ABSTRACT
Sulfate‐reducing bacteria (SRB) have been recognized as key players in the precipitation of calcium carbonate in lithifying microbial communities. These bacteria increase the alkalinity by ...reducing sulfate ions, and consuming organic acids. SRB also produce copious amounts of exopolymeric substances (EPS). All of these processes influence the morphology and mineralogy of the carbonate minerals. Interactions of EPS with metals, calcium in particular, are believed to be the main processes through which the extracellular matrix controls the precipitation of the carbonate minerals. SRB exopolymers were purified from lithifying mat and type cultures, and their potential role in CaCO3 precipitation was determined from acid‐base titrations and calcium‐binding experiments. Major EPS characteristics were established using infrared spectroscopy and gas chromatography to characterize the chemical functional groups and the sugar monomers composition. Our results demonstrate that all of the three SRB strains tested were able to produce large amounts of EPS. This EPS exhibited three main buffering capacities, which correspond to carboxylic acids (pKa = 3.0), sulfur‐containing groups (thiols, sulfonic and sulfinic acids – pKa = 7.0–7.1) and amino groups (pKa = 8.4–9.2). The calcium‐binding capacity of these exopolymers in solution at pH 9.0 ranged from 0.12gCa gEPS−1–0.15 gCa gEPS−1. These results suggest that SRB could play a critical role in the formation of CaCO3 in lithifying microbial mats. The unusually high sulfur content, which has not been reported for EPS before, indicates a possible strong interaction with iron. In addition to changing the saturation index through metabolic activity, our results imply that SRB affect the rock record through EPS production and its effect on the CaCO3 precipitation. Furthermore, EPS produced by SRB may account for the incorporation of metals (e.g. Sr, Fe, Mg) associated with carbonate minerals in the rock record.
The use of metals as biosignatures in the fossil stromatolite record requires understanding of the processes controlling the initial metal(loid) incorporation and diagenetic preservation in living ...microbialites. Here, we report the distribution of metals and the organic fraction within the lithifying microbialite of the hypersaline Big Pond Lake (Bahamas). Using synchrotron‐based X‐ray microfluorescence, confocal, and biphoton microscopies at different scales (cm–μm) in combination with traditional geochemical analyses, we show that the initial cation sorption at the surface of an active microbialite is governed by passive binding to the organic matrix, resulting in a homogeneous metal distribution. During early diagenesis, the metabolic activity in deeper microbialite layers slows down and the distribution of the metals becomes progressively heterogeneous, resulting from remobilization and concentration as metal(loid)‐enriched sulfides, which are aligned with the lamination of the microbialite. In addition, we were able to identify globules containing significant Mn, Cu, Zn, and As enrichments potentially produced through microbial activity. The similarity of the metal(loid) distributions observed in the Big Pond microbialite to those observed in the Archean stromatolites of Tumbiana provides the foundation for a conceptual model of the evolution of the metal distribution through initial growth, early diagenesis, and fossilization of a microbialite, with a potential application to the fossil record.
