Oxidative stress biomarkers and free amino acid concentrations in the blood plasma of moderately exercised horses indicate adaptive response to prolonged exercise training.

Oxidative stress caused by routine physical stressors may negatively impact the performance of equine athletes; thus, the present study identifies oxidative biomarkers in the blood plasma of exercising horses. Stock-type horses were subject to a standardized moderate-intensity exercise protocol 3 times per week for 8 wk. Exercise protocol followed NRC guidelines consisting of 30% walk, 55% trot, and 15% canter, with a target heart rate (HR) of 90 BPM. Blood plasma was collected in wk 1, 2, 7, and 8 immediately before and 0, 30, 60, and 90 min after exercise and analyzed for total antioxidant capacity (TAC), thiobarbituric acid reactive substance (TBARS), glutathione peroxidase activity (GPx), and superoxide dismutase activity (SOD). Data were analyzed as repeated measures with wk, d, time, and their interactions as fixed effects. The TAC on day 2 (0.40 mM Trolox) was 7.5% greater than on day 3 (P = 0.013). There were wk × d × time interactions for SOD, TBARS, and GPx (P < 0.001). The TBARS remained at pre-exercise baseline (d-1 wk-1; 2.7 µM malondialdehyde) for most collection times within weeks 1, 7, and 8 (P ≥ 0.058); however, TBARS increased by 0.24 to 0.41 µM on day 2 of week 2 post-exercise (P < 0.001) and remained similarly elevated on day 3 pre- and immediately post-exercise (P < 0.001). The GPx similarly remained at baseline (172.6 µM/min; P ≥ 0.621) but increased by 48.18 to 83.4 µM/min at most collection times on days 1 and 2 of week 2 (P ≤ 0.023). The SOD remained at baseline (167.2 U/ mL; P ≥ 0.055) until increasing by 11.28 to 15.61 U/mL at 30 min post-exercise on day 1, week 1 and at most collection times on day 3, week 8 (P ≤ 0.043). Amino acids with antioxidant properties such as Met, Tyr, and Trp drastically decreased from weeks 2 to 8 (P < 0.001). Met and Tyr also decreased from -60 to 90 min (P < 0.047), whereas there was no time effect on Trp concentration (P = 0.841). The current study indicates the time-dependent nature of oxidative stress concerning persistent stressors such as exercise.

Performance horses are subjected to numerous stressors. These stressors may subsequently impact their overall performance. The present study measured oxidative stress biomarkers in the blood of exercising horses. Horses were moderately exercised over an 8-wk period and blood plasma was collected to measure total antioxidant capacity (TAC), thiobarbituric acid reactive substance (TBARS), glutathione peroxidase activity (GPx), and superoxide dismutase activity (SOD). Amino acid concentration was also evaluated. The TAC was greater on day 2 vs. day 3. The TBARS remained at pre-exercise (baseline) at most times except for increasing on day 2 of week 2 post-exercise. The GPx also remained at baseline for most times but increased on days 1 and 2 of week 2. The SOD remained at baseline until increasing at 30 min post-exercise on day 1, week 1 and at most collection times on day 3, week 8. Amino acids with antioxidant properties drastically decreased from weeks 2 to 8. Horses are exposed to a variety of physical stressors on a regular basis that may produce similar effects in the equine stress response. Understanding the response in the equine athlete when exposed to new stressors is crucial in determining how to prevent oxidative damage in future athletes.

Development of a mathematical model for predicting digestible energy intake to meet desired body condition parameters in exercising horses.

