Reasons and timing of Holstein dairy cows culls during heat stress in Iran

The objective of this study was to consider the reasons and timing of cows leaving herd during heat stressfor 10 years in Iran. Data regarding dates of birth, calving status, reasons for culling, parity at culling, calving to culling interval were collected from March 2004 to April 2014. Out of a total of 6462 culled cows, reproduction failure (22.5% of all culls) was the most prevalent reason of culling followed by lameness (11.5%) and mastitis (9.4%). Average ± SD of parity at culling was 3.27 ± 2.01. Mean ± SD of last calving to culling interval was 217.88 ± 202.80 days and nearly 38.6% of cows were culled in the first 100 days after calving. Cows culled for milk fever left the herd early in lactation (88.56±127.46, Days in milk), but at a higher parity than other cows (4.50±2.18, P