Simulation of beef cattle production systems in the Llanos of Colombia—part I. Methodology: An alternative technology for the tropics     

J.M. Levine  W. Hohenboken  A. Gene Nelson 《Agricultural Systems》1981,7(1):37-48

A simulation model was developed to study voluntary forage intake, energy requirements for maintenance, liveweight change and calving rate of grade Zebu cows in the Llanos of Colombia. Multiplicative correction factors were fitted to intake and maintenance requirement prediction equations researched from the literature to account for reduced intake due to sparse regrowth of recently burned native savanna and to conditions of mineral deficiency, increased intake and decreased maintenance requirement during periods of high compensatory gain during the rainy season, and increased intake and maintenance requirement due to the effects of lactation and gestation. A frequency distribution was constructed relating liveweight at time of mating to subsequent calving rate, and this was used to simulate the calving rates of cow herds in the Llanos. Use of the model would allow prediction of the amount of improved pasture or supplemental feed that would be necessary to raise calving rates in a particular herd to an acceptable level, defined as at least three calves per cow every four years. The model was fitted by computer and was then run on programmable calculators. This type of simulation is suited to regions of the world in which computer time is expensive or unavailable. Verifications, validations and experimentation with the model are presented in a companion paper.  相似文献   

LBJ's "Great Congress": Rubber Stamp or Creativity?     

Nelson B 《Science (New York, N.Y.)》1966,154(3749):620-622

  相似文献   

Antigenic comparison of Canadian and US isolates of porcine reproductive and respiratory syndrome virus using monoclonal antibodies to the nucleocapsid protein.   总被引：14，自引：4，他引：10       下载免费PDF全文

R Magar  R Larochelle  S Dea  C A Gagnon  E A Nelson  J Christopher-Hennings    D A Benfield 《Canadian journal of veterinary research》1995,59(3):232-234

Fifteen Canadian field isolates of porcine reproductive and respiratory syndrome (PRRS) virus from Quebec and Ontario were compared with 5 US PRRS virus (PRRSV) isolates and with the European Lelystad isolate using monoclonal antibodies (MAbs) SDOW17, EP147, and VO17 directed to the 15-kDa nucleocapsid protein of PRRSV. All Canadian and US isolates tested by indirect immunofluorescence were recognized by the 3 MAbs, and individual titers of MAbs towards Canadian and US PRRSV isolates were similar as well. In contrast, the Lelystad virus isolate reacted only with the SDOW17 MAb and showed no reactivity with either EP147 or VO17. The reactivity pattern with these MAbs suggests that the Canadian isolates of PRRSV tested are antigenically similar to US isolates of PRRSV, and that these North American isolates share highly conserved epitopes on the 15-kDa nucleocapsid protein that clearly differentiate them from the European Lelystad virus isolate.  相似文献   

Comparison of two grafting methods in 4.0-mm drill defects in the third metacarpal bone of horses.     

E A Hanie  K E Sullins  B E Powers  P R Nelson 《Equine veterinary journal》1992,24(5):387-390

In 6 horses, bilateral metacarpal vertical series of three 4.0-mm unicortical drill holes were made. At random, one of each series of 3 holes was filled using a sternal 4.0-mm cancellous bone cylinder or a slurry of cancellous bone injected into the hole or left as an empty control. All horses had lateral metacarpal xeroradiographs at monthly intervals. Three horses (6 metacarpi) were examined post mortem after 4 months and 3 others after 6 months. Immediate through 4-month post-operative xeroradiographs demonstrated increased density in the holes with cancellous cylinders and no difference could be seen between the untreated controls and holes injected with slurry. From 5 months, no radiographic difference could be seen between the treatment groups. No consistent histological difference between treatment groups could be detected. In conclusion, no justification for clinical grafting of 4.0-mm unicortical dorsal metacarpal drill holes could be found.  相似文献   

Metabolites of carbofuran: Effect on indole-3-acetic acid degradation     

Cesar Franco  Nelson Durán 《Pesticide biochemistry and physiology》1981,16(2):136-140

Oxygen uptake, product formation, and photon emission in the indole-3-acetic acid/peroxidase/O₂ system were inhibited by carbofuran and its metabolites, the 3-ketocarbofuran phenol and carbofuran phenol. These metabolites acted as competitive inhibitors and concomitantly were degraded. Photon emission, together with uv spectrophotometry and oxygen measurements, shows this to be a rapid and reproducible method to study insecticide interaction with the indole-3-acetic oxidase system in vitro. 3-Ketocarbofuran phenol was metabolized by peroxidase with excited-state production.  相似文献   

Purification and characterization of a 94-kDa Pasteurella haemolytica antigen     

S L Nelson  G H Frank 《Veterinary microbiology》1989,21(1):57-66

A 94-kDa antigen of Pasteurella haemolytica Serotype 1, which was previously shown to elicit serum and nasal secretion antibody response to the bacterium, was purified and characterized. The antigen was purified by high performance liquid chromatography utilizing ion exchange, then size exclusion columns. It was a membrane protein that was copurified with 6-7% lipopolysaccharide. It had an isoelectric point of 4.6. Most other serotypes of P. haemolytica possessed a similar antigen.  相似文献   

Human genotoxicity: pesticide applicators and phosphine   总被引：2，自引：0，他引：2  

V F Garry  J Griffith  T J Danzl  R L Nelson  E B Whorton  L A Krueger  J Cervenka 《Science (New York, N.Y.)》1989,246(4927):251-255

