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

Corn is a feedstuff commonly fed to dairy cows as a source of energy. The objective of this study was to evaluate whether partially replacing dietary corn with molasses or condensed whey permeate, in lactating dairy cow diets in a dual-flow continuous culture system, can maintain nutrient digestibility by ruminal microorganisms. Furthermore, this study evaluated whether treating condensed whey permeate before feeding could aid the fermentation of the condensed whey permeate in the rumen. Eight fermentors were used in a 4 × 4 replicated Latin square with 4 periods of 10 d each. The control diet (CON) was formulated with corn grain, and the other diets were formulated by replacing corn grain with either sugarcane molasses (MOL), condensed whey permeate (CWP), or treated condensed whey permeate (TCWP). Diets were formulated by replacing 4% of the diet dry matter (DM) in the form of starch from corn with sugars from the byproducts. Sugars were defined as water-soluble carbohydrates (WSC) in the rations. The fermentors were fed 52 g of DM twice daily of diets containing 17% crude protein, 28% neutral detergent fiber, and 45% nonfiber carbohydrates. Liquid treatments were pipetted into each fermentor. After 7 d of adaptation, samples were collected for analyses of volatile fatty acids (VFA), lactate, and ammonia, and fermentors' pH were measured at time points after the morning feeding for 3 d. Pooled samples from effluent containers were collected for similar analyses, nutrient flow, and N metabolism. Data were statistically analyzed using Proc MIXED of SAS version 9.4 (SAS Institute Inc.); fixed effects included treatment and time, and random effects included fermentor, period, and square. The interaction of treatment and time was included for the kinetics samples. The TCWP and MOL treatments maintained greater fermentor pH compared with CWP. Total VFA concentration was increased in CWP compared with MOL. The acetate:propionate ratio was increased in TCWP compared with CON, due to tendencies of increased acetate molar proportion and decreased propionate molar proportion in TCWP. Lactate concentration was increased in MOL. Digestibility of WSC was increased in the diets that replaced corn with byproducts. The partial replacement of 4% of DM from corn starch with the sugars in byproducts had minimal effects on ruminal microbial fermentation and increased pH. Treated CWP had similar effects to molasses.

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

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(CO3)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 (NH3-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 supplementation 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 NH3-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.