Abstract
Training has a huge effect on physiological homeostasis. The Thoroughbred racehorse is a valid animal model to investigate such changes for training schedule fine-tuning. As happens in human athletes, it is hypothesized that biochemical and immune response changes and related biomolecular variations could be induced by training programs. The aim of this study was to investigate, for the first time, the long-term metabolic and biomolecular modifications in young untrained Thoroughbred racehorses in the first 4-month timeframe training period. Twenty-nine clinically healthy, untrained, two-year-old Thoroughbred racehorses were followed during their incremental 4-month sprint exercise schedule. Blood collection was performed once a month, five times (T-30, T0, T30, T60, and T90). For each sample, lactate concentration, plasma cell volume (PCV), and hematobiochemical parameters (glucose, urea, creatinine, aspartate aminotransferase (AST), γ-glutamyltransferase (GGT), alkaline phosphatase (ALP), total bilirubin (Tbil), lactate dehydrogenase (LDH), creatine kinase (CK), cholesterol, triglycerides, albumin (Alb), total proteins (TPs), phosphorus (P), calcium (Ca2+), magnesium (Mg), sodium (Na+), potassium (K-), and chloride (Cl)) were determined. At T-30 and T90, serum protein electrophoresis (SPE), serum amyloid A (SAA), and real-time qPCR were performed on all samples to evaluate the expression of key genes and cytokines related to inflammatory and Th2 immunity responses: Interleukin-4 (IL-4), Interleukin-6 (IL-6), Interleukin-10 (IL-10), Interleukin-1β (IL-1β), Octamer-Binding Transcription Factor 1 (OCT1), B-cell lymphoma/leukemia 11A (BCL11A). Statistical analysis was performed (ANOVA and t test, p < 0.05). Significant modifications were identified compared with T-30 for PCV, glucose, triglycerides, cholesterol, lactate, urea, creatinine, Tbil, ALP, LDH, Na+, K-, Ca2+, SAA, TPs, SPE, IL-6, IL-4, Oct-1, and BCL11A. In conclusion, the first long-term training period was found to induce fundamental systemic changes in untrained Thoroughbreds.
Highlights
The Thoroughbred racehorse is a supreme athlete due to a high number of physiological and anatomical adaptations to exercise
There are studies focused on the modifications occurring immediately after exercise or competitions in racehorses that have demonstrated an increase of hematobiochemical parameters
Few studies have focused on long-term changes [6,7], and no studies have examined long-term variations during the first training period in a significant number of untrained Thoroughbred racehorses
Summary
The Thoroughbred racehorse is a supreme athlete due to a high number of physiological and anatomical adaptations to exercise. We hypothesized that the first long-term training season could induce in young untrained Thoroughbred racehorses metabolic and immune response changes reflected by modifications in the expression of related key genes, as occurs in human athletes [8,9,10]. These effects have to be deeply investigated to prevent low-performance syndromes such as overtraining, which are frequently reported to exacerbate other pathological conditions in racehorses: muscle damage (recurrent rhabdomyolysis and delayed-onset muscle soreness (DOMS)), electrolyte abnormalities, onset of blood lactate accumulation (OBLA), and exercise-induced pulmonary hemorrhage [2]. Scant data on this subject have been reported regarding racehorses [10,11]
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