Published estimates of natural recharge in Las Vegas Valley range between 21,000 and 35,000 acre‐feet per year. This study examined the underlying assumptions of previous investigations and evaluated the altitude‐precipitation relationships. Period‐of‐record averages from high altitude precipitation gages established in the 1940s through the 1990s, were used to determine strong local altitude‐precipitation relationships that indicate new total precipitation and natural recharge amounts and a new spatial distribution of that recharge. This investigation calculated about 51,000 acre‐feet per year of natural recharge in the Las Vegas Hydrographic Basin, with an additional 6,000 acre‐feet per year from areas tributary to Las Vegas Valley, for a total of 57,000 acre‐feet per year. The total amount of natural recharge is greater than estimates from earlier investigations and is consistent with a companion study of natural discharge, which estimated 53,000 acre‐feet per year of outflow. The hydrologic implications of greater recharge in Las Vegas Valley infer a more accurate ground‐water budget and a better understanding of ground‐water recharge that will be represented in a ground‐water model. Thus model based ground‐water management scenarios will more realistically access impacts to the ground‐water system.

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An essential component to the ground water budget for the Las Vegas Valley (LVV) in southern Nevada is discharge from the ground water system. Discharge for the LW has been based on estimates made more than 50 years ago of 35,524,224 m3 per year as evapotranspiration (ET) and 0 m3 per year as subsurface outflow. Newly published values for recharge based on a more robust data set (70,308,360 m3) indicate a large imbalance associated with the earlier discharge estimates, providing the basis for the reevaluation conducted in this study. ET estimates in this study, as opposed to previous studies, were assigned a range in values that included an approach that assigned higher weight to the unique soil, plant, water, and climatic conditions that existed in predevelopment (1905) LW. The earlier discharge estimates also assumed that the basin was hydrologically closed; however, based on our evaluation, a range in yearly discharge by subsurface outflow from 1,480,176 m3 to 19,735,680 m3 could be assigned. Likewise, a range in yearly ET from 20,475,768 m3 to 78,819,372 m3 could be assigned. Based on newly published recharge values, closure can only occur if higher values are assigned to both the subsurface outflow and/or ET components of ground water discharge. We cannot provide a complete water balance closure with our ground water discharge estimate of 64,140,960 m3. However our reevaluation gives support to the higher recharge estimates and provides the rationale for future studies to be conducted based on a more rigorous scientific assessment.

A series of four floor pen trials was conducted to evaluate the effects of narasin and roxarsone, both alone and in combination, on their capacity to control severe Eimeria tenella infections in broilers. Three levels of narasin (0, 60, and 80 ppm) were fed to chickens receiving either 0, 25, or 50 ppm roxarsone in a factorial design. Cecal coccidiosis was induced by seeding the litter with ionophore-tolerant and ionophore-sensitive strains of E. tenella. After 8 days, 10 birds/pen were killed and their cecal lesions scored. Performance (body weight and feed consumption) and mortality were measured at the termination of the trials. Narasin reduced the severity of cecal coccidiosis as measured by a reduction in cecal lesions and an improvement in bird performance. Roxarsone also reduced cecal lesion scores. The highest level of roxarsone (50 ppm) in combination with 60 or 80 ppm narasin produced additive responses in the control of E. tenella infections. Maximum performance was obtained when narasin alone was fed at 80 ppm; drug combinations improved performance when compared with that of nontreated or roxarsone only-medicated groups.