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A major objective of pork producers is to reduce production cost. Feeding may account for over 75% of pork production costs. Thus, selecting pigs for feed efficiency (FE) traits is a priority in pig breeding programs. While in the Americas, pigs are typically fed high-input diets, based on corn and soybean meal (CS); in Western Europe, pigs are commonly fed diets based on wheat and barley with high amounts of added protein-rich coproducts (WB), e.g., from milling and seed-oil industries. These two feeding scenarios provided a realistic setting for investigating a specific type of genotype by environment interaction; thus, we investigated the genotype by feed interaction (GxF). In the presence of a GxF, different feed compositions should be considered when selecting for FE. This study aimed to 1) verify the presence of a GxF for FE and growth performance traits in different growth phases (starter, grower, and finisher) of 3-way crossbred growing-finishing pigs fed either a CS (547 boars and 558 gilts) or WB (567 boars and 558 gilts) diet; and 2) to assess and compare the expected responses to direct selection under the 2 diets and the expected correlated responses for one diet to indirect selection under the other diet. We found that GxF did not interfere in the ranking of genotypes under both diets for growth, protein deposition, feed intake, energy intake, or feed conversion rate. Therefore, for these traits, we recommend changing the diet of growing-finishing pigs from high-input feed (i.e., CS) to feed with less valuable ingredients, as WB, to reduce production costs and the environmental impact, regardless of which diet is used in selection. We found that GxF interfered in the ranking of genotypes and caused heterogeneity of genetic variance under both diets for lipid deposition (LD), residual energy intake (REI), and residual feed intake (RFI). Thus, selecting pigs under a diet different from the diet used for growing-finishing performance could compromise the LD in all growth phases, compromise the REI and RFI during the starter phase, and severely compromise the REI during the grower phase. In particular, when pigs are required to consume a WB diet for growing-finishing performance, pigs should be selected for FE under the same diet. Breeding pigs for FE under lower-input diets should be considered, because FE traits will become more important and lower-input diets will become more widespread in the near future.

The LocalPork project aims to improve the efficiency of pork production in Brazil. Pigs in Brazil are usually fed a diet based on corn and soybean. Growing these pigs on a diet that includes local alternative ingredients raises a number of questions related to breeding for such an environment. First, what is the economic and environmental impact of alternative local diets. Second, what are the purebred-crossbred genetic correlations and the extent of genotype by environment interaction. Third, how to accurately predict breeding values based on crossbred performance. Performance of pigs in Brazil that are fed a reference or alternative diets was predicted and alternative diets that include Macaúba or other co-products were found to improve the economic and environmental performance of pork production. Genotype by feed interaction was investigated in crossbred pigs that were fed either a corn and soybean based diet or a diet based on wheat, barley and co-products. Genetic correlations between the diets for growth and residual feed intake were found to be high. The genetic correlation between purebreds and crossbreds for residual feed intake was however found to be only moderate, 0.62. Taking into account the breed origin of haplotypes in crossbreds when predicting breeding values did not substantially increase their accuracies. We speculate that the moderate value of the purebred-crossbred genetic correlation is mainly due to GxE caused by differences in environmental factors, other than diet.