Effects of lauric acid on fermentation patterns, ruminal protozoa, and performance of dairy cows

Os protozoários ruminais exercem efeito negativo sobre a utilização de proteína em ruminantes, reduzindo a proteína de origem microbiana sintetizada no rúmen e a PNDR, que são as principais fontes da AA para os ruminantes. Dessa forma, os objetivos deste trabalho foram: (1) Avaliar a viabilidade do uso do Ácido Láurico (C12:0) como um defaunador de rotina e (2) avaliar os efeitos da defaunação parcial do rúmen sobre a fermentação ruminal e o desempenho de vacas leiteiras. No primeiro experimento, seis vacas da raça Holandesa (sendo uma seca), com media de 660 (SD 46) kg de PV; 3,5 (SD 1) partos; 102 (SD 23) dias de lactação e 40,4 (SD 6,2) kg/leite/dia; canuladas no rúmen foram divididas com base nos dias em lactação em 2 grupos de três, em um delineamento inteiramente casualisado. Os tratamentos foram: 1) Controle, 2) 160 g/d de AL e 3) 160 g/d de laurato de sódio. Ambos AL e LANa foram infundidos em dose única via canula ruminal diariamente antes da alimentação. A ração total continha (na base da MS): 15% de silagem de alfafa, 40% de silagem de milho, 30% de silagem de milho úmido, 14% de farelo de soja, 1% de premix de vit. e minerais, tendo a dieta total, 16,6% PB e 29% FDN. No Segundo experimento, 32 vacas da raça Holandesa multíparas (8 canuladas no rúmen) com média de 633 (SD 52) kg de PV; 152 (SD 72) dias em lactação; 2,6 (SD 1) partos e 43,1 (SD 11) kg/leite/dia e 20 vacas da raça Holandesa primíparas com media de 566 (SD 39) kg de PV; 123 (SD 42) dias em lactação e 40,5 (SD 2,6) kg/leite/dia foram divididas com base nos dias em lactação em grupos de 4, formando 8 blocos de multíparas (2 com vacas canuladas) e 5 blocos de primíparas em um delineamento interamente casualisado. Antes do início dos tratamentos, todas os animais foram alimentados com a mesma dieta (controle) por 2 semanas em um período de co-variância, onde a produção de leite e a contagem de protozoários foram determinadas para utilização nas análises estatísticas. Os animais dentro dos blocos foram então aleatóriamente distribuídos em um dos quatro tratamentos, onde foram alimentadas por 8 semanas. As quatro dietas experimentais foram semelhantes, onde parte do milho moído foi substituído por um premix constituído de 8% de AL e 92% de milho moído. O premix com AL foi adicionado nas proporções de 0; 4,05; 8,11 e 12,16% na base da MS da dieta (0, 80, 160 e 240g/LA/d). Todos os animais foram injetados com bST a cada 14 dias. Os dados foram analisados usando o procedimento Proc Mixed do programa estatístico SAS. Ambos AL e LANa apresentaram efeito altamente inibitórios aos protozoários ruminais quando dosados em 160 g/d via canula ruminal, reduzindo a população de protozoários em 90%. AL reduziu a concentração de amônia ruminal em 60% sem reduzir o CMS. Ambos agentes reduziram a concentração de aminoácidos livres no rúmen. AL não afetou o pH ruminal, nem reduziu a concentração total de AGV no rúmen. Nas condições do primeiro experimento, AL se mostrou um potente agente dafaunador, evitando a necessidade de utilizar LANa que é mais caro. AL fornecido na dieta em níveis de 80, 160 e 240 g/d não reduziu o CMS, não afetou o pH ruminal, os parâmetros fermentativos no rúmen e a produção de leite. AL misturado na dieta total de vacas da raça Holandesa, em níveis de 160 e 240 g/d reduziu a população de protozoários ruminais em apenas 25 e 30%, respectivamente, mostrando que estes níveis de AL na dieta não foram suficientes para permitir atingir uma concentração no rúmen que fosse suficiente para promover os efeitos defaunadores do AL.Ruminal ciliate protozoa have a negative effect on protein utilization in ruminants by reducing both microbial protein and RUP flow out of the rumen. The aims of this study were: (1) To evaluate lauric acid as a practical defaunating agent, (2) to assess the effects of partial defaunation on fermentation patterns and milk production in dairy cows. In the first trial, six multiparous Holstein cows (one dry), averaging 660 (SD 46) kg of BW, parity 3.5 (SD 1), 102 (SD 23) DIM, and 40.4 (SD 6.2) kg/d of milk; fitted with ruminal cannulae were blocked into groups of 3 by DIM to give 2 blocks in a trial of randomized complete block design. The treatments were: 1) Control, 2) 160g/d of LA, or 3) 160g/d of sodium laurate. Both LA and NaLA were given in a single dose into the rumen via cannulae before feeding. The TMR contained (DM basis): 15% alfalfa silage, 40% corn silage, 30% rolled high moisture corn, 14% soybean meal, 1% Vit. & Min. premix, 16.6% CP and 29% NDF. In the second trial, thirty-two multiparous Holstein cows (8 with ruminal cannulae) averaging parity 2.6 (SD 1), 633 (SD 52) kg of xvBW, 152 (SD 72) DIM, and 43.1 (SD 11) kg milk/d, and twenty primiparous Holstein cows averaging 566 (SD 39) kg of BW, 123 (SD 42) DIM, and 40.5 (SD 2.6) kg milk/d were blocked into groups of 4 by DIM to give 8 multiparous blocks (2 cows with ruminal cannulae) and 5 primiparous blocks in a trial of randomized complete block design. Prior to starting the experimental phase of the trial, all cows were fed the same diet (control) for a 2-wk covariate period and production of milk and protozoal counts were determined for use in statistical analysis. Cows within blocks of 4 were then randomly assigned to one of the 4 diets and fed only that diet during the remaining 8 weeks of the study. The four experimental diets were similar, except that some of the finely ground dry corn was replaced with finely ground dry corn plus lauric acid (8% LA and 92% corn, DM basis) in stepwise increments from 0 to 12.16% of dietary DM. All cows were injected biweekly with bST. Data were analyzed using the Proc Mixed procedure of SAS. Both lauric acid and sodium laurate showed high anti-protozoal activity when dosed at 160 g/d via ruminal canulae, reducing the ciliate population within the rumen by 90%. Lauric acid reduced ruminal ammonia concentration by 60% without reducing DMI. Both agents reduced ruminal free amino acid concentration. Lauric acid did not affect ruminal pH, nor reduce total ruminal VFA concentration. Under the condition of the first trial, Lauric Acid was shown to be a potent defaunation agent, obviating the need to use Na-laurate, which is more costly. Lauric acid fed on the diets at 80, 160, and 240 g/d did not reduce DMI, did not affect ruminal pH, ruminal parameters, or milk production. Lauric acid fed at 160 and 240 g/d on the TMR of Holstein's dairy cows reduced ruminal protozoal population by only 25 and 30% respectively, showing that these levels on the diet were not sufficient to achieve a concentration within the rumen that promote the anti-protozoal effect of lauric acid.Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

