We have studied, together with Geno, a Norwegian cooperative organization owned by 11 000 Norwegian dairy farmers, and the Norwegian School of Veterinary Science, the frequency of various estrus signs between cows. Cows are inseminated when we believe they are ready to be impregnated. It is not always easy to see when a cow ovulates, but cows give and receive a series of signs frequently when they are in oestrus. Examples can be to rub their head against other cows or to put their head on another cow´s backside. Such signs will typically become more frequent when the cow is ready to be inseminated.

We analysed a series of estrus signs for Holstein dairy cows that were monitored round the clock for 22 days. A cow´s cycle can be divided into several phases. We studied the frequency of the signs, the average number of signs per hour, for different phases and signs. We have also studied how the cows give and receive signs in group during their cycle.

There are several measures per cow, and we therefore have correlations both within and between cows. To be able to express the uncertainty in the average number of signs per hour we carried out a simulation procedure.

Such analyses aid the farmer to look for relevant signs and the frequency of these in order to find the time of impregnation