Suppression of host humoral immunity by Borrelia burgdorferi varies over the course of infection.

Borrelia burgdorferi, the spirochetal agent of Lyme disease, utilizes a variety of strategies to evade and suppress the host immune response, which enables it to chronically persist in the host. The resulting immune response is characterized by unusually strong IgM production and a lack of long-term protective immunity. Previous studies in mice have shown that infection with B. burgdorferi also broadly suppresses host antibody responses against unrelated antigens. Here, we show that mice infected with B. burgdorferi and concomitantly immunized with recombinant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein had an abrogated antibody response to the immunization. To further define how long this humoral immune suppression lasts, mice were immunized at 2, 4, and 6 weeks post-infection. Suppression of host antibody production against the SARS-CoV-2 spike protein peaked at 2 weeks post-infection but continued for all timepoints measured. Antibody responses against the SARS-CoV-2 spike protein were also assessed following antibiotic treatment to determine whether this immune suppression persists or resolves following clearance of B. burgdorferi. Host antibody production against the SARS-CoV-2 spike protein returned to baseline following antibiotic treatment; however, anti-SARS-CoV-2 IgM remained high, comparable to levels found in B. burgdorferi-infected but untreated mice. Thus, our data demonstrate restored IgG responses following antibiotic treatment but persistently elevated IgM levels, indicating lingering effects of B. burgdorferi infection on the immune system following treatment.

Symposium review: Integrating the control of energy intake and partitioning into ration formulation.

Energy intake and partitioning are determined by many interacting factors and their prediction is the Achilles' heel of ration formulation. Inadequate energy intake can limit milk yield and reproductive performance, whereas excessive energy intake will increase body condition, increasing the risk of health and reproductive issues in the subsequent lactation. Ration composition interacts with the physiological state of cows, making it difficult to predict DMI and the partitioning of energy accurately. However, understanding the factors controlling these allows us to devise grouping strategies and manipulate rations to optimize energy intake through lactation. Eating is controlled by the integration of signals in brain feeding centers. Ration composition affects DMI of cows via signals from ruminal distention and the hepatic oxidation of fuels. Dairy cow rations must contain a minimal concentration of relatively low-energy roughages for proper rumen function, but signals from ruminal distension can limit DMI when the drive to eat is high. Signals from the hepatic oxidation of fuels likely dominate the control of DMI in the peripartum period when cows are in a lipolytic state and later in lactation when signals from distension diminish. Therefore, the effects of the ration on DMI vary with the physiological state of the animal. Furthermore, they interact with environmental stressors such as social (e.g., overcrowding) and thermal stress. The objective of this article is to discuss the effects of ration composition on energy intake and partitioning in lactating cows and how they can be manipulated to optimize productive performance.

Effects of corn grain endosperm type and conservation method on site of digestion, ruminal digestion kinetics, and flow of nitrogen fractions to the duodenum in lactating dairy cows.

Our objective was to evaluate the relative effects of endosperm type and conservation method of corn grain on ruminal kinetics, site of nutrient digestion, and flow of nitrogen fractions to the duodenum in lactating dairy cows. Seven ruminally and duodenally cannulated Holstein cows (73 ± 39 d in milk; mean ± SD) were used in a duplicated 4 × 4 Latin square design with 21-d periods. A 2 × 2 factorial arrangement of treatments was used, with main effects of corn grain endosperm type (floury or vitreous) and conserved as dry ground corn (DGC) or high-moisture corn (HMC). Rations were formulated to contain 27.0% starch, 26.6% neutral detergent fiber (NDF), 19.1% forage NDF, and 16.5% crude protein. Corn grain treatments supplied 86.6% of dietary starch, and alfalfa silage was the sole forage. True ruminal starch digestibility was increased by HMC compared with DGC (87.2 vs. 64.3%) and by floury compared with vitreous corn grain (83.7 vs. 67.7%). The increase for HMC compared with DGC was because of an increase in the degradation rate (33.8 vs. 23.1%/h) and a decrease in passage rate of starch (7.6 vs. 15.2%/h). The increase for floury compared with vitreous corn grain was because of an increase in the degradation rate (31.5 vs. 25.4%/h) and a decrease in rate of starch passage from the rumen (7.9 vs. 14.9%/h). Apparent total-tract starch digestibility was increased by HMC compared with DGC and by floury compared with vitreous corn, but the increase for floury corn was greater for the DGC treatment. Dry ground corn compared with HMC tended to increase nonammonia N flow to the duodenum (466 vs. 431 g/d) by increasing flow of nonammonia nonmicrobial N (211 vs. 111 g/d) despite a decrease in microbial N flow (255 vs. 320 g/d). Vitreous corn increased nonammonia nonmicrobial N flow to the duodenum (187 vs. 135 g/d) compared with floury corn, but microbial N flow to the duodenum was not affected by endosperm type. Efficiency of microbial N production was not affected by treatment. Endosperm type and conservation method of corn grain greatly affect digestion kinetics and ruminal digestibility of starch as well as flow of N fractions to the duodenum and should be considered during diet formulation for lactating cows.

