**Abstract**

Parallel with the successful genetic selection for higher milk production in Holstein-Friesian cows, a dramatic decline in fertility rates has been observed around the world. Therefore, to achieve an optimum herd reproductive performance, we must focus on the first 100 days postpartum. During and after calving, a cow overcomes a series of physiological hurdles before becoming pregnant. By selecting accurate diagnostic devices and/or methods, such as predicting the onset of calving, monitoring activity and rumination time to determine cows for early treatment of clinical metritis and/or metabolic diseases, long-term measurement of reticuloruminal pH to monitor subclinical acidosis, perform metabolic profile tests to diagnose subclinical metabolic diseases at the herd level, estrous detectors and/or detection aids, on-farm/in-line P4 test to monitor specific events in the postpartum periods, diagnosis of early pregnancy and pregnancy loss using ultrasonography to correctly identify problems and their potential causes to enable these issues are to be rectified. Despite higher milk production, acceptable fertility results can be achieved, even on large-scale dairy farms, if the impacts of the above factors that contribute to reduced fertility can be moderated. The advantages and disadvantages of the different diagnostic methods are discussed to help the dairy select the most accurate method.

**Keywords:** calving, uterine diseases, metabolic disorders, estrous, artificial insemination, pregnancy diagnosis, diagnosis of pregnancy loss
