Effect of a commercial anionic dietary supplement on urinary pH and concentrations of electrolytes and pH in blood of horses.

Aims: To compare urine urinary pH, blood pH and concentration of electrolytes in blood of healthy horses fed an anionic salt supplement to achieve diets with a dietary cation-anion difference (DCAD) of -40 or 0 mEq/kg DM, with horses a fed a diet with a DCAD of 85 mEq/kg DM.Methods: Eight healthy horses received each of three diets in a randomised crossover design. Diets consisted of grass hay and concentrate feed, with a varying amount of an anionic supplement to achieve a DCAD of 85 (control), 0 or -40 mEq/kg DM. They were fed for 14 days each with a washout period of 7 days between. Urine pH was measured daily and blood samples were collected on Days 0, 7 and 14 of each study period for the measurement of pH and concentration of electrolytes.Results: Four horses voluntarily consumed the anionic supplement with their feed, but four horses required oral supplement administration via dose syringe. During the study period mean urine pH was lower in horses fed diets with a DCAD of 0 (6.91; SD 0.04) and -40 (6.83; SD 0.04) mEq/kg DM compared to the control diet (7.30; SD 0.04). Compared with horses fed the control diet, mean urine pH was lower in horses fed the 0 and -40 mEq/kg DM diets on Days 1-12 and 14 (p < 0.05) of the study period. On Day 13 it was only lower in horses fed the -40 mEq/kg DM diet (p < 0.01). Urine pH was similar for horses fed the 0 and -40 mEq/kg DM diets (p = 0.151). The DCAD of the diet had no effect on blood pH, ionised Ca or anion gap. Mean concentrations of bicarbonate in blood were affected by diet (p = 0.049); they were lower when horses were fed the 0 mEq/kg diet relative to the control diet on Day 14.Conclusions and clinical relevance: The anionic supplement reduced urine pH in horses fed diets with a DCAD of 0 or -40 mEq/kg DM compared with 85 mEq/kg DM. However as urinary pH did not fall below pH 6.5, the pH below which calcium carbonate uroliths do not form, this reduction in urine pH is unlikely to be clinically significant. The supplement was variably palatable and showed minimal promise as an effective urinary acidifier at the doses administered in this study.

Submaximal exercise training, more than dietary selenium supplementation, improves antioxidant status and ameliorates exercise-induced oxidative damage to skeletal muscle in young equine athletes.

Exercise is associated with increased production of reactive oxygen species (ROS) as metabolism is upregulated to fuel muscle activity. If antioxidant systems become overwhelmed, ROS can negatively affect health and performance. Adaptation to exercise through regular training has been shown to improve defense against oxidative insult. Given selenium's role as an antioxidant, we hypothesized that increased Se intake would further enhance skeletal muscle adaptations to training. Quarter Horse yearlings (18 ± 0.2 mo; 402 ± 10 kg) were randomly assigned to receive either 0.1 or 0.3 mg Se/kg DM and placed in either an untrained or a trained (30 min walk-trot-canter, 4 d/wk) group for 14 wk. Phase 1 (wk 1 to 8) consisted of 4 treatments: trained and fed 0.1 mg Se/kg DM through wk 14 (CON-TR; n = 10), trained and fed 0.3 mg Se/kg DM through wk 14 (HIGH-TR; n = 10), untrained and fed 0.1 mg Se/kg DM through wk 14 (CON-UN; n = 5), or untrained and fed 0.3 mg Se/kg DM through wk 14 (HIGH-UN; n = 5). During Phase 2 (wk 9 to 14), dietary Se level in half of the trained horses was reversed, resulting in 6 treatments: CON-TR (n = 5), trained and fed 0.1 mg/kg Se in Phase 1 and then switched to 0.3 mg/kg Se for Phase 2 (ADD-TR; n = 5), trained and fed 0.3 mg/kg Se in Phase 1 and then switched to 0.1 mg/kg Se for Phase 2 (DROP-TR; n = 5), HIGH-TR (n = 5), CON-UN (n = 5), or HIGH-UN (n = 5). All horses underwent a 120-min submaximal exercise test (SET) at the end of Phase 1 (SET 1) and 2 (SET 2). Blood samples and biopsies from the middle gluteal muscle were collected before and after each phase of the study and in response to each SET and analyzed for markers of oxidative damage and antioxidant enzyme activity. In both phases, serum Se was higher (P < 0.0001) when horses received a diet with 0.3 than 0.1 mg Se/kg DM. Throughout the 14-wk study, resting activities of muscle glutathione peroxidase (GPx; P = 0.004) and superoxide dismutase (SOD; P = 0.06) were greater in trained horses than in untrained horses. In response to SET 1, serum creatine kinase (CK) activity was lower in trained horses than in untrained horses (P < 0.0001), indicating less muscle damage, but plasma lipid hydroperoxides (LPO) and muscle GPx and SOD activities were unaffected by training or Se. In response to SET 2, trained horses had greater muscle SOD activity (P = 0.0002) and lower serum CK activity (P = 0.003) and showed a trend for lower plasma LPO (P = 0.09) and muscle malondialdehyde (P = 0.09) than untrained horses. Muscle GPx activity did not change in response to SET 2 and was unaffected by training or Se. Results indicate that exercise training lessens muscle damage and improves antioxidant defense following an acute bout of prolonged exercise and was not further enhanced by feeding Se above the NRC requirement.

