Browsing by Author "Cassell, Bennet G."

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    The All-Breed Animal Model
    Cassell, Bennet G. (Virginia Cooperative Extension, 2009-05-01)
    The all-breed animal model is the genetic-evaluation system used to evaluate dairy animals in the United States.
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    An analysis of sire-son and dam-daughter relationships for type traits in the Holstein descriptive type classification system
    Cassell, Bennet G. (Virginia Polytechnic Institute and State University, 1972)
    Age correction factors were developed from 336,253 individual classification results and were applied to final score, final classification, general appearance, dairy character, body capacity, and mammary system. Using a within-herd model, 30,715 daughter dam pairs were 2 analyzed to determine estimates of heritability (h²) and genetic and phenotypic correlations. Heritability estimates were: final classification, 0.31; final score, 0.25; general appearance, 0.26; dairy character, 0.15; body capacity, 0.23; mammary system, 0.20; stature, 0.38; head, 0.11; front end, 0.11; back, 0.14; rump, 0.21; hind legs, 0.07; feet, 0.08; fore udder, 0.16; rear udder, 0.17; udder support, 0.13; udder quality, 0.04; and teats, 0.17. When traits were expressed as 1 for desirable and 0 for undesirable, h² estimates were lower. Genetic correlations were generally positive, ranging from 1.01 ± 0,08 between final score and final classification to -0.17 ± 0.22 between dairy character and udder quality expressed as a binomial. Regression of the son progeny test on that of his sire indicated that head, front end, hind legs, feet, rear udder, and udder quality were poor indicators of son's performance when the sire's progeny test result was used for selection decisions. Considerable emphasis was placed on type in selecting sires of sons, especially for final score, hind legs, fore udder, udder support, and teats, since bulls whose daughters scored high in these traits sired more future sires than other bulls.
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    The animal model
    Cassell, Bennet G. (Virginia Cooperative Extension, 1998)
    The Animal Model is the procedure used by USDA to evaluate genetic merit of dairy animals for production.
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    The animal model
    Cassell, Bennet G. (Virginia Cooperative Extension, 1992)
    The animal model is a system for genetic evaluations that estimates breeding values of bulls and cows at the same time.
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    Comparisons of Holstein, Brown Swiss, and Jersey cows for age at first calving, first calving interval, and true herd-life up to five years in seven regions of the United States
    Garcia-Peniche, Teresa Beatriz (Virginia Tech, 2004-12-10)
    The objectives of this research were to evaluate breed differences for heat-stress resistance using age at first calving and first calving interval, and to assess breed by region interactions for seven regions of the United States for survival-related traits up to five years of age in Brown Swiss, Holstein, and Jersey cows. Age at first calving and first calving interval were studied in farms with two breeds, with Holstein and Brown Swiss or Holstein and Jersey cows. The survival-related traits were analyzed in farms with one or two breeds. Seven regions within the United States were defined: Northeast, Northwest, Central north, Central, Central south, Southwest and Southeast. The fertility traits were also analyzed in seven individual states: Wisconsin, Ohio, Oregon, California, Arizona, Florida, and Texas. Brown Swiss were older than Holsteins at first calving (833 ± 2.4 d vs. 806 ± 2.0 d in regions, and 830 ± 3.1 d vs. 803 ± 2.4 d in states), but Holsteins and Brown Swiss did not differ for first calving interval. Jerseys were younger than Holsteins at first calving and had shorter first calving intervals (P < 0.01). In data from individual states, Holsteins housed with Brown Swiss were older at first calving than Holsteins housed with Jerseys (800 ± 2.7 d vs. 780 ± 2.5 d). Holsteins housed with Jerseys had slightly shorter first calving intervals than Holsteins housed with Brown Swiss, and the interaction of "type of Holstein: with season of the first calving was highly significant (P < 0.01). Region and season effects were smaller for Jerseys than for Holsteins, thus, Jerseys showed evidence of heat-stress resistance with respect to Holsteins. Management modified age at first calving in Holsteins, depending on the type of herd they were located in. Longer calving intervals might have been partly due to voluntary waiting period to breed the cows. The survival-related traits were evaluated up to five years of age. They consisted of stayability, number of completed lactations, days lived, herd-life, and total days in milk. For herds with one breed, the order for stayability to five years of age, from longer to shorter-lived breed was: Brown Swiss, Jersey and Holstein, but for the ratio of days in milk to herd-life the order was: Holstein, Jersey and Brown Swiss, and for the ratio of days in milk to days lived, it was: Jersey, and Holstein and Brown Swiss tied. This last ordering was the same for number of lactations completed by five years of age. The results for two-breed herds were similar since Brown Swiss and Jerseys had larger (Chi-square P < 0.01) probabilities of living past five years of age than Holsteins, and for days in milk and number of lactations completed, Jerseys had higher values than Holsteins (P < 0.01), but Holsteins and Brown Swiss tied in some analyses. Breed by region interaction was always significant. If all other conditions were assumed equal, Jerseys would give fastest returns by five years of age. The overall conclusion is that Jerseys performed better for the traits analyzed, all of them highly influenced by environmental conditions.
