Selection and segregation of herds for a valuable milk trait

Abstract: Dairy processors are seeking to exploit the natural variation in milk components at the farm level to produce high margin niche products. On-farm segregation of milk within or between herds and enhancement of desired traits are mechanisms to increase supply. A simulation modelling approach was used to investigate the genetic effects of breeding and segregating cows for an illustrative milk attribute, milk fat colour. This trait is valuable to New Zealand seasonal supply dairy farmers. Changes in production and the proportion of cows producing “white” (lighter milk fat colour) milk were predicted for a 20 year period for several selection strategies. Genetic gains relative to the status quo were predicted using sires from a small breeding scheme selecting for milk fat colour and yield. It took 18 years or more of continuous breeding for the whole herd to produce “white” milk, although not necessarily over the whole of the lactation under a pasture-based farming system. Selection on colour reduced yield of other valuable traits relative to the status quo herd. Initial selection of cows, reproduction and management strategies can all speed up progress but add cost. Premiums for segregated milks need to compensate owners for transition costs, production losses (if any) relative to the status quo, and the risk associated with long term change. [Copyright &y& Elsevier]