Browsing by Author "McIntosh, Bridgett J."
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- Circadian and Seasonal Variation in Pasture Nonstructural Carbohydrates and the Physiological Response of Grazing HorsesMcIntosh, Bridgett J. (Virginia Tech, 2006-12-14)Nonstructural carbohydrates (NSC), which includes sugars, starches and fructans in pasture forages, undergo circadian and seasonal variation which has direct effects on metabolism in grazing horses. Increased intake of NSC is implicated in the development of digestive and metabolic disorders, such as laminitis. A series of five studies at Virginia Tech's M.A.R.E. Center in April, May, August, and October 2005, and January 2006, examined circadian and seasonal variability in forage NSC content and metabolic and digestive variables in horses over a 36 h sampling period. Fourteen mares were randomly assigned to grazing (housed on a 5-ha predominantly tall fescue pasture; n = 10) or control (stabled within the pasture and fed timothy/alfalfa hay; n = 4) groups. Blood samples were collected hourly from the horses which corresponded to hourly pasture forage samples. In all five studies, plasma glucose and insulin were measured and proxies for insulin resistance were calculated. In the April study, plasma L-lactate and fecal pH, L-lactate, D-lactate and volatile fatty acids (VFAs) were also measured. Two approaches were used for the determination of carbohydrate profiles in pasture forage samples. For the first (LAB1), sugar was water soluble carbohydrates extracted prior to analysis for starch, and included fructans. The NSC was the sum of starch and sugar. For the second (LAB2), samples were analyzed for specific NSC fractions using hydrolytic enzymes, with the addition of HCL for the determination of fructans including graminans, the type of fructans in cool season grasses. Both the LAB1 and LAB2 analyses revealed circadian and seasonal patterns in forage NSC and its constituents. In general, pasture forage NSC content was lowest in the morning and highest in the late afternoon. April had the highest NSC content which was comprised mostly of simple sugars. Forage NSC content (LAB1) was associated with environmental variables in all months with strongest correlations in April; ambient temperature (r = 0.72, P < 0.001), solar radiation (r = 0.62, P < 0.001), and humidity (r = -0.84, P < 0.001). In the animals, plasma insulin was highest in grazing horses in April (P < 0.001) followed by May (P < 0.001). Plasma insulin was higher in grazing compared to control horses at all sample points in April, and a circadian pattern was evident (P = 0.012). In grazing horses, plasma glucose was higher in April than all months except for May, and plasma glucose was higher in grazing horses compared to controls in April. In grazing horses, plasma insulin was significantly correlated with NSC and sugar in April (r = 0.69 and r = 0.67, respectively); May (r = 0.46 and r = 0.47, respectively); and January (r = 0.44 and r = 0.46, respectively). In April only, individual mean insulin response was proportional to the increase in insulin per increase in unit of NSC (r2 = 0.033, P < 0.001). Sinusoidal circadian patterns in NSC (r2 = 0.51, P < 0.001) and insulin in grazing horses (r2 = 0.12, P < 0.001) had similar frequency (P = 0.36). Plasma L-lactate was higher in grazing horses (0.64 mmol/L) than control horses (0.40 mmol/L) (P < 0.001). Fecal pH was lower in grazing horses (pH 6.9) than control horses (pH 7.2) (P = 0.008). Fecal VFAs, including acetic acid, butyric acid, and D- and L-lactate were higher in grazing horses compared to control horses (P < 0.05). These studies identified a link between forage NSC content and alterations in carbohydrate metabolism and digestion that may increase risk of laminitis via exacerbation of insulin resistance. Strategies for management practices to decrease intakes of pasture NSC by horses at risk of developing metabolic disorders are needed.
- Pharmacokinetics and Safety of Acetaminophen in Adult HorsesMercer, Melissa Ann (Virginia Tech, 2018-10-15)Due to the detrimental side effects of NSAID administration, such as gastrointestinal ulceration and renal papillary necrosis, there is a profound need for clinical pain relief in horses with long term orthopedic disease whereby gastrointestinal side effects are obviated. Acetaminophen is one of the most commonly used analgesic drugs in humans, and is readily available as an inexpensive generic over-the-counter preparation. Acetaminophen has a number of mechanisms of action that differ from NSAIDs, including actions on the serotonergic, opioid, endocannabinoid and lipoxygenase pathways. These alternate pathways may provide greater efficacy against chronic or neuropathic pain in equine patients. Acetaminophen was preferred by physicians over COX-2 and nonselective NSAIDs, even when those drugs were coupled with proton-pump inhibitors to reduce gastrointestinal side effects; due to cost considerations and the occurrence of adverse side effects from those drugs. In horses, acetaminophen has been reported to be efficacious as an adjunct treatment for laminitis in one pony, and was an effective analgesic agent when combined with NSAIDs in a model of inducible foot pain. However, no studies have been performed to validate a dose-response curve in horses. A study recently completed by our group demonstrated rapid absorption following oral administration of acetaminophen. Reported human therapeutic plasma concentrations were achieved within 30 minutes of administration, with no clinical or clinicopathologic evidence of adverse side effects after two weeks of repeated dosing. Dose simulation trials indicate that a change in dosage schedule may be required in order to provide adequate plasma concentrations.
