|JENKINS, CHAD - University Of Nebraska|
|FERNANDO, S - University Of Nebraska|
|ANDERSON, CHRISTOPHER - University Of Nebraska|
|ALUTHGE, N - University Of Nebraska|
|CASTILLO-LOPEZ, EZEQUIAS - University Of Nebraska|
|KONONOFF, PAUL - University Of Nebraska|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2020
Publication Date: 11/20/2020
Citation: Jenkins, C., Fernando, S., Anderson, C., Aluthge, N., Castillo-Lopez, E., Zanton, G.I., Kononoff, P. 2020. The effects of 2-hydroxy-4-methylthio-butanoic acid supplementation on the rumen microbial population and duodenal flow of microbial nitrogen. Journal of Dairy Science. 103:10161-10174. https://doi.org/10.3168/jds.2019-17664.
Interpretive Summary: This experiment evaluated effect of 2-hydroxy-4-methylthio-butanoic acid (HMTBa, a methionine analogue) on milk production and composition, rumen microbial activity and protein flow out of the rumen, and rumen bacterial community composition when cows were fed diets differing in metabolizable protein supply. Milk production and composition were similar among treatments and flow of microbial protein was not affected by supplement, but rumen volatile fatty acids and ammonia concentrations increased with addition of HMTBa. Rumen bacterial community was also affected at the phylum level by supplementation with HMTBa. Results suggest that HMTBa affects rumen microbial activity and rumen chemistry, irrespective of dietary MP level.
Technical Abstract: Four multiparous, lactating Holstein cows (average DIM 169.5 ± 20.5 d), fitted with ruminal and duodenal cannulae, were used in a 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments to investigate the effects of 2-hydroxy-4-methylthio-butanoic acid (HMTBA) when fed with diets deficient or in excess of metabolizable protein (MP) on milk production and composition, rumen microbial activity and duodenal protein flow, and rumen bacterial community composition in vivo and in vitro. Experimental periods were 28 d in length. Cows were housed in individual tie stalls and fed diets designated as “Low MP” or “High MP”, which were top dressed with 25 g of 2-hydroxy-4-methylthio-butanoic acid (HMTBA), once daily at 0930 h. No interactions were observed between HMTBA and level of dietary MP, with the exception of ruminal acetate to propionate ratio (P = 0.04). Milk yield was not affected by treatment and averaged 23.8 ± 2.06 kg/d. There was a tendency (P = 0.06) for increased milk protein percent in cows receiving Low MP diets, averaging 3.30 ± 0.09 % and 3.21 ± 0.09 % for Low MP and High MP, respectively. The DM, OM, NDF, and N digestibilities were greater (P = 0.03) in cows consuming the Low MP diet. Rumen pH was lower (P = 0.05) in cows consuming High MP diets as well as in those consuming HMTBA (P < 0.01). Rumen kinetics were not affected by treatment. Rumen ammonia concentrations tended to be greater (P = 0.06) in cows consuming HMTBA, and VFA concentrations were greater (P = 0.02) in cows consuming HMTBA. Duodenal DM flow, N flow, and bacterial N flow did not differ between treatments (P = 0.15). The bacterial community structure of cows receiving HMTBA was affected at the phylum level, the proportion of Fibrobacteres was increased (P = 0.04) in vivo. The relative abundance of bacterial phyla in vivo differed when compared to in vitro conditions (P = 0.01) for Firmicutes, Bacteroidetes, Proteobacteria, TM7, Tenericutes, Spirochaetes, SR1, and Verrucomicrobia. A number of associations (P = 0.05) of specific bacterial species and metadata were observed, including HMTBA supplementation, level of dietary MP, DMI, digestibility, rumen ammonia, microbial N flow, and milk production and composition. Results suggest that HMTBA affects rumen microbial activity, irrespective of dietary MP level. Consequently, further investigation is warranted into the mechanism of these effects within the rumen.