Two experiments were conducted to compare the effect of inorganic and organic trace mineral supplementation on performance and carcass characteristics of phase-fed, growfinish swine. Crossbred pigs (EXP. 1, Iowa State University Lauren Christian Farm, Atlantic, IA (n=528); EXP. 2, Wilson's Prairie View Farms, Burlington, WI (n=560)) were blocked by weight, penned by sex, and randomly assigned to treatment pens at approximately 18 kg BW. Pigs were housed in two identical, totally-slatted, confinement barns and provided ad libitum access to feed and water. Dietary treatments were allocated in a general randomized complete block design with 12 replicate pens per treatment (TRT) and 9-12 pigs per pen throughout the grow-finish period. In EXP. 1, the control diet (TRT 1) contained 1 This journal paper of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project No. 3 614, was supported by State of Iowa funds. Additional funding and support was provided by Alltech Inc., Nicholasville, Kentucky 40356. The authors would like to acknowledge Kent Feeds Inc., Muscatine, Iowa; Nevada Feed and Seed Company, Nevada, Iowa; and Allflex Inc., Dallas-Ft. Worth Airport, Texas, for their contributions to this project. *Department of Animal Science, Iowa State University, Ames 50011 '"Department of Statistics, Iowa State University, Ames 50011 fiAlltech Inc., Nicholasville, Kentucky 40356 2Correspondence: 109 Kildee Hall, Iowa State University, Ames, IA 50011 (phone: 515-2944683; fax: S 15-294-5698; e-mail: stade:~~~~.iast~~:e.ed~~)

Transport of weaned pigs poses special challenges because of their size and thermal needs as well as the extended distances and transport times. The resultant economic impact can be substantial. Compared to transport of market pigs, weaned pigs generally encounter much farther travel distances with different adapting abilities to the environmental conditions. The objectives of this study were: 1) to characterize the environmental conditions within a typical transport trailer for weaned piglets to determine if current management practices and trailer design provides an acceptable environment as evidenced by mortality rates and environmental parameters, and 2) to analyze airflow patterns of the tranport trailer using a scale model in a wind tunnel. Data from 78 usable transport trips were collected for air temperature in each trailer compartment, ambient temperature, distance traveled, time traveled, stocking density, and mortality by compartment. The 78 trips had an average distance of 778 km (range of 264 to 1016 km), travel time of 8.51 h (range of 3.4 to 12.3 h), and mortality rate of 0.031% (range of 0 to 1.11%). There was no significant difference in mortality by compartment (p>0.05). The results indicate that if pigs are transported at a higher stocking density, the compartment temperatures would be similar during cold weather (e.g., 2 degrees C). Under mild weather condition (e.g., 16 degrees C), significant differences could exist in compartment temperature between part of the upper deck (Upper 1) and the lower deck (Lower 4) (p<0.05). In comparison, no significant differences were found at warm conditions (e.g., 29 degrees C) (p>0.05). In addition to the weather influence, in-trailer environment is affected by the side openings which may be adjusted by the driver. A 1/7th scale model of a livestock trailer was placed in a wind tunnel to examine flow characteristics within the trailer including velocity by location and direction. Trials were run with and without the front vents covered and with and without compartment partitions in place. The sides remained open for all trials. Centerline velocities in the compartments varied from 11% to 22% of the wind tunnel speed with trailer averages ranging from 14% to 16%. Pen partitions within the trailer had an impact on centerline velocity averaging 14.3% to 15.4% of wind tunnel speed (p<0.05); whereas covering the front vents or not had no effect on the centerline velocities. When the front air vents on the trailer were uncovered, air flow was from the back of the trailer toward the front. When the front air vents were covered, air flow direction was mixed with most of the upper compartments having front to back flow and most of the lower compartments having back to front flow. The lower rear compartment (Lower 4) tended to have the lowest air velocity rates with Upper 3 and Upper 4 being only slightly higher. Lower 3, Lower 2, and Upper 1 compartments tended to have the highest air velocities. Conclusions support the further investigation of changes to compartment partition and trailer rear panel design, as well as investigation of additional trailer options that may enhance or deter air flow through the trailer.

