Tracing Acid-Base Variables in Exercising Horses: Effects of Pre-Loading Oral Electrolytes

Oral electrolyte supplementation may influence acid-base state during exercise due to the intestinal absorption of administered water and electrolytes used to mitigating sweat losses. This study examined the effect of pre-exercise electrolyte supplementation (3 and 8 L) on plasma acid-base variables at rest, during moderate intensity exercise and during recovery. It was hypothesized that electrolyte supplementation will result in improved acid-base state compared to the alkalosis typical of prolonged exercise. In randomized crossover fashion, four horses were administered 3 L or 8 L of a hypotonic electrolyte solution (PNW) intended to replace sweat losses, or water alone (CON), 1 h before treadmill exercise to fatigue (at 35% of peak VO2) or for 45 min at 50% peak VO2. Blood was sampled at 10-min intervals before, during and after exercise, and analyzed for dependent and independent acid-base variables. Effects of 3 L of supplementation at low exercise intensities were minimal. In the 8 L trials, plasma [H+] decreased (p < 0.05) during exercise and early recovery in CON but not PNW. Plasma TCO2 decreased (p < 0.05) by 30 min after PNW reaching a nadir of 28.0 ± 1.5 mmol/L during the early exercise period (p = 0.018). Plasma pCO2 and strong ion difference [SID] were the primary contributors to changes in [H+] and [TCO2], respectively. Pre-exercise PNW of 8 L intended to fully replenish sweat loses maintained [H+], decreased [TCO2] and mitigated the mild alkalosis during moderate intensity exercise.

Physicochemical Analysis of Mixed Venous and Arterial Blood Acid-Base State in Horses at Core Temperature during and after Moderate-Intensity Exercise

The present study determined the independent contributions of temperature, strong ion difference ([SID]), total weak acid concentration ([Atot]) and PCO2 to changes in arterial and mixed venous [H+] and total carbon dioxide concentration ([TCO2]) during 37 min of moderate intensity exercise (~50% of heart rate max) and the first 60 min of recovery. Six horses were fitted with indwelling carotid and pulmonary artery (PA) catheters, had PA temperature measured, and had blood samples withdrawn for immediate analysis of plasma ion and gas concentrations. The increase in core temperature during exercise (+4.5 °C; p < 0.001) significantly (p < 0.05) increased PO2, PCO2, and [H+], but without a significant effect on [TCO2] (p > 0.01). The physicochemical acid-base approach was used to determine contributions of independent variables (except temperature) to the changes in [H+] and [TCO2]. In both arterial and venous blood, there was no acidosis during exercise and recovery despite significant (p < 0.05) increases in [lactate] and in venous PCO2. In arterial blood plasma, a mild alkalosis with exercise was due to primarily to a decrease in PCO2 (p < 0.05) and an increase in [SID] (p < 0.1). In venous blood plasma, a near absence of change in [H+] was due to the acidifying effects of increased PCO2 (p < 0.01) being offset by the alkalizing effects of increased [SID] (p < 0.05). The effect of temperature on PO2 (p < 0.001) resulted in an increased arterio-venous PO2 difference (p < 0.001) that would facilitate O2 transfer to contracting muscle. The simultaneous changes in the PCO2 and the concentrations of the other independent acid-base variables (contributions from individual strong and weak ions as manifest in [SID] and [Atot]) show complex, multilevel control of acid-base states in horses performing even moderate intensity exercise. Correction of acid-base variables to core body temperature presents a markedly different physiological response to exercise than that provided by variables measured and presented at an instrument temperature of 37 °C.