Effects of corn grain endosperm type and conservation method on feed intake, feeding behavior, and productive performance of lactating dairy cows.

Our objective was to evaluate the effects of corn grain varying in endosperm type and conserved as high-moisture or dry ground corn on dry matter intake (DMI), feeding behavior, ruminal fermentation, and yields of milk and milk components of cows in early to mid-lactation. Seven ruminally and duodenally cannulated Holstein cows (73 ± 39 d in milk; mean ± SD) were used in a duplicated 4 × 4 Latin square design with 21-d periods. A 2 × 2 factorial arrangement of treatments was used with main effects of corn grain endosperm type (floury or vitreous) conserved as high-moisture corn (HMC) or dry ground corn (DGC). Rations were formulated to contain 27.0% starch, 26.6% neutral detergent fiber (NDF), 19.1% forage NDF, and 16.5% crude protein. Corn grain treatments supplied 86.6% of dietary starch and contained alfalfa silage as the sole forage. Dry matter intake was increased 1.3 kg/d by DGC compared with HMC. The increase in DMI by DGC was related to a shorter intermeal interval (104.4 vs. 118.2 min/d), and meal size was not affected by treatment. Dry ground corn decreased rumination bout length and number of chews per bout compared with HMC. No differences were detected between endosperm treatments for DMI, yields of milk, 3.5% fat-corrected milk (FCM), milk fat, protein, lactose, or solids-not-fat (SNF). Mean yield of 3.5% FCM across treatments was 47.5 kg/d. However, a tendency for an interaction was observed for feed efficiency; floury endosperm increased efficiency 0.05 kg 3.5% FCM per kg of DMI for DGC but decreased it by 0.14 kg 3.5% FCM per kg of DMI for HMC relative to vitreous endosperm. Vitreous compared with floury corn tended to increase true protein concentration in milk when conserved as DGC (2.68% vs. 2.62%) but not as HMC. Concentration of SNF was increased by DGC compared with HMC (8.45 vs. 8.37%) due, in part, to the effect of treatment on milk protein concentration. Body weight was not affected by treatment, but vitreous endosperm tended to increase loss of body condition compared with floury endosperm. Corn endosperm type and conservation method had little effect on productive performance of high-producing cows.

Effects of corn grain endosperm type and fineness of grind on site of digestion, ruminal digestion kinetics, and flow of nitrogen fractions to the duodenum in lactating dairy cows.

Our objective was to evaluate effects of corn grain endosperm type and fineness of grind on feed intake, feeding behavior, and productive performance of lactating cows. Eight ruminally and duodenally cannulated Holstein cows in mid lactation (130 ± 42 d in milk; mean ± standard deviation) were used in a duplicated 4 × 4 Latin square design with 21-d periods. A 2 × 2 factorial arrangement of treatments was used with main effects of corn grain endosperm type (floury or vitreous) and fineness of grind (fine or medium). Rations included alfalfa silage, corn treatments, protein supplement, minerals, and vitamins and were formulated to contain 29% starch, 27% neutral detergent fiber, 18.2% forage neutral detergent fiber, and 18% crude protein. Corn grain treatments supplied 86.2% of dietary starch. Endosperm was 25% vitreous for the floury treatment and 66% vitreous for the vitreous treatment. The floury treatment increased rate of starch degradation by 94% (19.2 vs. 9.9%/h) and decreased rate of starch passage by 38% (16.1 vs. 25.8%/h), increasing apparent ruminal starch digestibility by 117% (53.7 vs. 24.7%). The floury treatment increased total-tract starch digestibility by 8% (92.2 vs. 85.1%) despite 37% lower postruminal starch digestion for the floury treatment compared with vitreous corn (38.4 vs. 60.7% of starch intake). Fine grind size increased apparent ruminal starch digestibility by 52% (47.2 vs. 31.1%) compared with medium grind size by increasing the rate of starch degradation by 105% (19.5 vs. 9.5%/h) with no effect on rate of starch passage. However, total-tract starch digestibility was not affected by fineness of grind because postruminal starch digestibility was 37% greater for medium compared with fine grind size (57.2 vs. 41.9% of starch intake). Endosperm type did not affect flow of nitrogen (N) fractions to the duodenum or microbial N efficiency, whereas fine grind size increased duodenal flow of nonammonia N by increasing duodenal flow of microbial N by 22% compared with medium grind size (438 vs. 359 g/d) but did not affect apparent total-tract N digestibility. No interactions were detected for any measure of starch digestion, ruminal N metabolism, or flow of N fractions to the duodenum. Endosperm type greatly affected ruminal and total-tract starch digestibility independent of the fineness of grind of corn grain with no effects on flow of N fractions.

Effects of corn grain endosperm type and fineness of grind on feed intake, feeding behavior, and productive performance of lactating dairy cows.