Shrink, weighing accuracy, and weighing precision of mineral supplement in five commercial dairies in the Western United States

Shrink, accuracy, and precision of ingredient weighing are critical factors of effi ciency in TMR-fed dairy systems. Those factors have been evaluated for major feeds; however, we are not aware of any reports for mineral sup plement. Farms commonly mix mineral sup plement with other low-inclusion ingredients into a premix which is used later as a single in gredient for TMR formulation. Our objectives were to evaluate shrink, weighing accuracy, and weighing precision of mineral supplement dur ing premix formulation, and variation in concen tration of minerals in mineral supplement and TMR, in five large dairies in the Western United States. We used the automated weight-tracking system at each farm to account for all the min eral supplement loaded into the mixing-wagon and collected samples of mineral supplement and TMR from time of mineral supplement de livery at the farm until 100% of it was consumed. Mean, standard deviation and coefficient of variation (CV) for each variable were calculated with SAS 9.4. Average shrink was estimated at 2.0% for mineral supplement during storage and loading, ranging from 0.37% to 3.25%. Mineral supplement weighing deviation from the targeted amount was 1.54% on average for the five dairies with a 95% CV. Mineral composition of mineral supplements averaged 11.3%, 0.27%, and 3.16% for Ca, P, and Mg, and 215, 881, and 1533 ppm for Cu, Mn, and Zn, respectively. Mineral com positions in TMR averaged 0.84%, 0.41%, and 0.37% for Ca, P, and Mg, respectively; and 15.1, 71, and 94.5 ppm for Cu, Mn, and Zn, respect ively. The CV of all minerals except Ca, were larger for mineral supplement than TMR, and with the exception of P in mineral supplement, CV of trace minerals were larger than CV values for macro minerals. Our shrink estimates for mineral supplement represent an initial approxi mation to this issue. Results of our weighing deviation analysis suggest some room for im provement on the precision of weighing mineral supplement at the time when premix is prepared at the farm, which could improve consistency in chemical composition of the premix and conse quently reduce the variation (CV values) of min eral concentrations in TMRUCR::Vicerrectoría de Docencia::Ciencias Agroalimentarias::Facultad de Ciencias Agroalimentarias::Escuela de Zootecni

