Effects of zinc and sodium monensin on ruminal degradation of lysine-HCl and liquid 2-hydroxy-4-methylthiobutanoic acid

Four nonlactating, mature, Holstein cows were fitted with ruminal cannula and used in a 4 x 4 Latin square-designed experiment to evaluate the impact of supplemental Zn and monensin on ruminal degradation of Lys and liquid 2-hydroxy-4-methylthiobutanoic acid (HMB). Cows were fed 4.54 kg (as fed) of alfalfa hay top-dressed with 4.54 kg (as fed) concentrate once daily. Concentrates were formulated to provide 0 or 500 mg/kg of Zn as ZnSO4 and 0 or 40 mg/kg of monensin in the total diet. Zinc supplementation provided approximately 22-fold greater dietary Zn than estimated by NRC requirements. On d 14 of each period, cows were dosed via the rumen cannula with 50 g of HMB and 100 g of Lys-HCl, and the concentrations of Lys and HMB were monitored every 0.5 h for 8 h. Supplemental Zn tended to decrease the proportion of acetate in ruminal fluid postfeeding and increased the proportion of propionate in ruminal fluid postfeeding. Supplemental Zn increased mean fluid passage rate from the rumen. Monensin decreased the proportion of acetate and increased the mean proportion of propionate in ruminal fluid, resulting in a decrease in the ratio of acetate to propionate. Monensin also increased the mean fluid passage rate from the rumen. Neither Zn nor monensin affected the apparent rate of ruminal disappearance of HMB or Lys. However, Zn and monensin interacted to alter the ruminal degradability of free Lys but not HMB. These data indicate that Zn and monensin may interact to alter ruminal degradability of free amino acids.     

Effect of low level monensin supplementation on the production of dairy cows fed alfalfa silage

Effectiveness of low level monensin supplementation on N utilization in lactating dairy cows fed alfalfa silage was assessed using 48 multiparous Holsteins. Cows were fed a covariate diet [% of dry matter (DM): 56% alfalfa silage, 39% ground high moisture corn, 3% soybean meal, 1% ground corn, 1% vitamin-mineral supplements] for 2 wk, then grouped by days in milk into blocks of 4. Cows were randomly assigned within blocks to 1 of 4 diets that were fed for 10 wk: 1) control (covariate diet), 2) control plus 3% fish meal (replacing DM from high moisture corn), 3) monensin (10 mg/kg DM), and 4) monensin plus 3% fish meal. Diets 1 and 3 averaged 16.7% crude protein (25% from free AA in alfalfa silage); diets 2 and 4 averaged 18.5% crude protein. Monensin intake averaged 16 mg/d on diets 1 and 2 (due to contamination) and 248 mg/d on diets 3 and 4. There was no effect of fish meal or monensin on DM intake. However, weight gain and yield of milk, protein, and SNF increased with fish meal feeding, indicating metabolizable protein limited production. Feeding monensin increased blood glucose but reduced yield of 3.5% fat-corrected milk, milk fat content and yield, and milk protein content and yield. Apparent N efficiency was greatest on monensin (diet 3) but lowest on monensin plus fish meal (diet 4). Fish meal reduced blood glucose concentration and apparent N efficiency, and increased concentrations of milk and blood urea. Monensin increased ruminal propionate concentration and decreased concentration of acetate and butyrate and acetate:propionate in ruminally cannulated cows fed the experimental diets. However, these changes were small, suggesting that too little monensin was fed. Fish meal reduced ruminal total amino acid (AA) but monensin did not alter ruminal NH(3) or total AA. Both fish meal and monensin increased NH(3) formation from casein AA using ruminal inoculum from the cannulated cows. There was no evidence from this trial that feeding 250 mg of monensin per day to lactating cows improved N utilization by reducing ruminal catabolism of the large amounts of free AA in alfalfa silage.     

Pancreatic amylase, plasma glucose, and insulin responses to propionate or monensin in sheep

Yearling wethers fitted with reentrant bile-pancreatic duct cannulae were in a two-part study of effects of duodenal propionate infusions or increased ruminal propionate caused by dietary monensin on pancreatic alpha-amylase secretion and glucose and insulin in blood plasma. Continuous duodenal infusion of propionate increased concentrations of glucose and insulin in blood plasma of wethers fed alfalfa. Results supported a direct response of insulin secretion to propionate. Amylase secretion was not affected. Addition of monensin (22 ppm) to an 80% corn diet reduced the ratio of acetate:propionate in rumen, but bile-pancreatic flow and amylase activity were unaffected. Monensin supplementation had little influence on glucose and insulin in blood plasma. Pancreatic alpha-amylase secretion of ruminants seems to be a complex phenomenon that is not regulated strictly by fluctuations of glucose or insulin.     