Our objective was to evaluate effects of corn grain endosperm type and fineness of grind on feed intake, feeding behavior, ruminal fermentation, and productive performance of lactating cows. Eight ruminally and duodenally cannulated Holstein cows in mid lactation (130 ± 42 d in milk; mean ± standard deviation) were used in a duplicated 4 × 4 Latin square design with 21-d periods. A 2 × 2 factorial arrangement of treatments was used with main effects of corn grain endosperm type (floury or vitreous) and fineness of grind of corn grain (fine or medium). Rations were formulated to contain 29% starch, 27% neutral detergent fiber, 18.2% forage neutral detergent fiber, and 18% crude protein. Corn grain treatments supplied 86.2% of dietary starch. Endosperm was 25% vitreous for floury corn and 66% vitreous for vitreous corn. Fineness of grind did not affect dry matter intake (DMI), but floury corn tended to reduce DMI (23.8 vs. 25.1 kg/d) compared with vitreous corn. Floury corn increased meal frequency more for fine grind size (9.57 vs. 9.41 meals/d) than medium grind size (9.78 vs. 9.75 meals/d). However, there were no effects of treatment on any other measure of feeding behavior. Endosperm type did not affect yields of milk or milk components or milk composition except that vitreous corn tended to decrease milk lactose concentration compared with floury corn. Finely ground corn decreased yields of milk (31.1 vs. 33.1 kg/d), 3.5% fat-corrected milk (33.1 vs. 35.1 kg/d), milk fat (1.22 vs. 1.32 kg/d), milk lactose (1.48 vs. 1.59 kg/d), and solids not fat (2.46 vs. 2.63 kg/d) compared with medium grind size. However, fineness of grind did not affect milk composition. Treatments had no effect on change in body weight or body condition score or efficiency of milk production (kg of 3.5% fat-corrected milk/kg of DMI). Mean ruminal pH was not affected by treatment, but pH variance was decreased by vitreous compared with floury corn. Total volatile fatty acids and propionate concentrations in the rumen were increased by floury compared with vitreous corn but were not affected by fineness of grind. Effects of fineness of grind on yield of milk and milk components were greater than the effects of corn grain vitreousness.

Effect of uncouplers of oxidative phosphorylation on metabolism of propionate in liver explants from dairy cows.

Our objective was to determine the effects of uncouplers of oxidative phosphorylation on the metabolism of propionate in liver tissue of dairy cows in the postpartum period. A total of 8 primiparous dairy cows were biopsied for liver tissue explants in 2 block-design experiments. Cows were 5.9 ± 2.8 (mean ± SD) days in milk, and the 2 experiments were run concurrently. Treatments for experiment 1 were 10 µM 2,4-dinitrophenol methyl ether (DNPME) or propylene carbonate (vehicle control). Treatments for experiment 2 were 5 mM sodium salicylate (SAL) or no treatment (control). Explants were incubated in 2.5 mM [13C3]propionate with treatments and terminated after 0.5, 15, and 60 min of exposure to tracer. Treatment with DNPME had no effects on measured metabolites compared with control. Treatment with SAL increased total 13C% enrichment of succinate (3.03 vs. 2.45%), but tended to decrease total 13C% enrichment of fumarate (2.86 vs. 3.10%) and decreased total 13C% enrichment of malate (3.96 vs. 4.58%) compared with the control. Treatment with DNPME appeared to have no effects on hepatic propionate metabolism, and treatment with SAL may impair the succinate dehydrogenase reaction.

Effects of inhaled air pollution on markers of integrity, inflammation, and microbiota profiles of the intestines in Apolipoprotein E knockout mice.

Air pollution exposure is known to contribute to the progression of cardiovascular disease (CVD) and there is increasing evidence that dysbiosis of the gut microbiome may also play a role in the pathogenesis of CVD, including atherosclerosis. To date, the effects of inhaled air pollution mixtures on the intestinal epithelial barrier (IEB), and microbiota profiles are not well characterized, especially in susceptible individuals with comorbidity. Thus, we investigated the effects of inhaled ubiquitous air-pollutants, wood-smoke (WS) and mixed diesel and gasoline vehicle exhaust (MVE) on alterations in the expression of markers of integrity, inflammation, and microbiota profiles in the intestine of atherosclerotic Apolipoprotein E knockout (ApoE-/-) mice. To do this, male 8 wk-old ApoE-/- mice, on a high-fat diet, were exposed to either MVE (300 µg/m3 PM), WS; (∼450 µg/m3 PM), or filtered air (FA) for 6 h/d, 7 d/wk, for 50 d. Immunofluorescence and RT-PCR were used to quantify the expression of IEB components and inflammatory factors, including mucin (Muc)-2, tight junction (TJ) proteins, matrix metalloproteinase (MMP)-9, tumor necrosis factor (TNF)-α, and interleukin (IL)-1ß, as well as Toll-like receptor (TLR)-4. Microbial profiling of the intestine was done using Illumina 16S sequencing of V4 16S rRNA PCR amplicons. We observed a decrease in intestinal Muc2 and TJ proteins in both MVE and WS exposures, compared to FA controls, associated with a significant increase in MMP-9, TLR-4, and inflammatory marker expression. Both WS and MVE-exposure resulted in decreased intestinal bacterial diversity, as well as alterations in microbiota profiles, including the Firmicutes: Bacteroidetes ratio at the phylum level. Our findings suggest inhalation exposure to either MVE or WS result in alterations in components involved in mucosal integrity, and also microbiota profiles and diversity, which are associated with increased markers of an inflammatory response.