Megasphaera elsdenii and Saccharomyces cerevisiae as direct fed microbials and their impact on ruminal microbiome during an acute acidosis challenge in continuous culture

Our objective was to evaluate the effects of combinations of Saccharomyces cerevisiae and Megasphaera elsdenii as direct fed microbials (DFM) on ruminal microbiome during an acute acidosis challenge in a continuous culture system. Treatments provided a DFM dose of 1 × 108 colony-forming unit (CFU)/mL, as follows: Control (no DFM); YM1 (S. cerevisiae and M. elsdenii strain 1); YM2 (S. cerevisiae and M. elsdenii strain 2); and YMM (S. cerevisiae and half of the doses of M. elsdenii strain 1 and strain 2). We conducted 4 experimental periods of 11 d, which consisted of non-acidotic days (1–8) and acidotic challenge days (9–11) to establish acute ruminal acidosis conditions with a common basal diet containing 12% NDF (neutral detergent fiber) and 58% starch. Treatments were applied from days 8–11, and samples of liquid and solid associated bacteria collected on days 9–11. Overall, 128 samples were analyzed by amplification of the V4 region of bacterial 16S rRNA, and data were analyzed with R and SAS for alpha and beta diversity, taxa relative abundance, and correlation of taxa abundance with propionate molar proportion. We observed a lower bacterial diversity (Shannon index, P = 0.02) when YM1 was added to the diet in comparison to the 3 other treatments. Moreover, compared to control, addition of YM1 to the diet increased relative abundance of phylum Proteobacteria (P = 0.05) and family Succinivibrioceae (P = 0.05) in the solid fraction and tended to increase abundance of family Succinivibrioceae (P = 0.10) and genus Succinivibrio (P = 0.09) in the liquid fraction. Correlation analysis indicated a positive association between propionate molar proportion and relative abundance of Proteobacteria (r = 0.36, P = 0.04) and Succinivibrioceae (r = 0.36, P = 0.05) in the solid fraction. The inclusion of YM1 in high grain diets with a high starch content resulted in greater abundance of bacteria involved in succinate synthesis which may have provided the substrate for the greater propionate synthesis observed.UCR::Vicerrectoría de Docencia::Ciencias Agroalimentarias::Facultad de Ciencias Agroalimentarias::Escuela de Zootecni

Effects of unprotected choline chloride on microbial fermentation in a dual-flow continuous culture depend on dietary neutral detergent fiber concentration