Characterizing ammonia emissions from horses fed different crude protein concentrations.

Evaluating impact of animal agriculture on air quality has been the focus of recent research. Ammonia (NH) volatilization occurs when undigested protein in feces and urea in urine is broken down by bacteria and enzymes. Information regarding NH emission from equine facilities is limited, and effects of CP intake on NH emissions have not been investigated. Nine mature geldings were used in a 3 × 3 replicated Latin square design study to determine effects of dietary CP on potential NH losses from feces and urine. We hypothesized feeding horses above the CP requirement would result in an increase in NH emissions from urine and feces and different bedding materials would affect NH emissions from urine. Diets were formulated using different ratios of bahiagrass () and Tifton-85 bermudagrass () hays, and a commercial vitamin mineral supplement to provide 3 different CP concentrations and labeled in relation to each other: LOW-CP, MED-CP, and HIGH-CP (10.6%, 11.5%, and 12%, respectively). Each study period consisted of an 11-d diet adaptation phase, followed by a 3-d total collection of urine and feces. To determine total nitrogen (TN) and urea-N concentrations, samples were pooled by period ( = 9). For in vitro determination of NH concentrations, urine and fecal samples were pooled within period by diet ( = 3) and mixed with either wheat straw or wood shavings. Ammonia emission of these samples was measured using a vessel system with an airflow rate (2.5 L/min) at 20°C over a 7-d period. Concentration of NH in each vessel was measured using a photoacoustic multigas analyzer. Temperature, airflow rate, and NH concentration in each vessel were used to calculate NH emission rate (ER). Data were analyzed using a mixed model ANOVA with repeated measures. Urinary TN and urea-N excretion increased as CP intake increased ( < 0.0001). Vessel urinary NH concentrations were not different across diets ( = 0.1225), ranging from 55.48 ppm (LOW-CP) to 101.14 ppm (HIGH-CP); however, they differed between bedding types ( < 0.0001), with straw higher than shavings (97 vs. 73.5 ppm, respectively). Cumulative urinary NH ER tended to be different across diets ( = 0.0550) ranging from 5.87 g/m to 9.97 g/m and bedding types ( = 0.0129), with straw being higher than shavings (11.1 vs. 6.9 g/m, respectively). Overfeeding CP to horses can lead to increased urinary TN and urea-N excretion, which could lead to greater of NH in the atmosphere.

Rapid Communication: Dietary selenium improves skeletal muscle mitochondrial biogenesis in young equine athletes.

