EN
The objectives of the studies were to establish causes of inefficient insemination in a herd of 162 milking cows at the age of 2—11 years of a mixed bred. Clinical examinations of the reproductive tracts were done at an oestrus day but the examination of ovaries was performed 1 day after insemination. The content of plasma progesteron and estradiol was determined. Also immunological tests eventual antisemen activity of blood were performed. It was found that insemination failed mostly due to environmental and organisational factors and that a key role played insemination performed in unproper time, mainly too early before ovulation. One can assume that better results would give insemination done by veterinarians having a special training in insemination, examining clinically cows at oestrus and one day after insemination and using methods of biotechni- cal control of reproduction.