La Universidad de Costa Rica apoyó el programa de doctorado de José Alberto Arce CorderoCholine is usually supplemented as ruminally protected choline chloride to prevent its degradation in the rumen, but the effects of unprotected choline on ruminal fermentation are unclear. Some research indicates a possible role of dietary fiber on microbial degradation of choline; therefore we aimed to evaluate the effects of unprotected choline chloride on ruminal fermentation and to investigate whether those effects depend on dietary neutral detergent fiber (NDF) concentration. Our hypothesis was that dietary NDF concentration would influence choline chloride effects on microbial ruminal fermentation. We used 8 fermentors in a duplicated 4 × 4 Latin square with a 2 × 2 factorial arrangement, combining 2 factors: (1) dietary NDF concentration and (2) unprotected choline chloride supplementation. Resulting treatments are (1) 30%NDF/Ctrl [30% NDF control diet without supplemental choline (Cho)]; (2) 30%NDF/Cho [30% NDF diet plus 1.9 g of choline ion per kg of dry matter (DM)]; (3) 40%NDF/Ctrl (40% NDF control diet without supplemental choline); and (4) 40%NDF/Cho (40% NDF diet plus 1.9 g of choline ion per kg of DM). Four 10-d periods were completed, each consisting of 7 d for adaptation and 3 d for collection of samples for estimation of nutrient disappearance and daily average concentrations of volatile fatty acids and NH3-N. In addition, kinetics of pH, acetate, and propionate were evaluated at 0, 1, 2, 4, 6, and 8 h after morning feeding. On the last day of each period, bacteria pellets were harvested for 15N analysis and N metabolism. Fixed effects of dietary NDF concentration, unprotected choline chloride supplementation, and their interaction (NDF × Cho) were tested using the MIXED procedure of SAS version 9.4 (SAS Institute Inc., Cary, NC). Choline tended to increase total volatile fatty acid concentrations and decreased acetate molar proportion regardless of dietary NDF concentration, but it increased propionate molar proportion and decreased acetate to propionate ratio only with the 30% NDF diet. Supplementing choline decreased NDF disappearance regardless of dietary NDF; however, organic matter disappearance tended to be re duced only when choline was added to 40% NDF. Our data indicate that unprotected choline chloride effects on ruminal fermentation depend on dietary NDF concentration, allowing for a greater propionate synthesis without decreasing organic matter disappearance when fed with a 30% NDF diet.Universidad de Costa Rica/[]/UCR/Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Agroalimentarias::Facultad de Ciencias Agroalimentarias::Escuela de Zootecni

Feeding Canola, Camelina, and Carinata Meals to Ruminants

Soybean meal (SBM) is a byproduct from the oil-industry widely used as protein supplement to ruminants worldwide due to its nutritional composition, high protein concentration, and availability. However, the dependency on monocultures such as SBM is problematic due to price fluctuation, availability and, in some countries, import dependency. In this context, oilseeds from the mustard family such as rapeseed/canola (Brassica napus and Brassica campestris), camelina (Camelina sativa), and carinata (Brassica carinata) have arisen as possible alternative protein supplements for ruminants. Therefore, the objective of this comprehensive review was to summarize results from studies in which canola meal (CM), camelina meal (CMM), and carinata meal (CRM) were fed to ruminants. This review was based on published peer-reviewed articles that were obtained based on key words that included the oilseed plant in question and words such as “ruminal fermentation and metabolism, animal performance, growth, and digestion”. Byproducts from oil and biofuel industries such as CM, CMM, and CRM have been evaluated as alternative protein supplements to ruminants in the past two decades. Among the three plants reviewed herein, CM has been the most studied and results have shown an overall improvement in nitrogen utilization when animals were fed CM. Camelina meal has a comparable amino acids (AA) profile and crude protein (CP) concentration to CM. It has been reported that by replacing other protein supplements with CMM in ruminant diets, similar milk and protein yields, and average daily gain have been observed. Carinata meal has protein digestibility similar to SBM and its CP is highly degraded in the rumen. Overall, we can conclude that CM is at least as good as SBM as a protein supplement; and although studies evaluating the use of CMN and CRM for ruminants are scarce, it has been demonstrated that both oilseeds may be valuable feedstuff for livestock animals. Despite the presence of erucic acid and glucosinolates in rapeseed, no negative effect on animal performance was observed when feeding CM up to 20% and feeding CMN and CRM up to 10% of the total diet

Effects of choline chloride on the ruminal microbiome at 2 dietary neutral detergent fiber concentrations in continuous culture

