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The study was aimed at describing the temperature humidity index (THI) dynamics over the Mediterranean basin for the period 1951-2007. The THI combines temperature and humidity into a single value, and may help to predict the effects of environmental warmth in farm animals. In particular, on the basis of THI values, numerous studies have been performed to establish thresholds for heat stress in dairy cows. The THI was calculated by using monthly mean values of temperature and humidity obtained from the National Center for Environmental Prediction/National Center for Atmospheric Research reanalysis project. The analysis demonstrated a high degree of heterogeneity of THI patterns over the Mediterranean basin, a strong north-south gradient, and an overall warming during the study period, which was particularly marked during summer seasons. Results indicated that several areas of the basin present summer THI values which were unfavorable to cow welfare and productivity, and that risk of heat stress for cows is generally greater in the countries of the south coast of the basin. Furthermore, THI data from the summer 2003 revealed that severe positive anomalies may impact areas normally characterized by a favorable climate for animal production. In conclusion, THI dynamics should be taken into careful consideration by farmers and policy makers operating in Mediterranean countries when planning investments in the sector of animal production. The investments should at least partially be directed towards implementation of adaptation measures, which may help to alleviate the impact of hot on farm animals welfare, performance and health.

The study was undertaken during spring and summer months in a territory representative of the Mediterranean climate to assess the effects of season on some immunological parameters of dairy cows. Twenty Holstein cows were used. Eleven of those cows gave birth during spring; the remaining nine cows gave birth in summer. The two groups of cows were homogeneous for parity. Values of air temperatures and relative humidity were recorded both during spring and summer, and were utilized to calculate the temperature humidity index (THI). One week before the expected calving, rectal temperatures and respiratory rates of the cows were recorded (1500 hours), and cell-mediated immunity was assessed by measuring the proliferation of mitogen-stimulated peripheral blood mononuclear cells (PBMC). Within 3 h of calving, one colostrum sample was taken from each cow and analysed to determine content of immunoglobulin (Ig) G1, IgG2, IgM and IgA. At 48 h after birth, passive immunization of the calves was assessed by measuring total serum IgG. During summer, daytime (0900-2000 hours) THI values were above the upper critical value of 72 [75.2, (SD 2.6)] indicating conditions that could represent moderate heat stress. That THI values were able to predict heat stress was confirmed by the values of rectal temperatures and respiratory rates, which were higher (P < 0.05 and P < 0.001 respectively) during summer. Proliferation of PBMC, the colostral concentration of Ig fractions and serum levels of IgG in their respective off-spring did not differ between spring and summer cows. Results indicated that moderate heat stress due to the hot Mediterranean summer does not modify cell-mediated immunity, the protective value of colostrum and passive immunization of the offspring in dairy cows.