Document Type : Research Paper


1 M. Sc. Graduate, Department of Animal Science, Faculty of Agriculture, Isfahan University of Technology, Isfahan 84156–83111, Iran

2 Associate Professor, Department of Animal Science, Faculty of Agriculture, Isfahan University of Technology, Isfahan 84156–83111, Iran

3 Professor, Department of Animal Science, Faculty of Agriculture, Isfahan University of Technology, Isfahan 84156–83111, Iran

4 Ph.D. Student of Animal Science, College of Agriculture Lorestan University, Khorramabad, Iran


The aim of this study was to consider reproductive performance parameters and blood progesterone concentration changes in high-producing dairy cows (39±2 kg per day) after artificial insemination, in summer and winter. 270 heads of Holstein dairy cattle were choose in three big dairy farms, and blood samples were collected at days seven, ten and fourteen after artificial insemination. Temperature-humidity index was calculated according to one proposed formula (Dikmen and Hansen, 2009). The results showed that the maximum temperature–humidity index(THI) was 77.35 and 57.47 in summer and winter respectively. Pregnancy rates in cows inseminated during the winter months was significantly higher (p<0.01) than cows inseminated during the summer, and the effects of lactation on conception rate was significant in both seasons (p<0.01). Open days (101.18 vs. 165.07) and number of services per conception (2.05 vs. 3/48) in the winter were significantly lower than cows inseminated during the summer (p<0.01). In day 14 after insemination, blood serum progesterone concentration in cows inseminated in the winter was significantly higher (p<0.01) than summer. Results of this study showed that summer heat stress has significantly affects reproductive performance of dairy cows in central of Iran.


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