Abstract

  Abstract In order to investigate reasons of culling cows in the commercial dairy herds of Zanjan province in Iran, nine groups of causes have been investigated in this study. These reasons were; dairy purposes selling, fertility and problems in reproductive organs, low milk production, mastitis and udder conformation, leg and feet problems, diseases, displaced abomasums and nutritional problems, death, and other. Culling reasons of 2796 Holstein dairy cows in eight herds have been studied. Data were analyzed by least square means, GLM proc of SAS software considering herd size with two levels (fewer than 100 & more than 100), season with four levels and their interaction all as fixed effects. The most important reasons for culling were selling for dairy purposes, reproduction and low milk production with 228, 120, 66 cows from 587 heads culled, respectively. The next reasons were other cases with frequency of 51 cows which 11 of them were resulted of foreign bodies in the stomach, 12 by dislocation of feet and legs, and the rest were due to age, Freemartin, and organs inflation. Forty five cases of culling were caused by displaced abomasums and gastrointestinal disorders. Total number of sold cows due to dairy purposes and low milk production is called voluntary culling which the rate was 50% in average. The most involuntary culling were due to infertility and reproduction problems which allocated 20.44% of total culling rate and 40.96% of involuntary culling. Small herds had higher percentage of leaving for reproduction and cow left herds for the reasons increased in the autumn (P<0.05).   Key word: Culling reasons; Holstein Dairy cows; Season; Zanjan