Maintaining optimal body condition is an important concern for horse owners and managers as it can affect reproductive efficiency, athletic ability, and overall health of the horse; however, information regarding dietary requirements to maintain or alter BCS in the horse is limited. A recently developed model had high accuracy in predicting the energy required to alter BCS in the horse. However, the model was restricted to sedentary mares, while many horses are subject to physical work. The objective of this study was to expand the scope of that model to include exercising horses by incorporating previously published estimates of exercise energy expenditure and then testing the expanded model. Stock type horses (n = 24) were grouped by initial BCS (3.0 to 6.5) and assigned to treatments of light (L), heavy (H), or no-exercise control (C). Horses were fed according to the model recommendations to increase (I) or decrease (D) two BCS within 60 d. Thus, six treatments were obtained: HD, HI, LD, LI, CD, CI. Mean DE intake Mcal/d for each group was HD = 19.3 ± 0.90, HI = 29 ± 0.84, LD = 13.2 ± 0.54, LI = 23.1 ± 1.39, CD = 12.1 ± 0.79, and CI = 21.9 ± 0.94. BCSs were evaluated by three independent appraisers, days 0 and 60 values were used to calculate the average BCS change for HD = -0.88 ± 0.24, HI = 1.13 ± 0.24, LD = -1.5 ± 0.29, LI = 0.88 ± 0.38, CD = -1.38 ± 0.13, and CI = 1.35 ± 0.14. Statistical comparison of final observed and model predicted values revealed acceptable precision when predicting BCS and BW respectively in control horses (r2 = 0.91, 0.98) but less precision when predicting body fat (BF) (r2 = 0.51). Model precision for BCS, BW, and BF respectively in lightly (r2 = 0.29, 0.85, 0.57) and heavily (r2 = 0.04, 0.84, 0.13) exercised horses was low. Model accuracy was acceptable across all treatments when predicting BW (Cb = 0.97, 0.96, 0.98). However, accuracy varied when predicting BCS (Cb = 0.82, 0.89, 0.41) and BF (Cb = 0.80, 0.55, 0.87) for the control, light, and heavy exercise groups, respectively. These results indicate that the revised model is acceptable for sedentary horses but the predictability of the model was insensitive to the exercising horse, therefore the exercise energy expenditure formulas incorporated into the model require revision. Packaging this model in a format that facilitates industry application could lead to more efficient feeding practices of sedentary horses, generating health, and economic benefit. Further investigation into energy expenditure of exercising horses could yield a model with broader applications.

Dexamethasone downregulates expression of several genes encoding orphan nuclear receptors that are important to steroidogenesis in stallion testes.

Glucocorticoids impair testosterone synthesis by an unknown mechanism. Stallions treated with the synthetic glucocorticoid dexamethasone had testes collected at 6 or 12 hours postinjection. The testicular expression of selected genes encoding nuclear receptors and steroidogenic enzymes was measured. At 6 hours, dexamethasone treatment decreased levels of NR0B2, NR4A1, NR5A1, and NR5A2 messenger RNAs (mRNAs) and NR5A2 mRNA levels remained depressed at 12 hours. In contrast, dexamethasone increased levels of NFKBIA mRNA at both time points. At 6 hours, dexamethasone did not alter levels of NR0B1, NR2F1, NR2F2, NR3C1, CYP11A1, CYP17A1, CYP19A1, DHCR24, GSTA3, HSD3B2, HSD17B3, LHCGR, or STAR mRNAs. In primary cultures of Leydig cells, 10 -9 and 10 -7 M dexamethasone decreased levels of NR4A1 and NR5A1 mRNAs and increased those of NFKBIA mRNA. Our discovery that dexamethasone downregulates NR4A1, NR5A1, and NR5A2 genes, known to be important for testicular functions, may be part of the mechanism by which glucocorticoids acutely decreases testosterone.

Real-Time Bioluminescence Analysis of Escherichia coli O157:H7 Survival on Livestock Meats Stored Fresh, Cold, or Frozen.

Foodborne bacteria such as Escherichia coli O157:H7 can cause severe hemorrhagic colitis in humans following consumption of contaminated meat products. Contamination with pathogenic bacteria is frequently found in the food production environment, and adequate household storage conditions of purchased foods are vital for illness avoidance. Real-time monitoring was used to evaluate bacterial growth in ground horse, beef, and pork meats maintained under various storage conditions. Various levels of E. coli O157:H7 carrying the luxCDABE operon, which allows the cells to emit bioluminescence, were used to inoculate meat samples that were then stored at room temperature for 0.5 day, at 4°C (cold) for 7 or 9 days, or -20°C (frozen) for 9 days. Real-time bioluminescence imaging (BLI) of bacterial growth was used to assess bacterial survival or load. Ground horse meat BLI signals and E. coli levels were dose and time dependent, increasing during room temperature and -20°C storage, but stayed at low levels during 4°C storage. No bacteria survived in the lower level inoculum groups (101 and 103 CFU/g). With an inoculum of 107 CFU/g, pork meats had higher BLI signals than did their beef counterparts, displaying decreased BLI signals during 7 days storage at 4°C. Both meat types had higher BLI signals in the fat area, which was confirmed with isolated fat tissues in the beef meat. Beef lean and fat tissues contrasted with both pork fat and lean tissues, which had significantly higher BLI signals and bacterial levels. BLI appears to be a useful research tool for real-time monitoring of bacterial growth and survival in various stored livestock meats. The dependence of E. coli O157:H7 growth on meat substrate (fat or lean) and storage conditions may be used as part of an effective antibacterial approach for the production of safe ground horse, beef, and pork meats.