Effects of propionate concentration on short-term metabolism in liver explants from dairy cows in the postpartum period.

Our objective was to determine the temporal effects of increasing supply of propionate on propionate metabolism in liver tissue of dairy cows in the postpartum (PP) period. A total of 6 dairy cows [primiparous: n = 3, 9.00 ± 1.00 d PP (mean ± SD) and multiparous: n = 3; 4.67 ± 1.15 d PP] were biopsied for liver explants in a block-design experiment. Explants were treated with 3 concentrations of [13C3]sodium propionate of 1, 2, or 4 mM. Explants were incubated in 2 mL of Medium 199 supplemented with 1% BSA, 0.6 mM oleic acid, 2 mM sodium l-lactate, 0.2 mM sodium pyruvate, and 0.5 mMl-glutamine at 38°C and sampled at 0.5, 15, and 60 min. Increasing the concentration of [13C3]propionate increased total 13C% enrichment of propionyl coenzyme A (CoA), succinate, fumarate, malate, and citrate with time. Concentration of propionate did not affect total 13C% enrichment of hepatic glucose or acetyl CoA, but total 13C% enrichment increased with time for hepatic glucose. The 13C labeling from propionate was incorporated into acetyl CoA, but increased concentrations of propionate did not result in greater labeling of acetyl CoA. However, increases in 13C% enrichment of [M+4]citrate and [M+5]citrate concentrations of [13C3]propionate indicate propionate conversion to acetyl CoA and subsequent entry of acetyl CoA into the tricarboxylic acid cycle in dairy cows in the PP period. This research presents evidence that despite an increase in hepatic acetyl CoA concentration and general consensus on the upregulation of gluconeogenesis of dairy cows during the PP period, carbon derived from propionate contributes to the pool of acetyl CoA, which increases as concentration of propionate increases, in addition to stimulating oxidation of acetyl CoA from other sources. Because of the hypophagic effects of propionate, but importance of propionate as a glucose precursor, a balance of propionate supply to dairy cows could lead to improvements in dry matter intake, and subsequently, health and production in dairy cows.

Immunological Responses to the Relapsing Fever Spirochete Borrelia turicatae in Infected Rhesus Macaques: Implications for Pathogenesis and Diagnosis.

The global public health impact of relapsing fever (RF) spirochetosis is significant, since the pathogens exist on five of seven continents. The hallmark sign of infection is episodic fever and the greatest threat is to the unborn. With the goal of better understanding the specificity of B-cell responses and the role of immune responses in pathogenicity, we infected rhesus macaques with Borrelia turicatae (a new world RF spirochete species) by tick bite and monitored the immune responses generated in response to the pathogen. Specifically, we evaluated inflammatory mediator induction by the pathogen, host antibody responses to specific antigens, and peripheral lymphocyte population dynamics. Our results indicate that B. turicatae elicits from peripheral blood cells key inflammatory response mediators (interleukin-1ß and tumor necrosis factor alpha), which are associated with preterm abortion. Moreover, a global decline in peripheral B-cell populations was observed in all animals at 14 days postinfection. Serological responses were also evaluated to assess the antigenicity of three surface proteins: BipA, BrpA, and Bta112. Interestingly, a distinction was observed between antibodies generated in nonhuman primates and mice. Our results provide support for the nonhuman primate model not only in studies of prenatal pathogenesis but also for diagnostic and vaccine antigen identification and testing.

Bacterial microbiomes of Ixodes scapularis ticks collected from Massachusetts and Texas, USA.