Rumen volatile fatty acid production and nutrient utilization in steers fed a diet supplemented with sodium bicarbonate and monensin

Effects of feeding dietary supplements of monensin and sodium bicarbonate singly or in combination on production of rumen volatile fatty acids, nitrogen balance, and rumen water kinetics were studied. Four rumen fistulated steers were fed a diet (50% concentrate mix and 50% corn silage) ad libitum in a 4 X 4 Latin square design (21-day periods) with a 2 X 2 factorial arrangement of treatments. Sodium bicarbonate increased feed intake, water intake, rumen pH, fluid dilution rate, and decreased both molar proportion and production rate of propionate in the rumen. Alteration of the ratio of acetate to propionate reflects the large decrease in propionate production relative to the small increase in acetate production. In contrast, monensin did not alter significantly rumen fluid dilution rate or ruminal pH but did decrease the molar proportion of acetate and increase that of propionate. Monensin increased production of both acetate and propionate in the rumen; however, the large increase in propionate production appears to account for more of the increase in molar proportion of propionate in the rumen. Increases in total volatile fatty acid production per kilogram of dry matter consumed with monensin supplementation appears to result from decrease in feed intake, thereby increasing ruminal retention time of dry matter and potentially the extent of digestion. Efficiency of nitrogen utilization was not altered by either sodium bicarbonate or monensin.     

Effects of acetate,propionate, and pH on volatile fatty acid thermodynamics in continuous cultures of ruminal contents

To investigate the effects of acetate, propionate, and pH on thermodynamics of volatile fatty acids (VFA) in the rumen, a dual-flow continuous culture study was conducted to quantify production of major VFA, interconversions among the VFA, and H₂ and CH₄ emissions in a 4 × 4 Latin square design. The 4 treatments were (1) control: pH buffered to an average of 6.75; (2) control plus 20 mmol/d of infused acetate (InfAc); (3) control plus 7 mmol/d of infused propionate (InfPr); and (4) a 0.5-unit decline in pH elicited by adjustment of the buffer (LowpH). All fermentors were fed 40 g of a pelleted diet containing whole alfalfa pellets and concentrate mix pellets (50:50) once daily. After 7 d of treatment, sequential, continuous infusions of [2-¹³C] sodium acetate (3.5 mmol/d), [U-¹³C] sodium propionate (2.9 mmol/d), and [1-¹³C] sodium butyrate (0.22 mmol/d) were carried out from 12 h before feeding for 36 h. Filtered liquid effluent (4 mL) was sampled at 0, 2, 4, 6, 8, 12, 16, and 22 h after feeding, and assessed for VFA concentrations, with another filtered sample (20 mL) used to quantify aqueous concentrations of CH₄ and H₂. Headspace CH₄ and H₂ gases were monitored continuously. Ruminal microbes were isolated from the mixed effluent samples, and the microbial community structure was analyzed using the 16S rRNA amplicon sequencing technique. The digestibility of neutral detergent fiber, acid detergent fiber, and starch and microbial C sequestrated from VFA were not affected by treatments. The LowpH treatment increased net propionate production and decreased H₂ and CH₄ headspace emissions, primarily due to shifts in metabolic pathways of VFA formation, likely due to the observed changes in bacterial community structure. Significant interconversions occurred between acetate and butyrate, whereas interconversions of other VFA with propionate were relatively small. The InfAc and InfPr treatments increased net acetate and propionate production, respectively; however, interconversions among VFA were not affected by pH, acetate, or propionate treatments, suggesting that thermodynamics might not be a primary influencer of metabolic pathways used for VFA formation.     

Effects of monensin on ruminal forage degradability and total tract diet digestibility in lactating dairy cows during grain-induced subacute ruminal acidosis

The effects of monensin premix supplementation on ruminal pH characteristics and forage degradability, and total tract diet digestibility during grain-induced subacute ruminal acidosis (SARA) in lactating dairy cows receiving a total mixed ration were investigated. Six multiparous, rumen-fistulated Holstein cows were used in a 2-treatment, 2-period (5 wk per period) crossover design. During wk 5 (d 29 to 35) of each period, SARA was induced using a grain challenge model, and ruminal pH was measured continuously using indwelling pH probes. Ruminal degradation of corn silage and alfalfa haylage was determined using the in situ (nylon bag) technique, and total tract diet digestibility was determined by total fecal collection during wk 5. Monensin supplementation did not affect dry matter intake, milk yield, and composition, and ruminal pH characteristics under these experimentally induced SARA conditions. Rates of ruminal forage fiber degradability were similar between control and monensin-treated cows; however, monensin supplementation increased total tract fiber digestion. This study indicates that monensin altered total tract nutrient digestion by increasing fiber digestion at postruminal sites.     