Background: The objectives of this study were to create an objective measurement method of joint angles for knee, hock, front and rear pasterns and a rear stance position in swine using digital imaging technology and to assess the repeatability of the objective measurement process. Methods and Findings: Forty-five multiparous sows (average parity 6.7 ± 2.5; parity range 5 to 14) from two commercial farms (n=21 farm 1 and n=24 farm 2) were used. Sows were moved to a pen where digital images of the profile and rear stance were captured. On average, 5.2 (± 2.6) profile and 2.6 (± 1.0) rear stance high quality images were used per sow. A joint angle measuring system was devised to collect angle measurements on the four feet and leg joints previously mentioned and the rear stance. Joint measurements were analyzed using repeated measure mixed model methods, including farm and parity (as 5, 6, and 7+) as fixed effects. Intraclass correlation coefficients were calculated to evaluate process repeatability. Joint angle measurement repeatability ranged from 0.63 to 0.82. Lowest and highest repeatabilities were observed for the front pastern and hock angle measurements, respectively. No significant farm or parity differences were observed for joint angles measured except for the knee angle between farms (P<0.05) and the hock angle between sows’ parities 5 and 6 and parity 7+ (P<0.05). Conclusions: Feet and leg conformation evaluation using digital images could be successfully used as an objective tool to aide in selection of replacement gilts. This could have a beneficial impact on sow longevity and farm productivity and profitability.

Ground transport of pigs at early ages may result in profit-stripping incidences of mortality and compromised animal welfare due to stress stemming from unfavorable transport conditions. The objective of this study was to examine possible causative relationships of mortality rate of weaned and feeder pigs to ground transport conditions. A total of 7056 transportation records of weaned pigs (3174 records) and feeder pigs (3882 records) for the period from April 2012 to January 2014 were provided by a U.S. swine company. Effects of pig type (weaned vs. feeder pigs), ambient temperature (<15 degrees C or cool/cold, 15 degrees C to 25 degrees C or mild, and >25 degrees C or warm/hot), travel distance (< 600 km, 600 to 900 km, 900 to 1200 km, 1200 to 1500 km, and >1500 km), and the interactive effects on dead-on-arrival (DOA) rate (DOA per head loaded, %) were evaluated. The effects of the same variables on post-transport mortality of weaned pigs were also evaluated. Results show that DOA rate was affected by pig type, ambient temperature, and travel distance interactively. Weaned pig DOA rates (mean +/- SE of 0.0333% +/- 0.0150%) tended to be higher than feeder pig DOA rates (0.0243% +/- 0.0110%) (p = 0.0004), and weaned pigs were more vulnerable to transport stress in warm/hot conditions. For weaned pigs, DOA rates were higher with >900 km travel distance (0.0543% +/- 0.0389%) than with <900 km travel distance (0.0118% +/- 0.0078%) in cool/cold conditions, and DOA rates significantly increased as travel distance increased in warm/hot conditions. For feeder pigs, DOA rates were not affected by travel distance in cool/cold or mild conditions; however, higher mortality rates were found with >1200 km travel distance (0.2717% +/- 0.1326%) than with <1200 km travel distance (0.0315% +/- 0.0151%) in warm/hot conditions. Statistical analysis showed that post-transport mortality rate of weaned pigs was affected by ambient temperature during transport and travel distance interactively for the first one or two weeks after transport. However, it should be noted that the relationship between post-transport mortality and transport conditions could have been confounded by other factors, such as management at the finishing farm. Outcomes of this study are expected to offer insight into improving the ground transport of pigs.

Adipocyte sizes from adult adipose tissue are distributed bimodally. Thus, the standard metric reported, mean cell size, could be misleading. The objectives of this study were to develop a novel method for testing bimodality of adipocytes in porcine adipose tissue, describe the size distribution with a more informative metric, and statistically test hypertrophy and hyperplasia. Testing distribution bimodality was done by describing two bins with bin 1 (adipocytes 25.0 - 40.1 µm in diameter) containing the suspected minor mode and bin 2 (adipocytes 50.2 - 65.4 µm in diameter) containing a region assumed to separate major and minor modes. For the kth cell, we defined the event [Xk = 1] with probability p = Pr[Xk = 1] if that cell's diameter falls in bin 1, and the event [Xk = 0] with probability 1 - p = Pr[Xk = 0] if it falls in bin 2. The following natural estimator of (p) was used: Bins 1 and 2 were chosen to have approximately the same width and bin 2 was scaled to match the width of bin 1 so the hypothesis test for distribution bimodality was: H0: p = 0.5 versus H1: p > 0.5. Because the sample size, N, associated with the number of cells falling in either bin was on average 6,600 adipocytes counted for a given test, the Central Limit Theorem applies and results in the following standard normal test statistic: Increased adiposity is correlated positively with an adipocyte being found in the minor mode (r = .46) and correlated negatively with an adipocyte being found in the major mode (adipocytes larger than 65.4 µm (r = -.22)), providing evidence of hyperplasia. Additionally, as adiposity increases, the mode of the major distribution of cells occurs at a larger diameter of adipocyte, indicating hypertrophy.