Exercise is known to promote mitochondrial biogenesis in skeletal muscle as well as enhance mitochondrial function and efficiency in human and rodent models. These adaptations help to decrease exercise-associated production of reactive oxygen species, which can negatively affect health and performance if antioxidant mechanisms are overwhelmed. Little is known about the adaptations of mitochondria in response to exercise training in the growing horse or if supplementation with a dietary antioxidant can improve mitochondrial function. To evaluate the separate and combined effects of selenium (Se) supplementation, training, and an acute strenuous exercise bout on mitochondrial adaptations in young horses, 30 American Quarter Horse yearlings were randomly assigned to an exercise training group or a no-training group and, within each group, received either 0.1 or 0.3 mg Se/kg DM for 14 wk. The study was split into 2 phases (wk 0 to 8 and wk 9 to 14), with half of the trained horses switched to the opposite dietary treatment in Phase 2. At the end of each phase, all horses underwent a 120-min submaximal exercise test (SET; SET 1 and SET 2). Biopsies of the middle gluteal muscle were collected before and after each phase of the study and in response to each SET and analyzed for markers of mitochondrial number and function. At rest, horses receiving 0.3 mg Se/kg DM had higher citrate synthase activity ( = 0.021) than horses receiving 0.1 mg Se/kg DM, indicating higher mitochondrial content. In contrast, cytochrome oxidase (CCO) activity was not affected by dietary Se overall, but horses that were dropped from 0.3 mg Se/kg DM to 0.1 mg Se/kg DM during Phase 2 showed a decrease ( = 0.034) in integrated CCO activity from wk 9 to 14, suggesting impaired mitochondrial function. Mitochondrial enzyme activities were unaffected by an acute, strenuous exercise bout (SET 1 and SET 2). Our relatively low-intensity exercise training protocol did not appear to induce functional mitochondrial adaptations. However, elevated dietary Se may impart beneficial effects on mitochondrial biogenesis during growth and training. A more strenuous exercise training protocol should be investigated to determine the potential benefits of elevated dietary Se for elite equine athletes.

Dietary selenium and prolonged exercise alter gene expression and activity of antioxidant enzymes in equine skeletal muscle.

Untrained Thoroughbred horses (6 mares and 6 geldings; 11 yr [SE 1] and 565 kg [SE 11]) were used to evaluate antioxidant gene expression and enzyme activity in blood and skeletal muscle in response to prolonged exercise after receiving 2 levels of dietary selenium for 36 d: 0.1 (CON; = 6) or 0.3 mg/kg DM (SEL; = 6). Horses were individually fed 1.6% BW coastal bermudagrass hay, 0.4% BW whole oats, and a mineral/vitamin premix containing no Se. Sodium selenite was added to achieve either 0.1 or 0.3 mg Se/kg DM in the total diet. On d 35, horses underwent 2 h of submaximal exercise in a free-stall exerciser. Blood samples were obtained before (d 0) and after 34 d of Se supplementation and on d 35 to 36 immediately after exercise and at 6 and 24 h after exercise. Biopsies of the middle gluteal muscle were obtained on d 0, before exercise on d 34, and at 6 and 24 h after exercise. Supplementation with Se above the NRC requirement (SEL) increased serum Se ( = 0.011) and muscle thioredoxin reductase (TrxR) activity ( = 0.051) but had no effect on glutathione peroxidase (GPx) activity in plasma, red blood cell (RBC) lysate, or muscle in horses at rest. Serum creatine kinase activity increased ( < 0.0001) in response to prolonged exercise but was not affected by dietary treatment. Serum lipid hydroperoxides were affected by treatment ( = 0.052) and were higher ( = 0.012) in horses receiving CON than SEL immediately following exercise. Muscle expression of was unchanged at 6 h but increased ( = 0.005) 2.8-fold 24 h after exercise, whereas muscle TrxR activity remained unchanged. Glutathione peroxidase activity increased in plasma (P < 0.0001) and decreased in RBC lysate ( = 0.010) after prolonged exercise. A Se treatment × time interaction was observed for RBC GPx activity (P = 0.048). Muscle and expression and GPx activity did not change during the 24-h period after exercise. Level of dietary Se had no overall effect on expression of , , , , , , or in muscle following exercise. The impact of prolonged exercise on the activities of antioxidant enzymes varied. Furthermore, changes in enzyme activity did not necessarily align with enzyme gene expression following exercise. A higher level of Se intake elevated Se status of untrained horses, increased GPx activity, and lessened lipid peroxidation following exercise, suggesting that Se may be beneficial for mitigating oxidative muscle damage and aiding in postexercise recovery.

L-Arginine supplementation 0.5% of diet during the last 90 days of gestation and 14 days postpartum reduced uterine fluid accumulation in the broodmare.