Our objective was to evaluate the effects of unprotected choline chloride (Cho) on the ruminal microbiome at 2 dietary neutral detergent fiber (NDF) concentrations. We hypothesized that the effects of Cho on ruminal bacterial populations would depend on NDF. Eight dual-flow continuous-culture fermentors were arranged in a duplicated 4 × 4 Latin square as a 2 × 2 factorial with the following treatments: (1) 30% NDF-control (30% NDF diet, no supplemental choline); (2) 30% NDF-Cho (30% NDF diet plus 1.9 g of choline ion per kg of dry matter); (3) 40% NDF-control (40% NDF diet, no supplemental choline); and (4) 40% NDFCho (40% NDF diet plus 1.9 g of choline ion per kg of dry matter). We did 4 fermentation periods of 10 d each and used the last 3 d for collection of samples of solid and liquid digesta effluents for DNA extraction. Overall, 32 solid and 32 liquid samples were analyzed by amplification of the V4 variable region of bacterial 16S rRNA. Data were analyzed with R (R Project for Statistical Computing) and SAS (SAS Institute Inc.) to determine effects of Cho, NDF, and NDF × Cho on taxa relative abundance. The correlation of propionate molar proportion with taxa relative abundance was also analyzed. At the phylum level, relative abundance of Firmicutes in the liquid fraction tended to be greater when Cho was supplemented with a 30% NDF diet. At the order level, Cho increased Coriobacteriales in solid fraction and decreased Fibrobacterales in liquid fraction. Moreover, Cho decreased abundance of Clostridiales and increased Selenomonadales in the solid fraction, only with the 30% NDF diet. For genera, lower abundance of Pseudobutyrivibrio resulted from Cho in solid and liquid fractions. Greater abundance of Succinivibrio in solid and Selenomonas and Selenomonas 1 in liquid resulted from Cho with the 30% NDF diet. Propionate molar proportion was positively correlated with relative abundance of order Selenomonadales in solid and liquid fractions, and with genus Succinivibrio in solid and genera Selenomonas and Selenomonas 1 in liquid. Our results indicate that Cho primarily decreases abundance of bacteria involved in fiber degradation and increases abundance of bacteria mainly involved in nonstructural carbohydrate degradation and synthesis of propionate, particularly when a diet with 30% NDF is provided.UCR::Vicerrectoría de Docencia::Ciencias Agroalimentarias::Facultad de Ciencias Agroalimentarias::Escuela de Zootecni

Adaptation of in vitro methodologies to estimate the intestinal digestion of lipids in ruminants

The objective of this study was to adapt existing in vitro methodologies to determine the extent of intestinal digestion of corn oil (CO), canola oil (CA), and beef tallow (BT) via manipulation of incubation length and concentrations of lipase, bile, and calcium within a buffer solution. Unless otherwise stated, 0.5 g of each lipid source were incubated separately and in triplicate, with triplicate batch culture runs for each treatment in 40 mL of 0.5 M KH2PO4 (pH = 7.6) for 24 h with pancreatin (8 g/L), bovine bile (2.5 g/L), and CaCl2 (10 mM). Individually, concentrations of pancreatin, bile, and CaCl2, as well as incubation length were tested. To examine the use of this assay to estimate in vitro total tract digestion, a KH2PO4 solution with concentrated amounts to reach the same final concentrations of pancreatin, bile, and Ca were used as the third step in a three-step total tract digestibility procedure. Free glycerol and free fatty acid (FFA) concentrations were measured using colorimetric assays as indicators of digestion. Data wereanalyzed as a completely randomized block design (block = run), using the Glimmix procedure of SAS. For each lipid source, free glycerol increased with increasing pancreatin; however, FFA was lowest at 0 g/L pancreatin but was similar at 6, 8, and 10 g/L. Both glycerol and FFA were greater for 2.5 and 5 g/L of bile than for 0 g/L for each lipid source. Calcium concentration did not affect glycerol or FFA for either CO or CA; however, glycerol and FFA for BT were greater when calcium was included at 5 and 10 mM than at 0 mM. For all fat sources, free glycerol and FFA increased after 1 h until 12 h, but did not increase from 12 to 24 h. When a concentrated mixture was used following fermentation and acidification steps, digestibility using FFA concentration increased as compared to just adding buffer; however, free glycerol concentration was indeterminable. Thus, free glycerol and FFA can be used as indicators of lipid digestion when a lipid source is incubated for at least 12 h in a buffer solution containing 8 g/L pancreatin, 2.5 g/L bile, and 5 mM Ca when only estimating in vitro intestinal digestion; however, when utilizing this assay in a three-step in vitro total tract digestibility procedure, only FFA can be used.UCR::Vicerrectoría de Docencia::Ciencias Agroalimentarias::Facultad de Ciencias Agroalimentarias::Escuela de Zootecni

