最佳乳糖水平获得最佳收益

给断奶仔猪提供乳糖是为了提高仔猪断奶期采食量和潜在的生长性能.乳糖的促生长作用是由于改善了饲料适口性并与饲料中的糖类相匹配,开发了仔猪断奶后的酶系统,但是研究者也建议可以采用其他复杂的机制,如:菌群的改变和对获得健康的影响. 许多因素影响仔猪饲料中乳糖的水平.如:应该采用何种饲料预算类型;大而健康的小猪是否断奶;在断奶年龄上是否有很多变化,是否是一个严密的年龄阶段;仔猪断奶年龄是在18日龄之前或之后;断奶采食量和饥饿的问题;仔猪在猪群中是否适应;经济模式是否适用于较大和较小的经济成本投入等.仍有许多问题需要解决,以便做出最好的决定,不仅为了获得最佳乳糖水平,也能满足一般仔猪饲料的需要.     

Effect of human interferon on vesicular stomatitis virus released from bovine embryonic kidney cells

Human lymphoblastoid interferon (IFN) had an antiviral activity in bovine embryonic kidney cells that resulted in the release of vesicular stomatitis virus (VSV) particles with decreased infectivity. The inhibition was dose dependent and the cells were highly sensitive to human IFN. Examination of the proteins of VSV released from bovine cells after IFN treatment showed a reduction in the glycoprotein. Electron microscopic studies revealed a large number of VSV particles with characteristic spike-like surface projections released from nontreated cells. There was a reduction in the number of mature virions produced in IFN-treated cells and the virions lacked the characteristic surface projections.     

Vertical transmission of channel catfish virus

Channel catfish broodfish were examined nondestructively for the presence of channel catfish virus (CCV), using a nucleic acid-probing technique. A dot blot assay was tested and shown to be accurate and rapid in the diagnosis of CCV. Two CCV-positive fish were successfully mated, and fertilized eggs were collected. Offspring that hatched were tested and were shown to have CCV. This result indicated vertical transmission of CCV, a herpesvirus.     

WHOLE‐BODY BIODISTRIBUTION OF 3′‐DEOXY‐3′‐[18F]FLUOROTHYMIDINE (18FLT) IN HEALTHY ADULT CATS

Positron emission tomography/computed tomography (PET/CT) utilizing 3′‐deoxy‐3′‐[¹⁸F]fluorothymidine (¹⁸FLT), a proliferation tracer, has been found to be a useful tool for characterizing neoplastic diseases and bone marrow function in humans. As PET and PET/CT imaging become increasingly available in veterinary medicine, knowledge of radiopharmaceutical biodistribution in veterinary species is needed for lesion interpretation in the clinical setting. The purpose of this study was to describe the normal biodistribution of ¹⁸FLT in adult domestic cats. Imaging of six healthy young adult castrated male cats was performed using a commercially available PET/CT scanner consisting of a 64‐slice helical CT scanner with an integrated whole‐body, high‐resolution lutetium oxy‐orthosilicate (LSO) PET scanner. Cats were sedated and injected intravenously with 108.60 ± 2.09 (mean ± SD) MBq of ¹⁸FLT (greater than 99% radiochemical purity by high‐performance liquid chromatography). Imaging was performed in sternal recumbency under general anesthesia. Static images utilizing multiple bed positions were acquired 80.83 ± 7.52 (mean ± SD) minutes post‐injection. Regions of interest were manually drawn over major parenchymal organs and selected areas of bone marrow and increased tracer uptake. Standardized uptake values were calculated. Notable areas of uptake included hematopoietic bone marrow, intestinal tract, and the urinary and hepatobiliary systems. No appreciable uptake was observed within brain, lung, myocardium, spleen, or skeletal muscle. Findings from this study can be used as baseline data for future studies of diseases in cats.     

Presumptive electric cataracts in a Great Horned owl (Bubo virginianus)

This case report describes suspected electrocution in a juvenile female Great Horned owl (Bubo virginianus) with subsequent bilateral cataract formation. The bird flew into a high‐voltage power line and was immediately rescued. Burn wounds of the head and ataxia with apparent blindness were noted. Initial ophthalmic examination 5 days after the incident revealed bilaterally symmetrical anterior subcapsular vacuolar cataracts with absence of intraocular inflammation and a predominantly clear view to the normal appearing fundus. The bird appeared to be nonvisual. No ophthalmic medications were prescribed at initial examination. Subsequent recheck examination at 8 weeks revealed moderate resolution of the cataracts and improved vision. To the authors’ knowledge, this is the first published report of suspected electric cataracts in an avian species.     