Sodium bicarbonate and alfalfa hay additions to wheat silage diets fed to lactating dairy cows

Two experiments were conducted to examine dietary effects of .8% sodium bicarbonate and 1.4 kg/d of alfalfa hay on performance and rumen metabolism of lactating dairy cows fed 50% wheat silage and 50% concentrate (dry basis). In Experiment 1 with 12 midlactation Holsteins in a 4 X 4 Latin square design, intake, milk production, and milk composition were not affected by treatment. Dietary sodium bicarbonate and alfalfa hay did not alter blood, rumen, or fecal pH. Rumen volatile fatty acid pattern was not affected by sodium bicarbonate, but addition of hay resulted in higher molar percentage propionate and lower acetate: propionate ratios. In Experiment 2 with 32 early lactation cows (20 Holsteins and 12 Jerseys) in a complete randomized block design, supplementation of sodium bicarbonate, alfalfa hay, or both did not affect intake, milk production, or milk composition in the first 8 wk of lactation. Blood, rumen, and fecal pH were not affected by treatment. Dietary sodium bicarbonate did not alter ruminal volatile fatty acid profile, whereas addition of hay increased molar proportion acetate and decreased molar proportion butyrate. A shift in rumen fermentation was observed across treatments from wk 1 through 8 postpartum with molar proportions of acetate and butyrate increasing and molar proportion of propionate decreasing.     

Diet supplementation with thyme oil and its main component thymol failed to favorably alter rumen fermentation,improve nutrient utilization,or enhance milk production in dairy cows

Phenolic compounds and essential oils with high content of phenolic compounds have been reported to exert antimicrobial activities in vitro. The objective of this study was to determine the effects of dairy cow diet supplementation with thyme oil and its main component thymol on intake and total-tract apparent digestibility of nutrients, rumen fermentation characteristics, ruminal protozoa, nitrogen excretion, and milk production. For this aim, we used 8 multiparous, ruminally cannulated Holstein cows in a replicated 4 × 4 Latin square design (28 d periods), balanced for residual effects. Cows were fed 1 of the 4 following experimental treatments: total mixed ration (TMR) with no additive (control); TMR + monensin [24 mg/kg of dry matter (DM)]; TMR + thyme oil (50 mg/kg of DM); and TMR + thymol (50 mg/kg of DM). Compared with the control diet, feeding thyme oil or thymol had no effect on DM intake, nutrient total-tract apparent digestibility, total N excretion, ruminal pH, ammonia concentration, total volatile fatty acid (VFA) concentration, or acetate:propionate ratio. Ruminal protozoa density was not modified by thyme oil, but decreased with thymol supplementation. Supplementation with thyme oil or thymol did not affect milk production, milk composition, or efficiency of milk production. Neither thyme oil nor thymol affected efficiency of dietary N use for milk N secretion (N intake/milk N). Supplementation with monensin tended to decrease DM intake (–1.2 kg/d) and milk fat yield. Total-tract apparent digestibility of nutrients did not differ between cows fed monensin and cows fed the control diet. Total VFA concentration was not changed by monensin supplementation compared with control, but adding monensin shifted the VFA profile toward more propionate and less acetate, resulting in a decrease of acetate:propionate ratio. Protozoa density and ammonia concentration were lower in the ruminal content of cows fed monensin compared with that of cows fed the control diet. Total N excretion was not affected by monensin supplementation. Likewise, efficiency of use of dietary N for milk N secretion was unchanged in cows fed monensin. The results of this study contrasted with the claimed in vitro antimicrobial activity of thyme oil and thymol: we observed no positive effects on rumen metabolism (i.e., N and VFA) or milk performance in dairy cows. Under the conditions of this study, including thyme oil or thymol at 50 mg/kg of DM had no benefits for rumen fermentation, nutrient utilization and milk performance in dairy cows.     

Effects of a Saccharomyces cerevisiae culture on in vitro mixed ruminal microorganism fermentation.

