Nitrate and certain short chain nitrocompounds and nitro-oxy compounds are being investigated as dietary supplements to reduce economic and environmental costs associated with ruminal methane emissions. Thermodynamically, nitrate is a preferred electron acceptor in the rumen that consumes electrons at the expense of methanogenesis during dissimilatory reduction to an intermediate, nitrite, which is primarily reduced to ammonia although small quantities of nitrous oxide may also be produced. Short chain nitrocompounds act as direct inhibitors of methanogenic bacteria although certain of these compounds may also consume electrons at the expense of methanogenesis and are effective inhibitors of important foodborne pathogens. Microbial and nutritional consequences of incorporating nitrate into ruminant diets typically results in increased acetate production. Unlike most other methane-inhibiting supplements, nitrate decreases or has no effect on propionate production. The type of nitrate salt added influences rates of nitrate reduction, rates of nitrite accumulation and efficacy of methane reduction, with sodium and potassium salts being more potent than calcium nitrate salts. Digestive consequences of adding nitrocompounds to ruminant diets are more variable and may in some cases increase propionate production. Concerns about the toxicity of nitrate's intermediate product, nitrite, to ruminants necessitate management, as animal poisoning may occur via methemoglobinemia. Certain of the naturally occurring nitrocompounds, such as 3-nitro-1-propionate or 3-nitro-1-propanol also cause poisoning but via inhibition of succinate dehydrogenase. Typical risk management procedures to avoid nitrite toxicity involve gradually adapting the animals to higher concentrations of nitrate and nitrite, which could possibly be used with the nitrocompounds as well. A number of organisms responsible for nitrate metabolism in the rumen have been characterized. To date a single rumen bacterium is identified as contributing appreciably to nitrocompound metabolism. Appropriate doses of the nitrocompounds and nitrate, singly or in combination with probiotic bacteria selected for nitrite and nitrocompound detoxification activity promise to alleviate risks of toxicity. Further studies are needed to more clearly define benefits and risk of these technologies to make them saleable for livestock producers.

A PCR technique to differentiate pathogenic enteric Escherichia coli strains in a field setting was evaluated. Among 76 children with acute diarrhea, this technique identified 12 children (16%) with enterotoxigenic E. coli, 6 (8%) with enteropathogenic E. coli, and 1 (1%) with enteroinvasive E. coli infection. Compared with the conventional assays, the PCR method proved to be simpler, more rapid, and inexpensive and therefore suitable for application in a developing-country field setting. Diarrheal disease remains a major public health problem in developing countries (25). Escherichia coli strains are among the most important bacterial causes of childhood diarrhea. At least five categories of diarrheagenic E. coli strains are recognized on the basis of distinct epidemiological and clinical features, specific virulence determinants, and association with certain serotypes (12, 15). Because of the costly and laborintensive diagnostic procedures, the epidemiology of E. coli infections remains obscure in many parts of the world. This study was undertaken to evaluate the application of a PCRbased test to differentiate E. coli isolates and determine their distribution among children with and without diarrhea. The study was conducted at Hospital Infantil of the Federal University of Bahia in Salvador de Bahia, Brazil. From 1 June to 31 August 1993, all children under 5 years of age with acute diarrhea who were brought to the hospital ambulatory clinic in the afternoon, Monday through Friday, were enrolled in the study. Two rectal swabs were collected from each child, placed in Cary-Blair transport medium, and processed within 4 h. One swab was processed by routine microbiological and biochemical tests to identify E. coli, Salmonella spp., Shigella spp., and Campylobacter jejuni, while the second swab was stored in 2 ml of phosphate-buffered saline (pH 7.4) at 4ЊC until tested for rotavirus by enzyme immunoassay (EIA) (LMD Laboratories, Inc., Carlsbad, Calif.). Fecal samples and/or rectal swab specimens were obtained for detection of Cryptosporidium parvum by enzyme-linked immunosorbent assay (ELISA) (Alexon Inc., Sunnyvale, Calif., and LMD Laboratories, Inc.). Three to six lactose-fermenting colonies and up to three lactose-negative colonies from each child were selected from MacConkey plates to be tested by conventional and PCR procedures. A total of 239 isolates were obtained from the 76 children and stored on tryptic soy agar (Difco Laboratories, Detroit, Mich.) gridplates for later testing by reference virulence assays. In addition, 43 isolates from 16 children without diarrhea were tested as controls.

Bos indicus typically perform better than Bos taurus when consuming a low-quality diet; however, the response to supplementation is generally greater in B. taurus. The underlying mechanisms supporting these responses have not been fully elucidated. Characterization of differences in rumen prokaryotic populations and their functional role in the two subspecies may provide additional insight. Ten cannulated steers (5 Angus and 5 Brahman) were used in concurrent 5 × 5 Latin squares. Animals were offered ad libitum access to rice straw (4.7% CP). Treatments consisted of an unsupplemented control diet and two levels (50 or 120 mg N/kg BW) of isonitrogenous supplements (30% CP), that were either high (H; 74%) or low (L; 26%) in undegradable intake protein. Rumen samples were collected at 0 and 4 h postfeeding and separated into liquid and solid fractions. Rumen bacterial taxa were sequenced utilizing a Roche 454 platform based on the 16s rRNA gene. At 97% sequence similarity, 97,826 operational taxonomic units were identified, which included 24 phyla, 108 families, and 255 genera. Analysis included SAS PROC mixed model, QIIME, and PICRUSt. Across all samples, Bacteroidetes and Firmicutes accounted for 65% and 28% of total bacterial abundance, respectively. The families Prevotellaceae (P = 0.05) and Ruminococcaceae (P = 0.004) and the genera Prevotellaceae (family; P = 0.003) within the phyla Bacteroidetes differed significantly in relative abundance with added protein when compared to the control. Consistent differences in the relative abundance of family and genus taxa between B. indicus and B. taurus suggest roles the symbiotic rumen microbiome may have in the capacity of B. indicus to utilize low-quality forage over a range of supplement types and levels including (Prevotella, Ruminococcus [family], Sphingobacteriaceae [family], Bacteroidales [order], Pontibacter, Bacteroides, Succiclasticum, Barnesiella, and Xylanibacter). Overall bacterial community diversity differences across parameters were limited. Rice straw is recalcitrant to bacterial digestion because of high levels of silica in the epidermis making this straw more resistant to bacterial attachment. Thus, this analysis represents the bacterial diversity and function of the rumen under conditions depleted CP, recalcitrant fiber matrix and restricted digestibility which appear to limit the microbial population to those capable of attaching and digesting complexed structural carbohydrates, resulting in reduced plasticity, and more evenness in diversity across parameters.

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