L-Arginine is an essential amino acid in many species that has been shown to influence reproduction. However, in horses a dose of 1% L-arginine of total dietary intake impaired absorption of other amino acids, whereas a dose of 0.5% did not. The objectives of this experiment were to evaluate postpartum parameters on mares supplemented with 0.5% L-arginine through the last 90d of gestation and 14d postpartum. Sixteen light-horse mares were randomly divided in two groups: 8 mares supplemented with 0.5% L-arginine and 8 mares fed an isonitrogenous equivalent. Gestation length, days to uterine clearance and days to first ovulation were compared. Uterine body depth, diameter of uterine horns, and length of largest pocket of uterine fluid were recorded daily via transrectal ultrasound. Measurements of foal weight, height, and cannon bone circumference were recorded for 9 weeks. Arginine treatment had no effect on gestation length (P=0.58). Supplemented mares cleared fluid quicker postpartum (6.8±0.53d; P=0.026) compared to control (9.0±0.38d). Mares supplemented with L-arginine had smaller diameter of fluid present in the postpartum uterus (P≤0.05). Days to first postpartum ovulation were not affected by treatment nor any influence on uterine involution. Finally, treatment had no effect on any foal's measured parameters. L-Arginine supplementation fed at 0.5% of daily intake during the last 90d of gestation and early postpartum in mares decreased uterine fluid accumulation, yet did not appear to have any effect on any other parameters measured.

Electromyographic activity of the long digital extensor muscle in the exercising Thoroughbred horse.

Surface electrodes were used to record electromyographic (EMG) activity of the long digital extensor muscle on the right hindlimb of 8 Thoroughbred horses for 8 s at the walk and 8 s at the trot before (unfatigued) and after (fatigued) an exercise test. The exercise test was performed on a motorised treadmill set on a 10% grade. Each test started at a speed of 6 m/s which was increased by 1 m/s each minute until the horse fatigued as indicated by its inability to keep pace with the treadmill with minimal encouragement. Observations were made on the horses prior to conditioning (untrained state) and after 8 weeks of regular exercise (trained state). The mean root-mean-square (rms) values of EMG bursts collected in each experimental trial were determined for each horse and group means were derived from the mean of independent subjects. Statistical comparisons for differences in rmsEMG were related to gait, fatigue and training. Mean rmsEMG at the trot was consistently higher than at the walk (P<0.05). At the walk, mean fatigued rmsEMG tended to be higher than the mean unfatigued rmsEMG in the untrained state and was significantly higher in the trained state (P<0.05). At the trot, mean fatigued rmsEMG was higher (P<0.05) than mean unfatigued rmsEMG in both the untrained and trained states. Training did not have an effect on mean rmsEMG of unfatigued muscles at the walk or the trot (P>0.05). However, fatigued muscles experienced higher EMG activity in the trained state at the walk (P<0.05). A similar tendency was observed at the trot. Results of this study suggest that surface EMG measurement may be useful for evaluating fatigue in exercising horses.

The influence of betaine on untrained and trained horses exercising to fatigue.

Because exercise fatigue has been associated with the accumulation of lactic acid, factors that influence lactate metabolism during exercise can potentially enhance performance. The objective of this study was to examine the effects of supplemental betaine on eight mature Thoroughbred horses before and after 8 wk of conditioning. The effects of betaine were tested in two cross-over design experiments, allowing each horse to receive both the control and betaine treatments at each fitness level. Ingestion of 80 mg of betaine/kg of BW for 14 d before exercise testing did not alter plasma lactate, glucose, free fatty acids (FFA), or triglyceride concentrations during exercise in the untrained or trained horses. A time x treatment interaction (P < .05) was observed for plasma lactate in untrained horses during recovery from exercise, and plasma lactate concentrations were lower (P < .05) at 60 min after exercise when untrained horses received betaine. Plasma FFA concentrations were lower (P < .05) before exercise and at 720 min after exercise when untrained horses received betaine. These data indicate that betaine may influence lactate metabolism following exercise in untrained horses; however, betaine does not seem beneficial for trained horses.

The effect of dietary fish oil supplementation on exercising horses.