Intramuscular fat (IMF) content is an important trait affecting the quality of pork. Two Duroc populations, one under positive selection for IMF and the other selected for decreased backfat but under stabilizing selection for IMF, were used to identify signatures of selection associated with IMF using 60,000 single-nucleotide polymorphism data. The effects of selection were analyzed between 2 lines or groups representing selected and control animals within each population using a discriminant analysis of principal components and Wright’s fixation index (FST). Moreover, extended haplotype homozygosity-based approaches were used to examine the changes in haplotype frequency due to recent selection. Each statistical method identified 10–20 selection signatures. A few haplotype-based signatures of selection agreed with results from a genome-wide association study (GWAS), while FST measures showed a better agreement with GWAS results. Agreement of marker-trait associations and signatures of selection was limited, and further examination will be necessary to understand the effect of selection on IMF and why some regions identified by GWAS did not appear to respond to the selection practiced. The genes in 21 consensus selection signatures were examined. Several genes with an effect on overall fatness were identified, but further research is needed to assess whether or not some of them could have a specific effect on IMF.

Daily feed intake during lactation was recorded in parity records from purebred Yorkshire (n = 1587), Landrace (n = 2197) and reciprocal cross F1 (n = 6932) females, and lactation feed intake (LFI) curves were predicted using a mixed model. Evaluation of the difference in feed intake between two consecutive days of lactation resulted in the following classifications: three periods for purebreds, days 1-6, days 7-10 and days 11-18, and two periods for F1 sows, days 1-5 and days 6-18. Average rate of change in intake (ARC), average daily intake (ADI) and variation from predicted LFI values (VAR) were computed for each period of lactation. Gibbs sampling was used to estimate genetic (co)variance components for LFI metrics and reproductive performance traits. Genetic variance estimates for each LFI metric were obtained with univariate animal models, and covariance estimates were estimated with bivariate models. Heritability estimates for ADI, ARC and VAR metrics computed over the duration of lactation were 0.37, 0.24, and 0.16, respectively. Heritability estimates were highly variable across periods of lactation for ARC (0.03-0.17), ADI (0.09-0.36) and VAR (0.04-0.18) metrics in purebred and F1 populations. Genetic correlations between LFI metrics and reproductive traits were relatively low, although LFI metrics later in lactation were more highly correlated with reproductive performance.

Days to reach 113.4 kg, adjusted backfat depth and adjusted loin muscle area to 113.4 kg were evaluated on pure-bred Landrace (n = 15 660) and Yorkshire (n = 14 808) boars and gilts. Daily lactation feed intake (LFI) was recorded within parity records from pure-bred Yorkshire (n = 1587) and Landrace (n = 2197) females during day 1-22 of lactation, and LFI curves were predicted using a mixed model. Evaluation of feed intake differences between 2 consecutive days of lactation resulted in the following periods: day 1-6 (PB1), day 7-10 (PB2) and day 11-18 (PB3). Average rate of change in intake (ARC), average daily intake (ADI) and variation from predicted daily LFI values (VAR) metrics were computed for each period of lactation. Gibbs sampling was used to estimate the genetic covariance between LFI metrics and grow-finish traits. Genetic correlations were strongest between grow-finish traits, and LFI metrics in first parity sows and were generally favourable, but correlations with LFI metrics during parity 2 or greater were low and not different from 0 (p > 0.05). Genetic correlations between LFI metrics in parity 1 sows with growth and composition traits varied greatly in strength and direction. Selection for leaner, heavier muscled gilts had a limited effect on LFI metrics. However, selection for increased growth rate was associated with higher ARC and ADI and smaller VAR values.