Modern horse management systems tend to limit a horse's opportunity to forage, rely on meal feeding, and may contribute to the increase in equine obesity. The use of slow-feed hay nets represents an ...opportunity to extend foraging time while feeding a restricted diet. The objectives of this study were to determine if limit feeding combined with a slow-feed hay net would affect morphometric measurements and postprandial metabolite and hormone patterns in overweight adult horses. Eight adult Quarter horses (BW 563 kg ± 4.6 kg; BCS 7.2 ± 0.3) were used in a randomized complete block design, with 4 horses assigned to feeding hay off the stall floor (FLOOR) and 4 horses assigned to feeding from a slow-feed hay net (NET). Horses were fed in individual stalls at 1% BW each day, split evenly between 2 meals at 0700 and 1600 h. Body weight, BCS, neck and girth circumference, cresty neck score, and ultrasound measurements of average rump fat, longissimus dorsi (LD) depth, and LD thickness were taken on d 0, 14, and 28. Three 24-h blood samplings were conducted on d 0, 14, and 28 and were analyzed for glucose, insulin, cortisol, and leptin concentrations. Samplings occurred every 30 min for 3 h postfeeding, with hourly samples occurring between feedings. Horses feeding from the FLOOR took less time to consume their hay meal compared with horses feeding from the NET ( < 0.001). All horses lost weight over the 28-d period ( < 0.0001); however, no difference was observed between treatments. There was no difference in BCS, neck and girth circumference, cresty neck score, rump fat, or LD depth between days or treatments ( ≥ 0.25). There was an effect of day on LD thickness in horses feeding from the NET. Longissimus dorsi thickness was lower on d 28 compared with that on d 0 ( = 0.0257). Only time to peak insulin and peak cortisol were affected by treatment ( ≤ 0.037), with horses feeding from the NET having lower values than horses feeding from the FLOOR. Average glucose, insulin, cortisol, and leptin were affected by day ( ≤ 0.0102). Glucose and insulin values increased, whereas cortisol and leptin levels decreased throughout the 28-d study. The use of a slow-feed hay net coupled with a limit-fed diet appears to be an effective method for decreasing BW and maintaining more homeostatic levels of postprandial metabolites and hormones when feeding overweight adult horses.
Eight mature horses were used in a 4 × 4 Latin square design to determine the effect of restricted pasture access on dry matter intake rate (DMIR), energy intake, and fecal pH. Horses were randomly ...assigned to one of four groups (HGRPs), each containing two horses. HGRPs were randomly assigned to one of four treatments consisting of 3, 6, 9, or 24 hours of pasture access, for a period of 7 days. Treatments were switched every 7 days. The 3- and 6-hour groups were fed free choice mature grass hay while not grazing. Daily pasture dry matter intake (DMI) for each HGRP was estimated by calculating the difference between initial herbage mass of the grazing cell before grazing and residual herbage mass after 7 days of grazing. Total dry matter intake was the sum of pasture and hay DMI for the 3- and 6-hour treatments. Fecal pH was measured on day 7 of each period. Response variables were analyzed using analysis of variance for Latin square design. Restricting pasture access decreased mean pasture DMI (P = .02), pasture dietary energy (DE) (P = .02), and fecal pH (P < .001), but increased DMIR (P = .02). Mean total dry matter intake was not different (P = .16) among treatments. In conclusion, restricting pasture access accelerates pasture DMIR and decreases fecal pH, and although restricting pasture access decreases DE intake from pasture, it did not result in a decrease in total DE intake for horses having ad libitum access to hay.
Modern horse management systems tend to limit a horse's opportunity to forage. The objective of this experiment was to investigate the effect of hay net design on the rate of forage consumption when ...feeding horses. Eight adult horses were fed in individual stalls in a replicated Latin square design, with two horses per treatment per week. Horses were fed hay off the stall floor (control), or from one of three hay nets: large (15.2 cm openings), medium (4.4 cm openings), and small (3.2 cm openings). Horses had access to hay for two 4-hour periods each day. When horses could not consume all forage from the medium and small hay nets in 4 hours, a second study using a crossover design gave horses an unlimited amount of time to feed from the hay nets. Stopwatches were used to calculate time to consumption and dry matter intake rates (DMIR). Mean time to consumption was 3.1 and 3.4 hours for the control and large hay net, respectively, in study 1, and 5.1 and 6.5 hours for the medium and small hay nets, respectively, in study 2. Mean DMIR during the 4-hour feeding period were 1.5, 1.3, 1.1, and 0.9 kg/hr for the control, large, medium, and small hay nets, respectively; all treatments were different (P < .0001). These results demonstrate that hay nets were effective at decreasing the rate of forage consumption when feeding adult horses. Long-term studies are warranted to determine if horses will adapt to feeding from hay nets.
