TEST DAY MODELS IN THE ANALYSIS OF DAIRY PRODUCTION DATA - A REVIEW

In recent years, attention among dairy cattle geneticists and practica l breeders has been drawn to the use of test (sampling) day records fo r the estimation of breeding values and as an alternative formulation of selection criteria as compared to records covering complete lactati ons. The use of test day records offers the conceptual advantage of di rectly considering records at their origin, i.e. at the day of recordi ng. Under this approach genetic and environmental effects specific to each single record can be considered. Results from the literature on t he nature of environmental effects associated with test day records an d on the estimation of genetic parameters for test day records are sum marized. For the evaluation of animals, two different approaches exist . The first concept consists of corrections for environmental effects via statistical methods at the test day level. In a further step then corrected records are aggregated into complete lactations for later pr ocessing. Under the second approach statistical models are fitted incl uding test day records directly. Records within lactation are taken as repeated measurements. Results on the estimation of genetic parameter s and breeding values under both approaches are discussed.