BACKGROUND: The blacklegged tick, Ixodes scapularis, is the primary vector of the Lyme disease spirochete Borrelia burgdorferi in North America. Though the tick is found across the eastern United States, Lyme disease is endemic to the northeast and upper midwest and rare or absent in the southern portion of the vector's range. In an effort to better understand the tick microbiome from diverse geographic and climatic regions, we analysed the bacterial community of 115 I. scapularis adults collected from vegetation in Texas and Massachusetts, representing extreme ends of the vector's range, by massively parallel sequencing of the 16S V4 rRNA gene. In addition, 7 female I. scapularis collected from dogs in Texas were included in the study. RESULTS: Male I. scapularis ticks had a more diverse bacterial microbiome in comparison to the female ticks. Rickettsia spp. dominated the microbiomes of field-collected female I. scapularis from both regions, as well as half of the males from Texas. In addition, the male and female ticks captured from Massachusetts contained high proportions of the pathogens Anaplasma and Borrelia, as well as the arthropod endosymbiont Wolbachia. None of these were found in libraries generated from ticks collected in Texas. Pseudomonas, Acinetobacter and Mycobacterium were significantly differently abundant (p < 0.05) between the male ticks from Massachusetts and Texas. Anaplasma and Borrelia were found in 15 and 63% of the 62 Massachusetts ticks, respectively, with a co-infection rate of 11%. Female ticks collected from Texas dogs were particularly diverse, and contained several genera including Rickettsia, Pseudomonas, Bradyrhizobium, Sediminibacterium, and Ralstonia. CONCLUSIONS: Our results indicate that the bacterial microbiomes of I. scapularis ticks vary by sex and geography, with significantly more diversity in male microbiomes compared to females. We found that sex plays a larger role than geography in shaping the composition/diversity of the I. scapularis microbiome, but that geography affects what additional taxa are represented (beyond Rickettsia) and whether pathogens are found. Furthermore, recent feeding may have a role in shaping the tick microbiome, as evident from a more complex bacterial community in female ticks from dogs compared to the wild-caught questing females. These findings may provide further insight into the differences in the ability of the ticks to acquire, maintain and transmit pathogens. Future studies on possible causes and consequences of these differences will shed additional light on tick microbiome biology and vector competence.

Effects of rate and amount of propionic acid infused into the rumen on feeding behavior of Holstein cows in the postpartum period.

The objective of this study was to determine the effects of 2 amounts of propionic acid (PA) infused intraruminally at 2 rates of infusion at the initiation of meals on the feeding behavior of Holstein cows in the postpartum period. We hypothesized that the amount and length of time of infusions would interact to affect feeding behavior: rapid infusion of a higher dose of PA would result in larger meal size with greater time between meals compared with a slower rate, whereas faster infusion of a lower dose of PA would reduce meal size and the time between meals compared with a slower infusion of the same dose. Eight ruminally cannulated, multiparous Holstein cows were used in a 4 × 4 Latin square design experiment. Cows were blocked by parturition date and randomly assigned to treatment sequence within square. Treatments were infusion of 2.5 L of 0.5 M (HI) or 0.2 M (LO) solutions of PA at initiation of meals over 5 min (FST) or 15 min (SLW) for 12 h following feed delivery. Contrary to our hypothesis, no interaction between amount and rate of infusion was detected for any feeding behavior parameter measured. The FST treatments did not affect dry matter intake or metabolizable energy intake compared with SLW. The FST treatments tended to increase meal length compared with SLW (28.1 vs. 22.7) but did not affect meal size. The FST treatments tended to decrease total eating time (108 vs. 122 min/12 h) but did not affect meal frequency compared with SLW. The HI treatments decreased dry matter intake (7.4 vs. 11.5 kg/12 h) and total metabolizable energy intake (22.5 vs. 29.1 Mcal/12 h) compared with LO by decreasing meal frequency (5.8 vs. 7.5 meals/12 h). The HI treatments decreased eating time (103 vs. 127 min/12 h) compared with LO but did not affect meal size. Further research is warranted on the effects of the temporal supply of propionate on propionate metabolism and feeding behavior.

Hepatic metabolism of propionate relative to meals for cows in the postpartum period.

The objective of this research was to identify potential short-term metabolic bottlenecks of propionate metabolism in the liver of dairy cows in the postpartum (PP) period and how such bottlenecks are affected by feeding status. Propionate, produced primarily from the fermentation of starch, decreases dry matter intake for cows in the postpartum period, likely by stimulating oxidation of acetyl-CoA in the liver. In this study, 8 dairy cows [2 blocks of 4 cows each, 6.63 ± 1.19 (mean ± SD) days PP; body condition score of 2.84 ± 0.39] were administered a pulse dose of either 1.5 mol/500 mL of propionic acid (PA) or 500 mL of water (control; CON) to the rumen either 1 h before or 2 h after feeding in a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Liver tissue was sampled at -1, 10 and 20 min relative to dosing, and blood was sampled at -30, -20, -10, -1, 5, 10, 15, 20, 25, 30, and 60 min relative to dosing. We hypothesized that rapid propionate absorption results in bottlenecks as enzymes become saturated and cofactors require regeneration. The PA treatment increased plasma propionate and insulin concentrations rapidly, with peaks reached by 5 min regardless of feeding status and cleared from the plasma within 30 min of dosing. The PA treatment decreased plasma nonesterified fatty acid concentration over 30 min compared with CON before but not after feeding. The PA treatment decreased plasma ß-hydroxybutyrate concentration and increased plasma lactate concentration compared with CON both before and after feeding. The PA treatment also increased hepatic pyruvate and lactate concentrations compared with CON. The PA treatment tended to increase hepatic isocitrate and fumarate concentrations but did not affect hepatic malate and oxaloacetate concentrations, suggesting that elevated mitochondrial NADH/NAD+ may have slowed the isocitrate dehydrogenase and fumarase reactions. The PA treatment also increased succinate concentration compared with CON, suggesting that a bottleneck may be present at succinate dehydrogenase. The PA treatment tended to increase citrate concentration despite having no effects on acetyl-CoA or oxaloacetate concentrations. These results are in agreement with our hypothesis that rapid absorption of propionate from the rumen and extraction by the liver results in metabolic bottlenecks in the liver that may affect feeding behavior and dry matter intake in dairy cows in the PP period.

