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Browsing by Author "Enns, Richard Mark, advisor"

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    Beef cattle maternal and terminal economic selection indices
    (Colorado State University. Libraries, 2013) Zeng, Xi, author; Enns, Richard Mark, advisor; Thomas, Milton G., committee member; Dalsted, Norman L., committee member
    The breeding objective in most livestock operations is to increase profit ability by improving production efficiency. Animals with different purposes are associated with different production systems. The objective of the study is to develop economic selection indices for females and males in three different production systems: maternal, terminal with self-replacement females, and terminal without self-replacement females, based on production characteristics in the intermountain region of the US. Profit equations were constructed to derive economic values under fixed herd size scenario. The parameters used to calculate the cumulative discounted gene expressions (CDGE) and genetic parameters were estimated from 10,007 individual records and 27,165 pedigree records from the Angus herd at the John E. Rouse Beef Improvement Center of Colorado State University. There were 313 sires with an average generation interval of 3.30 years involved in the study, as well as 2,160 dams with an average generation interval of 5.32 years. Sensitivity tests were performed to test the effect of changing production and economic variables on economic selection indices weights. The impacts on selection index for all systems were small with changing production variable. Also, varying economic variables had small effect on selection index of maternal system with correlations among objectives more than 0.80. However, it affects the selection index of two terminal systems a lot with low (-0.05) or even negative (-0.82) correlation between one and another other. The selection responses with considering the cumulative discounted gene expression and based on six economic selection indices were $259.77, $957.10, $93.901, $361.58, $71.81 and $279.30 per generation for females and male in the three production systems, maternal, terminal with self-replacement heifer and terminal without self-replacement heifer, assuming that the selection intensity is one standard deviation. Under all scenarios, selection will lead to increasing profit.
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    Genetics of bovine respiratory disease in feedlot cattle
    (Colorado State University. Libraries, 2010) McAllister, Chase, author; Enns, Richard Mark, advisor; Crews, Denny H., 1967-, advisor; Van Campen, Hana, committee member
    Bovine respiratory disease (BRD) is one of the most prevalent and economically limiting diseases facing the United States beef industry today. Therefore, the objectives of this study were to (1) characterize the occurrence and prevalence of BRD in feedlot steers utilizing three disease classifications; treatment records (Trt), lung lesions present at harvest, and total BRD (treatment or lung lesion or both), (2) to examine the effects of Trt, number of treatments (NumTrt), mean lung score, lesions present, and total BRD on economically relevant carcass traits, and(3) to estimate heritabilities for BRD classifications and associated genetic and environmental correlations with economically relevant carcass traits. Data included health and carcass records on 2,870 crossbred steers managed in a commercial feedlot in Southeast Colorado over a two year period. Disease prevalence varied from 45% (n = 698) to 7% (n = 94) in years one and two, respectively. Averaged across the two year period, 27.6% of the steers exhibited clinical signs and were treated for BRD. Lung lesions were collected on 1,226 and 1,261 steers in year one and year two, respectively. Lesions were present in 71% in of steers year one and 47% in year two, and were present in 59% (n=1,461) of the steers over the two year period. Incidence for total BRD, was 76%, 59%, and 64% for years one, two, and overall, respectively. A subset of data (n = 1,260) of animals with birth information was used to evaluated the effect of age (P > 0.05) and BRD classification on carcass traits. Similarly, two models were fitted to the complete data to test the effect of receiving BW as an approximation for age. Evaluation of the models indicated receiving weight to be a significant fixed effect for prediction of carcass merit (P < 0.001). Incidence of BRD in the feedlot had a negative impact on both marbling score (MS) and subcutaneous backfat thickness (Fat) (P < 0.001), while accounting for minimal variation (P > 0.05) in HCW and LM area after adjusting for fixed contemporary group effects and receiving BW. However, animals that were chronically infected (at least 3 treatments) had reduced HCW (-16.5 ± 4.5 kg) and LM area (4.9 ± 1.25) (P < 0.05) compared to steers that were never treated. Lesions present at harvest did not have a significant effect (P > 0.05) on any evaluated traits. Animals that were categorized as suffering from BRD by the definition of total BRD had reduced MS (6.1 ± 2.8) and Fat (0.39 ± 0.18) (P < 0.05) when compared to healthy steers. Heritability estimates of BRD susceptibility were 0.15 ± 0.06, 0.04 ± 0.03, 0.0 ± 0.0, 0.04 ± 0.06, and 0.07 ± 0.06 for Trt, NumTrt, mean lung score, lesions present, and total BRD, respectively. Genetic correlations were not estimated for mean lung score due to the lack of genetic variability. Genetic correlations of Trt with carcass traits were unfavorable (0.19 ± 0.30) for HCW and LM area (0.03 ± 0.25), and favorable for MS (-0.30 ± 0.21) and Fat (-0.004 ± .26). Genetic correlations for NumTrt were similar at 0.23 ± 0.42, -0.05 ± 0.35, -0.29 ± 0.29, and -0.06 ± 0.35, between HCW, LM area, MS, and Fat, respectively. Estimates of genetic correlations for presence of lesions were zero for all traits. Estimates for total BRD were opposite when compared to Trt, and NumTrt at -0.03 ± 0.4, -0.35 ± 0.36, 0.28 ±0.30, and 0.12 ± 0.35 between HCW, LM area, MS, and Fat, respectively. Results indicate that with selection genetic improvement can be made over time by utilizing feedlot health records. Genetic correlations between treatments records and carcass traits were in general favorable and would increase profitability when incorporated into selection programs.