2006 Abstracts - American Society of Animal Science

150 Genetic change in intramuscular fat: Correlated responsesin performance and meat quality traits. C. Schwab*, N. Berry, T.Baas, and K. Stalder, Iowa State University, Ames.A study was conducted to evaluate the efficacy of selection for intramuscularfat (IMF) in purebred Duroc swine. A base population of 56litters was produced from forty-five gilts that were randomly mated fortwo generations to boars available in regional boar studs. Littermatepairs of gilts were randomly assigned to either a select line (SL) orcontrol line (CL) and mated to the same boar to establish genetic tiesbetween lines. At an average weight of 110 kg, four longitudinal ultrasoundimages were collected seven cm off-midline across the 10th-13thribs of all pigs for prediction of IMF. At least one barrow or gilt washarvested from each litter and carcass data were collected. A slice of thelongissimus muscle from the 10th – 11th rib interface was analyzed forcarcass IMF. Breeding values for IMF were estimated by fitting a twotraitanimal model and the full relationship matrix in MATVEC. In theSL, selection in each subsequent generation was based on EBV for IMFwith the top 10 boars and top 50% of gilts used to produce the nextgeneration. One boar from each sire family and 50 gilts representing allsire families were randomly selected to maintain the CL. A total of 288CL and 260 SL pigs have been harvested. Least squares means forcarcass traits were estimated using PROC MIXED in SAS with a modelthat included fixed effects of line, generation, harvest group within generation,and sex. Sire and dam within line were random effects in themodel. After four generations of selection for IMF, the average EBV forselect line pigs is 1.03% greater than for control line pigs. Of the pigsharvested, line LS means for tenth rib backfat and loin muscle area were19.66 mm and 42.80 cm2 in the CL, and 21.79 mm and 40.73 cm2 in theSL (P < 0.05), respectively. Line LS means measured at 24 h for HunterL and Minolta were 48.05 and 23.47 in the CL, and 49.44 and 24.47 inthe SL (P < 0.05), respectively. Selection for IMF has resulted in slightlymore backfat and less LMA through four generations.Key Words: Intramuscular fat, Ultrasound, Breeding value151 Molecular dissection of porcine chromosome 17 QTL formeat quality: From genome scan to sequence information. A.Ramos* 1 , Z. Hu 1 , S. Humphray 2 , J. Rogers 2 , J. Reecy 1 , and M.Rothschild 1 , 1 Iowa State University, Ames, 2 The Wellcome Trust SangerInstitute, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK.The last decade proved fertile for studies that identified numerous QTLfor a variety of economically important traits for the swine industry.However, these QTL usually span large distances, which makes theiruse in pig breeding schemes very difficult, if not impossible. In order toovercome this problem the identification of the underlying mutationsresponsible for these QTL is necessary. Previously, several meat qualityQTL were identified on pig chromosome 17. Fine mapping of theQTL of interest has begun in the relevant region by adding geneticmarkers and increasing the marker density to the linkage map. As newmaps are obtained, new QTL analyses are then performed. An extremelyvaluable tool to identify the mechanisms responsible for the QTL is thefull DNA sequence of the region where specific QTL are located. Ahighly contiguous, integrated BAC physical map of the porcine genomehas been completed by members of the Swine Genome SequencingConsortium. This resource allows the selection of a minimally overlappingtile path of BAC clones covering the entire genome as well asspecific QTL regions. A BAC tile path spanning the meat quality QTLon chromosome 17 has recently been selected and sequenced by theSanger Institute. The unfinished sequence was then assembled to coverthe whole pig QTL region, whose size was estimated to be approximately6 Mbp. With the high quality finished sequence informationbecoming available it is now possible to look for polymorphisms, insertions,deletions and gene candidates, which will ultimately lead to theidentification of the causative mutation(s) underlying these QTL. Theapproach and the added value of the sequence can be illustrated withthis example of a QTL on chromosome 17.Key Words: QTL, Pig, SequenceRuminant Nutrition - Dairy Cattle Nutrition152 Does prepartum rumen epithelial development limit earlypostpartum performance? W. Miller* and J. Shirley, Kansas StateUniversity, Manhattan.The rumen epithelium is responsible for absorbing the majority of substratesthat supply the daily energy requirements to the dairy cow,regardless of her physiological state. As the physiological status of thedairy cow changes from late lactation/gestating stage to the dry/gestatingstage, daily energy requirements are reduced dictating a reduction indiet energy density, which causes the rumen epithelium to undergo aninvolution period. Rumen papillae become shorter and narrower in responseto the reduction in VFA production while maintaining suitableabsorptive ability to support the current physiological status. As parturitionapproaches DMI declines and the normal practice involvesincreasing the energy density of the diet with the addition of concentrateto offset the decline in energy intake as well as adapt the rumen to anenergy dense lactating diet. The response of rumen epithelium to theincrease in dietary concentrate levels involves the growth of papillaeand subsequently increased surface area which likely enhances absorptionof VFA from the rumen. Improvement in the ability to absorb agreater amount of VFA from the rumen VFA pool would diminish theaccumulation of VFA within the rumen and supply a greater amount ofsubstrate to be utilized for gluconeogenesis, suggesting an improvementin energy balance immediately postpartum. Rumen epithelial responseto diet modifications was investigated by Dirksen et al. (1985) in thatrumen papillae growth was stimulated when cows were switched froma high crude fiber diet to one of lesser crude fiber and increased energycontent. Additionally, the ability of the rumen epithelium to absorbVFA from a buffered VFA mixture was much greater after 20 days ofreceiving a diet with increased energy content (Dirksen et al., 1985).Unfortunately research investigating the absorptive ability of rumenepithelium in vivo has been minimal in the dairy field. Strategies inducingrumen papillae proliferation and/or absorptive capacity during thedry period may stimulate DMI, improve the energy status, and reduceperiparturient disorders of the early lactating cow.Key Words: Rumen, Epithelium, Dairy48