The effect of uncouplers of oxidative phosphorylation on the feeding behavior of lactating dairy cows.

Our objective was to determine the effects of uncouplers of oxidative phosphorylation on feeding behavior of lactating dairy cows. We hypothesized that uncouplers of oxidative phosphorylation would increase meal size and meal length and performed 2 experiments to test our hypothesis. In experiment 1, 4 late-lactation cows (345 ± 48.4 d in milk; mean ± SD) were administered a daily intrajugular injection of either 10 mg/kg of BW0.75 of 2,4-dinitrophenol methyl ether (DNPME) and propylene carbonate or propylene carbonate (control; CON) in a crossover design with 2-d periods. In experiment 2, 8 early-lactation cows (11.3 ± 0.89 d in milk) were administered a daily intrajugular injection via jugular catheter of either 50 mg/kg of BW of sodium salicylate (SAL) and saline or saline (control; CON) in a crossover design with 1-d periods. Feeding behavior was recorded by a computerized data acquisition system and analyzed for the first 4 h after access to feed within 15 min of treatment for both experiments. Neither DNPME nor SAL affected meal size over the first 4 h after access to feed. However, DNPME increased meal length by 6.4 min (26.3 vs. 19.9 min) and tended to decrease the number of meals (2.55 vs. 2.78 meals/4 h) over the first 4 h after access to feed compared with CON. Both DNPME and SAL decreased eating rate over the first 4 h after access to feed compared with their respective controls (0.10 vs. 0.12 kg/min for DNPME vs. CON; 0.06 vs. 0.07 kg/min for SAL vs. CON). Lack of treatment effects on meal size may have been caused by increased rate of oxidation of fuels compensating for the disruption of oxidative phosphorylation.

Temporal effects of ruminal infusion of propionic acid on hepatic metabolism in cows in the postpartum period.

A faster rate of infusion of propionic acid into the rumen of cows in the postpartum period increased meal size compared with a slower rate of infusion in a previous experiment. Because propionate is anaplerotic and stimulates oxidation of acetyl coenzyme A (CoA) in the liver, and hepatic oxidation has been linked to satiety, this result was opposite to our expected response. We then hypothesized that the faster rate of infusion might have saturated the pathway for propionate metabolism in hepatocytes resulting in lower first-pass extraction by the liver. Because we were measuring feeding behavior, we could not sample blood and liver tissue over time in that experiment. Therefore, to determine the temporal effects of propionic acid (PA) infusion on hepatic metabolism and plasma metabolites over the time course of a meal, we infused 1.25 mol of PA (2.5 L of 0.5M PA) over 5 min (FST) or 15 min (SLW) into the rumen. We evaluated response to PA infusions both before feeding, when ruminal PA production by rumen microbes is lower and hepatic acetyl CoA concentration is greater, and 4 h after feeding, when PA production is greater and hepatic acetyl CoA concentration is lower. Blood and liver samples were collected before, and after 5, 15, and 30 min of infusion. Contrary to our hypothesis, the rate of PA infusion into the rumen did not affect plasma propionate concentration, indicating the FST effects on feeding behavior were not because of a limitation on propionate uptake by the liver. However, FST increased plasma glucose and insulin concentrations faster than SLW, resulting in a reduction in plasma nonesterified fatty acid concentration during the time frame of meals. Decreased plasma nonesterified fatty acid concentration during infusion likely decreased the supply of acetyl CoA for oxidation in the liver. The FST treatment also increased fumarate concentration at 5 min after the initiation of infusion but did not affect oxaloacetate concentration compared with SLW, consistent with a limitation to propionate metabolism at that reaction. A metabolic bottleneck at the malate dehydrogenase reaction for FST compared with SLW would further contribute to a reduction in hepatic oxidation within the time frame of a meal, allowing greater meal size, consistent with the hepatic oxidation theory and our previous results.

Alterations to the Intestinal Microbiome and Metabolome of Pimephales promelas and Mus musculus Following Exposure to Dietary Methylmercury.

