Defoliation Effects On Bromus Tectorum Seed Production: Implications For Grazing

Cheatgrass (Bromus tectorum L.) is an invasive annual grass that creates near-homogenous stands in areas throughout the Intermountain sagebrush steppe and challenges successful native plant restoration in these areas. A clipping experiment carried out at two cheatgrass-dominated sites in eastern Oregon (Lincoln Bench and Succor Creek) evaluated defoliation as a potential control method for cheatgrass and a seeding preparation method for native plant reseeding projects. Treatments involved clipping plants at two heights (tall = 7.6 cm, and short = 2.5 cm), two phenological stages (boot and purple), and two frequencies (once and twice), although purple-stage treatments were clipped only once. Treatments at each site were replicated in a randomized complete block design that included a control with no defoliation. End-of-season seed density (seeds · m⁻²) was estimated by sampling viable seeds from plants, litter, and soil of each treatment. Unclipped control plants produced an average of approximately 13 000 and 20 000 seeds · m⁻² at Lincoln Bench and Succor Creek, respectively. Plants clipped short at the boot stage and again 2 wk later had among the lowest mean seed densities at both sites, and were considered the most successful treatments (Lincoln Bench: F_6,45 = 47.07, P < 0.0001; Succor Creek: F_6,40 = 19.60, P < 0.0001). The 95% confidence intervals for seed densities were 123–324 seeds · m⁻² from the Lincoln Bench treatment, and 769–2 256 seeds · m⁻² from the Succor Creek treatment. Literature suggests a maximum acceptable cheatgrass seed density of approximately 330 seeds · m⁻² for successful native plant restoration through reseeding. Thus, although this study helped pinpoint optimal defoliation parameters for cheatgrass control, it also called into question the potential for livestock grazing to be an effective seed-bed preparation technique in native plant reseeding projects in cheatgrass-dominated areas.     

Native Plant Growth and Seedling Establishment in Soils Influenced by Bromus Tectorum

The invasion of 40 million hectares of the American West by cheatgrass (Bromus tectorum L.) has caused widespread modifications in the vegetation of semi-arid ecosystems and increased the frequency of fires. In addition to well-understood mechanisms by which cheatgrass gains competitive advantage, it has been implicated in reducing arbuscular mycorrhizal fungi (AMF) abundance and taxa diversity. We evaluated this possibility at a high elevation site in a two-pronged approach. To test whether cheatgrass changed native AMF communities in ways that affected subsequent native plant growth, we grew cheatgrass and native plants in native soils and then planted native plants into these soils in a greenhouse experiment. We found that cheatgrass-influenced soils did not inhibit native plant growth or AMF sporulation or colonization. To test whether soils in cheatgrass-dominated areas inhibited establishment and growth of native plants, cheatgrass was removed and six seeding combinations were applied. We found that 14.02 ±  seedlings · m⁻² established and perennial native plant cover increased fourfold over the three years of this study. Glyphosate reduced cheatgrass cover to less than 5% in the year it was applied but did not facilitate native plant establishment or growth compared with no glyphosate. We conclude that cheatgrass influence on the soil community does not appear to contribute to its invasion success in these high elevation soils. It appears that once cheatgrass is controlled on sites with sufficient native plant abundance, there may be few lingering effects to inhibit the natural reestablishment of native plant communities.     

Factors Affecting Efficacy of Prescribed Fire for Western Juniper Control

Western juniper (Juniperus occidentalis Hook.) is a tree species occurring on 3.6 million ha in the northern Great Basin. This native species can be quite invasive, encroaching into sagebrush-grassland vegetation, forming woodlands, and dominating extensive landscapes. Control of encroaching juniper is often necessary and important. Efficacy of prescribed fire for western juniper control depends on many factors for which our understanding is still quite incomplete. This knowledge gap makes fire management planning for western juniper control more difficult and imprecise. Natural resource managers require a fire efficacy model that accurately predicts juniper mortality rates and is based entirely on predictors that are measurable prefire. We evaluated efficacy models using data from a fall prescribed fire conducted during 2002 in southwestern Idaho on mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana [Rydb.] Beetle) rangelands with early to midsuccessional juniper encroachment. A logistic regression model, which included vegetation cover type, tree height, fire type, and bare ground as predictors, accurately predicted (area under the receiver operating characteristic [ROC] curve [AUC] = 0.881 ± 0.128 standard deviation [SD]) the mortality rate for a random sample of western juniper trees marked and assessed prefire and 5 yr post fire. Trees occurring in an antelope bitterbrush (Purshia tridentata [Pursh] DC.) type, which had a heavy fuel load, were 8 times more likely to be killed by fire than trees in a mountain big sagebrush type, where loading was typically lighter. Probability of mortality decreased by 28.8% for each 1-meter increase in tree height. Trees exposed to head fire were 3 times as likely to be killed as those exposed to backing fire. Findings from this case study suggest that with just four factors which are readily quantifiable prefire, managers can accurately predict juniper mortality rate and thus make better informed decisions when planning prescribed fire treatments.     

