Optimizing Selection on Major Genes

Molecular genetics technology is leading to the discovery of individual genes with large effects for traits of interest in swine. Although the use of such major genes can enhance rates of genetic improvement in the short term, their injudicious use can lead to less response to selection in the longer term. This article describes the development of a method to optimize the use of a major gene in selection. Results show that optimal strategies for selection on the major gene can lead to increased response to selection, in particular for major genes that show dominance. The results imply that major genes can substantially enhance rates of genetic improvement in both the short and long term, provided selection on the major gene is integrated properly within existing selection strategies. Thus, the use of major genes in selection, requires careful formulation of the objectives and strategies for selection. The methods developed in this research provide a framework to formulate such strategies. Further extension of methods to deal with the complexities of practical breeding programs is, however, required

Dealing with Errors in Data from Electronic Swine Feeders

Data from electronic swine feeders contain errors that must be identified, edited, and corrected. The objectives of this study were to develop comprehensive criteria to identify errors in feed intake data from FIRE electronic feeders and to compare the ability of five editing methods to accurately estimate daily feed intake (DFI) and average daily feed intake (ADFI). Data from FIRE feeders on 591 pigs from the National Pork Board’s Maternal Line Genetic Evaluation Program were used. Errors in each visit were identified using 16 criteria. To create an error-free data set as a basis for comparison, data from 124 pigs with few errors were selected and visits with errors were replaced by error-free visits from the same pig. Resulting DFI and ADFI were assumed to be the true trait values. Error visits were then introduced, representative of field data. Data were edited using five methods (EM1-5). For EM1, a DFI record was deleted if DFI \u3c 1000 g or \u3e4500 g. For EM2-5, the 16 criteria were used to identify errors in each visit. For EM2 and 3, all DFI records with \u3e1 and \u3e2 error visits were deleted. For EM4-5, DFI was obtained by summing feed intake over error-free visits. For EM5, DFI records were then adjusted for the effects of presence of error visits on unadjusted DFI, which were estimated from a linear model analysis. For EM1-4, missing DFI records were replaced by linear regression estimates of DFI on test day for each pig. DFI and ADFI from the edited data sets were correlated to true values. Correlations were high (.90 to .99) for both traits for all editing methods except EM1. EM5 had the highest correlation for DFI (.99). EM2 and EM5 had the highest correlations for ADFI (.98 to .99). EM1 had the lowest correlations for both traits (.82 to .93). Results indicate that editing methods affect the accuracy of data from electronic feeders. EM5 is recommended for maximum accuracy for DFI and EM2 is recommended for ADFI for maximum accuracy and ease of implementation

Performance of Growing Pigs Fed Using Electronic Versus Commercial Feeders

The effect of electronic feeders on performance of growing boars and gilts was evaluated. Yorkshire boars and gilts (n=475) were randomly assigned to pens with single-space FIRE (electronic) feeders and pens with fivespace SMIDLEY feeders. Pigs began and ended test at an average body weight of 39 and 116 kg. Over the whole test period, pigs on electronic feeders did not differ significantly in growth rate, backfat thickness, and loin muscle area from pigs on commercial feeders. They did, however, use less feed and converted this more efficiently. Further inspection of growth and feed intake curves revealed that gilts on electronic feeders used less feed and grew slightly slower, in particular during early growth, but no differences were found for boars. Results indicate that electronic feeders may cause a genotype by environment interaction for gilts but not for boars

Analysis of Body Weight and Feed Intake Curves in Selection Lines for Residual Feed Intake in Pigs

A selection experiment for reducing residual feed intake (RFI= feed consumed over and above expected requirements for production and maintenance) in Yorkshire pigs consists of a line selected for lower RFI (LRFI) and a random control line (CTRL). Using 64 LRFI and 87 CTRL boars from generation 5 of the selection experiment, cubic polynomial random regression with heterogeneous residual variance for daily feed intake (DFI) and with homogeneous residual variance for bi-weekly body weight (BW) were identified as the best linear mixed models to describe feed intake and body weight curves. Based on the Gompertz model, significant differences in the decay parameter for DFI and in mature body weight and the inflection point for BW were observed between the lines. In conclusion, selection for lower RFI has resulted in a lower feed intake curve toward maturity, lower mature body weight, and earlier inflection points for growth

Selection for Lean Growth Rate in a Synthetic Line of YorkshireMeishan Pigs 1. Selection Pressure Applied and Direct Response

Selection for lean growth rate (LGR) was conducted for four generations in a synthetic line of YorkshireMeishan pigs. In the select line, seven boars and 20 gilts with the highest LGR were selected from each generation to produce the subsequent generation. A contemporaneous control line was maintained by randomly selecting five boars and 15 gilts to produce the next generation. Inbreeding coefficients averaged .198 and .207 for the select and control line pigs and .173 and .162 for the select and control line dams, respectively, in the fourth generation. LGR was estimated from ultrasound measures of 10 th -rib backfat thickness and longissimus muscle area from 1,057 pigs. These pigs were sired by 58 boars and out of 133 sows. The generation interval was 13 months and the average selection differential per generation was 1.1 phenotypic standard deviation units for LGR. Heritability and response were estimated from the deviation of select line from the control line and multiple trait derivative free restricted maximum likelihood (MTDFREML) on the same material. Realized heritability was .29 ± .12 for LGR in the control line. Corresponding estimates from MTDFREML were .32 and .37. The estimate of direct genetic change per generation using the deviation from the control line was 9.4 g/day for LGR. Corresponding estimates from MTDFREML were similar but were more precisely estimated

Selection Lines for Residual Feed Intake in Yorkshire Swine

A line of Yorkshire pigs was selected for 3 generations for reduced residual feed intake (RFI), a measure of feed efficiency defined as feed consumed over and above average requirements for maintenance and growth. Heritability estimates of RFI, feed intake, growth, and backfat were 0.30, 0.46, 0.33, and 0.67. Comparison of performance of gilts from the selected line (n=49) to those of a randomly selected control line (n=38) from ~40 to ~70 kg showed that selection had significantly decreased feed intake by 123 g/d. There were no significant differences in average daily gain and backfat between the lines, although the selection line tended to have 22 g/d less growth. In conclusion, RFI is a heritable trait and selection for RFI has significantly decreased the amount of feed required for a given rate of growth and backfat

Feeding Behavior of Yorkshire Pigs Selected for Residual Feed Intake

Feeding behavior traits were evaluated in Yorkshire gilts from the fourth generation of the ISU residual feed intake (RFI) selection experiment. Gilts were fed using FIRE feeders. Compared to the randomly selected control line, pigs from the line selected for lower RFI, had lower residual feed intake, ate less per day, spent less time eating per day, and ate faster per visit, regardless of whether analysis was over the whole test period, the first half of test period, or the second half of test period. In conclusion, selection for lower RFI has significantly changed feeding behavior, which could be part of the reason why they are more efficient