Effects of supplemental source of magnesium and inclusion of buffer on ruminal microbial fermentation in continuous culture

Abstract

Magnesium oxide (MgO) is the most common supplemental source of Mg for dairy cows and a proven ruminal alkalizer when supplemented above NRC (2001) recommendations. However, overfeeding MgO may increase feeding costs, whereas the effects of alternative sources of Mg on ruminal fermentation are not well known. Moreover, it is still unclear if Mg supplementation influences the effects of bicarbonate-based buffers on ruminal fermentation. We aimed to evaluate the effect of Mg source on ruminal fermentation with diets formulated to a final concentration of 0.25% Mg, and to determine if the effect of sodium sesquicarbonate as a buffer varies with the source of Mg. We used 8 fermentors in a duplicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments, by combining 2 factors: (1) Mg source: using either MgO or an alternative source consisting of a blend of CaMg(OH) 4 and CaMg(CO 3 ) 2 (BLN) and (2) sodium sesquicarbonate buffer inclusion, at 0 or 0.6% of dry matter intake. Based on preliminary tests of reactivity, we hypothesized that BLN plus buffer would allow for greater ruminal pH, acetate molar proportion, and NDF digestibility than diets with MgO or without buffer. Four 10-d periods were completed, where the last 3 d were used for pH measurements and collection of samples for volatile fatty acids (VFA), ammonia (NH 3 -N), Mg solubility, N metabolism, and nutrient digestibility. Effects of Mg source (source), sodium sesquicarbonate inclusion (buffer), and their interaction (source × buffer) were tested with the MIXED procedure of SAS (SAS Institute Inc.). We did not find an effect of Mg source on ruminal fermentation variables; however, concentration of soluble Mg in ruminal fluid was greater for MgO compared with BLN. On the other hand, buffer supple-mentation increased average ruminal pH, acetate molar proportion, and branched-chain VFA molar proportion; tended to increase NDF digestibility; and decreased both area under the curve and time below pH 6.0. An interaction of source × buffer was found for propionate, butyrate, and NH 3 -N, the first one decreasing and the 2 others increasing only when buffer was supplemented to the BLN diet. Our results indicate that supplementing Mg with either MgO or BLN promotes similar ruminal fermentation in diets with total concentration of 0.25% Mg. Further evaluations are needed to assess Mg availability and animal performance in dairy cows fed BLN.

The Effects of Incremental Doses of Aflatoxin B1 on In Vitro Ruminal Nutrient Digestibility and Fermentation Profile of a Lactating Dairy Cow Diet in a Dual-Flow Continuous Culture System

“…However, in the present study no treatment effects were observed on OM digestibility resulting in lack of effects on microbial N flow and microbial efficiency. Microbial efficiency of 17.5 g [ 23 ] and 18.4 g of microbial N flow/kg of digested OM [ 24 ] observed in previous studies using similar continuous culture fermenter system with comparable liquid and solid passage rates are in agreement with values observed in this study. In contrast, others reported 34.6 and 22.7 g of microbial N flow/kg of OM truly digested [ 25 , 26 ], respectively.…”

Effects of partially replacing dietary corn with molasses, condensed whey permeate, or treated condensed whey permeate on ruminal microbial fermentation

“…A dual-flow continuous culture system, as developed by Hoover et al (1976) and described by Arce-Cordero et al (2021b) and Wenner et al (2021), was used for this experiment. The fermentation vessels used had an average volumetric capacity of 1.82 L when filled until the solid effluent outflow port.…”

Effects of partially replacing dietary corn with sugars in a dual-flow continuous culture system on the ruminal microbiome

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