Mercury is a global contaminant, which may be microbially transformed into methylmercury (MeHg), which bioaccumulates. This results in potentially toxic body burdens in high trophic level organisms in aquatic ecosystems and maternal transfer to offspring. We previously demonstrated effects on developing fish including hyperactivity, altered time-to-hatch, reduced survival, and dysregulation of the dopaminergic system. A link between gut microbiota and central nervous system function in teleosts has been established with implications for behavior. We sequenced gut microbiomes of fathead minnows exposed to dietary MeHg to determine microbiome effects. Dietary exposures were repeated with adult CD-1 mice. Metabolomics was used to screen for metabolome changes in mouse brain and larval fish, and results indicate effects on lipid metabolism and neurotransmission, supported by microbiome data. Findings suggest environmentally relevant exposure scenarios may cause xenobiotic-mediated dysbiosis of the gut microbiome, contributing to neurotoxicity. Furthermore, small-bodied teleosts may be a useful model species for studying certain types of neurodegenerative diseases, in lieu of higher vertebrates.

Temporal effects of ruminal propionic acid infusion on feeding behavior of Holstein cows in the postpartum period.

The objective of this study was to determine the temporal effects of intraruminal infusion of propionic acid at the initiation of meals on feeding behavior of cows in the postpartum period. Propionic acid derived from ruminal fermentation can reduce energy intake of dairy cows. The suppression of appetite by propionic acid is likely caused by a signal related to the hepatic oxidation of fuels. Greater propionate flux to the liver is expected to result in faster oxidation of acetyl coenzyme A, which can stimulate satiety and reduce feed intake. Therefore, the rate of propionate supply to the liver, within the timeframe of meals, might be an important limitation to feed intake. Our hypothesis was that faster rate of propionate infusion during meals would decrease meal size and feed intake by decreasing the time required to stimulate satiety within a meal. Six ruminally cannulated, multiparous Holstein cows in the postpartum period were used in a duplicated 3 × 3 Latin square design experiment balanced for carryover effects. Treatments included control (no infusion) or 1.25 mol of propionic acid infused over 5 min (FST) or 15 min (SLW) at each meal. Infusions were initiated at the conditioned meal at feeding (1200 h) and were triggered at each spontaneous meal for 22 h. Contrary to our hypothesis, SLW decreased meal size 29% (0.87 vs. 1.23 kg of dry matter) compared with FST, and FST decreased meal frequency 27% (8.5 vs. 11.2 per d) compared with SLW. Dry matter intake was similar between FST and SLW, but propionic acid decreased dry matter intake 46% compared with control. A potential explanation is that FST resulted in greater liver bypass of propionate compared with SLW, extending anaplerosis of the tricarboxylic acid cycle, hepatic oxidation of acetyl coenzyme A, and satiety over a longer time after meals.

Highly fermentable starch at different diet starch concentrations decreased feed intake and milk yield of cows in the early postpartum period.

The objective of this study was to evaluate the effects of diet starch concentration and fermentability (SF) fed during the early postpartum (PP) period on dry matter intake (DMI), yields of milk and milk components, body reserves, and metabolism. Fifty-two multiparous Holstein cows were used in a randomized block design with a 2 × 2 factorial arrangement of treatments. Treatment diets were formulated to 22% (LS) or 28% (HS) starch with dry ground corn (DGC) or high-moisture corn (HMC) as the primary starch source. Treatments were fed from 1 to 23 d PP and cows were switched to a common diet until 72 d PP to measure carryover (CO) effects. Treatment period (TP) diets were formulated for 22% forage neutral detergent fiber and 17% crude protein, and starch concentration was adjusted by substitution of corn grain for soyhulls. Throughout the experiment DMI and milk yield were measured daily, and milk components, body condition score (BCS), and body weight were measured weekly. Blood was collected weekly during the TP and every second week during the CO period. During the TP, HMC decreased DMI more when included in the HS (3.9 kg/d) than in the LS (0.9 kg/d) diets and HMC decreased yields of milk, fat, and FCM by 4.3, 0.19, and 4.8 kg/d, respectively. Treatments also interacted over time to decrease DMI and yields of milk and milk components more for HMC compared with DGC as time progressed during the TP. Loss of BCS was increased when HMC was fed in a HS diet (-0.38 vs. -0.17) and decreased when included in a LS diet (-0.21 vs. -0.29) with no effects on body weight change during the TP. Treatments interacted with time to affect plasma concentrations of glucose and insulin with HS increasing concentrations early in the TP compared with LS but with similar effects by the end of the TP. During the CO period, treatment effects on DMI diminished over time with no main effects of treatment for the entire period. Starch concentration and SF interacted to affect yields of milk, fat, and FCM during the CO period, which were greater for HS-DGC and LS-HMC (54.8 and 52.8, 1.76 and 1.81, and 51.3 and 52.2 kg/d, respectively) than for LS-DGC and HS-HMC (51.2 and 51.0, 1.68 and 1.64, and 48.4 and 48.6 kg/d, respectively). Treatments did not affect BCS change during the CO period but HS lost body weight compared with LS (-5.7 vs. 7.0 kg). Blood glucose and insulin concentrations were not affected by treatments during the CO period. Feeding a highly fermentable starch source during the early PP period decreased DMI and yields of milk and milk components compared with a less fermentable starch source and the depression in DMI was greater when fed in the higher starch diet. However, diet starch concentration had no effects on yield of milk or milk components.

