Serum pharmacokinetics of oxytetracycline in sheep and calves and tissue residues in sheep following a single intramuscular injection of a long-acting preparation

The pharmacokinetics of a long‐acting oxytetracycline (OTC) formulation (Liquamycin® LA‐200®) injected intramuscularly (i.m.) at a dose of 20 mg/kg were determined in four calves and 24 sheep to determine if the approved label dose for cattle provided a similar serum time/concentration profile in sheep. The AUC for the calves was 168±14.6 (μg ? h/mL) and was significantly less than the AUC for sheep (209±43 μg ? h/mL). Using the standard two‐stage approach and a one‐compartment model, the mean Cmax for the calves was 5.2±0.8 μg/mL, and for the sheep was 6.1±1.3 μg/mL. The mean terminal phase rate constants were 0.031 and 0.033 h, and the Vdss were 3.3 and 3.08 L/kg for the calves and sheep respectively. Analysis of the data using the standard two‐stage approach, the naive pooled‐data approach and a population model gave very similar results for both the cattle and sheep data. Sheep tissue residues of OTC in serum, liver, kidney, fat, muscle and injection site were measured at 1, 2, 3, 5, 7 and 14 days after a single i.m. injection of 20 mg/kg OTC. Half‐lives of OTC residues in the tissues were 38.6, 33.4, 28.6, 25.4, 21.3, and 19.9 h for injection site, kidney, muscle, liver, mesenteric fat and renal fat, respectively. The ratio of tissue to serum concentration was fairly consistent at all slaughter times, except for the fat and injection sites. The mean ratios were 1.72, 4.19, 0.11, 0.061, 0.84 and 827 for the liver, kidney, renal fat, mesenteric fat, muscle and injection sites, respectively. The tissue concentrations of OTC residues were below the established cattle tolerances for OTC in liver (6 p.p.m.), muscle (2 p.p.m.) and kidney (12 p.p.m.) by 48 h, and in injection site muscle by 14 days after the single i.m. injection of 20 mg/kg.     

Natural transplacental infection of dairy calves with bovine immunodeficiency virus and estimation of effect on neonatal health

Many experimental infection studies with bovine immunodeficiency virus (BIV) have been conducted, but neither virus transmission under natural conditions nor longitudinal clinical effects of naturally occurring infections in non-experimental populations are well explored. We tested the hypotheses that BIV is transmitted across the placenta during gestation and that intragestionally infected calves are at increased risk of neonatal disease. A cohort of 59 dairy cows on one farm were enrolled at parturition and the BIV serostatus of the cows and their pre-colostral calves determined with an indirect fluorescent-antibody assay. Moreover, the enrolled calves were monitored thrice weekly for specific clinical signs through the duration of the 30 day neonatal period and the occurrence of clinical signs analyzed for association with calf pre-colostral BIV serostatus and dam BIV serostatus. Confounding due to calf passive immunity and season of birth were also explored. Forty percent of seropositive cows (14/35) gave birth to seropositive calves but no seropositive calves (0/19) were born to seronegative dams (estimated relative risk 16, 95% exact confidence interval 2.6–5.8×10²⁹). Calf pre-colostral BIV serostatus was not associated with the occurrence or frequency of clinical signs — but dam BIV serostatus was associated with the odds of occurrence of calf hyperthermia and with the frequency of occurrence of calf hyperthermia and hyperventilatory events. This study is inconclusive about the effects of prenatal BIV infection on neonatal health — but it does provide evidence for the natural occurrence of transplacental BIV infection.     

Phytoplasma identity and disease etiology

ABSTRACT Many plant diseases believed to be caused by phytoplasmas were described before phytoplasma groups were delineated through molecular analyses. It is now possible to assess the relationships between phytoplasma identity or classification and specific plant diseases. Data were consistent with the hypothesis of a common ancestral origin of pathogenicity genes in many phytoplasmas and a limited repertoire of plant responses to certain pathogen signals. Observations also were consistent with the hypotheses that the botanical host ranges of some phytoplasmas reflect specificities in transmission by vectors and vector feeding preferences; phytoplasma-insect vector relationships are keys to understanding evolutionary divergence of phytoplasma lineages; small differences in a highly conserved phytoplasma gene may be regarded as potential indicators of separate gene pools; the reliability of a diagnosis based on symptoms must be learned empirically (i.e., through case study for each syndrome); and some discrete diseases can be ascribed to phytoplasma taxa at the 16S rRNA group level, whereas others are clearly associated with phytoplasma taxa below this level.     