The objectives of this study were to quantify significant negative deviations (DEV) from predicted daily lactation feed intake values and to estimate their effect on reproductive performance and subsequent intake in purebred and F1 sows. Daily lactation feed intake (LFI) records from day 1 to 22 of lactation from purebred Yorkshire (n=1587 parity records), purebred Landrace (n=2197 parity records), and reciprocal cross F1 (n=6932 parity records) females were used to predict daily LFI values. The mixed model included fixed effects of breed, season, parity group (1, 2, 3 and ≥4), day of lactation, and interactions of day with breed and parity group, and a covariate of litter size after cross-fostering. Random effects included litter, contemporary group (herd–year–month), dam, and sire nested within breed. Deviations from predicted LFI values were quantified using an internally studentized residual (SR). A SR≤−1.71, equivalent to observed LFI at least 1.9kg less than predicted, was considered a DEV. Zero DEV occurred in 60% of lactation records, while 18% of lactation records had 1 DEV, and 22% of lactation records had ≥2 DEV. Thirty-four percent of negative deviations occurred during the summer months (June, July, August) which was more frequent when compared to the spring (26%), fall (23%), and winter (17%) months. Adjusted 21-day litter weaning weight (LW21) decreased as the number of DEV increased within a single lactation period, and wean-to-first service interval (WTSI) increased when at least 3 DEV occurred within a single lactation. An increase in DEV during early lactation did not affect LW21 or WTSI (P>0.05), though an increase in number of DEV after day 5 of lactation was associated with lower LW21 and longer WTSI. Odds of a negative deviation from predicted LFI occurring on any given day of lactation were estimated as odds ratios. If a DEV occurred the prior day, a DEV was 8.7 and 39.5 times more likely to occur than if a DEV had not occurred for purebred and F1 sows, respectively. In F1 sows, a DEV was 3.1 (P<0.01) times more likely to occur after day 5 of lactation when a DEV occurred on day 1 to 5 of lactation. Negative deviations from predicted LFI values decreased reproductive performance and had a larger effect on performance when they occurred during late lactation.

Daily feed intake during lactation was recorded on purebred Yorkshire (n=1587), Landrace (n=2197), and F1 Yorkshire x Landrace (n=6932) litters from day 1 to 22 of lactation. Lactation feed intake (LFI) curves were predicted using a mixed model which included fixed effects of breed, season, parity group (PG), day of lactation, interactions of day with breed and PG, and a covariate for litter size after cross-fostering. Random effects included litter, contemporary group (herd–year–month), dam, and sire nested within breed. Least squares means for each day were used to express LFI curves by breed through day 22 of lactation. Yorkshire and Landrace LFI curves were not different (P=0.09), though both differed from the LFI curve (P<0.05) of F1 sows. Due to a limited number of observations in late lactation, LFI data from days 19 to 22 were not included. Evaluation of the difference in feed intake between 2 consecutive days (DC) of lactation resulted in the following classifications: 3 periods for purebreds, day 1 to 6 (PB1), day 7 to 10 (PB2), and day 11 to 18 (PB3); 2 periods for F1 sows, day 1–5 (C1) and day 6–18 (C2). Average rate of change in intake (ARC), average daily intake (ADI), and variation from predicted LFI values (VAR) metrics were estimated for each period in purebred and F1 sows. Parity group 1 in both purebred and F1 sows had the lowest ARC and ADI metrics, but highest VAR (P<0.05) in each period of lactation. Similar differences were observed for seasonal effects (P<0.05) as LFI curves during summer months represented lower ARC and ADI and higher VAR values compared to all other seasons. For all breeds, increased ARC and ADI metrics resulted in higher 21-day litter weaning weights (P<0.05), while decreasing VAR metrics late in lactation (PB3 and C2) resulted in higher 21-day litter weaning weights and shorter wean-to-first service intervals (P<0.05). Average rate of change increased more quickly in early periods (PB1, PB2, C1) and was lower in late lactation (PB3, C2). An increase in average rate of change in intake, average daily intake, and decreased variation from predicted LFI values during a period of lactation resulted in improved measures of maternal performance.

