Twenty stock-type horses (589 ± 126 kg BW; 13 ± 8 yr) were used in a completely randomized design for 28-d to evaluate the impact of a joint supplement on gait kinematics, inflammation and cartilage metabolism. Horses were stratified by age, sex, body weight (BW), and initial lameness scores and were randomly assigned to 1 of 2 dietary treatments consisting of either a 100 g placebo top-dressed daily to 0.6% BW (as-fed) commercial concentrate (CON; n=10; SafeChoice Original, Cargill, Inc.), or an oral joint supplement (SmartPak Equine LLC) containing glucosamine, chondroitin sulfate, hyaluronic acid, methylsulfonylmethane, turmeric, resveratrol, collagen, silica, and boron (TRT; n=10). Horses were group-housed with ad libitum access to coastal bermudagrass hay (Cynodon dactylon) and allowed to graze pasture 2 h/d. Horses were exercised progressively 4 d/wk at 45 min each. On d 13 and 27, blood was harvested followed by a 19.3 km exercise stressor on concrete. Horses travelled at the walk, with no more than 15 min at the trot. Every 14 d, BW and BCS were recorded, and blood was collected for plasma prostaglandin E2 (PGE2), serum collagenase cleavage neopeptide (C2C), carboxypropeptide of type II collagen (CPII), and chondroitin sulfate 846 epitope (CS846) analysis. Kinematic gait analysis was performed every 14 d (Kinovea v.0.8.15) to determine stride length (SL) and range of motion (ROM) of the knee and hock at the walk and trot. Data were analyzed using PROC MIXED of SAS. All horses increased BW and BCS over time (P ≤ 0.01). Hock ROM increased in TRT horses (P ≤ 0.02) at the walk and tended to increase at the trot compared to CON (P = 0.09). At the walk, SL and knee ROM increased over time, independent of dietary treatment (P ≤ 0.01); no time effect was observed at the trot (P > 0.15). Regardless of treatment, C2C and CPII increased over time (P ≤ 0.05) and no effect was observed for CS846 or PGE2 (P > 0.12). In response to the exercise stressor, CPII and PGE2 decreased (P ≤ 0.05) from d 13 to 14, and CS846 and PGE2 tended to decrease (P ≤ 0.10) from d 27 to 28, independent of dietary treatment. In conclusion, hock ROM at the walk and trot was most sensitive to dietary treatment. Supplementation did not alter biomarker concentration of collagen metabolites or systemic inflammation in the 28-d period, but a future study utilizing arthrocentesis may be warranted to specifically evaluate intra-articular response to dietary treatment.

In livestock species, the enterocytes of the small intestine are responsible for the synthesis of citrulline and arginine from glutamine and proline. At present, little is known about de novo synthesis of citrulline and arginine in horses. To test the hypothesis that horses of different age groups can utilize glutamine and proline for the de novo synthesis of citrulline and arginine, jejunal enterocytes from 19 horses of three different age groups: neonates (n = 4; 7.54 ± 2.36 d of age), adults (n = 9; 6.4 ± 0.35 yr), and aged (n = 6; 22.9 ± 1.0 yr) with healthy gastrointestinal tracts were used in the present study. Enterocytes were isolated from the jejunum and incubated at 37°C for 30-min in oxygenated (95% O2/5% CO2) Krebs bicarbonate buffer (pH 7.4) containing 5 mM D-glucose and 0 mM, 2-mM L-[U- 14C]glutamine, or 2 mM L-[U- 14C]proline plus 2 mM L-glutamine. Concentrations of arginine, citrulline, and ornithine in cells plus medium were determined using high-performance liquid chromatography. Results indicate that the rate of oxidation of glutamine to CO2 was high in enterocytes from neonatal horses, but low in cells from adult and aged horses. Enterocytes from all age groups of horses did not degrade proline into CO2. Regardless of age, equine enterocytes formed ornithine from glutamine and proline, but failed to convert ornithine into citrulline and arginine. Because arginine is an essential substrate for the synthesis of proteins, but also nitrogenous metabolites (e.g., nitric oxide, polyamines, and creatine), our novel findings have important implications for the nutrition, performance, and health of horses.