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

The objective of this study was to evaluate the effects of feeding sugars as a replacement for starch on the ruminal microbiome using a dual-flow continuous culture system. Four periods of 10 days each were conducted with 8 fermenters in a 4 × 4 replicated Latin square design. Treatments included: 1) control with corn—CON, 2) molasses—MOL, 3) untreated condensed whey permeate—CWP, and 4) CWP treated with a caustic agent—TCWP as a partial substitute for corn. Sugars were defined as the water-soluble carbohydrates (WSC) concentration. Diets were formulated by replacing 4% of the diet DM in the form of starch from corn with the sugars in byproducts. Microbial samples for DNA analysis were collected from the solid and liquid effluent containers at 3, 6, and 9 h after feeding. Bacterial community composition was analyzed with sequencing the V4 region of the 16S rRNA gene using Illumina MiSeq platform. Data were analyzed with R 4.1.3 packages vegan, lmer, and ggplot to determine the effects of treatment on the relative abundance of taxa in the solid and liquid fractions, as well as the correlation of Acetate: Propionate ratio and pH to taxa relative abundance. Treatments did not affect alpha or beta diversity. At the phylum level the relative abundance of Proteobacteria was increased in CON compared to sugars in the solid fraction. In the liquid fraction, Firmicutes had greater relative abundance in sugar treatments while Bacteroidota and Spirochaetota were present in lower relative abundance in CWP. For solid and liquid samples, the family Lachnospiraceae had greater relative abundance in sugar treatments compared to CON. The decreased relative abundance of Christensenellaceae and Rikenellaceae paired with the greater relative abundance of Selenomonadaceae in CWP could help explain greater propionate molar proportion and decreased ruminal pH previously observed for this treatment. The genera Olsenella a lactic acid-producing bacterium, had the greatest relative abundance in MOL. Incorporating TCWP or MOL as a partial replacement for starch was more conservative of fibrolytic bacterial taxa compared to CWP. Additionally, TCWP did not increase bacterial taxa associated with synthesis of lactate as compared to MOL. Overall, replacing starch with sugars is mostly conservative of the ruminal microbiome; however, changes observed coincide with differences observed in acetate and propionate proportions and ruminal pH.UCR::Vicerrectoría de Docencia::Ciencias Agroalimentarias::Facultad de Ciencias Agroalimentarias::Escuela de Zootecni

Effects of neutral detergent fiber digestibility estimation method on calculated energy concentration of canola meals from 12 Canadian processing plants

Our aim was to determine whether the method used to estimate truly digestible neutral detergent fiber (tdNDF) affects calculated concentrations of total digestible nutrients (TDN1x) and net energy of lactation (NEL3x) of canola meal (CM). Samples were collected from 12 CM processing plants in Canada over 4 yr (2011 to 2014, n = 47) and analyzed for dry matter (DM), crude protein (CP), ether extract (EE), ash, neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin (ADL), and neutral detergent insoluble CP (NDICP). Ruminal in situ incubation of CM samples was performed at 0, 24, 48, 96, and 288 h to determine NDF fractions (A, B, and C), effective ruminal NDF digestibility (ERNDFD), and indigestible NDF (iNDF) of CM. Three tdNDF-estimation methods were evaluated: 1) National Research Council (NRC) = 0.75 × (NDF − NDICP − ADL) × {1− [ADL/ (NDF − NDICP)]0.667}; 2) iNDF = 0.75 × (NDF − NDICP − NDF remaining after 288 h in situ); and 3) ERNDFD estimated from in situ NDF digestion kinetics. Resulting tdNDF values were used for calculation of TDN1x and NEL3x according to NRC (2001) equations. Data were analyzed with MIXED procedure of SAS 9.4 to determine the effect of processing plant on chemical composition, NDF degradation kinetics and NEL3x of CM. Effect of tdNDF estimation method on calculated TDN1x and NEL3x of CM was also evaluated. Model for analysis of processing plant included the fixed effect of plant and the random effect of year (plant) as replication, while analysis of tdNDF methods included the fixed effect of tdNDF estimation method and the random effects of processing plant and of year(plant) as replication. There was an effect of processing plant on DM (P = 0.03), CP (P < 0.01), EE (P < 0.01), and NDF (P < 0.01) of CM. Processing plant also had an effect on NDF fractions A (P < 0.01) and B (P = 0.02) but did not affect fraction C and ERNDFD. The tdNDF estimation method had an effect on tdNDF (P < 0.01), TDN1x (P < 0.01), and NEL3x (P < 0.01) of CM, yielding average NEL3x values of 1.72, 1.87, and 2.07 Mcal/kg for NRC, iNDF, and ERNDFD, respectively. Our results indicate that calculated energy concentration of CM according to NRC (2001) equations varies depending on the method used for estimation of tdNDF. Further research will be needed to determine the most accurate estimation method.UCR::Vicerrectoría de Docencia::Ciencias Agroalimentarias::Facultad de Ciencias Agroalimentarias::Escuela de Zootecni

