In this paper we analysed the change of the chemical composition and nutritive value of Timothy observed during the spring of 2005. The nutritive value of Timothy was observed between the end of April and the beginning of June relating to the following parameters: crude protein, crude fibre, crude fat, ash, N-free extract, net-energy growth, net-energy lactation, net-energy maintenance, Metabolizable Protein Energy dependent, Metabolizable Protein N-dependent. We also analysed whether a relationship between the environmental factors that affect the
growing period of grasses and the chemical composition can be detected or not. While testing for correlation, the number of days from 1st January, the amount of heat accumulation, solar radiation and rainfall were considered as independent coefficients.
For the estimation of weather conditions we calculated the climate index. The observed year can be described as a year with a rainfall above the average and abundant solar radiation. A correlation can be detected between the change of parameters of nutritive value and the quality of the current year. In 2005 the result of the analysis of nutritive value was showed a significance difference with respect to each chemical composition at the rate of P<0.001 depending on the time when the samples were taken.
According to the outlined data it can be stated that the change of the value of crude protein and ash show decreasing tendency agreeing the research literature. In parallel with the change of nutritive value, the amount of crude fibre and N-free extract increased. However, the value of Net-Energy maintenance showed an alteration only in the first half of the observed period. The same alteration tendency can be detected in the Net-Energy growth and the Net-Energy lactation.