Previous research has shown that Saccharomyces cerevisiae culture increases lactate utilization and cellulose digestion by pure cultures of ruminal bacteria. Based on these pure culture results, in vitro mixed ruminal microorganism fermentations were conducted to determine the effects of 0.35 and 0.73 g/L of Sacc. cerevisiae culture on the fermentation of ground corn, maltose, alfalfa hay, bermudagrass hay, and lactate. In addition, experiments were performed to evaluate the effects of Sacc. cerevisiae culture and monensin on the mixed ruminal microorganism fermentation. In the presence of ground corn, both concentrations of Sacc. cerevisiae culture had little effect on final pH or fermentation products, except the 0.35 g/L treatment increased valerate concentration. Saccharomyces cerevisiae culture had little effect on final pH or fermentation products in maltose or lactate fermentations. When alfalfa hay was the substrate, 0.73 g/L of Sacc. cerevisiae culture increased propionate concentration and both treatments decreased the acetate to propionate ratio. In the case of Coastal bermudagrass hay, 0.73 g/L Sacc. cerevisiae culture increased concentrations of acetate, propionate, CH4, butyrate, isovalerate, valerate, and decreased the acetate to propionate ratio, whereas both treatments increased total volatile fatty acid concentrations. Similar to alfalfa hay, in vitro dry matter disappearance of Coastal bermudagrass hay was numerically increased in the presence of Sacc. cerevisiae culture. Monensin altered the fermentation by decreasing concentrations of CH4 and lactate and increasing concentrations of propionate. There was no interaction between Sacc. cerevisiae culture and monensin. In conclusion, the incorporation of Sacc. cerevisiae culture into mixed ruminal microorganism fermentations of ground corn, maltose, or lactate had little effect on final pH and fermentation products. However, in the presence of alfalfa hay or Coastal bermudagrass hay Sacc. cerevisiae culture increased concentrations of several fermentation products and numerically increased in vitro dry matter disappearance of forage fiber.     

Corn silage-based diet supplemented with increasing amounts of linseed oil: Effects on methane production,rumen fermentation,nutrient digestibility,nitrogen utilization,and milk production of dairy cows

In this study, we assessed the effects of increasing amounts of linseed oil (LSO) in corn silage-based diets on enteric CH₄ production, rumen fermentation characteristics, protozoal population, nutrient digestibility, N utilization, and milk production. For this purpose, 12 multiparous lactating Holstein cows (84 ± 28 d in milk; mean ± SD) fitted with ruminal cannula were used in a replicated 4 × 4 Latin square design (35-d period). The cows were fed ad libitum a total mixed ration without supplementation (control) or supplemented [on a dry matter (DM) basis] with LSO at 2% (LSO2), 3% (LSO3) or 4% (LSO4). The forage:concentrate ratio was 61:39 (on DM basis) and was similar among the experimental diets. The forage portion consisted of corn silage (58% diet DM) and timothy hay (3% diet DM). The proportions of soybean meal, corn grain and soybean hulls decreased as the amount of LSO in the diet increased. Daily methane production (g/d) decreased quadratically as the amount of LSO increased in the diet. Increasing LSO dietary supplementation caused a linear decrease in CH₄ emissions expressed on either DM intake (DMI) basis (?9, ?20, and ?28%, for LSO2, LSO3, and LSO4, respectively) or gross energy intake basis (?12, ?22, and ?31%, for LSO2, LSO3, and LSO4, respectively). At 2 and 3% LSO, the decrease in enteric CH₄ emissions occurred without negatively affecting DMI or apparent total-tract digestibility of fiber and without changing protozoa numbers. However, these 2 diets caused a shift in volatile fatty acids pattern toward less acetate and more propionate. The effect of the LSO4 diet on enteric CH₄ emissions was associated with a decrease in DMI, fiber apparent-total-tract digestibility, protozoa numbers (total and genera), and an increase in propionate proportion at the expense of acetate and butyrate proportions. Methane emission intensity [g of CH₄/kg of energy-corrected milk (ECM)] decreased linearly (up to 28% decrease) with increasing LSO level in the diet. Milk fat yield decreased linearly (up to 19% decrease) with increasing inclusion of LSO in the diet. Milk protein yield increased at 2% or 3% LSO and decreased to the same level as that of the nonsupplemented diet at 4% LSO (quadratic effect). Yield of ECM was unchanged by LSO2 and LSO3 treatments but decreased (?2.8 kg/d) upon supplementation with 4% LSO (quadratic effect). Efficiency of milk production (kg ECM/kg DMI) was unaffected by the 3 levels of LSO. Ruminal NH₃ concentration was quadratically affected by LSO supplementation; decreasing only at the highest level of LSO supplementation. The amount (g/d) of N excreted in feces and urine decreased linearly and quadratically, respectively, as the amount of LSO increased in the diet, mainly because of the reduction in N intake. Efficiency of dietary N used for milk N secretion increased linearly with increasing LSO supplementation in the diet. We conclude that supplementing corn silage-based diets with 2 or 3% of LSO can reduce enteric CH₄ emissions up by to 20% without impairing animal productivity (i.e., ECM yield and feed efficiency).     

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

Choline 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 reduced 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.     