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    Dairy Crossbreeding Research: Results from Current Projects
    Cassell, Bennet G.; McAllister, Jack (Virginia Cooperative Extension, 2009-05-01)
    Summarizes the results of several research groups to develop crossbreeding trials.
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    Dairy Guidelines. Dairy Crossbreeding: Why and How
    Cassell, Bennet G.; McAllister, Jack (Virginia Cooperative Extension, 2009-05-01)
    The primary genetic interest in crossbreeding is in whether animals with genes from different parent breeds perform better in combination than the average of their parent breeds.
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    Dairy Pipeline. April 2010
    Callan, Peter L.; Cassell, Bennet G. (Virginia Cooperative Extension, 2010-03-29)
    Discusses working with your lender to develop strategies to insure the survival of your farm during economic hardship, and a new genetic profile of service sires in DHI 202
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    Dairy Pipeline. June 2010
    Currin, John F.; Cassell, Bennet G. (Virginia Cooperative Extension, 2010-06-01)
    Discusses management and prevention of metritis and correctly identifying sires of cows in Virginia.
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    Dairy Pipeline. September 2009
    Cassell, Bennet G.; Petersson-Wolfe, Christina S.; Scott, Michael Chase (Virginia Cooperative Extension, 2009-09-02)
    Discusses selection based on genomic proofs, highlights research from the ADSA annual meeting, and packing corn silage.
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    The Effect of Inbreeding on Lifetime Performance of Dairy Cattle
    Smith, Lori A. (Virginia Tech, 1997-01-27)
    Data for this study were age-adjusted linear scores on all cows scored between 1980 and 1993. Lifetime production information on these cows and their herdmates was used to calculate Relative Net Income adjusted for opportunity cost (RNIOC) for the 2,249,835 cows with an 84 month herdlife opportunity. The effect of inbreeding was analyzed using both a fixed and animal model, with little difference in results. Inbreeding depressed RNIOC by $12.69 in a fluid market and $11.53 in a manufacturing market per 1% increase in inbreeding. Addition of somatic cell information in the profit function had little effect. Heritabilities of profit functions were .16 and .14 for a fluid and manufacturing market, respectively. Animal model estimates of inbreeding depression were +.16 days, -6.7 days and -5.1 days for age at first freshening (AFF), days of productive life (DPL) and days in milk (TDIM), respectively. Inbreeding decreased first lactation mature equivalent milk, fat, and protein by 23.7 kg, .85 kg, and .76 kg, respectively and lifetime milk, fat, and protein production by 176.9 kg, 6.4 kg, 5.6 kg, respectively per 1% increase in inbreeding. Inbreeding had little effect on conformation traits. Effects of inbreeding were cumulative, exacting a larger effect on lifetime profit functions than on individual traits, when expressed as a percent of additive standard deviation. This study gives evidence that though not alarming, inbreeding has a deleterious effect on the lifetime performance of dairy cattle.