Effects of calcium–magnesium carbonate and calcium–magnesium hydroxide as supplemental sources of magnesium on microbial fermentation in a dual-flow continuous culture

La Universidad de Costa Rica apoyó el programa de doctorado de José Alberto Arce CorderoSupplemental sources of Mg can also aid in ruminal pH regulation due to their al kaline properties. Magnesium oxide (MgO) is the most common source of Mg for ruminants and can help controlling ruminal pH; however, the al kaline potential of other sources of Mg has not been evaluated. We aimed to evaluate the inclusion of calcium–magnesium carbonate (CaMg(CO3 )2 ) and calcium–magnesium hydroxide (CaMg(OH)4 ) alone or in combination as supplemental sources of Mg in corn silage-based diets and its impact on ruminal microbial fermentation. We hypothe sized that inclusion of CaMg(OH)4 would allow for ruminal fermentation conditions resulting in a greater pH compared to the inclusion of CaMg(CO3 )2 . Four treatments were defined by the supplemental source of Mg in the diet: 1) Control (100% MgO, plus sodium sesquicarbonate as a buffer); 2) CO3 [100% CaMg(CO3 )2 ]; 3) OH [100% CaMg(OH)4 ]; and 4) CO3 /OH [50% Mg from CaMg(CO3 )2 , 50% Mg from CaMg(OH)4 ]. Nutrient concentration was held constant across treatments (16% CP, 30% NDF, 1.66 Mcal NEl/ kg, 0.67% Ca, and 0.21% Mg). Four fermenters were used in a 4 × 4 Latin square design with four periods of 10 d each. Samples were collected for analyses of nutrient digestibility, soluble Mg, VFA, and NH3 , while pH was measured at 0, 1, 2, 4, 6, 8, and 10 h post morning feeding to estimate % time when pH was below 6 (pH-B6) and area under the pH curve for pH below 6.0 (pH-AUC). Bacteria pellets were harvested for 15N analysis and estimates of N metabolism. Treatment ef fects were analyzed with the mixed procedure of SAS, while effects of using either CaMg(CO3 )2 or CaMg(OH)4 as Mg source in comparison to Control treatment were evaluated by orthog onal contrasts. Similar pH-related variables were observed for Control, OH, and CO3 /OH treat ments, which had smaller pH-AUC and pH-B6 than CO3 (P ≤ 0.01). Butyrate molar proportion was greater in Control and CO3 /OH than in CO3 and OH (P = 0.04). Orthogonal contrasts showed lower flow of bacterial N (P = 0.04), lower bu tyrate molar proportion (P = 0.08) and greater pH-AUC (P = 0.05) for diets with CaMg(CO3 )2 in comparison with the Control. Concentration of soluble Mg in ruminal fluid (P = 0.73) and nu trient digestibility (P ≥ 0.52) were similar across treatments. Under the conditions of this experi ment, using CaMg(OH)4 alone or combined with CaMg(CO3 )2 allowed for a less acidic rumi nal fermentation pattern than a diet with only CaMg(CO3 )2 .Universidad de Costa Rica/[]/UCR/Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Agroalimentarias::Facultad de Ciencias Agroalimentarias::Escuela de Zootecni