- Physiological response of grazing horses to seasonal fluctuations in pasture nonstructural carbohydratesKaufman, Katelyn Lucille (Virginia Tech, 2019-04-16)Forage is an essential part of the equine diet for health and performance. Pasture nonstructural carbohydrates (NSC) have been shown to fluctuate diurnally and seasonally throughout the year due to various factors including environmental conditions and plant stress. The intake of elevated NSC content is linked with metabolic and digestive diseases, including colic and laminitis. A yearlong grazing study was conducted at the Virginia Tech Middleburg Agricultural Research and Extension Center from October 2016 through September 2017 to investigate fluctuations in pasture NSC concentrations as well as the metabolic and digestive response of grazing horses. Twelve sporthorse mares (15 ± 3.4 yrs) were maintained on an 8.5-ha cool season mixed grass pasture with water, mineral (Buckeye Nutrition, Dalton, OH), and white salt ad libitum. Weekly pasture samples (200 g wet weight) were clipped at random 2.5 cm from the plant base at 0800 (AM) and 1600 h (PM) on d 1 and 0800 (AM) and 1300 h (PM) on d 2. Samples were weighed and dried at 70º C and submitted to a commercial laboratory (Equianalytical, Ithaca, NY) to determine NSC content (water soluble carbohydrates [WSC] + starch). Environmental conditions were measured including ambient temperature, relative humidity, solar radiation, rainfall, soil and canopy temperature, and photosynthetically active radiation (PAR). Corresponding weekly blood samples were collected at 1300 h on d 2 via jugular venipuncture into 4 mL potassium oxalate, and 7 mL EDTA vacutainer tubes and analyzed for glucose (mg/dL), insulin (μIU/mL), and L-lactate (mg/dL). Each month, fecal grab samples were collected from the midrectum to measure pH and Dlactate (µM). Additionally, monthly glucose and insulin dynamics (% ∆) were assessed via a modified oral sugar test. Pasture nutrients including DE (2.35 ± 0.12 Mcal/kg), NSC (25.45 ± 4.02% DM), WSC (19.65 ± 3.47% DM), and starch (7.25 ± 1.29% DM) were higher in the afternoon hours (PM) compared to morning measurements (AM). Pasture CP and carbohydrate fractions were higher in the spring and fall months compared to summer and winter months with NSC concentrations being highest in May (wk 19) at 25.45% DM. Pasture NSC content was correlated (P ≤ 0.05) with relative humidity (r = 0.38), solar radiation (r = 0.32), and PAR (r = 0.51) and tended (P ≤ 0.1) to have a relationship with ambient temperature (r = 0.23) and rainfall (r = 0.23). There was seasonal variation in all morphometric measures in grazing horses. BW was highest in the spring (P < 0.0001), while BCS and CNS were highest in the fall (P = 0.0021 and P < 0.0001, respectively). Metabolic responses in grazing horses also fluctuated seasonally with glucose and insulin concentrations being most elevated in the spring (P < 0.0001). There was also seasonal variation in digestive measures in grazing horses. Plasma Llactate and fecal D-lactate means differed by month (P < 0.05) with the highest concentrations in April (11.8 ± 0.91 mg/dL and 4220.4 ± 185.5 µM, respectively). Fecal pH was most acidic in April (6.52 ± 0.08). Pasture NSC content was correlated with weight (r = 0.35), glucose (r = 0.21), and insulin (0.26) in grazing horses and tended to have a relationship with CNS (r = 0.14). There was also a relationship between NSC and plasma L-lactate (r = 0.33), fecal D-lactate (r = 0.48) and pH (r = -0.27). Lastly, glucose and insulin % ∆ (P < 0.0001) were greatest during spring months, but there was no effect of fasting insulin (P < 0.2787) or fasting glucose (P < 0.2055) on glucose % ∆. These data indicate a relationship between seasonal changes in pasture NSC content and the physiological response in grazing horses. Future aims include evaluating possible seasonal fluctuations in the hindgut microbiome of grazing horses to better understand the link between the equine microbiome and nutritionally-related disturbances. Improved grazing management strategies are needed to reduce the risk of metabolic and gastrointestinal disorders in horses, which may lead to subsequent colic and pasture associated laminitis.