Design of breeding programs requires knowledge of variance components that exist for traits included in specific breeding goals and the genetic relationships that exist among traits of economic importance. A study was conducted to evaluate direct and correlated genetic responses to selection for intramuscular fat (IMF) and to estimate genetic parameters for economically important traits in Duroc swine. Forty gilts were purchased from US breeders and randomly mated for 2 generations to boars available in regional boar studs to develop a base population of 56 litters. Littermate pairs of gilts from this population were randomly assigned to a select line (SL) or control line (CL) and mated to the same boar to establish genetic ties between lines. In the SL, the top 10 boars and 75 gilts were selected based on IMF EBV obtained from a bivariate animal model that included IMF evaluated on the carcass and IMF predicted via ultrasound. One boar from each sire family and 50 to 60 gilts representing all sire families were randomly selected to maintain the CL. Carcass and ultrasound IMF were both moderately heritable (0.31 and 0.38, respectively). Moderate to high genetic relationships were estimated among carcass backfat and meat quality measures of IMF, Instron tenderness, and objective loin muscle color. Based on estimates obtained in this study, more desirable genetic merit for pH is associated with greater genetic value for loin color, tenderness, and sensory characteristics. Intramuscular fat measures obtained on the carcass and predicted using ultrasound technology were highly correlated (rg = 0.86 from a 12-trait analysis; rg = 0.90 from a 5-trait analysis). Estimated genetic relationships among IMF measures and other traits evaluated were generally consistent. Intramuscular fat measures were also genetically associated with Instron tenderness and flavor score in a desirable direction. Direct genetic response in IMF measures observed in the SL corresponded to a significant decrease in EBV for carcass loin muscle area (−0.90 cm2 per generation) and an increase in carcass backfat EBV (0.98 mm per generation). Selection for IMF has led to more desirable EBV for objective tenderness and has had an adverse effect on additive genetic merit for objective loin color.

The purpose of this study was to determine the association of production factors with stayability to parity 4 (STAY4) under controlled experimental conditions. Data were from 2,293 female pigs, sampled from 6 genetic lines that were entered into the National Pork Producers Council Maternal Line National Genetic Evaluation Program. Genetic lines evaluated included Newsham (NH), National Swine Registry (NSR), American Diamond Swine Genetics (ADSG), Danbred (DAN), and 2 Dekalb-Monsanto lines (DK44 and GPK347). Stepwise logistic regression was utilized in the analysis of STAY4. All effects were nested within genetic line. Categorical effects in the model were arrival date to the wean-to-finish unit (entry date) and breed-gestation-farrowing facility (farm). Continuous effects in the model were gilt backfat, LM depth, ADG, age at puberty, age at first farrowing, and traits recorded before the last litter of the sow (prefarrow backfat, number born alive, number weaned, litter weaning weight, lactation feed intake, lactation backfat loss, and lactation length). Factors significant for STAY4 included farm, entry date, age at first farrowing, ADG, gilt backfat, and lactation before removal effects, as well as feed intake, number born alive, and lactation length. Age at first farrowing and lactation feed intake affected all genetic lines. Regression coefficients for STAY4 on age at first farrowing were -0.014, -0.022, -0.017, -0.016, -0.011, and -0.021 (all P < 0.05), respectively, for NH, NSR, ADSG, DK44, GPK347, and DAN genetic lines. Regression coefficients for STAY4 on lactation feed intake were 0.043, 0.049, 0.051, 0.061, 0.120, and 0.097 (all P < 0.05), respectively, for NH, NSR, ADSG, DK44, GPK347, and DAN females. Age at puberty, age at first farrowing, and lactation feed intake had the greatest effect on STAY4.

Concentrated livestock production has led to soil nutrient accumulation concerns. To reduce the environmental impact, it is necessary to understand current recommended livestock feeding practices. Two experiments were conducted to compare the effects of trace mineral supplementation on performance, carcass composition, and fecal mineral excretion of phase-fed, grow-finish pigs. Crossbred pigs (Experiment I (Exp. 1). (n = 528); Experiment 2 (Exp. 2), (n = 560)) were housed in totally-slatted, confinement barns, blocked by weight, penned by sex, and randomly assigned to pens at approximately 18 kg BW. Treatments were allocated in a randomized complete block design (12 replicate pens per treatment) with 9 to 12 pigs per pen throughout the grow-finish period. In Exp. 1, the control diet (Io100) contained Cu as CuSO4, Fe as FeSO4, and Zn (of which 25% was ZnO and 75% was ZnO4) at concentrations of 63 and 378 mg/kg, respectively. Treatment 2 (O100) contained supplemental Cu, Fe, and Zn from organic sources (Bioplex, Alltech Inc., Nicholasville, KY) at concentrations of 19, 131, and 91 mg/kg, respectively, which are the commercially recommended dietary inclusion levels for these organic trace minerals. Organic Cu. Fe, and Zn concentrations from O100 were reduced by 25% and 50% to form treatments 3 (O75) and 4 (O50-1), respectively. In Exp. 2, treatment 5 (Io25) contained 25% of the Cu. Fe, and Zn (inorganic sources) concentrations found in Io100. Treatment 6 (O50-2) was identical to the O50-1 diet from Exp. 1. Treatment 7 (O25) contained the experimental microminerals reduced by 75% from concentrations found in O100. Treatment 8 (O0) contained no trace mineral supplementation and served as a negative control for Exp. 2. In Exp. 1, tenth-rib backfat, loin muscle area and ADG did not differ (p>0.05) between treatments. Pigs fed the control diet (Io100) consumed less feed (p<0.01) compared to pigs fed diets containing organic trace minerals. thus, G:F was greater (p = 0.03). In Exp. 2, there were no differences among treatment means for loin muscle area, but pigs fed the reduced organic trace mineral diets consumed less (p<0.05) feed and tended (p = 0.10) to have less tenth-rib backfat compared to pigs fed the reduced inorganic trace mineral diet. Considering that performance and feed intake of pigs was not affected by lower dietary trace mineral inclusion, mineral excretion could be reduced during the grow-finish phase by reducing dietary trace mineral concentration.