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    The Effect of Maternal and Fetal Inbreeding on Dystocia, Calf Survival, Days to First Service and Non-Return Performance in U.S. Dairy Cattle
    Adamec, Vaclav (Virginia Tech, 2002-01-07)
    Intensive selection for increased milk production over many generations has led to growing genetic similarity and increased relationships in dairy population. In the current study, inbreeding depression was estimated for number of days to first service, summit milk, conception by 70 days non-return, and calving rate with a linear mixed model (LMM) approach and for calving difficulty, calf mortality with a Bayesian threshold model (BTM) for categorical traits. Effectiveness of classical and unknown parentage group procedures to estimate inbreeding coefficients was evaluated depending on completeness of a 5-generation pedigree. A novel method derived from the classical formula to estimate inbreeding was utilized to evaluate completeness of pedigrees. Two different estimates of maternal inbreeding were fitted in separate models as a linear covariate in combined LMM analyses (Holstein registered and grade cows and Jersey cows) or separate analyses (registered Holstein cows) by parity (1-4) with fetal inbreeding. Impact of inbreeding type, model, data structure, and treatment of herd-year-season (HYS) on magnitude and size of inbreeding depression were assessed. Grade Holstein datasets were sampled and analyzed by percentage of pedigree present (0-30%, 30-70% and 70-100%). BTM analyses (sire-mgs) were performed using Gibbs sampling for parities 1, 2 and 3 fitting maternal inbreeding only. In LMM analyses of grade data, the least pedigree and diagonal A matrix performed the worst. Significant inbreeding effects were obtained in most traits in cows of parity 1. Fetal inbreeding depression was mostly lower than that from maternal inbreeding. Inbreeding depression in binary traits was the most difficult to evaluate. Analyses with non-additive effects included in LMM, for data by inbreeding level and by age group should be preferred to estimate inbreeding depression. In BTM inbreeding effects were strongly related to dam parity and calf sex. Largest effects were obtained from parity 1 cows giving birth to male calves (0.417% and 0.252% for dystocia and calf mortality) and then births to female calves (0.300% and 0.203% for dystocia and calf mortality). Female calves from mature cows were the least affected (0.131% and 0.005% for dystocia and calf mortality). Data structure was found to be a very important factor to attainment of convergence in distribution.
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    Effects of within herd variation on the relationship between genetic evaluations and performance of offspring
    Meinert, Todd Richard (Virginia Tech, 1987-05-12)
    1,032,438 Jersey and 1,162,578 Holstein official Dairy Herd Improvement Association (DHIA) records from 20,380 and 34,000 herd-years, respectively, were used to compute herd-year means and within herd-year standard deviations for individual mature equivalent (ME) milk, fat, and fat percent. These herd-year means and within standard deviations were used to stratify records into five classes. Regressions for individual daughter's modified contemporary deviation (MCD) on sire's predicted difference (PD) were calculated for each class. The within herd-year standard deviations were also used in some of the six different MCD calculations used to compute six different cow indexes (CI) for each cow and trait. The six MCDs calculated were either the current deviation, log adjusted deviation, or the deviation standardized to a constant variance in combination with either the current correction for contemporaries merit or an adjusted correction. The six different CI for each trait were compared by how accurately they predicted the son's MCD trait and the daughter's MCD trait.