Effects of bacterial direct-fed microbials on ruminal characteristics,methane emission,and milk fatty acid composition in cows fed high- or low-starch diets

This study investigated the effects of bacterial direct-fed microbials (DFM) on ruminal fermentation and microbial characteristics, methane (CH₄) emission, diet digestibility, and milk fatty acid (FA) composition in dairy cows fed diets formulated to induce different ruminal volatile fatty acid (VFA) profiles. Eight ruminally cannulated dairy cows were divided into 2 groups based on parity, days in milk, milk production, and body weight. Cows in each group were fed either a high-starch (38%, HS) or a low-starch (2%, LS) diet in a 55:45 forage-to-concentrate ratio on a dry matter (DM) basis. For each diet, cows were randomly assigned to 1 of 4 treatments in a Latin square design of (1) control (CON); (2) Propionibacterium P63 (P63); (3) P63 plus Lactobacillus plantarum 115 (P63+Lp); (4) P63 plus Lactobacillus rhamnosus 32 (P63+Lr). Strains of DFM were administered at 10¹⁰ cfu/d. Methane emission (using the sulfur hexafluoride tracer technique), total-tract digestibility, dry matter intake, and milk production and composition were quantified in wk 3. Ruminal fermentation and microbial characteristics were measured in wk 4. Data were analyzed using the mixed procedure of SAS (SAS Institute Inc., Cary, NC). The 2 diets induced different ruminal VFA profiles, with a greater proportion of propionate at the expense of acetate and butyrate for the HS diet. Greater concentrations of total bacteria and selected bacterial species of methanogenic Archaea were reported for the HS diet, whereas the protozoa concentration in HS decreased. For both diets, bacterial DFM supplementation raised ruminal pH (+0.18 pH units, on average) compared with CON. Irrespective of diet, P63+Lp and P63+Lr increased ruminal cellulase activity (3.8-fold, on average) compared with CON, but this effect was not associated with variations in ruminal microbial numbers. Irrespective of diet, no effect of bacterial DFM on ruminal VFA was observed. For the LS diet, supplementing cows with P63+Lr tended to decrease CH₄ emission (26.5%, on average, when expressed per kilogram of milk or 4% fat-corrected milk). Only P63 supplementation to cows fed the HS diet affected the concentration of some milk FA, such as cis isomers of 18:1 and intermediates of ruminal biohydrogenation of polyunsaturated FA. Overall, bacterial DFM could be useful to stabilize ruminal pH. Their effects on CH₄ production mitigation and milk FA profile depended on DFM strain and diet and should be confirmed under a greater variation of dietary conditions.     

Effects of feeding monensin sodium to lactating goats: milk composition and ruminal volatile fatty acids

When diets containing 33 and 18 ppm monensin sodium were fed for ad libitum intake to dairy goats, milk fat content was reduced by 15 and 5%. Milk protein content was increased 10% when 33 ppm sodium monensin was fed with diet at restricted intake. Milk yield was not affected. Both ad libitum and restricted consumption of diet containing 33 ppm monensin sodium reduced ratios of ruminal acetate:propionate. These resulted from increased propionate concentration with ad libitum consumption and from reduced acetate with restricted feeding. Diets containing 18 ppm monensin sodium resulted in slightly higher concentrations of both propionate and acetate. Monensin sodium did not reduce feed intake significantly.     

Effect of replacing calcium salts of palm oil with camelina seed at 2 dietary ether extract levels on digestion,ruminal fermentation,and nutrient flow in a dual-flow continuous culture system

Camelina is a drought- and salt-tolerant oil seed, which in total ether extract (EE) contains up to 74% polyunsaturated fatty acids. The objective of this study was to assess the effects of replacing calcium salts of palm oil (Megalac, Church & Dwight Co. Inc., Princeton, NJ) with camelina seed (CS) on ruminal fermentation, digestion, and flows of fatty acids (FA) and AA in a dual-flow continuous culture system when supplemented at 5 or 8% dietary EE. Diets were randomly assigned to 8 fermentors in a 2 × 2 factorial arrangement of treatments in a replicated 4 × 4 Latin square design, with four 10-d experimental periods consisting of 7 d for diet adaptation and 3 d for sample collection. Treatments were (1) calcium salts of palm oil supplementation at 5% EE (MEG5); (2) calcium salts of palm oil supplementation at 8% EE (MEG8); (3) 7.7% CS supplementation at 5% EE (CS5); and (4) 17.7% CS supplementation at 8% EE (CS8). Diets contained 55% orchardgrass hay, and fermentors were fed 72 g of dry matter/d. On d 8, 9, and 10 of each period, digesta effluent samples were taken for ruminal NH₃, volatile fatty acids, nitrogen metabolism analysis, and long-chain FA and AA flows. Statistical analysis was performed using the MIXED procedure (SAS Institute Inc., Cary, NC). We detected an interaction between FA source and dietary EE level for acetate, where MEG8 had the greatest molar proportion of acetate. Molar proportions of propionate were greater and total volatile fatty acids were lower on CS diets. Supplementation of CS decreased overall ruminal nutrient true digestibility, but dietary EE level did not affect it. Diets containing CS had greater biohydrogenation of 18:2 and 18:3; however, biohydrogenation of 18:1 was greater in MEG diets. Additionally, CS diets had greater ruminal concentrations of trans-10/11 18:1 and cis-9,trans-11 conjugated linoleic acid. Dietary EE level at 8% negatively affected flows of NH₃-N (g/d), nonammonia N, and bacterial N as well as the overall AA outflow. However, treatments had minor effects on individual ruminal AA digestibility. The shift from acetate to propionate observed on diets containing CS may be advantageous from an energetic standpoint. Moreover, CS diets had greater ruminal outflow of trans-10/11 18:1 and cis-9,trans-11 conjugated linoleic acid than MEG diets, suggesting a better FA profile available for postruminal absorption. However, dietary EE at 8% was deleterious to overall N metabolism and AA outflow, indicating that CS can be fed at 5% EE without compromising N metabolism.     

