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.