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    Estimation of the Economic Impact of a Unit Change in Predicted Transmitting Ability for Daughter Pregnancy Rate and Other Predicted Transmitting Ability in the Merit Indexes
    Yook, Eunsun (Virginia Tech, 2004-04-28)
    These studies deal with lifetime profit analyses for individual cows, and using these estimates to determine the economic value of genetic changes in traits for which genetic evaluations (predicted transmitting ability, PTA) are currently available. Data were collected from six states processed by Dairy Records Management Systems (DRMS) from herds on continuous test for at least 10 yr. The purpose of the first study was to determine how well estimators of lifetime net income based on 305-d lactation yields and a 10-yr opportunity (RNI305.10) and based on complete lactation data but a 5-yr opportunity (RNIc.5) predict the estimate based on complete lactations and a 10-yr opportunity (RNIc.10). Records for 22,854 cows in Virginia herds born in 1988, 1990, and 1992 from the DRMS in Raleigh, NC were used. Each RNI was calculated using fluid (skim/fat) pricing and milk-fat-protein pricing. Regression analyses including herd and birth year were used in the model to estimate the regression of RNIc.10 on RNIc.5, and RNIc.10 on RNI305.10. The resulting regression coefficients for fluid (skim/fat) pricing were $1.53 and $1.12 explaining 67 and 97% of the variation of RNIc.10, respectively. The corresponding results for milk-fat-protein pricing were $1.52 and $1.14 explaining 68 and 96% of the variation of RNIc.10, respectively. Using RNIc.10 as the measure to estimate lifetime profit is strongly recommended over the two alternatives tested. In the second study, the economic impacts of a unit change in PTA of daughter pregnancy rate (DPR) and other PTA in the merit indexes on lifetime profit estimates of a bull's daughters were estimated to determine an economic weight for the PTADPR and other PTA in economic indexes. Records for 71,094 cows born in 1988, 1990, and 1992 from six states processed at DRMS were used: Florida [10,940 cows], Indiana [8,231 cows], North Carolina [12,280 cows], Texas [4,786 cows], Virginia [20,341 cows], and Vermont [14,516 cows]. The basic RNI function consisted of [total milk, fat, and protein income ?feed cost for production] (yield income, YI) + [net value of calves + net salvage value] (non yield income, NYI) ?rearing cost (RC) ?[(daily cost for labor, maintenance feed, supplies, and fixed expenses) x days in herd] (daily cost, DC). Some of the economic impacts of PTA described for the merit indexes were not included in the basic RNI. These were added to RNI by multiplying the respective sire PTA by the economic impact. These included -165*PTASCS (M); 33*udder composite + 15*feet and legs composite -14.86*body size composite (T); and 8.064*PTA for daughter pregnancy rate -4.80*PTA for daughter calving ease (PRCE). Each ARNI was calculated using all production records initiated prior to the cow's tenth birthday with three milk pricing systems comparable to the prices in USDA three merit indexes: fluid (skim/fat) pricing (FARNI), milk-fat-protein pricing (NMARNI), and cheese pricing (CARNI). Two levels of prices for rearing cost per day and daily cost were used for calculating FARNI, NMARNI, and CARNI. Regression analyses including herd and birth year in the model were used to estimate the simple and partial regressions of ARNI or partitioned ARNI on sire PTA. Partial regression included all PTA in Net Merit, except service sire calving ease. Ignoring other PTA, one unit increase in PTADPR increased 476.25kg of lifetime total milk or 18 days of total DIM. One unit decrease in PTASCS increased 4372.50kg of lifetime total milk. With low daily and rearing costs, each 1% change in PTADPR increased ARNI by $59.31 to $55.82 depending on the milk pricing systems. The corresponding results with high daily and rearing costs were $27.50 to $24.01. Standardized multiple regression enabled the comparison of the economic weights of this study with those of USDA. The PTA for productive life (PL) in all three USDA merit index was emphasized less than the results from this study; however, PTADPR in USDA indexes was emphasized more than this study. In this study, the economic weight of PTADPR was negative within the low daily and rearing costs, but it was positive in the high daily and rearing costs.
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    Evaluation of optimum and near optimum pair selection methods for increasing predicted relative net income in Jersey cattle
    Green, Ronald T. (Virginia Tech, 1987-08-20)
    To evaluate the importance of non-linear relationships between Relative net income per day of productive life (RNI/DPL) and individual traits, 921,915 potential offspring were simulated from all possible matings of 20,487 Jersey cows and 45 active AI sires. Predicted milk yield, fat yield, and 13 linear type traits of potential progeny were used to predict RNI/DPL of all potential progeny. Five methods of mate selection and pairing were evaluated for their effectiveness in choosing mates and the amount of computer time required to choose those pairings. Results of a linear programming (LP) method were used as a comparison for the other four more easily applied methods. Two of the other four methods were not significantly (P > .01) different from the LP method. Although the random pairing method was significantly different, similarity of results, for this method indicated non-linear relationships between RNI/DPL and individual trait scores are of minor importance. A11 four methods used considerable less computer time than the LP method. Analysis of variance for predicted RNI/DPL (all possible offspring) indicated herd, dam within herd, sire, and inbreeding class to be significant (P < .01) variables in determining RNI/DPL. However the sire by dam within herd interaction did not significantly affect RNI/DPL, again indicating non-linear relationships between traits and RNI/DPL were not very important. Regressing PD's, Cl's, and their crossproducts for milk yield, fat yield, and 13 linear type traits showed the relative importance of crossproducts to be minimal in comparison to the linear effects of parental genetic evaluations.