Nutrient Availability in Rangeland Soils: Influence of Prescribed Burning,Herbaceous Vegetation Removal,Overseeding with Bromus Tectorum,Season, and Elevation

Soil nutrient availability influences plant invasions. Resin capsules were used to examine soil nutrient bioavailability along 2 sagebrush–grassland elevation transects in the east Tintic Range (Utah) and Shoshone Range (Nevada). In the fall of 2001, treatments were applied to 3 replicate plots at each site, which included prescribed burning, herbaceous vegetation removal, and controls. Cheatgrass (Bromus tectorum L.) was overseeded in small subplots within each treatment. Following treatments in each plot, resin capsules were installed at 15-cm depth in a shrub interspace and a B. tectorum–overseeded area. Nutrient availability was integrated during late fall to spring and spring to late fall for 2 years. Herbaceous vegetation removal increased availability of nitrate (Nevada and Utah) and Ca and Mg (Nevada only) but only during the second sampling period (growing season). Availability of K and ortho-P (Nevada and Utah) and nitrate (Nevada only) was greater on prescribed burned plots. For Utah, availability of ortho-P, K, Ca, Mg, and Fe generally increased with increasing elevation. Availability of Ca, Mg, K, and Fe was greatest during late fall to spring integration periods for Nevada. Overseeding with B. tectorum interacted with the burn treatment to influence availability of Ca, Mg, and Fe (Nevada sites only). Patterns of nutrient availability can be explained by a combination of decreased root uptake in relation to mineralization, differences in soil water content with season and elevation, and nutrient release from vegetation and soil as a consequence of prescribed burning. Herbaceous vegetation removal and burning can raise nitrate availability and increase risk of invasion by nitrophilic species such as B. tectorum. Nutrient availability can be out of phase with plant growth; plants capable of taking up nutrients during cold periods may have a competitive advantage. Resin capsules have utility in quantifying the effects of treatments on the availability of many soil nutrients.     

地球上也有火星的生活

犹他州位于美国西部,面积在美国50个州中名列第13,但人口仅250万,人口密度排到第41位,而且80％的人都居住在州府盐湖城.因此,地广人稀就成为了犹他州的代名词——除了极少数几个城市之外,这里最常见的是险峻的高山深谷、亘古荒凉的盐滩、无边无际的荒漠、毫无生气的咸水湖.被称作北美脊梁的落基山脉自北向南从州内穿过,将犹他州划为东西两半.东边是美国唯一的沙漠高原——科罗拉多高原,它占据了整个州面积的一半以上.     

Factors Affecting Dystocia in Cattle

The paper reviews the various factors affecting dystocia in cattle. It is based mainly on the recent studies found in the literature of the subject but refers occasionally to some older papers as well. The factors are grouped into four main categories: direct factors, phenotypic factors related to calf and cow, non-genetic and genetic factors. The first group includes malpresentations and uterine torsion. The second one includes: calf birth weight, multiple calvings, perinatal mortality, cow pelvic area, cow body weight and body condition at calving, gestation length. The non-genetic factors are: cow age and parity, year and season of calving, place of calving, maintenance practises, disorders, calf sex and nutrition. Other non-genetic factors are the level of hormones in the periparturient period, in vitro production of embryos and embryo cloning. Finally, the genotypes of cow, bull and calf, inbreeding, muscular hypertrophy, selection and quantitative trait loci form the fourth group of genetic factors.     

牛乳中乳过氧化物酶活性的影响因素

牛乳中乳过氧化物酶活性是巴氏杀菌热处理强度的重要指标,过度热处理会明显破坏牛乳本身的营养,也会导致不良物质的产生。测定经不同工艺处理后的牛乳中乳过氧化物酶活性,研究贮藏温度、贮藏时间对牛乳中乳过氧化物酶活性的影响。结果表明：经低温陶瓷膜过滤处理的牛乳中乳过氧化物酶活性损失率明显小于经75 ℃、15 s巴氏杀菌处理的牛乳;过多的工艺流程也会导致乳过氧化物酶活性损失,同时过高的贮藏温度会导致牛乳中乳过氧化物酶失活更快,且随着贮藏时间的延长,牛乳中乳过氧化物酶活性逐渐降低,原料乳中乳过氧化物酶活性降低更快。     

影响奶牛繁殖力的因素

奶牛的繁殖力在生产实践中具有重要的意义,繁殖力的高低不仅影响牛群的增殖,而且影响牛群的产奶水平和牛场的经济效益。影响奶牛繁殖力的因素是多方面的,下面从五个方面给与剖析和介绍。1营养对奶牛供给合理平衡的营养是保证奶牛繁殖力的重要因素,营养对奶牛的发情、配种、受胎起决定性作用,其中以能量和蛋白质对奶牛的繁殖力影响最大,矿物质和维生素也对繁殖力起重要作用。能量、蛋白质、维生素和矿物质缺乏可导致流产、早产和产出发育不完全的小牛。1.1能量能量水平过高过低都会影响奶牛的繁殖力。能量水平长期不足,会导致发情症状不明显…     

