The effects of 2-hydroxy-4-methylthio-butanoic acid supplementation on the rumen microbial population and duodenal flow of microbial nitrogen

摘要

Four multiparous, lactating Holstein cows (averageDIM 169.5 ± 20.5 d), fitted with ruminal and duodenalcannulas, were used in a 4 × 4 Latin square with a 2 ×2 factorial arrangement of treatments to investigate theeffects of 2-hydroxy-4-methylthio-butanoic acid (HMTBA)when fed with diets differing in metabolizableprotein (MP) supply and equal levels of crude proteinon milk production and composition, rumen microbialactivity, duodenal protein flow, and rumen bacterialcommunity composition in vivo and in vitro. Experimentalperiods were 28 d in length. Cows were housedin individual tie stalls and were randomly assigned to 4dietary treatments: low MP or high MP, supplementedwith or without 25 g of HMTBA, which was top-dressedonce daily at 0930 h. No interactions were observedbetween HMTBA and level of dietary MP, with theexception of ruminal acetate-to-propionate ratio. Milkyield was not affected by treatment and averaged 23.8± 2.06 kg/d. There was a tendency for increased milkprotein percent in cows receiving low MP diets, averaging3.30 ± 0.09% and 3.21 ± 0.09% for low MP and highMP, respectively. The total-tract apparent digestibilityof organic matter, neutral detergent fiber, and nitrogenwere greater in cows consuming the low MP diet. RumenpH was lower in cows consuming high MP diets aswell as in those consuming HMTBA. Rumen ammoniaconcentrations tended to be greater in cows consumingHMTBA, and volatile fatty acid concentrations weregreater in cows consuming HMTBA. Duodenal drymatter flow, nitrogen flow, and microbial nitrogen flowdid not differ between treatments. The bacterial communitystructure of cows receiving HMTBA was notaffected at the phylum level. The relative abundanceof bacterial phyla in vivo differed when compared within vitro conditions for Firmicutes, Bacteroidetes, Proteobacteria,TM7, Tenericutes, Spirochaetes, SR1, andVerrucomicrobia.