During early lactation, various studies have demonstrated a substantial change in the endocrinological-metabolic profile. The aim of this research was to study the characteristics of the pulsatile liberation of LH (luteinizing hormone) using a new mathematical approach in Simmental cows during the dry period and the early stage of lactation. Blood samples (every 10 min for 12 h) from 5 mature Simmental cows were collected every 7-10 days before calving until 130 days post-partum. The plasma were analyzed for their concentrations of LH. To confirm post-partum negative energy balance, NEFA (non esterified fatty acids) and IGF-I (insulin-like growth factor-I) were determined in the plasma while progesterone was evaluated in the milk whey to characterize when the cyclic ovaric activity restarted. A detailed statistical analysis was performed in order to check the normality of the distribution of LH concentrations, the definition and randomness of the spikes and the existence of periodicity. In conclusion, it is clear that a correct definition of the LH spike can only be achieved by a determination of the distribution of values that permits the statistical definition of outlying values by comparison with the frequency density histogram. To have a good distribution histogram, a large number of LH values need to be recorded over a long period. In any case, the theoritical form of the distribution could not be determined and it appears that it does not belong to a
ny of the classical distributions. Therefore this point will require supplementary studies.
