The frequency of measuring a phenotype depends on many factors. A milking robot is recording the milk yield of individual cows at each milking. The conformation of animals established by an inspector requires an expensive visit to a farm or and is done only a few times per year. The incidence of a disease is only recorded when a veterinarian is called in by a farmer. Performance of a horse is established at a test-show. Conformation of a dog is recorded at special shows. In general you increase the number of recordings per animal when a trend in a trait may exist. E.g. milk production curves of cows, sheep and goats may differ over the lactation period: top production (kg and days in lactation) and persistency (shape of the curve: flat or sharp decline after the top). To get a reliable estimate of lactation yield (the breeding goal trait) it was figured out that milk recording at least once every six weeks is necessary. At many milk producing farms the first argument for milk recording is to support a proper feeding management of the animals and the second argument is to detect the best animals for milk production.