Ten horses of Thoroughbred or Standardbred breeding were used to study the effects of dietary fish oil supplementation on the metabolic response to a high-intensity incremental exercise test. Horses were assigned to either a fish oil (n = 6) or corn oil (n = 4) treatment. The fish oil (Omega Protein, Hammond, LA) contained 10.6% eicosapentaenoic acid and 8% docosahexaenoic acid. Each horse received timothy hay and a textured concentrate at a rate necessary to meet its energy needs. The supplemental oil was top-dressed on the concentrate daily at a rate of 324 mg/kg BW. Horses received their assigned diet for 63 d, during which time they were exercised 5 d/wk in a round pen or on a treadmill. During wk 1, horses exercised for 10 min at a trot. After wk 1, exercise time and intensity were increased so that at wk 5, exercise time in the round pen increased to 30 min (10 min of cantering and 20 min of trotting) per day. Starting at wk 6, horses were exercised 3 d/wk in the round pen for 30 min and 2 d/wk on a treadmill for 20 min. After 63 d, all horses performed an exercise test consisting of a 5-min warm-up at 1.9 m/s, 0% grade, followed by a step test on a 10% grade at incremental speeds of 2 to 8 m/s. Blood samples were taken throughout exercise. During exercise, horses receiving fish oil had a lower heart rate (treatment x time interaction; P < 0.05) and tended to have lower packed cell volume (treatment effect; P = 0.087). Plasma lactate concentrations were not affected by treatment. Plasma glucose concentrations were not different between groups during exercise but were lower (treatment x time interaction; P < 0.01) for the fish oil group during recovery. Serum insulin tended to be lower in fish oil horses throughout exercise (treatment effect; P = 0.064). There was a tendency for glucose:insulin ratios to be higher for fish oil-treated horses throughout exercise (treatment effect; P = 0.065). Plasma FFA were lower (treatment x time interaction; P < 0.01) in horses receiving fish oil than in horses receiving corn oil during the initial stages of the exercise test. Serum glycerol concentrations also were lower in fish oil-treated horses (P < 0.05). Serum cholesterol concentrations were lower in horses receiving fish oil (treatment effect; P < 0.05), but serum triglycerides were not affected by treatment (P = 0.55). These data suggest that addition of fish oil to the diet alters exercise metabolism in conditioned horses.

Orally supplemented L-arginine impairs amino acid absorption depending on dose in horses.

The beneficial effect of L-arginine (L-Arg) supplementation, on the physiology of several species, has generated an interest in the use of L-Arg as a nutraceutical in horses, but dosage and absorption of orally supplemented L-Arg must be inferred from other species. The study objective was to determine the effect of 2 oral L-Arg doses on plasma arginine concentrations and the effect on absorption of other amino acids in mares. In Experiment 1, mares were blocked by age and breed and were fed L-Arg supplemented (supplemented with 0.025% BW L-Arg; n=6) or control (no supplement; n=6) concentrate on a single day with blood samples taken at 0, 0.5, 1, 2, 3, 4, and 5 h relative to feeding. In Experiment 2, mares (n=6) were used in a 3×3 Latin square design with L-Arg (0.0125% of BW), urea (0.0087% of BW), and control (no supplement) fed mixed into a grain concentrate as single meal with blood samples taken at 0, 1,2, 4, 6, 8,10, and 12 h relative to feeding. In Experiment 1, L-Arg supplementation increased (P<0.05) plasma L-Arg and ornthine concentrations and decreased (P<0.05) lysine and methionine concentrations compared with the control group. At 1 h post feeding, L-Arg mares had lower (P<0.05) plasma concentrations of histidine, glutamic acid, proline, isoleucine, threonine, phenylalanine, leucine, valine, alanine, and taurine. In Experiment 2, L-Arg supplementation increased (P<0.05) arginine and ornithine concentrations compared with urea and control; there was no difference among other amino acids. These experiments indicate that L-Argis absorbed and, dependent on the dose, alters the absorption of other amino acids in mares.

Effect of dietary omega-3 fatty acid source on plasma and red blood cell membrane composition and immune function in yearling horses.

