Guidelines to measure individual feed intake of dairy cows for genomic and genetic evaluations

The widespread use of genomic information in dairy cattle breeding programs has presented the opportunity to select for feed intake and feed efficiency. This is because animals from research herds can be used as a reference population to calibrate a genomic prediction equation, which is then used to predict the breeding value for selection candidates based on their own genotype. To implement genomic prediction and perform genetic analysis for feed intake, several partners have brought together their expertise and existing feed intake records. Based on this experience we aim to provide some guidelines on the recording and handling of feed intake records. The consortium used a mixture of standardised experimental data coming from larger genetic experiments or several smaller nutritional studies. The latter has provided some statistical challenges. Also, data was combined across countries, experimental herds and feeding systems. Despite the perceived roughness of such data, it has proven to be very successful for genomic prediction, with proper statistical modelling. Ideally the whole lifetime of all cows should be measured, but this is unrealistic. Often, animals are recorded for part of one (or more) lactation(s) only. Guidelines on the proper statistical modelling and usefulness of existing data are needed. Selection index theory can help to establish the optimal recording period across and within lactation. It is also critical to identify how many records are required and what are the most informative animals for measuring feed intake. Genetic relationships with the selection candidates are an important criterion. Finally, since (residual) feed intake is only part of the breeding goal, it is important to consider recording of other traits as well, and the genetic parameters are needed to define the breeding goals properly.