The Sage-Grouse Habitat Mortgage: Effective Conifer Management in Space and Time

Management of conservation-reliant species can be complicated by the need to manage ecosystem processes that operate at extended temporal horizons. One such process is the role of fire in regulating abundance of expanding conifers that disrupt sage-grouse habitat in the northern Great Basin of the United States. Removing conifers by cutting has a beneficial effect on sage-grouse habitat. However, effects may last only a few decades because conifer seedlings are not controlled and the seed bank is fully stocked. Fire treatment may be preferred because conifer control lasts longer than for mechanical treatments. The amount of conservation needed to control conifers at large temporal and spatial scales can be quantified by multiplying land area by the time needed for conifer abundance to progress to critical thresholds (i.e., “conservation volume”). The contribution of different treatments in arresting conifer succession can be calculated by dividing conservation volume by the duration of treatment effect. We estimate that fire has approximately twice the treatment life of cutting at time horizons approaching 100 yr, but, has high up-front conservation costs due to temporary loss of sagebrush. Cutting has less up-front conservation costs because sagebrush is unaffected, but it is more expensive over longer management time horizons because of decreased durability. Managing conifers within sage-grouse habitat is difficult because of the necessity to maintain the majority of the landscape in sagebrush habitat and because the threshold for negative conifer effects occurs fairly early in the successional process. The time needed for recovery of sagebrush creates limits to fire use in managing sage-grouse habitat. Utilizing a combination of fire and cutting treatments is most financially and ecologically sustainable over long time horizons involved in managing conifer-prone sage-grouse habitat.     

Forest fragmentation and duration of forest tent caterpillar (Malacosoma disstria Hübner) outbreaks in northern hardwood forests

In northern forests dominated by aspen (Populus spp.), the duration of outbreaks of forest tent caterpillar (Malacosoma disstria Hübner) has been reported to increase with forest fragmentation. This relationship has not been tested in other forest types affected by this widespread native defoliator. From 2002 to 2007, a large-scale outbreak of this insect in the northeastern United States defoliated millions of hectares, with sugar maple (Acer saccharum Marsh.) the primary host. We used digital defoliation maps generated from aerial surveys and national land cover data to assess the effect of fragmentation on outbreak duration in areas of NY, MA, VT, and NH. We found that outbreak duration increased with forest cover and decreased with the forest edge, in opposition to the pattern previously reported for aspen-dominated forests in Canada. This pattern was significant from plot sizes ranging from 100 m to 1000 m in radius. The relationship between FTC and its natural enemies, which was postulated to underlie the effect of fragmentation on outbreaks in aspen forests, may be affected differently in northern hardwood forests, or other factors may be more important in determining outbreak duration in this forest type.     

Avian community response to vegetation and structural features in grasslands managed with fire and grazing

This study examined the importance of natural and manmade structural features on the avian community relative to management-induced vegetation dynamics. The study was conducted within the context of two alternative vegetation management treatments applied to pastures on a tallgrass prairie site in northcentral Oklahoma from 2001 to 2003. The brown-headed cowbird, a brood parasite, and the grasshopper sparrow, a common grassland obligate species, were most abundant in areas managed under a traditional treatment in which entire pastures were annually burned. Conversely, Henslow’s sparrow, a grassland obligate of conservation concern, was completely absent from traditional treatment pastures. Total bird species diversity and grassland obligate richness was highest in the patch-burn treatment, in which only discrete portions of each pasture were burned each year to create a mosaic of vegetation ‘patches’ in various stages of recovery from disturbance. Models of bird abundance reflected not only species-specific vegetation preferences, but also the often negative influence of structural features such as woody edges, roads, and ponds on breeding bird use of grasslands. Our study demonstrated that both disturbance-derived vegetation attributes and structural features contribute to heterogeneity and influence subsequent use by and composition of grassland bird communities.