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A study was conducted to evaluate the efficacy of selection for intramuscular fat (IMF) in a population of purebred Duroc swine using real-time ultrasound. Forty gilts were purchased from US breeders and randomly mated for 2 generations to boars available in regional boar studs, resulting in a base population of 56 litters. Littermate pairs of gilts from this population were randomly assigned to a select line (SL) or control line (CL) and mated to the same sire to establish genetic ties between lines. At an average BW of 114 kg, a minimum of 4 longitudinal ultrasound images were collected 7 cm off-midline across the 10th to 13th ribs of all pigs for the prediction of IMF (UIMF). At least 1 barrow or gilt was slaughtered from each litter, and carcass data were collected. A sample of the LM from the 10th to 11th rib interface was analyzed for carcass IMF (CIMF). Breeding values for IMF were estimated by fitting a 2-trait (UIMF and CIMF) animal model in MATVEC. In the SL, selection in each subsequent generation was based on EBV for IMF with the top 10 boars and top 75 gilts used to produce the next generation. One boar from each sire family and 50 to 60 gilts representing all sire families were randomly selected to maintain the CL. Through 6 generations of selection, an 88% improvement in IMF has been realized (4.53% in SL vs. 2.41% in CL). Results of this study revealed no significant correlated responses in measures of growth performance. However, 6 generations of selection for IMF have yielded correlated effects of decreased loin muscle area and increased backfat. Additionally, the SL obtained more desirable objective measures of tenderness and sensory evaluations of flavor and off-flavor. Meat quality characteristics of pH, water holding capacity, and percent cooking loss were not significantly affected by selection for IMF. Selection for IMF using real-time ultrasound is effective but may be associated with genetic ramifications for carcass composition traits. Intramuscular fat may be used in purebred Duroc swine breeding programs as an indicator trait for sensory traits that influence consumer acceptance; however, rapid improvement should not be expected when simultaneous improvement in other trait categories is also pursued.

A sufficient level of intramuscular fat (IMF) is needed to enhance consumer acceptance of pork products, and is currently receiving greater attention within swine genetic improvement programmes. An examination of previously described and novel genetic variants within candidate genes for IMF deposition was performed to evaluate potential use of genetic markers in marker-assisted selection (MAS). Biological candidate genes implicated to play a role in adipogenesis were investigated within two different lines of purebred Duroc pigs. These included MC4R, FABP3, DLK1, and TCF7L2. Significant variation in IMF within the control line was described by the MC4R genotype and a novel BsrfI single nucleotide polymorphism within the FABP3 gene. Genetic markers for DLK1 and TCF7L2 evaluated in this population are not currently recommended for selection in Duroc swine. Existence of MC4R and FABP3 mutations may be useful markers in MAS aimed at IMF improvement, provided that gene effects are segregating and the presence of an association is detected within the population. However, additional work to confirm the use of the investigated genetic markers in selection programmes is needed.

Nick L. Berry, graduate research assistant; Anna K. Johnson, assistant professor; Steven M. Lonergan, associate professor; Tom J. Baas, associate professor; Locke Karriker, assistant professor; Ken J. Stalder, associate professor, Iowa State University, Ames, IA; Jeffery Hill, consultant, Innovative Livestock Solutions, Alberta, Canada; Collette Schultz-Kaster, V.P. Quality Technical Services; Neal Matthews, Farmland Foods, Milan, MO

After five generations of selection for IMF using realtime ultrasound, the select line pigs had more IMF. Selection for IMF has, however, resulted in slightly more backfat and less loin muscle area. A correlated response to selection for IMF has yielded a response in pork flavor and overall fatty acid composition. Genetic selection for IMF may be feasible without ramifications on nutritional value of pork.