摘要 : Holstein cattle performance is negatively affected by heat stress conditions. The objective of the present study was to determine the effect of a spray and fan cooling system on lactating cows performance under hot environment tem... 展开 Holstein cattle performance is negatively affected by heat stress conditions. The objective of the present study was to determine the effect of a spray and fan cooling system on lactating cows performance under hot environment temperatures at Mexicali Valley, Baja California. Sixty one cows (2 to 5 lactations) were randomly assigned to one of two treatments at the start of the lactation period: a control group that had only shades at the central part of the housing pen (S); and a treated group thathad a cooling system under the shade (E). This study lasted 135 d (May to September) with daily maxima temperatures between 39 and 49 degC and relative humidity between 30 and 50%. Cooled cows had higher (p < 0.01) average milk production (30.5+-0.94 kg/d)than control cows (26.6+-0.98 kg/d). Fat and protein in milk were riot different (p > 0.05) between cooled (3.30+-0.061 and 3.19+-0.047%) and control (3.30+-0.062 and 3.28+-0.048%) cows, but somatic cell count average was higher (p < 0.05) in the control group (313 919+-120 503 cells) compared with the cooled group (293 019+-118 542 cells). Breathing rate was greater (p < 0.01) for S cows (87.8+-1.8 breathings/min) than E cows (68.7+-1.7 breathings/min). Pregnancy rate was higher (p < .05) in the S group (92%),than in the E group (50%). At the end of the experiment, body condition score was not different (p > 0.05) between treatments. These results indicate that a cooling system based on spray and fans is an effective alternative to increase productive and reproductive efficiency in lactating Holstein cows under hot environmental conditions. 收起