Effects of acetic acid or sodium acetate infused into the rumen or abomasum on feeding behavior and metabolic response of cows in the postpartum period.

Effects of continuous isomolar infusions of acetic acid (AcA) or sodium acetate (NAc) infused into the rumen (RU) or into the abomasum (AB) on feeding behavior, dry matter intake (DMI), and metabolic response of cows in the early postpartum period were evaluated. Six rumen-cannulated multiparous Holstein cows (11.8 ± 3.9 d in milk; mean ± SD) were utilized in a 6 × 6 Latin square design experiment balanced for carryover effects with a 2 × 3 factorial arrangement of treatments. Treatments were AcA and NAc, with sodium chloride (CON) as a control, infused at a rate of ˜0.75 mol/h (0.5 L/h) into the RU or AB for the first 8 h following feeding, with a rest day between infusion days. Treatment sequences were assigned randomly to cows. Feeding behavior was recorded by a computerized data acquisition system and blood was sampled at 0, 4, and 8 h relative to the start of infusion. We hypothesized that AcA is more hypophagic than NAc, and that infusion into the AB is more hypophagic than infusion into the RU. Dry matter intakes (DMI) for the CON treatments were similar at 6.2 kg/8 h for RU and 6.1 kg/8 h for AB, and the AcA and NAc treatments interacted with site of infusion to affect DMI. The NAc-RU treatment did not reduce DMI (7.0 kg/8 h), whereas AcA-RU (2.6 kg/8 h), AcA-AB (3.7 kg/8 h), and NAc-AB (4.0 kg/8 h) decreased DMI compared with CON. Following infusions of AcA compared with NAc, there was a residual effect on DMI for the remainder of the day, but treatments did not affect DMI during the rest day. Treatments increased plasma acetate and ß-hydroxybutyrate concentrations over time (interaction) and decreased plasma insulin concentration compared with CON. Plasma glucose concentration decreased over time after AcA-AB infusion compared with other treatments and CON. Plasma nonesterified fatty acid concentration increased over time for AcA compared with NAc and CON, suggesting an increase in lipolysis to compensate the decrease in DMI. In contrast to the other treatments, NAc-RU did not decrease DMI compared with control but we cannot determine the reason for this from the data available from the current study.

Fuels derived from starch digestion have different effects on energy intake and metabolic responses of cows in the postpartum period.

Absorbed fuels from the digestion of starch include propionic acid (PA) produced by ruminal fermentation and glucose (GLU) from intestinal digestion, which may be partially metabolized to lactic acid (LA) by intestinal tissues. Our objective was to evaluate the effects of these fuels on dry matter intake (DMI) and feeding behavior of cows in the postpartum period. We hypothesized that these fuels affect feed intake differently and that their effects are related to differences in their hepatic metabolism. Glucose was expected to have little effect on feed intake because little or no GLU is extracted from the blood by the liver. Whereas both LA and PA are anaplerotic and can stimulate oxidation of acetyl CoA in hepatocytes, hepatic extraction of PA is greater than LA, which depends on cytosolic redox state. Continuous isoenergetic infusions (150 kcal of ME/h) of PA, LA, or GLU or no infusion were administered abomasally to 8 ruminally cannulated multiparous Holstein cows (12.4 ± 6.2 d postpartum) in a duplicate 4 × 4 Latin square design experiment, with four 1-d infusion periods, balanced for carry-over effects. Treatment sequences were assigned to cows randomly, and treatments included control (CON, no infusion), PA (0.41 mol/h), LA (0.46 mol/h), and GLU (0.22 mol/h). Solutions containing treatments were infused at 500 mL/h for 22 h/d and provided ∼3.3 Mcal/d. Feeding behavior was recorded by a computerized data acquisition system. Gross energy digestibility of the diet was determined for each cow and used to calculate metabolizable energy intake (MEI) from the diet. Total MEI was calculated as the sum of MEI from the diet plus energy from infusions. Data were analyzed statistically with a mixed model including the fixed effect of treatment and random effects of block and cow within block. Each treatment was compared with CON by contrasts. Compared with CON, PA decreased DMI by 24% (14.3 vs. 18.9 kg/d) and total MEI by 13% (34.8 vs. 40.2 Mcal/d) with a tendency to decrease meal frequency. Lactic acid decreased DMI by 14% (16.3 vs. 18.9 kg/d) compared with CON by decreasing meal size 20% but did not affect MEI. Glucose infusion did not affect DMI or MEI. Treatment effects on DMI and MEI were consistent with their expected effects on hepatic oxidation. Depression of feed intake in diets containing highly fermentable starch is likely because of differences in hepatic metabolism.