One of very important prerequisites for achieving good results in races, in addition to genetic predisposition, quality training and good health, are optimal values for number of erythrocytes, concentration of haemoglobin and hematocrit, of which depends efficient oxygen supply of muscles during great efforts. The stated values, along with data on heart rate, are useful indicators of the degree of horse fitness and readiness for horse race. The influence of physical exertion on the values of basic hematological parameters as well as on heart rate, was investigated on 6 trotters, in training at the Belgrade racetrack (one head of Italian trotter, male, 3 years old; 3 heads of American trotter, male, 3,4 and 6 years old and two heads of Serbian trotter, female, 4 and 5 years old). The blood samples for hematological tests were taken by punction of jugular vein in resting phase - immediately before the commencement of work, after light trot warming for 3000 m and fast trot for 1000 m, with 30 minutes rest between the two runnings. The heart rate was monitored continuously by radio telemetry cardiometer, from the moment they were taken from their boxes and harnessing to the completion of work. The obtained results confirm the relationship between the rise of heart rate and hematocrit values: maximal hematocrit values were determined after the first running (0.49?0.05, in regard to 0.42?0.03 in resting phase), but 30 minutes after the second running there was a slight drop of hematocrit values (0.46?0.04). The blood samples in both cases were taken after fast trot during which there were recorded maximal pulse values, so in the moment of sampling the pulse lowered close to the values in resting - after the first running from 192.23?19.66, and after the second from 180.33?17.22 to 40.67?5.76.

Meat is a product formed from skeletal muscles of animals through different biochemical processes following rigor mortis. Therefore, characteristics of muscle tissue, its structure, number, diameter and percentage of different muscle fiber types would greatly determine the quantity and the quality of meat. Having in mind that selection and nutrition led to nearly a maximum in meat production, and consumers are having higher and higher demands for „organic“ products, products from more natural production, their concern for animal welfare is rising, the implementation of physical activity in animal rearing could be of more importance in the future. Physical activity could imply outdoor systems, or semi-confinement systems with enriched environment. Also, the impact of this factor could be of higher importance in pigs and chicken, where intensive selection towards lean meat content increased the number of glycolytic fibers in muscles, leading to more pronounced problems with meat quality (PSE meat).

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