FEED ADDITIVES CAN INFLUENCE RUMEN BACTERIAL PROTEIN COMPOSITION

To maximise production, dairy cow diets are balanced for amino acids through the use of feed formulation programmes. A limitation of these programmes is that the bacterial amino acid profile used is considered constant and based on assumptions about the composition of mixed ruminal bacteria. However, research has shown that the amino acid composition differs between the fluid-associated bacteria (FAB) and the particle-associated bacteria (PAB) and also depends on factors such as diet composition, feed intake, protein source and thus potentially, feed additives. To test the effect of dietary feed additives the aim of the study cited below was to determine their effect on the amino acid composition of the fluid- and particle-associated fractions of ruminal bacteria.

Four Holstein-Friesian cows were utilised in a 4 x 4 Latin square design, comprised of 25 day periods, during which whole rumen contents were collected over four sampling days for the isolation and determination of the amino acid composition of the ruminal FAB and PAB. The basal diet fed was a total mixed ration (TMR) comprising 40% high quality lucerne hay and 60% concentrates. Treatments were: (1) control diet (C), (2) control diet plus 90 g/day of the calcareous marine algae buffer Acid Buf 10 (AB10), (3) control diet plus 10 g/day of the direct-fed microbial AchieveFE (DFM) inserted directly into the rumen daily, and (4) control diet plus 250 mg/day of monensin sodium (Rumensin 200) (MON). Cows were fed their respective diets ad libitum twice daily, with the DFM product being placed directly into the rumen daily prior to the morning feeding. Whole rumen content collected underwent fractionation and differential centrifugation for the isolation of the ruminal bacteria, isolated bacteria were freeze-dried and ground for the determination of amino acid composition via high-performance liquid chromatography (HPLC). Data were statistically analysed as a Latin square design using the GLM analysis of variance.    

The feed additives altered the amino acid composition of the ruminal bacteria. For the FAB, the methionine and valine content were altered by AB10, whereas lysine, methionine and valine were altered by the DFM. MON altered valine and glutamine (P<0.05). For the PAB, AB10 did not alter the amino acid composition (P>0.05), whereas the DFM and MON treatments altered the composition of histidine, glycine and tyrosine, and lysine, asparagine, glutamine, glycine and serine, respectively (P<0.05). The amino acid composition of the two bacterial fractions were also shown to differ (P<0.05); the difference being in: leusine, lysine, arginine, asparagine, proline, serine and glutamine. Overall, MON appeared to have the greatest capability to alter the amino acid composition of both bacterial fractions.

The results suggest that feed additives have the potential to modify the amino acid composition of the ruminal bacteria but further research on the potential changes in the microbial populations within the microbiome and the amino acid profiles of the various populations are needed to enable prediction with more accuracy.

Reference:

L.J. Erasmus & C. de Vos, 2019. Effect of feed additive supplementation on rumen bacterial amino acid profiles in dairy cows. In: Proc of the 51st SASAS Congress, Bloemfontein, 10-12 June 2019, Abstract 41.