total and fibrolytic bacteria Fibrobacter succinogenes, Ruminococcus flavefaciens and Ruminococcus albus in total rumen contents or adhering to in sacco residues were estimated using quantitative polymerase-chain reaction (qPCR). HMB and HMBi supplementation increased VFA concentrations in the rumen as well as the ruminal abundance of F. succinogenes (P=0.03) and R. flavefaciens (P=0.05), although these increases had no effect on the CMCase and xylanase activities of the rumen contents, nor on in sacco bacterial colonization and degradation of the two corn substrates. Under our experimental conditions, Met analogues enhanced growth of two cellulolytic bacterial representatives, but did not improve rumen fibrolytic activity.