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A common strategy to mitigate feed costs is to include less costly ingredients in the diet. Also, genetic selection for feed efficiency has been another approach. Residual feed intake (RFI) is defined as feed intake (FI) and predicted FI difference, given expected growth and maintenance requirements. Therefore, understanding the combined effects less costly ingredients (usually less energetic) and RFI is relevant for the swine industry. Divergent selection for increased (Low RFI) and decreased (High RFI) feed efficiency based on RFI was carried out over 10 generations (G) while feeding a corn- and soybean-meal-based, higher-energy, lower-fiber (HELF) diet.
In G8 to G10, representing 4 replicates, barrows and gilts (n = 649) were fed the HELF diet, or a lower energy and higher-fiber (LEHF) diet that incorporated coproducts. The diets differed in ME, 3.32 vs. 2.87 Mcal/kg, and in neutral detergent fiber (NDF), 9.4% vs. 25.9%, respectively. The assessment included the impact of diets on 1) performance traits, 2) diet digestibility, 3) genetic parameter estimates, and 4) responses to selection for RFI. In general, the LEHF diet decreased performance for both lines. Feeding the HELF diet, the Low RFI pigs had lower ADFI (−12%), energy intake (−12%), ADG (−6%), and backfat depth (−12%); but similar loin muscle area (+5%); and greater feed efficiency (8% higher G:F and 7% lower RFI) than the High RFI line. Similar patterns of selected RFI line were observed under the LEHF diet. However, performance traits ADFI (−11%), energy intake (−10%), G:F (+2%), and RFI (−6%) were worsened compared with the HELF diet. To apparent total tract digestibility (ATTD), 116 barrows and gilts from G8 were used. The ATTD of DM, GE, N, and NDF feeding the HELF diet, were similar between lines. However, feeding the LEHF diet, the Low RFI pigs had greater digestibility (7%, 7%, 10%, and 32%) than the High RFI line. To estimate genetic parameters of selection, data from all 10 generations were used (HELF; n = 2,310; LEHF, n = 317). Heritability estimates ranged from 0.19 to 0.63 regarding performance traits. By G10, the RFI in Low RFI pig line had genetic SD lower compared with the High RFI line; 3.86 when fed the HELF diet and 1.50 when fed LEHF.
In conclusion, the responses to selection for RFI when fed a HELF diet are not fully realized when pigs are fed an extremely LEHF diet. This study suggest that genotype-by-diet interactions should be considered when making the decisions of what feed should be used during FE selection. Feeding diets that differ from those used for selection may not maximize genetic potential for feed efficiency.
Mauch, E. D., Young, J. M., Serão, N. V. L., Hsu, W. L., Patience, J. F., Kerr, B. J., Weber, T. E., Gabler, N. K., Dekkers, J. C. M. 2018. Effect of lower-energy, higher-fiber diets on pigs divergently selected for residual feed intake when fed higher-energy, lower-fiber diets. Journal of Animal Science, 96(4), 1221-1236. https://doi.org/10.1093/jas/sky065
