Genotype by environment interaction for feed efficiency in growing-finishing pigs in Brazil versus the Netherlands

In pig breeding programs, purebred (PB) boars are selected in a nucleus, and mated with crossbred (CB) dams to produce CB growing-finishing pigs used for pork production in commercial farms. The majority of the cost of pork production comes from feeding CB pigs. Therefore, increasing attention is given to selection for feed efficiency and to include in the genetic evaluations the performance records of CB pigs in commercial production circumstances. In addition, sustainability should be at the top of the agenda for all livestock production systems, and thus, improving the feed efficiency of CB pigs farmed around the globe is necessary. Differences between the genetic background of PB and CB, as well as differences between the nucleus and the commercial farms environments will lower the genetic correlation of feed efficiency for PB performance in the nucleus level and CB performance in the commercial level (rpc). My main aim in this thesis was to investigate the possible causes of an rpc in growing-finishing pigs between the feed efficiency in CB pigs kept under Brazilian commercial production circumstances and PB pigs kept under Dutch circumstances being below 1. Another aim was to compare the properties of different traits to represent feed efficiency and the implications of their adoption by pig breeding programs. The results of this thesis show that the collection of feed intake data on CB at commercial farms is worthwhile to increase genetic progress in CB feed efficiency and that residual energy intake is an attractive trait for pig breeding programs. Depending on the definition of feed efficiency, this trait is variably sensitive to changes in the ingredients of the two most common pig commercial rations (corn/soy or wheat/barley/co-products). Breeding for feed efficiency under lower-input diets, such as wheat/barley/co-products, should be considered as feed efficiency will become more important, and lower-input diets will become more widespread in the near future. Feed efficiency can be improved by changing the trajectory of feed intake as a function of body weight, i.e., the feed intake curves. A flatter feed intake curve, and high feed intake precocity (higher feed intake in early stages of growth associated with a higher growth maturation rate and a consequent lower feed intake later on the finishing period) is a desired profile in pig breeding. Collection of production data in a tropical climate is worthwhile, and feed efficiency is expected to be sensitive to climate