Characterizing biological variability in livestock blood cholinesterase activity for biomonitoring organophosphate nerve agent exposure.

A biomonitoring protocol, using blood cholinesterase (ChE) activity in livestock as a monitor of potential organophosphate nerve agent exposure during the planned destruction of US unitary chemical warfare agent stockpiles, is described. The experimental design included analysis of blood ChE activity in individual healthy sheep, horses, and dairy and beef cattle during a 10- to 12-month period. Castrated and sexually intact males, pregnant and lactating females, and adult and immature animals were examined through at least one reproductive cycle. The same animals were used throughout the period of observation and were not exposed to ChE-inhibiting organophosphate or carbamate compounds. A framework for an effective biomonitoring protocol within a monitoring area includes establishing individual baseline blood ChE activity for a sentinel group of 6 animals on the bases of blood samples collected over a 6-month period, monthly collection of blood samples for ChE-activity determination during monitoring, and selection of adult animals as sentinels. Exposure to ChE-inhibiting compounds would be suspected when all blood ChE activity of all animals within the sentinel group are decreased greater than 20% from their own baseline value. Sentinel species selection is primarily a logistical and operational concern; however, sheep appear to be the species of choice because within-individual baseline ChE activity and among age and gender group ChE activity in sheep had the least variability, compared with data from other species. This protocol provides an effective and efficient means for detecting abnormal depressions in blood ChE activity in livestock and can serve as a valuable indicator of the extent of actual plume movement and/or deposition in the event of organophosphate nerve agent release.     

Fine-Scale Spatial Genetic Structure in Perennial Grasses in Three Environments

Past research has shown that changes in grazing-resistance traits may be associated with genetic changes in plant populations. Little is known about spatial genetic relationships within plant populations (spatial genetic structure) and any grazing effects on these relationships. Here we present observations of the fine-scale spatial genetic structure in three grass species in semiarid environments (Arizona, Mexico, and Argentina). In each environment, populations of a dominant grass species were sampled from two sites with contrasting livestock grazing histories. Plant genotypes were described with the use of amplified fragment length polymorphism markers. In Arizona, populations of sideoats grama (Bouteloua curtipendula var. caespitosa Gould and Kapadia) differed in that one has never experienced livestock grazing, whereas cattle have grazed the other. In the other two environments, populations exposed to long-term heavy grazing were examined, along with those that experienced either moderate grazing (Mexico, blue grama [Bouteloua gracilis {Willd. ex Kunt} Lag. ex Griffiths]) or extended exclusion of livestock (Argentina [Poa ligularis Nees ex Steud.]). Based on independent analysis of each population, we observed no differences in average gene diversity between populations of each species. With the use of analysis of molecular variance we found slight but significant genetic differentiation between populations with different grazing histories in Arizona and Argentina. Significant genetic structure was present in all populations and indicated an inverse relationship between spatial and genetic distance. Interestingly, this relationship was most pronounced in the cattle-free sideoats grama population, suggesting larger genetic neighborhood areas in the absence of livestock. Less distinct differences in spatial genetic structure associated with grazing history were evident in the other two species. We hypothesize that livestock grazing may lead to increased homogeneity in genetic structure at the landscape scale. Effectively examining this hypothesis presents many experimental challenges.     

Effect of direct-fed microbial and antibiotic supplementation on gastrointestinal microflora, mucin histochemical characterization, and immune populations of weanling pigs

Direct-fed microbials (DFM) have the ability to alter gastrointestinal microflora, morphology and immunity. Denaturing gradient gel electrophoresis was used to analyze the effect of Lactobacillus brevis, Bacillus, and antibiotic supplementation on the gastrointestinal microbiota. Treatments were arranged in a 2 × 3 factorial arrangement with two levels of L. brevis supplementation and three diets (control, Bacillus, and antibiotic) fed during the nursery period. Microbial diversity of the gastrointestinal microbiota increased in response to any of the treatments containing L. brevis, Bacillus, or antibiotic compared to unsupplemented pigs. Pigs provided L. brevis and Bacillus in combination exhibited more bands of high G/C content than pigs provided only the antibiotic treatment. Supplementation with L. brevis resulted in a unique band that was identified as unculturable, low G/C content, gram positive bacteria. Furthermore, L. brevis increased pig body weight at the end of the nursery by 1.6 kg compared to pigs not provided L. brevis. L. brevis increased the number of acidic goblet cells present on villi within the duodenum and jejunum, and decreased the number of sulfated goblet cells, whereas Bacillus and antibiotic supplementation decreased the number of sulfated goblet cells on villi within the duodenum. Immunohistochemical evaluation revealed that L. brevis supplementation lowered the number of CD2⁺ cells, antigen presenting cells (MHCII⁺), and CD4⁺ T cells within jejunal villi. These data illustrate the potential for DFM to improve pig growth rate after weaning, as well as elicit alterations in the gut microbial community, mucin-producing goblet cells, and immune cells.