Modern horse management systems tend to limit a horse's opportunity to forage, rely on meal feeding, and may contribute to the increase in equine obesity. The use of slow-feed hay nets represents an ...opportunity to extend foraging time while feeding a restricted diet. The objectives of this study were to determine if limit feeding combined with a slow-feed hay net would affect morphometric measurements and postprandial metabolite and hormone patterns in overweight adult horses. Eight adult Quarter horses (BW 563 kg ± 4.6 kg; BCS 7.2 ± 0.3) were used in a randomized complete block design, with 4 horses assigned to feeding hay off the stall floor (FLOOR) and 4 horses assigned to feeding from a slow-feed hay net (NET). Horses were fed in individual stalls at 1% BW each day, split evenly between 2 meals at 0700 and 1600 h. Body weight, BCS, neck and girth circumference, cresty neck score, and ultrasound measurements of average rump fat, longissimus dorsi (LD) depth, and LD thickness were taken on d 0, 14, and 28. Three 24-h blood samplings were conducted on d 0, 14, and 28 and were analyzed for glucose, insulin, cortisol, and leptin concentrations. Samplings occurred every 30 min for 3 h postfeeding, with hourly samples occurring between feedings. Horses feeding from the FLOOR took less time to consume their hay meal compared with horses feeding from the NET (P < 0.001). All horses lost weight over the 28-d period (P < 0.0001); however, no difference was observed between treatments. There was no difference in BCS, neck and girth circumference, cresty neck score, rump fat, or LD depth between days or treatments (P ≥ 0.25). There was an effect of day on LD thickness in horses feeding from the NET. Longissimus dorsi thickness was lower on d 28 compared with that on d 0 (P = 0.0257). Only time to peak insulin and peak cortisol were affected by treatment (P ≤ 0.037), with horses feeding from the NET having lower values than horses feeding from the FLOOR. Average glucose, insulin, cortisol, and leptin were affected by day (P ≤ 0.0102). Glucose and insulin values increased, whereas cortisol and leptin levels decreased throughout the 28-d study. The use of a slow-feed hay net coupled with a limit-fed diet appears to be an effective method for decreasing BW and maintaining more homeostatic levels of postprandial metabolites and hormones when feeding overweight adult horses.
The impact of horse preference and grass morphology on grazing muzzle effectiveness has not been investigated. The objective of this study was to determine the effectiveness of grazing muzzle use at ...reducing forage intake when horses grazed grasses with different morphology and preferences. The study was conducted in 2012 and 2013. Four horses were grazed in 2012, and three horses were grazed in 2013. Four species of perennial cool-season grasses were grazed in 2012 including Kentucky bluegrass (Poa pratensis L.), meadow fescue (Schedonorus pratensis Huds.), perennial ryegrass (Lolium perenne L.), and reed canarygrass (Phalaris arundinacea L.). In 2013, only Kentucky bluegrass and reed canarygrass were grazed because of winter kill of other species. Horses were allowed to graze a small pasture seeded with an individual species for 4 hours each day in June and August of 2012 and August and September of 2013. Horses grazed the same grass species for two consecutive days, one day with a muzzle and one day without. Before and after each grazing, a strip was mechanically harvested to determine initial and residual herbage mass. The difference was used to estimate forage intake. The effectiveness of a grazing muzzle was not affected by forage species (P ≥ .05). Use of a grazing muzzle decreased the amount of forage consumed by an average of 30% compared with not using a grazing muzzle (P < .0001). Results will aid horse owners and professionals in estimating forage intake of muzzled horses on pasture.