Effect of low dietary concentrations of Acacia mearnsii tannin extract on chewing,ruminal fermentation,digestibility, nitrogen partition,and performance of dairy cows

The supplementation of dairy cows with tannins can reduce the ruminal degradation of dietary protein and urine N excretion, but high concentration in the diet can impair ruminal function, diet digestibility, feed intake, and milk yield. This study evaluated the effect of low concentrations (0, 0.14, 0.29, or 0.43% of diet in DM basis) of a tannin extract from the bark of Acacia mearnsii (TA) on milking performance, dry matter intake (DMI), digestibility, chewing behavior, ruminal fermentation, and N partition of dairy cows. Twenty Holstein cows (34.7 ± 4.8 kg/d, 590 ± 89 kg, and 78 ± 33 d in lactation) were individually fed a sequence of 4 treatments in 5, 4 × 4 Latin squares (with 21-d treatment periods, each with a 14-d adaptation period). The TA replaced citrus pulp in the total mixed ration and other feed ingredients were kept constant. Diets had 17.1% crude protein, mostly from soybean meal and alfalfa haylage. The TA had no detected effect on DMI (22.1 kg/d), milk yield (33.5 kg/d), and milk components. The proportions in milk fat of mixed origin fatty acids (16C and 17C) and the daily secretion of unsaturated fatty acids were linearly reduced and the proportion of de novo fatty acids was increased by TA. Cows fed TA had linear increase in the molar proportion of butyrate and linear reduction in propionate in ruminal fluid, whereas acetate did not differ. There was a tendency for the ratio of acetate to propionate to be linearly increased by TA. Cows fed TA had a linear reduction in the relative ruminal microbial yield, estimated by the concentrations of allantoin and creatinine in urine and body weight. The total-tract apparent digestibility of neutral detergent fiber, starch, and crude protein also did not differ. The TA induced a linear increase in meal size and duration of the first daily meal and reduced meal frequency. Rumination behavior did not differ with treatment. Cows fed 0.43% TA selected against feed particles >19 mm in the morning. There were tendencies for linear decreases in milk urea N (16.1–17.3 mg/dL), urine N (153–168 g/d and 25.5–28.7% of N intake), and plasma urea N at 6, 18, and 21 h postmorning feeding, and plasma urea N 12 h postfeeding was reduced by TA. The proportion of N intake in milk (27.1%) and feces (21.4%) did not differ with treatment. Reductions in urine N excretion and milk and plasma urea N suggest that TA reduced ruminal AA deamination, whereas lactation performance did not differ. Overall, TA up to 0.43% of DM did not affect DMI and lactation performance, while there was a tendency to reduce urine N excretion.     

Linseed oil and DGAT1 K232A polymorphism: Effects on methane emission,energy and nitrogen metabolism,lactation performance,ruminal fermentation,and rumen microbial composition of Holstein-Friesian cows