To determine the effect of different sources of dietary n-3 fatty acids (FA) on plasma and red blood cell (RBC) FA composition and immune response, 18 Quarter Horse yearlings were randomly and equally assigned to 1 of 3 treatments: encapsulated fish oil (n = 6), milled flaxseed (n = 6), or no supplementation (control, n = 6). Fish oil contained 15 g of eicosapentaenoic acid (C20:5n-3) and 12.5 g of docosahexaenoic acid (C22:6n-3), and flaxseed contained 61 g of alpha-linolenic acid (C18:3n-3) per 100 g of FA. Horses had free access to bahiagrass pasture during the active growing season and were individually fed a grain mix concentrate at 1.5% BW/d. Fish oil and flaxseed were mixed into the concentrate in amounts to provide 6 g of total n-3/100 kg of BW. Horses were fed their respective treatments for 70 d. Blood samples were obtained to determine plasma and RBC FA composition and for isolation of peripheral blood mononuclear cells. Peripheral blood mononuclear cells were stimulated with concanavalin A and phytohemagglutinin (PHA) to determine lymphocyte proliferation and were challenged with lipopolysaccharide to determine PGE(2) production. In vivo inflammatory response was assessed on d 70 by measuring skin thickness and area of swelling in response to intradermal injection of PHA. Treatment did not affect BW gain, which averaged 0.6 +/- 0.03 kg/d. Horses fed fish oil had greater (P < 0.05) proportions of eicosapentaenoic acid, docosahexaenoic acid, and sum of n-3 in plasma and RBC compared with those in the flaxseed and control treatments. In addition, plasma arachidonic acid was greater (P < 0.05) and plasma linoleic and alpha-linolenic acids were less (P < 0.05) in the fish oil treatment compared with the flaxseed and control treatments. Dietary treatment did not affect lymphocyte proliferation or PGE(2) production. Across treatments, the peak increase in skin thickness was observed 4 to 8 h after PHA injection. At 4 h postinjection, horses fed fish oil and those fed flaxseed had a greater increase in skin thickness than those in the control treatment (P < 0.05) and horses fed fish oil had a larger area of swelling than those in the control treatment (P < 0.05). Skin thickness remained greater (P < 0.05) in horses fed flaxseed than in control horses 6 h after injection. Although fed to supply a similar amount of n-3 FA, fish oil had a greater impact on plasma and RBC n-3 FA content than did flaxseed. However, supplementing horses with both fish oil and flaxseed resulted in a more pronounced early inflammatory response to PHA injection as compared with nonsupplemented horses.

Digestibility and nutrient retention of perennial peanut and bermudagrass hays for mature horses.

Mature horses were used to determine apparent DM, OM, NDF, and CP digestibility values of 2 bermudagrass (BG; Cynodon dactylon) hays, Coastal (CB) and Tifton 85 (T85), and Florigraze perennial peanut (PP; Arachis glabrata) hay. In addition, N, Ca, and P balances were determined in horses fed those hays. Five mature Thoroughbred geldings and 1 Quarter Horse gelding (mean initial BW = 542 +/- 37 kg) were used (5 horses for the last period) in a 3 x 3 repeated Latin square design, with 2 horses per hay and 3 adjustment and collection periods. Horses were randomly assigned to pairs and the initial hay to be fed. Each period consisted of a 10-d adjustment phase, followed by a 4-d total fecal and urine collection phase. Horses were fed at 1.5 (period 1), 1.7 (period 2), or 2% (period 3) of their BW daily (DM basis). The 2 BG were grown under similar conditions, with CB and T85 being cut at 4 and 5 wk of regrowth, respectively, and PP being of a late first cutting. The compositions (DM basis) of PP, CB, and T85, respectively, were 93, 94, and 93% DM; 92, 94, and 94% OM; 46, 73, and 77% NDF; 34, 37, and 42% ADF; 11, 10, and 8% CP; 1.10, 0.28, 0.27% Ca; and 0.19, 0.15, and 0.19% P, respectively. Least squares means (pooled SE) for apparent digestibility of PP, CB, and T85, respectively, were 65, 53, and 52% (1) DM digestibility; 67, 53, and 52% (1) OM digestibility; 44, 50, and 46% (4) NDF digestibility; and 66, 60, and 57% (1) CP digestibility. Digestibility values of DM and OM were greater (P < 0.001) for PP than for the BG. Digestibility of CP was greater (P = 0.001) for PP than for CB or T85, with no difference (P = 0.37) between PP and BG hays in NDF digestibility. There were no differences between CB and T85 for DM digestibility (P = 0.67), OM digestibility (P = 0.59), CP digestibility (P = 0.11), and NDF digestibility (P = 0.48). Nitrogen (P = 0.01) and P balances (P = 0.04) were greater for PP than BG hays, whereas N balance of CB was greater (P = 0.01) than that of T85. There were no differences among all hays in Ca balance (P = 0.54) and between the BG in P balance (P = 0.34). Results indicated that PP, CB, and T85 are suitable forages for horses.

Maintenance of bodyweight during a multiple-day chuckwagon race meet.

