Identifying some factors affecting open days in Iranian Holstein dairy cows

In order to identify factors affecting days open in Holstein dairy cows were used 9534 reproductive records of a dairy herd in Alborz province from 1993 to 2009. Effects like parity, calving month, calving year, raw milk production class, age at calving, retained placenta, dystocia, abortion were considered as fixed factors in a model. A general linear model (GLM) was applied for analyzing of data. The result showed open days of dairy cows increases significantly after forth parity. For every 100 kg of 305 day standardized milk yield, open days increased by 0.7 day. Also, the lowest and the highest open days were in September and March calving month respectively. The effects of abortion and dystocia on open days were high significant. By contrast, the effect of retained placenta was not significant on open days of dairy cows. To sum up, control of open days is possible by applying some management strategies like concentrating calving month on summer and autumn, preventing abortion and decreasing dystocia by selecting suitable sperms especially for heifers.