Complex interactions between rumen microbiota, cow genetics, and diet composition may exist. Therefore, the effect of linseed oil, DGAT1 K232A polymorphism (DGAT1), and the interaction between linseed oil and DGAT1 on CH₄ and H₂ emission, energy and N metabolism, lactation performance, ruminal fermentation, and rumen bacterial and archaeal composition was investigated. Twenty-four lactating Holstein-Friesian cows (i.e., 12 with DGAT1 KK genotype and 12 with DGAT1 AA genotype) were fed 2 diets in a crossover design: a control diet and a linseed oil diet (LSO) with a difference of 22 g/kg of dry matter (DM) in fat content between the 2 diets. Both diets consisted of 40% corn silage, 30% grass silage, and 30% concentrates (DM basis). Apparent digestibility, lactation performance, N and energy balance, and CH₄ emission were measured in climate respiration chambers, and rumen fluid samples were collected using the oral stomach tube technique. No linseed oil by DGAT1 interactions were observed for digestibility, milk production and composition, energy and N balance, CH₄ and H₂ emissions, and rumen volatile fatty acid concentrations. The DGAT1 KK genotype was associated with a lower proportion of polyunsaturated fatty acids in milk fat, and with a higher milk fat and protein content, and proportion of saturated fatty acids in milk fat compared with the DGAT1 AA genotype, whereas the fat- and protein-corrected milk yield was unaffected by DGAT1. Also, DGAT1 did not affect nutrient digestibility, CH₄ or H₂ emission, ruminal fermentation or ruminal archaeal and bacterial concentrations. Rumen bacterial and archaeal composition was also unaffected in terms of the whole community, whereas at the genus level the relative abundances of some bacterial genera were found to be affected by DGAT1. The DGAT1 KK genotype was associated with a lower metabolizability (i.e., ratio of metabolizable to gross energy intake), and with a tendency for a lower milk N efficiency compared with the DGAT1 AA genotype. The LSO diet tended to decrease CH₄ production (g/d) by 8%, and significantly decreased CH₄ yield (g/kg of DM intake) by 6% and CH₄ intensity (g/kg of fat- and protein-corrected milk) by 11%, but did not affect H₂ emission. The LSO diet also decreased ruminal acetate molar proportion, the acetate to propionate ratio, and the archaea to bacteria ratio, whereas ruminal propionate molar proportion and milk N efficiency increased. Ruminal bacterial and archaeal composition tended to be affected by diet in terms of the whole community, with several bacterial genera found to be significantly affected by diet. These results indicate that DGAT1 does not affect enteric CH₄ emission and production pathways, but that it does affect traits other than lactation characteristics, including metabolizability, N efficiency, and the relative abundance of Bifidobacterium. Additionally, linseed oil reduces CH₄ emission independent of DGAT1 and affects the rumen microbiota and its fermentative activity.     

Effect of nitrate supplementation,dietary protein supply,and genetic yield index on performance,methane emission,and nitrogen efficiency in dairy cows

The objective was to investigate the effect of nonprotein nitrogen source, dietary protein supply, and genetic yield index on methane emission, N metabolism, and ruminal fermentation in dairy cows. Forty-eight Danish Holstein dairy cows (24 primiparous cows and 24 multiparous cows) were used in a 6 × 4 incomplete Latin square design with 4 periods of 21-d duration. Cows were fed ad libitum with the following 6 experimental diets: diets with low, medium, or high rumen degradable protein (RDP):rumen undegradable protein (RUP) ratio (manipulated by changing the proportion of corn meal, corn gluten meal, and corn gluten feed) combined with either urea or nitrate (10 g NO₃⁻/kg of dry matter) as nonprotein nitrogen source. Samples of ruminal fluid and feces were collected from multiparous cows, and total-tract nutrient digestibility was estimated using TiO₂ as flow marker. Milk samples were collected from all 48 cows. Gas emission (CH₄, CO₂, and H₂) was measured by 4 GreenFeed units. We observed no significant interaction between dietary RDP:RUP ratio and nitrate supplementation, and between nitrate supplementation and genetic yield index on CH₄ emission (production, yield, intensity). As dietary RDP:RUP ratio increased, intake of crude protein, RDP, and neutral detergent fiber and total-tract digestibility of crude protein linearly increased, and RUP intake linearly decreased. Yield of milk, energy-corrected milk, and milk protein and lactose linearly decreased, whereas milk fat and milk urea nitrogen concentrations linearly increased as dietary RDP:RUP ratio increased. The increase in dietary RDP:RUP ratio resulted in a linear increase in the excretion of total purine derivatives and N in urine, but a linear decrease in N efficiency (milk N in % of N intake). Nitrate supplementation reduced dry matter intake (DMI) and increased total-tract organic matter digestibility compared with urea supplementation. Nitrate supplementation resulted in a greater reduction in DMI and daily CH₄ production and a greater increase in daily H₂ production in multiparous cows compared with primiparous cows. Nitrate supplementation also showed a greater reduction in milk protein and lactose yield in multiparous cows than in primiparous cows. Milk protein and lactose concentrations were lower for cows receiving nitrate diets compared with cows receiving urea diets. Nitrate supplementation reduced urinary purine derivatives excretion from the rumen, whereas N efficiency tended to increase. Nitrate supplementation reduced proportion of acetate and propionate in ruminal volatile fatty acids. In conclusion, no interaction was observed between dietary RDP:RUP ratio and nitrate supplementation, and no interaction between nitrate supplementation and genetic yield index on CH₄ emission (production, yield, intensity) was noted. Nitrate supplementation resulted in a greater reduction in DMI and CH₄ production, and a greater increase in H₂ production in multiparous cows than in primiparous cows. As the dietary RDP:RUP ratio increased, CH₄ emission was unaffected and RDP intake increased, but RUP intake and milk yield decreased. Genetic yield index did not affect CH₄ production, yield, or intensity.     