While beneficial in rehabilitation, aquatic exercise effects on cartilage and bone metabolism in young, healthy horses has not been well described. Therefore, thirty Quarter Horse yearlings (343 ± 28 kg; 496 ± 12 d of age) were stratified by age, body weight (BW), and sex and randomly assigned to one of three treatments for 140-d to evaluate effects of aquatic, dry, or no exercise on bone and cartilage metabolism in young horses transitioning to an advanced workload. Treatments included non-exercise control (CON; n=10), dry treadmill (DRY; n=10), or aquatic treadmill exercise (H2O; n=10; water: 60% wither height, WH). Horses were housed individually (3.6×3.6 m) from 0600 to 1800, allowed turnout (74×70 m) from 1800 to 0600, and fed to meet or exceed requirements. During Phase I (d 0-112), DRY and H2O walked on treadmills 30 min/d, 5 d/wk. Phase II (d 113-140) transitioned to an advanced workload 5 d/wk. Every 14-d, WH, hip height (HH), and BW were recorded. Left third metacarpal radiographs on d 0, 112, and 140 were analyzed for radiographic bone aluminum equivalence (RBAE). Every 28-d, serum samples were analyzed for osteocalcin and C-telopeptide crosslaps of type I collagen (CTX-1), and synovial fluid samples were analyzed for prostaglandin E2 (PGE2), collagenase cleavage neopeptide (C2C), collagenase of type I and type II collagen (C1,2C), and carboxypeptide of type II collagen (CPII) using ELISAs. All data were analyzed using PROC MIXED of SAS, including random effect of horse within treatment, and repeated effect of day. Baseline treatment differences were accounted for using a covariate. There were treatment × day interactions (P<0.01) where OC and CTX-1 remained consistent in both exercise groups while inconsistently increasing in CON. There were no treatment differences (P>0.30) in RBAE, BW, or HH, but all increased over time (P<0.01). There were no treatment × day interactions of synovial inflammation or markers of cartilage metabolism, however there was an effect of day for each marker (P<0.03). Changes in biomarkers of cartilage turnover in horses exercised at the walk, whether dry or aquatic, could not be distinguished from horses with access to turnout alone. This study indicates that early forced exercise supports consistent bone metabolism necessary for uniform growth and bone development, and that there are no negative effects of buoyancy on cartilage metabolism in yearlings transitioned from aquatic exercise to a 28-d advanced workload.

Aquatic treadmills improve range of motion and increase muscular strength in mature horses; however, effects of buoyancy on inflammation and cartilage metabolism in young horses are not well investigated. Therefore, thirty Quarter Horse yearlings of similar breeding were stratified by age, BW, and sex and randomly assigned to one of three treatment groups during a 140-d trial to evaluate the influence of aquatic vs. dry exercise on joint inflammation and cartilage metabolism in young horses transitioning to an advanced workload. Treatment groups included non-exercise control (CON; n = 10), dry treadmill exercise (DRY; n = 10), or aquatic treadmill exercise (H2O; n = 10; water at 60% wither height). Animals were housed in individual stalls and allowed turnout for a minimum of 10 h/d. During Phase I, DRY and H2O walked on treadmills 30 min/d, 5 d/wk from d 0 to d 112. Phase II represented transition to an advanced workload 5d/wk for 28 d (Table 1). Every 28 d following exercise, synovial fluid samples were collected and analyzed for prostaglandin E2 (PGE2), collagenase cleavage neopeptide (C2C), collagenase of type I and type II collagen (C1,2C), and carboxypeptide of type II collagen (CPII) using commercial ELISA kits. All data were analyzed using PROC MIXED of SAS, including random effect of horse within treatment, and repeated effect of day. Baseline treatment differences were accounted for using a covariate structure. There were no treatment ′ day interactions of synovial inflammation or markers of cartilage metabolism; however, there was an effect of day for each selected marker (P < 0.03). Changes in biomarkers of cartilage turnover in horses exercised at the walk, whether dry or aquatic, could not be distinguished from horses with access to turnout alone. This indicates that there are no negative effects of buoyancy on cartilage metabolism in yearlings transitioned from aquatic exercise to 28-d advanced workload.