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    Factors affecting the accuracy and stability of sire proofs from progeny test herds
    Meinert, Todd Richard (Virginia Tech, 1991)
    Change in Modified Contemporary Comparison proofs during first and second crop period was computed from up to eight proofs during both periods for AI and non-AI sampled Holstein bulls with repeatability of last evaluation≥.90. Effect of proof number within testing period on the bull's milk or fat evaluation was estimated with bull absorbed. AI and non-AI sampled bulls' proofs increased from initial first crop proof and then remained fairly constant during the remainder of first crop period. With inclusion of second crop daughters, proofs dropped significantly more for non-AI than AI sampled bulls. This drop increased for non-AI sampled bulls born after 1976, but was unchanged for AI sampled bulls. A measure of change was calculated using last second crop proof minus the second to last first crop proof. Expected standard deviation of change was calculated and used to stratify bulls into eight change classes. A larger proportion of non-AI sampled bulls have proofs that dropped than could be explained by chance alo e. Results indicated that non-AI sampled bulls were less stable than AI sampled bulls' proofs and that stability of non-AI sampled bulls has diminished over time. For one of the studs that had stability of their bulls' proofs examined, their young sire sampling program was investigated. Individual phenotypic and genetic records of first crop and non-first crop cows in 3449 herds participating in the AI stud's young sire sampling program from 1971 to 1987 were used to characterize the sampling program, to estimate genetic trend across and within the progeny test herds, and to compute within herd means and standard deviations of various traits (herd characteristics). Herd characteristics of progeny test herds were utilized in predicting within herd genetic trend d in predicting changes in proofs of bulls sampled by the stud. For bulls sampled by this stud, average herd characteristics and variability of herd characteristics across the contributing herds was calculated and used to predict the measure of proof change in the first study. Average herd-year characteristics and variability of herd-year characteristics explained 39% to 46% of the variation in milk. and fat proof changes. In general, variability of herd-year characteristics and average within herd-year standard deviation herd-year characteristic variables explained most of the changes in proofs. Genetic trend across the progeny test herds was large for milk (105 kg) and fat (3.1 kg) yield. Genetic trend computed from PTAs of sires of first crop cows increased 58 kg milk and 1.5 kg fat per year from 1971 to 1978 and 176 kg milk. and 5.5 kg fat per year from 1979-87. The genetic level of daughters of young sires born after 1983 was equivalent or exceeded the genetic level of cows from other sires in the herd. Results indicated that within herd genetic improvement will not be hurt and may actually be enhanced from participating in a young sire sampling program depending upon sire selection of cows not bred to young sires. Herd characteristics explained forty-five and fifty-one percent of the differences in within herd genetic trends for milk and fat yield, respectively. Average sire PTA of non-first crop daughters accounted for 80% and 67% of the explainable differences. Other herd characteristics indicated that herds with larger within herd standard deviation milk yields, larger number of young sires represented, younger cows, less average days open, and greater percentage of cows sired by AI sires made faster rates of genetic improvement.
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    Fat-corrected milk
    Cassell, Bennet G. (Virginia Cooperative Extension, 1992)
    Fat-corrected milk is one method of standardizing milk production for comparisons between cows.