Fumigant applicators who, 6 weeks to 3 months earlier, were exposed to phosphine, a common grain fumigant, or to phosphine and other pesticides had significantly increased stable chromosome rearrangements, primarily translocations in G-banded lymphocytes. Less stable aberrations including chromatid deletions and gaps were significantly increased only during the application season, but not at this later time point. During fumigant application, measured exposure to phosphine exceeds accepted national standards. Because phosphine is also used as a dopant in the microchip industry and is generated in waste treatment, the possibility of more widespread exposure and long-term health sequelae must be considered.  相似文献   

Infection of the middle nasal meatus of calves with Pasteurella haemolytica serotype 1     

G H Frank  S L Nelson  R E Briggs 《American journal of veterinary research》1989,50(8):1297-1301

Eight healthy nonstressed calves were inoculated with Pasteurella haemolytica serotype 1, by instilling a broth culture into the middle nasal meatus of the left nostril. The inoculated left nostrils shed P haemolytica from the ventral nasal meatus at a steady rate for a mean of 7 days, whereas the uninoculated right nostrils of the same calves shed P haemolytica sporadically and in lower concentrations. The duration, frequency, and concentration of P haemolytica shed from the inoculated nostrils was significantly (P less than 0.05) greater than from the nostrils of other healthy calves that had been exposed by instilling the culture into the ventral nasal meatus of both nostrils in a previous study. The concentration of antibodies (IgG, IgA, and IgM) to P haemolytica increased significantly (P less than 0.05) in serum and nasal secretions after exposure. Four weeks after initial P haemolytica exposure, calves were exposed to infectious bovine rhinotracheitis virus and became clinically ill. Four calves were induced to shed P haemolytica from both nostrils by the virus infection; thus, they were harboring the bacterium and were susceptible to active recolonization. Four calves were not induced to shed P haemolytica. The apparent reason was not that they were resistant to active colonization, but that they were no longer harboring the bacterium, because they became active shedders after they were reinfected with P haemolytica.  相似文献   

Pituitary macroadenomas and macroadenocarcinomas in dogs treated with mitotane for pituitary-dependent hyperadrenocorticism: 13 cases (1981-1986)     

R W Nelson  S L Ihle  E C Feldman 《Journal of the American Veterinary Medical Association》1989,194(11):1612-1617

Pituitary macroadenoma/macroadenocarcinoma (PMA; tumor size greater than or equal to 1 cm in diameter) was diagnosed in 13 dogs after 0.5 to 24 months of mitotane treatment for pituitary-dependent hyperadrenocorticism (PDH). The diagnosis of PDH was established on the basis of results of common tests of the pituitary-adrenocortical axis in conjunction with results of x-ray computed tomography or necropsy. Initial clinical findings and clinicopathologic test results were typical of PDH. Signs referable to the CNS developed in 7 of the 13 dogs. The most common neurologic sign was stupor. Pituitary macroadenoma/macroadenocarcinoma was an unexpected finding in the other 6 dogs, because none had clinical signs of disease referable to the CNS at the time that pituitary tumor was documented. In the 13 dogs, strong correlation existed between tumor volume, compression/invasion of the surrounding nervous tissue, and development of neurologic signs, ie, neurologic signs were most frequently associated with larger tumors. The size of the tumor, however, was not always an indication of whether neurologic signs would be observed. All 7 dogs with neurologic signs were euthanatized because of the deleterious effects of the PMA. Of the 6 dogs without neurologic signs, 2 died of unrelated cause. Alternative treatment (ie, hypophysectomy, 60Co-teletherapy) was used successfully in 2 other dogs. Alternative treatment would seem indicated if PMA is documented in a dog with PDH. However, identification of PMA is dependent on evaluation of x-ray computed tomographic images. Signalment, history, physical examination, and alterations in routine clinicopathologic findings in these 13 dogs of our study were similar to previously reported findings in dogs with PDH but apparently without large pituitary tumors.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

Effects of rapeseed silage variety and dietary level on digestion and growth performance of beef steers     

L L Lancaster  C W Hunt  J C Miller  D L Auld  M L Nelson 《Journal of animal science》1990,68(11):3812-3820

A digestion and ruminal fermentation trial involving five ruminally cannulated steers assigned to a 5 x 5 Latin square with a 2 x 2 + 1 arrangement of dietary treatments was conducted to evaluate the effects of variety of rapeseed silage (RS) containing either a high (HG) or a low (LG) glucosinolate concentration when fed at 100 or 50% of diet DM. A bromegrass hay-corn-soybean meal mixture, which was expected to be isocaloric and isonitrogenous with the RS, was used as the control (C) treatment and replaced RS in the 50% diets. In situ disappearance of substrate from both RS varieties was measured in ruminal environments created by each diet. No dietary treatment x RS substrate interactions were observed for any in situ variable. Total tract digestibility and extent of in situ disappearance of both DM and NDF were greater (P less than .01) for HG than for LG. In situ DM and NDF disappearance at 8, 16 and 24 h was greater (P less than .01) for RS than for the C diet. Similarly, total tract DM digestibility was greater (P less than .01) for RS (61.0%) vs C (56.0%) diets. Diets with 50% RS had greater (P less than .01) NDF digestibility (50.4%) than 100% RS (43.6%) diets. Variety of RS had no effect on particulate passage rate. In a 77-d growth trial with 60 beef steers, ADG was greater (P less than .01) for HG vs LG (.46 vs .36 kg), 50 vs 100% (.52 vs .31) and C vs RS (.64 vs .41) diets.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献