Good detection of estrus is critically important in dairy husbandry. Incorrect detection
of estrus is related to loss of profit due to extended calving intervals, milk loss,
veterinary costs, etc. Detection of estrus remains a major problem despites enormous
progress in the knowledge of reproductive physiology of the cow and in development
of estrus detection aids. To achieve good estrus detection, many factors have to be
taken into account. On one hand a cow has to express estrus and on the other hand
the farmer has to detect it. Combined action of several hormones causes physiological
changes that lead to ovulation and an environment in the uterus that allows sperm
to fertilize the egg. Besides these internal actions, a number of external changes
can be observed. When using visual observations, time of the day and time spend on
observation have a great impact on detection rates. Many devices are available to
aid in estrus detection, such as pedometers, mount devices, temperature, and hormone
measurements. Expression of estrus can be influenced by many factors. Heritability,
number of days postpartum, lactation number, milk production, and health are known
to influence estrus expression. Environmental factors like nutrition, season, housing,
herd size, etc. also play a role in estrus expression. To evaluate estrus detection,
record keeping is very important; a number of formulas can be used to assess detection
efficiency. Besides the farmer, the veterinarian and inseminator can play an important
role in estrus confirmation and good insemination strategy. In the end, the time of
ovulation and the age of the egg at sperm penetration is critical for conception.
Therefore, emphasis in research needs to be on the timing of insemination relative
to ovulation, and thus on the detection of ovulation.