Browsing by Subject "n-alkanes"
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Item Predicting Forage Nutritive Value Using an In Vitro Gas Production Technique and Dry Matter Intake of Grazing Animals Using n-Alkanes(2011-08-08) Aguiar, Andre D.In the first experiment, forage samples (n = 39) were collected during 4 years (2006 ? 2009) from pastures grazed by Santa Gertrudis cattle at the King Ranch, TX. The in vitro gas production technique (IVGP) was performed to understand the pattern of fermentation parameters of the forage and obtain fractional digestion rate (kd) values to predict total digestible nutrients (TDN). The best nonlinear model to describe the IVGP values of the forages was the two-pool logistic equation. The passage rate (kp) of 4%/h was used.. The kp predicted by the Large Nutrient Ruminant System (LNRS) model was 3.66%/h. The average TDN was 55.9% compared to 53.8% using a theoretical equation. In the second experiment, Brahman bulls (n = 16) grazed Coastal bermudagrass pastures [Cynodon dactylon (L.) Pers.] and stocked at a moderate to low grazing pressure. Three periods of fecal collections were made within each period. Bulls were individually fed at 0700 and 1900 h of 400 g of corn gluten pellets containing C32 n-alkanes. Each period was divided in 2 sub periods in which fecal samples were collected 4 times a day (0700, 1100, 1500 and 1900 h). N-alkanes in the forage and feces were determined using gas chromatography. In the third experiment, four methods were used to estimate dry matter intake (DMI): C31 or C33 with or without adjustment for forage C32 (C31_0 and C33_0, respectively). There was a difference between morning (0700 and 1100 h) and afternoon fecal collections (1500 and 1900 h) on the predicted DMI using C31 (P = 0.0010), C33 (P = 0.0001), C31_0 (P = 0.0010), or C33_0 (P < 0.0001). There was no difference in average daily gain (ADG) between low and high residual feed intake (RFI) (P = 0.5709). The nonparametric analysis indicated that preranking animals for efficiency under confinement conditions does not guarantee (P < 0.0001) similar ranking under grazing conditions when using the alkane technique to determine forage DMI. In order to estimate DMI at least 5 d of fecal collection and 2 times a day of collection (0700 and 1500h) are needed to decrease the variability.Item Tracking Oil from the Deepwater Horizon Oil Spill in Barataria Bay Sediments(2013-05-03) Dincer, ZeynepIn April 2010, approximately 4.9 million barrels of oil were accidentally released into the Gulf of Mexico during the Deepwater Horizon Macondo Mc252 Oil Spill. Some of the surface oil was carried by prevailing winds and currents and reached the coast of Louisiana impacting marsh and marine ecosystems. One and a half years after this incident, a set of oiled marsh samples (2 grab samples) coupled with nearby subtidal and intertidal cores (12 cores) were collected from Barataria Bay, Louisiana to determine the probable source of petroleum residues present and to characterize the chemical composition of the oil. Plus, pre-spill core which was collected from Barataria Bay in 2007 was analyzed to identify the background hydrocarbon composition of the area. Polycyclic aromatic hydrocarbons (PAH), total petroleum hydrocarbons (TPH), biomarker, and stable carbon isotope compositions of selected samples were detected using a GC-MS and an elemental analyzer Conflo system coupled to a DeltaPlusXP isotope ratio mass spectrometer. The comprehensive chemical data allowed us to classify the pre and post-spill samples into 4 Groups. According to this classification, Group 1 and Group 2 samples had the highest concentrations of petroleum-derived hydrocarbons. Group 3 and background samples, on the other hand, was dominated by biogenic signatures. Although a direct connection between the detected and spilled Macondo oils results are complicated due to confounding factors (e.g., already present hydrocarbons and weathering processes), our biomarker data indicates that both oils have similar signatures. This close genetic relationship was also identified by stable carbon isotope analysis. The impact of the Macondo Mc252 Oil Spill in Barataria Bay appears to be limited to areas closer to the source. The oil has undergone moderate weathering and has penetrated into, the at least, the top 9 cm sediments. Additionally, to examine the decadal-scale history of sedimentation in these marshes, a sediment core was analyzed for the radioisotope 137Cs. The observed sedimentation rate of 0.39 cm/yr shows that oil pollutant input into Barataria Bay has been ongoing for at least 50-60 years.