Simulating effects of fire on northern Rocky Mountain landscapes with the ecological process model FIRE-BGC

A mechanistic, biogeochemical succession model, FIRE-BGC, was used to investigate the role of fire on long-term landscape dynamics in northern Rocky Mountain coniferous forests of Glacier National Park, Montana, USA. FIRE-BGC is an individual-tree model-created by merging the gap-phase process-based model FIRESUM with the mechanistic ecosystem biogeochemical model FOREST-BGC-that has mixed spatial and temporal resolution in its simulation architecture. Ecological processes that act at a landscape level, such as fire and seed dispersal, are simulated annually from stand and topographic information. Stand-level processes, such as tree establishment, growth and mortality, organic matter accumulation and decomposition, and undergrowth plant dynamics are simulated both daily and annually. Tree growth is mechanistically modeled based on the ecosystem process approach of FOREST-BGC where carbon is fixed daily by forest canopy photosynthesis at the stand level. Carbon allocated to the tree stem at the end of the year generates the corresponding diameter and height growth. The model also explicitly simulates fire behavior and effects on landscape characteristics. We simulated the effects of fire on ecosystem characteristics of net primary productivity, evapotranspiration, standing crop biomass, nitrogen cycling and leaf area index over 200 years for the 50,000-ha McDonald Drainage in Glacier National Park. Results show increases in net primary productivity and available nitrogen when fires are included in the simulation. Standing crop biomass and evapotranspiration decrease under a fire regime. Shade-intolerant species dominate the landscape when fires are excluded. Model tree increment predictions compared well with field data.     

Water use by whitebark pine and subalpine fir: potential consequences of fire exclusion in the northern Rocky Mountains

In subalpine forests of the northern Rocky Mountains, fire exclusion has contributed to large-scale shifts from early-successional whitebark pine (Pinus albicaulis Engelm.) to late-successional subalpine fir (Abies lasiocarpa (Hook.) Nutt.), a species assumed to be more shade tolerant than whitebark pine and with leaf to sapwood area ratios (A(L):A(S)) over twice as high. Potential consequences of high A(L):A(S) for subalpine fir include reduced light availability and, if hydraulic sufficiency is maintained, increased whole-tree water use. We measured instantaneous gas exchange, carbon isotope ratios and sap flow of whitebark pine and subalpine fir trees of different sizes in the Sapphire Mountains of western Montana to determine: (1) whether species-specific differences in gas exchange are related to their assumed relative shade tolerance and (2) how differences in A(L):A(S) affect leaf- and whole-tree water use. Whitebark pine exhibited higher photosynthetic rates (A = 10.9 micromol x m(-2) x s(-1) +/- 1.1 SE), transpiration rates (E = 3.8 mmol x m(-2) x s(-1) +/- 0.7 SE), stomatal conductance (g(s) = 166.4 mmol x m(-2) x s(-1) +/- 5.3 SE) and carbon isotope ratios (delta13C = -25.5 per thousand +/- 0.2 SE) than subalpine fir (A = 5.7 micromol x m(-2) x s(-1) +/- 0.9 SE; E = 1.4 mmol x m(-2) x s(-1) +/- 0.3 SE; g(s) = 63.4 mmol x m(-2) x s(-1) +/- 1.2 SE, delta13C = -26.2 per thousand +/- 0.2 SE; P < 0.01 in all cases). Because subalpine fir had lower leaf-area-based sap flow than whitebark pine (QL = 0.33 kgx m(-2) x day(-1) +/- 0.03 SE and 0.76 kg x m(-2) x day(-1) +/- 0.06 SE, respectively; P < 0.001), the higher A(L):A(S) in subalpine fir did not result in direct proportional increases in whole-tree water use, although large subalpine firs used more water than large whitebark pines. The linear relationships between tree size and daily water use (r2 = 0.94 and 0.97 for whitebark pine and subalpine fir, respectively) developed at the Sapphire Mountains site were applied to trees of known size classes measured in 12 natural subalpine stands in the Bob Marshall Wilderness Complex (western Montana) ranging from 67 to 458 years old. Results indicated that the potential for subalpine forests to lose water by transpiration increases as succession proceeds and subalpine fir recruits into whitebark pine stands.