Trends in calving ages and calving intervals for Iranian Holsteins in Fars province, southern Iran

To determine trends in calving ages and calving interval as measures of reproductive performance in Iranian Holsteins in Fars province, southern Iran during 2000-2005. Data about birth dates and previous calving dates for cows which calved between 21 March 2004 to 20 March 2005 were retrieved from the database of the Agricultural Jihad Organization of the province. Overall, calving records for 1134 cows from 12 herds during 2000-2005 were included in the statistical models. Mean calving interval was 435 days in 2000 and declined significantly to 389 days during the study period (P < 0.001). Age at first calving decreased significantly from 30 months in 2000 to 26 months in 2005 (P < 0.001). The corresponding measures for age at second calving were 44 and 41 months, respectively (P = 0.003). Cows which calved during warm months had significantly (P < 0.001) higher calving interval (420 days) compared with calving in cold months (411 days). No significant effect for parity on calving interval was observed in this study. Reproductive performance revealed relatively positive trend in the Iranian Holsteins in Fars province. This could be attributed to better management and nutrition practices during this period and also to the fact that large genetic trend for milk which has been observed in countries with decreasing reproductive performance has not occurred in these herds yet.