A study of horse’s blood constituents and weight variations during endurance competitions Joana Nery 1 , Anna Assenza 2 , Walter Pinna 3 , Antonio Sfuncia 3 and Domenico Bergero 1 Dipartimento di Produzioni Animali, Epidemiologia ed Ecologia, Università di Torino 1 , Dipartimento MOBIFIPA, Università di Messina 2 and Dipartimen- to di Biologia Animale, Università di Sassari 3 (Italy) Introduction Endurance horses have been the target of several exercise physiology studies over the past few years due to the particu- larly prolonged exercise and physical demand to the animal. Previous studies (Farris et al. 1998, Assenza et al. 2004, Ber- gero et al. 2005) have focused deeply the variation of blood serum concentration on branched chain amino acids (BCAA), and its’ use as energy source, tryptophan, non-esterified fatty acids (NEFA) and serotonin during exercise and its’ associa- tion with the concept of overall fatigue (Newsholme et al. 1987). Miller-Graber et al. (1991) studies suggested a mus- cle’s amino acid catabolism during exercise due to the obser- ved increase in alanine blood concentration. Haematologi- cally, an increase on haematocrit (packed cell volume, PCV) levels during exercise was reported (Farris et al. 1998) and explained by the mobilization of red blood cells to the blood stream during strenuous exercise (Persson et al. 1973, Pagan 2000). According to Bergero (2004), electrolytes, particular- ly potassium and chloride, are lost with sweat during exercise while Harris (2000) refers the water loss from sweating as a cause of decrease in the circulatory volume. According to Pagan (2000), in a performance horse nutrition perspective, it is fundamental to consider carefully both energy and elec- trolytes. The aim of this study was to set the framework of endurance exercise physiology features during competitions regarding blood concentration variations of several components, weight variation related to water and electrolyte losses and control of the feeding plan in order to understand the extent of its’ influence on horses’ performance. Material and methods Six endurance competition horses were monitored during 4 competitions. Blood sampling was undertaken before com- petition, after each 30 km (until 90), and after competition (1, 6, 12 and 48 hours). Blood analysis considered the blood levels of amino acids (arginine, aspartic acid, methionine, alanine, glycine, isoleucine, lysine, leucine, valine, tyrosine, phenylalanine and tryptophan), serotonin, NEFA, urea, creatinine, total protein, electrolytes (calcium, chloride, potassium, magnesium and sodium) and haema- tological constituents (blood cells, PCV, haemoglobin and platelets). Weighting was accomplished, in the last two competitions, immediately before and after each 30 km and one hour after competition. Both blood sampling values and weights were statistically analysed throughout the competition and recove- ry period. The feeding plan, ingredients and quantities, was monitored between the third and fourth competitions. Results The blood analysis results have highlighted a steady decrea- se of BCAA and a decrease with no statistical evidence of tryptophan blood serum concentration throughout all compe- titions. Regarding recovery period both BCAA and tryptophan have shown a tendency to return to the resting values (except leucine). All the other amino acids monitored, except aspar- tic acid and methionine, have revealed a steady decrease during competition; recovery was characterized by different patterns among amino acids. NEFA blood concentration decreased during competition and a recovery to resting values during the post-competition period was observed. Urea blood concentration has slightly increased during late competition while maintenance of this concentration during recovery was observed. Both creatinine and total protein have shown a slight decrease in the second 30 kilometres compe- tition; during recovery a statistical decrease for total protein was observed. Serotonine blood concentration has shown, despite the statistical evidence, a peak at 60 km competition and a slight increase during recovery. All electrolyte blood concentrations have shown a significant decrease during competition except sodium and magnesium (the last with no statistical evidence). During recovery all electrolytes’ concen- tration, besides magnesium, differed significantly from the resting value at six hours recovery (higher for sodium and lower for chloride, calcium and potassium). Blood cell analy- sis did not show many significant variations throughout com- petition and recovery (monitored for the first hour) except regarding leukocytes and erythrocytes. Erythrocytes, PCV and haemoglobin have shown to increase slightly during compe- tition (with no statistical evidence). Leukocytes variation was associated to the statistical difference found in the percenta- ge of granulocytes that has increased significantly between 30 and 60 km competition reaching a statistically different percentage from the resting value. Weight variation and electrolyte loss were also monitored: at a 60-kilometer competition there is a statistically significant impact on horse’s weight (from 417.44±27.19 kg to 379.00±15.56 kg) and that recovery’s first hour is the peri- od in which weight values return to resting values. Dehydra- tion extent values ranged between 4.88% and 11.84% and sodium, potassium and chloride observed average losses were 52.00±16.55g, 37.79±12.03g and 128.80±41.00g respectively. From the feeding plan analysis it was possible to observe a slightly lower supply of energy, an evident higher supply of protein, a modest higher supply of electrolytes and a marked lower supply of sodium compared to the horses’ require- ments, estimated according to the French system. Equine Nutrition Conference Hannover 2005 Pferdeheilkunde 21 103