Hay waste during feeding represents a costly expense for horse owners. The objectives of this study were to determine hay waste, herd body weight (BW) change, hay intake, and economics of small ...square-bale feeders used in outdoor feeding of horses. Feeder designs included a hayrack, slat feeder, basket feeder, and a no-feeder control. Feeders were placed in separate outdoor dirt paddocks. Twelve horses were divided into four groups and rotated through the paddocks in a Latin square design. Horses were weighed before and after each rotation. Horses were fed grass hay at 2.5% of the herd BW split evenly at 8 AM and 4 PM. Waste hay and orts were collected before each feeding. The number of months to repay the feeder cost (payback) was calculated using hay valued at $250 per ton and improved efficiency over the no-feeder control. Mean hay waste was 13%, 5%, 3%, and 1% for the no-feeder control, hayrack, basket feeder, and slat feeder, respectively (P < .001). The hayrack, basket feeder, and slat feeder paid for themselves in 12, 11, and 9 months, respectively (P = .0049). Herds gained 10 and 7 kg when feeding from the basket feeder and hayrack, and lost 3 and 11 kg when feeding from the slat feeder and no-feeder control (P ≤ .0015). Estimated hay intake was 2.4% BW for the basket feeder and hayrack and 2.2% BW for the slat feeder and no-feeder control (P < .0001). Small square-bale feeder design affected hay waste, hay intake, herd BW change, and payback.
•Small square-bale feeder design affected hay waste and payback.•Hay waste ranged from 13% (no-feeder control) to 1% (slat feeder).•All feeders paid for themselves in 12 months.•No injuries were observed when horses were fed from the small square-bale feeders.•This information will aid horse owners when purchasing small square-bale feeders.
Horses have evolved to be hindgut fermenters, requiring small amounts of forage to be consumed throughout the day 1. However, due to the recent increase in equine obesity 2–4, it has become necessary ...to restrict the amount of feedstuffs a horse consumes, often resulting in a restriction of forage intakes. In order to maintain a healthy gastrointestinal system, management strategies should attempt to replicate a horse's natural foraging habits. The objectives of the following studies were: 1) to investigate the effectiveness of decreasing pasture forage intakes via use of a grazing muzzle, and whether the effectiveness could be altered by grass morphology and palatability, 2) to investigate the effectiveness of "slow-feed hay nets" at increasing time to consumption of a preserved forage meal in stalled horses and 3) to observe the effects of increased time to consumption of daily rations on the post-prandial metabolic response. To determine objective 1, a two-year study was designed where four horses were used in a Latin square design in Year 1, while 3 horses were used in a completely randomized design in Year 2. Horses were grazed for 4 hours on monoculture plots four days per month for four months. Initial herbage mass and residual herbage mass measurements were taken to determine forage intakes. For objective 2, 8 horses were used in a replicated Latin square design, with 2 horses assigned to a treatment at a time. There was a control (C) of feeding hay on the ground, as well as three treatments: small-opening net (SN), medium-opening net (MN) and large-opening net (LN). Horses were allowed 4 h to consume their hay meal. Time to consumption and dry matter intake rate were measured using a stopwatch and any orts remaining after the 4 h were collected and weighed. To estimate objective 3, 8 overweight horses were enrolled in a randomized complete block design. Horses were blocked by bodyweight, BCS, and gender. Horses were fed a control diet of hay at 2% BW for a period of 10 days, and were then switched to a restricted diet of hay fed at 1.08% and ration balancer fed once daily at a rate of 0.001% BW. Horses were assigned to one of two treatments: hay fed off the floor (FLOOR) and hay fed in a small-opening hay net (HN). Serial 24 h blood samples were taken on day 0, when horses were still on baseline diet, as well as days 14 and 28. Plasma glucose, insulin, cortisol, and leptin values were estimated. Results of objective 1 found that grazing muzzles were effective at decreasing pasture intakes by 30% (P < 0.0001). Species had no effect on intakes in Year 1 (P = 0.27), but did impact intakes in Year 2 (P = 0.042). Results of objective 2 found that SN and MN were effective at increasing total time to consumption (P < 0.0001) compared to horses on the control and LN, more closely mimicking a horses' natural foraging behavior. Results of objective 3 found that hay nets decreased overall stress of horses on a restricted diet (P < 0.05), however length of sampling and weight loss had a larger impact on post-prandial metabolite. Horses on day 28 of the trial had higher average glucose, insulin and cortisol values, as well as lower AUC cortisol. Increasing time to consumption of forages is a healthy method of decreasing body weight while maintaining healthy post-prandial metabolite values.
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