The effect of selection for residual feed intake during the grow/finish phase of production on feeding behavior traits and sow reproduction and lactation efficiency in Yorkshire pigs
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Residual feed intake (RFI) is a measure of feed efficiency defined as the difference between observed and predicted feed intake based on average requirements for maintenance and production. At Iowa State University, two lines of Yorkshire pigs were developed to study the effects of selection for RFI during the grow/finish phase of production (RFIG/F). One line was selected over 7 generations for decreased RFIG/F (LRFI) to improve feed efficiency and the other line (HRFI) was selected randomly for 4 generations and then for increased RFIG/F. The main objectives of this dissertation were to evaluate feeding behavior traits and sow reproductive performance and lactation efficiency. Pigs from the LRFI line had significantly lower feed intake (FI) per day than did HRFI pigs. After adjusting for FI per day, number of visits (NV) per day and per hour did not differ significantly between the two lines but the trend was for LRFI pigs to have fewer visits, particularly during peak eating times. Furthermore, pigs from the LRFI line ate faster and spent less time in the feeder per day, per visit, and per hour than HRFI pigs. Feeding behavior traits were moderately to highly heritable, with heritabilities ranging from 0.36 for FI per visit to 0.71 for occupation time (OT) per day. Feed intake rate was also highly heritable at 0.59. Heritabilities of NV per day, OT per visit, and FI per day were similar (0.44, 0.42, and 0.42, respectively). FI per day was strongly correlated, both phenotypically and genetically, with RFIG/F, average daily gain (ADG), and backfat depth (BF). FI per visit was moderately correlated, both phenotypically and genetically, with ADG and BF. OT per day was moderately correlated, both phenotypically and genetically, with RFIG/F and BF. Other correlations between feeding behavior traits and performance traits were low. For each feeding behavior trait, one or two genomic regions were identified as being important in a whole genome association study. SNPs located adjacent to MC4R (a gene already shown to be associated with FI, fatness, and growth) were significant for FI per day. Other genes with nearby SNPs found to be associated with feeding behavior traits included several related to different transcription regulators. After 7 generations, selection for decreased RFIG/F has improved piglet performance and increased sow weight loss during lactation. LRFI sows had more piglets farrowed, born alive, and weaned than did HRFI sows. LRFI piglets were heavier at birth and had better litter growth than did HRFI piglets. However, this increased piglet performance came at a cost to the sow During lactation, LRFI sows consumed less feed and lost more body weight, fat mass, and BF than did HRFI sows. LRFI sows had a greater negative energy balance but more favorable lactation efficiency and RFI during lactation than HRFI sows. Heritabilities were high (h2 > 0.4) for sow weights, body composition, and maintenance requirements and piglet birth weights. Piglet growth during lactation, mobilization of the sow's body tissue, sow feed intake and total born were moderately heritable (0.2 < h2 < 0.4). Correlations with RFIG/F were not significant for most traits. However, strong, positive genetic correlations with RFIG/F were found for sow weight at farrowing and weaning, sow maintenance requirements, and sow RFI and strong, negative genetic correlations with RFIG/F were found for sow protein mass loss and lactation efficiency. In conclusion, feed efficiency may be affected by feed intake behavior because selection for decreased RFIG/F has resulted in pigs which spend less time eating and eat faster. A large genetic component to feeding behavior is evident and measuring and selecting for these traits may allow for other opportunities to improve traits of economic importance. Selection for RFIG/F has positively affected piglet performance and lactation efficiency but has negatively affected sow body condition change and energy balance during lactation.