Effect of potassium carbonate and soybean oil supplementation on rumen microbial population linked to lipid metabolism

Abstract Text:

The rumen microbial ecosystem plays a crucial role in productivity through digestion of feeds and supply of nutrients to the host animal. It was suggested that milk fat synthesis in dairy cows is stimulated by a positive dietary cation-anion difference (DCAD). Despite that rumen bacteria are largely involved in hydrolysis and biohydrogenation of dietary lipids, the impact of DCAD on rumen microbiome is unknown. The objective of this study was to evaluate the effect of increasing DCAD, using K₂CO₃, in diets containing soybean oil (SBO) on rumen microbial population associated with lipid metabolism. Twenty four early lactation Holstein dairy cows (39±22 DIM) were used in a randomized complete block design (6 blocks) based on DIM and number of calving with a 2x2 factorial arrangement of treatments. Within each block, cows were fed a basal diet formulated to achieve 40% forage (58% corn silage), 60% concentrate, and 47% non-fibrous carbohydrates, with 0 (DCAD: +95 mEq/kg) or 1.5% K₂CO₃ (DM basis; DCAD: +316 mEq/kg), and 0 or 2% SBO. Effects of K₂CO₃, SBO and the interaction K₂CO₃ × SBO were evaluated. Treatment period lasted 28 d; the last 5 d were used for data and sample collection. Equal volumes (∼1.0 L) of rumen fluid and solid digesta were collected from different rumen sites 4 h postfeeding. Extracted DNA was amplified by quantitative real-time PCR. The absolute amount for each microbial group was expressed as logarithm (base 10) of DNA copies/g of fresh matter. A companion abstract showed an interaction between K₂CO₃ and SBO on milk fat yield and t10/t11 ratio (JDS 98-Suppl. 2:128). Supplementing diets with K₂CO₃ stimulated the growth of Butyrivibrio hungatei (5.79 vs. 5.62; P=0.03), a bacteria recognized to produce t11 18:1 during biohydrogenation. Conversely, feeding SBO reduced the growth of i) Butyrivibrio/Pseudobutyrivibrio group (8.60 vs. 8.80; P=0.04), also known to produce t11 18:1, ii) fibrolytic Fibrobacter succinogenes (9.34 vs. 9.63; P=0.04), iii) Butyrivibrio proteoclasticus, a bacteria involved in 18:0 production (6.67 vs. 6.79; P=0.06), and iv) amylolytic Streptococcus bovis (6.84 vs. 7.01; P=0.06). Feeding K₂CO₃ had no effect on these four bacteria. Total eubacteria and total protozoa did not differ between treatments (P>0.13). Feeding K₂CO₃ and SBO had distinct effects on rumen bacteria. However, the absence of interaction between treatments on microbial population does not allow to establish a clear link with previously observed effects on milk fat yield and t10/t11 ratio.

Keywords: DCAD, rumen bacteria, biohydrogenation