- The Suitability of Native Warm-Season Grasses for EquineGhajar, Shayan M. (Virginia Tech, 2020-06-22)Introduced cool-season grasses are dominant in Virginia's grasslands, but their high digestible energy and non-structural carbohydrate (NSC) levels pose a risk for horses prone to obesity and laminitis. Native warm-season grasses (NWSG) have lower digestible energy and NSC levels that may be more suitable for horses susceptible to laminitis. The overall objectives of this research were to 1) assess voluntary intake, toxicological response, and apparent digestibility of NWSG hays fed to horses; 2) evaluate the characteristics of three NWSG species under equine grazing; and 3) evaluate establishment strategies for NWSG and wildflowers in Virginia. For the first objective, a hay feeding trial was conducted with 9 Thoroughbred geldings in a 3 x 3 Latin square design. Voluntary dry matter intake of indiangrass (Sorghastrum nutans) and big bluestem (Andropogon gerardii) hays by horses were 1.3% and 1.1% of BW/d, significantly lower than orchardgrass (Dactylis glomerata), an introduced cool-season grass, at 1.7% of BW/d. Biomarkers for toxicity remained within acceptable ranges for all treatments. Apparent DMD did not differ among hays, ranging from 39 to 43%. Non-structural carbohydrate levels were below the maximum recommended concentration for horses susceptible to laminitis. For the second objective, a grazing trial was conducted comparing indiangrass (IG), big bluestem (BB), and eastern gamagrass (Tripsacum dactyloides) (EG) yields, forage losses, changes in vegetative composition, and effects on equine bodyweight. Nine, 0.1-hectare plots were seeded with one of the three native grass treatments, and each plot was grazed by one Thoroughbred gelding in two grazing bouts, one in July and another in September 2019. Indiangrass had the highest available forage, at 4340 kg/ha, compared with 3590 kg/ha from BB (P < 0.0001). Eastern gamagrass plots established poorly, and had only 650 kg/ha available forage during the experiment. Grazing reduced standing cover of native grasses in IG and BB treatments by about 30%, and trampled forage constituted 36-68% of groundcover in those plots after each grazing bout. Horses lost weight on all treatments, but tended (P=0.09) greater weight loss on the indiangrass treatment at 1.5 kg/d compared to 0.5 kg/d in the BB and EG treatments. For the third objective, three experiments were conducted to evaluate different strategies for establishing NWSG and wildflowers. The first experiment compared large grazed plots with or without a 2 oz/acre rate of the herbicide imazapic. Imazapic led to higher biomass and percent cover in plots seeded only with NWSG. For plots seeded with a mix of NWSG and wildflowers, imazapic reduced wildflower establishment and resulted in higher biomass and percent cover of weeds over the course of the experiment. The second experiment examined four rates of imazapic application for NWSG and wildflower establishment in small plots seeded with either NWSG or a NWSG and wildflower mix, and found biomass and percent cover of weeds was lowest at a 6 oz/acre rate, while NWSG biomass and cover did not differ between treatments. Wildflower establishment was again reduced by imazapic. The third establishment experiment compared four site preparation strategies for wildflower establishment and found tillage resulted in the most cover and biomass of wildflowers.
- Trends in Equine Nutrition and the Effects of a Hindgut Buffer Product in Overconditioned HorsesDelano, Katlyn Marie (Virginia Tech, 2017-11-30)Nearly 50% of the equine population is overweight due to feeding and management practices. Obesity is related to development of diseases that are detrimental to performance and potentially fatal in horses, including insulin resistance, laminitis, and equine metabolic syndrome (EMS). Objectives of this research included first, characterization of nutrition-related management practices of hunter/jumper show industry via a voluntary survey; second, evaluating the Body Condition Index (BCI) in comparison to the Body Condition Scoring system (BCS) in sporthorses; and lastly, determining the effects of a hindgut buffer in overconditioned horses following an abruptly introduced moderate nonstructural carbohydrate (NSC) meal. There were no differences in nutritional management between hunter and jumper disciplines and most representatives (n=89) had no nutritional concerns. Many used trainers (38%) and veterinarians (36%) as sources of nutritional advice rather than professional equine nutritionists (7%). BCI had consistently higher scores than BCS (P<0.01), with the largest differences in horses with BCS < 5. Horses were offered a concentrate meal containing 1.2g NSC/kg BW with and without DigestaWell® Buffer (DB). Horses receiving DB had decreased plasma L-lactate (P=0.05), and a tendency for increased fecal pH (P=0.08) and decreased fecal D-lactate (P=0.07). These studies demonstrate a need to improve horse owner education and the relationship between representatives and trained nutritionists to reduce disease incidence, that different equations may need to be developed for a more consistently accurate BCI across various breed and body types, and that DB may have a positive impact on the equine digestive response to NSC.