The gruelling race schedules maintained by horses competing in chuckwagon racing raises concern for the horses' ability to recover quickly and continue to perform at a high level. The amount of bodyweight lost and the time required for recovery of this weight loss have been used to assess the level of stress imposed on horses competing in various multiple-day events. In this study, bodyweights were obtained from 40 Thoroughbred geldings (mean +/- s.e.; bodyweight 521.5 +/- 4.4 kg) before and after racing during a 5 day chuckwagon race meet. Body condition score (BCS) was determined on the first and last day of competition. Comparisons were based on the number of consecutive days the horse raced. Average bodyweight loss (P = 0.039) from each race was 3.5 +/- 0.3 kg (0.7% of initial bodyweight) and was not affected by the number of days the horse raced. The largest bodyweight deficit (P = 0.005) occurred within the 24 h period after their first race (5.3 +/- 0.5 kg; 1.0% of initial bodyweight). Horses racing on 2-5 consecutive days retained a 4.8 +/- 0.3 kg deficit (P = 0.01), which was maintained throughout the remainder of the race meet. Horses began and ended the race meet with a BCS of 4.9 +/- 0.2 and 4.7 +/- 0.2, respectively (using the 1 to 9 BCS system). Although chuckwagon horses compete in a strenuous event on several consecutive days, they appear to be managed well and have the ability to maintain their bodyweight despite the physical and psychological demands of frequent racing.

The effect of dietary fibre on hydration status after dehydration with frusemide.

Three diets were fed to 6 horses in a 3 x 6 Latin rectangle experiment to determine if dietary fibre could improve hydration status in response to dehydration with frusemide. Frusemide was used to simulate dehydration from exercise-induced sweat loss. Diets contained similar dry matter (DM), energy, protein and electrolyte content, but differed in total dietary fibre (TDF) and/or soluble fibre (SDF). The 3 diets were: 1) HIGH-HIGH (high TDF, high SDF); 2) HIGH-LOW (high TDF, low SDF); and 3) LOW-LOW (low TDF, low SDF). In each 10 day period, water intake and faecal moisture content were assessed on Day 7. On Day 10, feed and water were withheld and horses were dehydrated with frusemide (1 mg/kg bwt, i.m.). Plasma volume (PV), plasma total protein (TP), packed cell volume (PCV) and plasma electrolyte concentrations were determined before and after frusemide administration. Water consumption was greater (P < 0.05) when horses received diets high in TDF. Faecal moisture content was greatest (P < 0.01) when horses received the HIGH-HIGH diet. The decline in PV and the rise in plasma TP concentration following frusemide administration were similar for all diets. When horses received the HIGH-HIGH diet, they had a greater (P < 0.05) bodyweight before dehydration and lost more (P < 0.05) bodyweight in response to frusemide. A greater loss of bodyweight in response to frusemide without a proportional loss of PV when horses received the HIGH-HIGH diet suggests that a diet high in SDF may provide the horse with a source of dispensable water in the hind gut during dehydration.

The effect of diet composition and feeding state on the response to exercise in feed-restricted horses.

Eight Thoroughbred horses were used to determine the effects of long-term calorie restriction and diet composition on serum T4 and T3 concentrations and metabolic responses with exercise. Horses were randomly assigned to 2 treatment groups (n = 4): Group 1, horses were fed a calorie-restricted diet designed to have 70% of the calories from the roughage source (RHR); Group 2, horses were fed a calorie-restricted diet designed to have 70% of the calories from the concentrate source (RHC). Horses then completed 2 step-wise exercise tests; one following a 12 h fast and one 2 h after a meal of 2 kg of a grain mix. Glucose concentrations declined (P < 0.01) in fed horses on the RHR diet but did not change in fed horses on the RHC diet. Fasted horses receiving the RHR diet had a more rapid increase in glucose concentration during exercise compared to fasted horses receiving the RHC diet (P < 0.01) as well as the highest glucose concentration at fatigue (P < 0.05). Insulin concentrations were higher (P < 0.05) at fatigue in fed horses on the RHR diet. Fasted horses receiving the RHR diet had higher (P < 0.01) pre-exercise FFA concentrations and a more rapid decline (P < 0.01) in FFA during exercise. Serum T3 concentrations increased (P < 0.01) in response to exercise within all treatments. The differences in thyroid hormone, glucose and FFA responses to exercise suggest that calorie source may be important in the hormonal regulation and energy metabolism of horses consuming calorie deficient diets.