Interaction of molasses and monensin in alfalfa hay- or corn silage-based diets on rumen fermentation, total tract digestibility, and milk production by Holstein cows

Sugar supplementation can stimulate rumen microbial growth and possibly fiber digestibility; however, excess ruminal carbohydrate availability relative to rumen-degradable protein (RDP) can promote energy spilling by microbes, decrease rumen pH, or depress fiber digestibility. Both RDP supply and rumen pH might be altered by forage source and monensin. Therefore, the objective of this study was to evaluate interactions of a sugar source (molasses) with monensin and 2 forage sources on rumen fermentation, total tract digestibility, and production and fatty acid composition of milk. Seven ruminally cannulated lactating Holstein cows were used in a 5 × 7 incomplete Latin square design with five 28-d periods. Four corn silage diets consisted of 1) control (C), 2) 2.6% molasses (M), 3) 2.6% molasses plus 0.45% urea (MU), or 4) 2.6% molasses plus 0.45% urea plus monensin sodium (Rumensin, at the intermediate dosage from the label, 16 g/909 kg of dry matter; MUR). Three chopped alfalfa hay diets consisted of 1) control (C), 2) 2.6% molasses (M), or 3) 2.6% molasses plus Rumensin (MR). Urea was added to corn silage diets to provide RDP comparable to alfalfa hay diets with no urea. Corn silage C and M diets were balanced to have 16.2% crude protein; and the remaining diets, 17.2% crude protein. Dry matter intake was not affected by treatment, but there was a trend for lower milk production in alfalfa hay diets compared with corn silage diets. Despite increased total volatile fatty acid and acetate concentrations in the rumen, total tract organic matter digestibility was lower for alfalfa hay-fed cows. Rumensin did not affect volatile fatty acid concentrations but decreased milk fat from 3.22 to 2.72% in corn silage diets but less in alfalfa hay diets. Medium-chain milk fatty acids (% of total fat) were lower for alfalfa hay compared with corn silage diets, and short-chain milk fatty acids tended to decrease when Rumensin was added. In whole rumen contents, concentrations of trans-10, cis-12 C_18:2 were increased when cows were fed corn silage diets. Rumensin had no effect on conjugated linoleic acid isomers in either milk or rumen contents but tended to increase the concentration of trans-10 C_18:1 in rumen samples. Molasses with urea increased ruminal NH₃-N and milk urea N when cows were fed corn silage diets (6.8 vs. 11.3 and 7.6 vs. 12.0 mg/dL for M vs. MU, respectively). Based on ruminal fermentation characteristics and fatty acid isomers in milk, molasses did not appear to promote ruminal acidosis or milk fat depression. However, combinations of Rumensin with corn silage-based diets already containing molasses and with a relatively high nonfiber carbohydrate:forage neutral detergent fiber ratio influenced biohydrogenation characteristics that are indicators of increased risk for milk fat depression.     

Methane production,digestion, ruminal fermentation,nitrogen balance,and milk production of cows fed corn silage- or barley silage-based diets

This study evaluated the effects of replacing barley silage (BS) with corn silage (CS) in dairy cow diets on enteric CH₄ emissions, ruminal fermentation characteristics, digestion, milk production, and N balance. Nine ruminally cannulated lactating cows were used in a replicated 3 × 3 Latin square design (32-d period) and fed (ad libitum) a total mixed ration (TMR; forage:concentrate ratio 60:40; dry matter basis) with the forage portion consisting of either barley silage (0% CS; 0% CS and 54.4% BS in the TMR), a 50:50 mixture of both silages (27% CS; 27.2% CS and 27.2% BS in the TMR), or corn silage (54% CS; 0% BS and 54.4% CS in the TMR). Increasing the CS proportion (i.e., at the expense of BS) also involved increasing the proportion of corn grain (at the expense of barley grain). Intake and digestibility of dry matter and milk production increased linearly as the proportion of CS increased in the diet. Increasing dietary CS proportion decreased linearly the acetate molar proportion and increased linearly that of propionate. Daily CH₄ emissions tended to respond quadratically to increasing proportions of CS in the diet (487, 540, and 523 g/d for 0, 27, and 54% CS, respectively). Methane production adjusted for dry matter or gross energy intake declined as the amount of CS increased in the diet; this effect was more pronounced when cows were fed the 54% CS diet than the 27% CS diet. Increasing the CS proportion in the diet improved N utilization, as reflected by decreases in ruminal ammonia concentration and urinary N excretion and higher use of dietary N for milk protein secretion. Total replacement of BS with CS in dairy cow diets offers a strategy to decrease CH₄ energy losses and control N losses without negatively affecting milk performance.