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    Genetic Characterization of Zambian Native Cattle Breeds
    Zulu, Dackson Nkonje (Virginia Tech, 2008-09-09)
    Breed characterization is a primary step in designing appropriate management and conservation programs of livestock in developing countries. Since cattle represent a major food animal species in Zambia, its conservation is a major goal for both the government and non-governmental organizations. To support the conservation effort, the objective of this thesis research was to assess the phenotypic and molecular characteristics of indigenous Zambian cattle breeds including Angoni, Barotse, Tonga, and Baila based on body measurements and randomly amplified polymorphic DNA (RAPD) markers, respectively. A total of 100 animals, 25 from each of the four breeds associated with different tribes and region of Zambia, were used in the molecular analysis research. Additionally, 10 Holstein x Jersey crossbred animals were used as a reference and to test the extent of cross-breeding, if any, of the indigenous stock with exotic breeds. To further compare the Zambian indigenous breeds, morphometric measurements including body length, heart girth, and height at withers on 50 animals of each breed were measured. Blood was collected from animals at randomly selected farms and DNA isolated by standard protocols in Zambia. A total of 10 primers, of the 20 evaluated for informativeness, were used in the RAPD-PCR analyses. Differences among the four breeds for all the three morphometric measurements were significant with the Barotse significantly higher than the other three (P<0.05). The average number of bands per primer was 7.1 and the percentage of polymorphic bands per primer ranged from 40 to 71.4 with an average of 64.8%. Breed divergence was highest between the Tonga and the Barotse and lowest between the Tonga and Baila breeds. Both the morphometric measurements and RAPD-based distance estimates suggest that the Barotse may be different from the other indigenous breeds while the Tonga and Baila were more closely related. In addition, the genetic distance estimates imply that the Holstein x Jersey crosses are different from the four Zambian indigenous cattle breeds evaluated. This thesis research provides, for the first time, the basic genetic information necessary for conservation of Zambian cattle breeds and the use of these populations for effective crossbreeding. The data suggest that though there is isolated by geographic distance and cultural differences among the tribes, two of the breeds are significantly related.
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    Genetic Improvement Using Young Sires With Genomic Evaluations
    Cassell, Bennet G. (Virginia Cooperative Extension, 2010-04-21)
    Reviews studies of the impact of genomic information on the accuracy of genetic evaluations and includes suggestions for the use of genome-tested young bulls for genetic improvement.
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    Genomics-Based Analysis of Antibody Response to Sheep Red Blood Cells in Chickens
    Geng, Tuoyu (Virginia Tech, 2007-05-18)
    Immune response provides vertebrates an important mechanism to fight pathogens and to reduce the incidence of diseases. Defining the molecular basis of antibody response may facilitate genetic improvement in the immune response of animals to pathogens. For almost 4 decades, antibody titers in response to challenge by sheep red blood cells (anti-SRBC) have provided an investigative tool in the efforts to define molecular mechanisms that underlie vertebrate immune response. The overall objective of this dissertation research was to identify DNA markers associated with anti-SRBC response in chickens. Specific objectives were: to develop a resource population for QTL analysis for anti-SRBC, to identify DNA markers and genes associated with primary anti-SRBC, and to evaluate the allelic frequencies in non-selected chicken populations of candidate markers associated with either high or low anti-SRBC response. These objectives tested the hypothesis that genetic control of a chicken's response to SRBC is polygenic. The resource population developed consisted of F1, backcross, and F2 derived from reciprocal crosses of birds from parental lines in the 28th generation of divergent selection for low (L) and high (H) anti-SRBC. The mean anti-SRBC titers of the parental lines were significantly different, with 11.5 for H and 2.6 for L (P<0.05). That for the 4 groups of F2 progeny ranged from 6.3 to 7.5, while those of the 8 groups of backcross progeny ranged from 3.9 to 13.3. Four of 555 random primers used to screen the parental H and L anti-SRBC lines were informative by amplifying seven line-specific fragments (P<0.0025). Each of the 7 line-specific fragments was converted to a sequence characterized amplified region (SCAR) within which single nucleotide polymorphisms (SNPs) were identified and tested for association with anti-SRBC. Only two of the seven SCARs in the parental lines were associated (P<0.05) with anti-SRBC level in the backcross resource population. Additionally, from analysis of the parental L and H anti-SRBC lines using microarrays, a total of 57 line-specific SNPs were also identified. Twenty of the line-specific SNPs were in and/or near genes previously reported to have immunity-related function. Microarray-based gene expression profiling of pooled RNA samples from L and H anti-SRBC birds identified three differentially expressed genes. In summary, this dissertation describes resources that include candidate SCARs and SNPs as well as differentially expressed genes that may be useful for the identification of genes that underlie antibody response.