The effect of 60 km endurance exercise on serum electrolytes and acid–base balance in the Žemaitukai horses

The Lithuanian Žemaitukai horse breed is one of the oldest in Europe. Currently, there is a lack of information about the effect of endurance competition on blood indices and acid–base balance in the Žemaitukai horses. The aim of this study was to evaluate the effect of endurance exercise on the acid–base balance and electrolyte indicators of the Žemaitukai horses in an official endurance competition. In total, 48 horses of the Žemaitukai breed competed in endurance competitions over the same distance (60 km). Samples were taken before and immediately after the exercise. The following indicators were analysed: the hydrogen potential (pH), partial carbon dioxide pressure (pCO2), partial oxygen pressure (pO2), base excess in blood (BE), base excess in the extracellular fluid [BE (ecf)], cHCO3 (bicarbonate), cSO2 (oxygen saturation), tCO2 (blood total carbon dioxide), haematocrit (HCT), haemoglobin concentration (cHgb), sodium (Na), potassium (K), calcium (Ca), chlorides (Cl), and lactate (Lac). Increase in pH showed adaptation of the horse metabolism to exercise. Blood changes were caused by the development of dehydration and metabolic alkalosis. According to Lac results, all horses were fit and tolerated well physical activity. The exercise did not significantly affect the demand for minerals. Based on the results obtained, it can be stated that horses of the Žemaitukai breed are suitable for endurance competing.

Parâmetros fisiológicos e bioquímicos de equinos em treinamento de três tambores: pós-condicionamento, pós-percurso e pós-descanso

RESUMO Foram avaliados parâmetros fisiológicos e bioquímicos em equinos Quarto de Milha durante treinamento de três tambores, antes do condicionamento (T0), após o condicionamento (T1), após um percurso (T2), após descanso do percurso, por 20 minutos (T3) e após descanso do percurso, por 40 minutos (T4). Os parâmetros físicos avaliados foram: frequência cardíaca (FC), frequência respiratória (FR), temperatura retal (TR) e tempo de enchimento capilar (TEC); e os bioquímicos: sódio, potássio, cloreto, cálcio total, ureia, creatinina, osmolaridade, creatinaquinase, aspartato transaminase, proteínas totais (PT), glicose e lactato. A FC, a FR e a TR aumentaram após o percurso (T2), mas foram recompostas após 40 minutos de descanso. A concentração do lactato pouco aumentou após o condicionamento, mas altas concentrações ocorreram após o percurso (T2), e embora ele tenha diminuído após 20 (T3) e 40 minutos (T4) do percurso, ainda permaneceu acima dos limites normais. Nos demais parâmetros, não houve variações significativas. Concluiu-se que, ao final de um percurso de três tambores, o exercício sob máxima intensidade não ocasionou variações bioquímicas significativas nos equinos, exceto para o lactato, pois gerou uma hiperlactatemia que não foi restaurada até 40 minutos de descanso pós-percurso, mesmo com os parâmetros físicos já recompostos do esforço.

The effect of stable bedding materials on dust levels, microbial air contamination and equine respiratory health

The choice of bedding material affects the quality of air in a stable and, consequently, the respiratory health of horses and humans. The risk of respiratory problems can be mitigated by improving the quality of air in the stable. The choice of bedding material is particularly important in cold climate conditions where horses are kept indoors throughout the year. This study examined the impact of three bedding materials: straw (S), peat with shavings (PS), and crushed wood pellets (CWP). The investigated factors were air contamination, including dust contamination and microbial (bacterial and fungal) contamination, and the condition of the equine respiratory tract. The condition of the respiratory tract was evaluated based on the results of arterial blood biochemistry tests and endoscopic evaluations of the upper respiratory tract. Mechanical dust contamination was lowest for PS (1.09mg/m³) and highest for CWP (4.07mg/m³). Bacterial contamination (in CFU - colony forming units) was highest for PS (5.14log₁₀CFU/m³) and lowest for CWP (4.81log₁₀CFU/m³). Fungal air contamination was lowest for CWP (4.54log₁₀CFU/m³) and highest for S (4.82log₁₀CFU/m³) and PS (4.88log₁₀CFU/m³). An analysis of physiological indicators revealed that all horses were clinically healthy regardless of the type of applied bedding. The type of bedding material did not exert a clear influence on arterial blood biochemistry or the results of endoscopic evaluations of the respiratory tract; however, the use of alternative for straw bedding materials improved endoscopy results.