影响家畜超数排卵效果的因素

超数排卵(MO,MultipleOvulation)乃是胚胎移植所需胚胎的主要来源。它充分挖掘良种母牛的遗传潜力,向社会提供大量的优质胚胎。本文阐述了国内外超数排卵的发展情况,从不的角度分析了影响超排效果的几个因素。     

黑龙江西部地区无芒雀麦引种试验

对不同来源的6种无芒雀麦进行了引种试验研究。结果表明,6个品种在黑龙江西部地区越冬率达93%以上,生育期为102～106d,均适宜在黑龙江西部地区种植;其中,公农无芒雀麦、内蒙无芒雀麦和波兰无芒雀麦生产性能优于其他品种,值得在黑龙江西部地区推广。     

影响家禽就巢发生的因素及其研究进展

本文对影响家禽就巢的内分泌、遗传和环境因素及其研究进展进行了阐述,分析了目前就巢性研究中存在的问题,并提出就巢性研究的策略和思路。     

Pathologic Factors Affecting Postsplenectomy Survival in Dogs

The apparently high prevalence of splenomegaly in dogs, along with the surgical accessibility of the spleen, results in a relatively large number of splenectomies in dogs in clinical veterinary practice. Splenic nodular lesions are widely considered to be indicative of hemangiosarcoma and thus a disease that is ultimately fatal. This study correlates the results of complete pathologic evaluation and classification of 500 spleens obtained by splenectomy with survival information for each dog. Among the spleens examined, 257 of 500 (51.4%) were classified nonneoplastic and 241 (48.2%) were neoplastic; 2 (0.4%) were unclassified. Miscellaneous non-nodular splenomegaly accounted for 46 of 257 (18%) of the nonneoplastic lesions; nodular splenomegaly accounted for 206 of 257 (79%) of nonneoplastic splenic lesions and was composed of lymphoid hyperplastic nodules and associated hematomas, hyperplastic lymphoid nodules alone, or hematomas with no apparent underlying cause. Nodular neoplastic diseases of the spleen were divided among benign tumors (11.5%) and a variety of primary sarcomas. Hemangiosarcoma made up 51% of splenic malignancies but accounted for less than 25% of the spleens evaluated. Survival of dogs with hematomas associated with nonneoplastic conditions of the spleen was markedly different from that in dogs with hemangiosarcoma-associated hematomas, even though most could not be effectively differentiated on gross inspection. Two month postoperative survival was 83% for dogs with nonneoplastic-related hematomas, whereas only 31% of dogs with hemangiosarcoma, with or without associated hematomas, were alive after 2 months. Twelve-month survival times were 64% and 7%, respectively. An overall postsplenectomy survival rate of 52% was based on the number of dogs surviving for a minimum of 6 months postoperatively.     

影响卵母细胞体外成熟的因素

卵母细胞体外成熟培养技术是现代生物技术中的重要内容之一。多年来科研人员为了进一步提高卵母细胞体外培养成熟率以及更深入了解卵母细胞成熟机制,对影响卵母细胞体外成熟的因素进行了大量的研究。本文较全面的综述了影响卵母细胞体外成熟培养的有关因素及其机制。     

影响牛乳中体细胞数的因素分析

本文通过对三坪牛场19头泌乳奶牛的体细胞测定资料进行统计,利用SAS8.1软件分析了胎次、泌乳月和乳区对SCC的影响,为有效指导该场生产提供科学依据。结果表明:胎次和泌乳月对SCC有极显著的影响(P0.01),乳区对SCC有显著的影响(P0.05)。SCC随胎次的增加而增加,SCC在泌乳后期有升高的趋势,左前和右后两个乳区SCC明显高于另外两个乳区,当一个乳区SCC超过50万/mL时,其相邻乳区SCC有逐渐增加的趋势。     

内蒙古乌兰察布西部温性荒漠草地土壤种子库初探

温性荒漠草地土壤种子库中有13种植物,其中灌木5种,多年生草本5种,一年生草本3种,分属于7个科,种子密度仅为46粒/m     

Factors Affecting Gestation Length in Heavy Draft Mares

The purpose of this study was to examine the factors affecting gestation length in 209 foalings from 65 heavy draft horses by multiple linear regression analysis. The objective variable was gestation length, and the explanatory variables were stud farm, year foaled, month foaled, age of mare, parity of mare, last gestation length, foal gender, and some meteorological parameters (the mean values of prepartum 10 days: maximum temperature, minimum temperature, average barometric pressure, and hours of sunshine in a day). The mean gestation length for 209 foalings was 334.9 (standard deviation = 8.3) days, with a range of 313-352 days. Stepwise regression analysis showed that last gestation length and foal gender had significant (P < .01) effects on gestation length. Multiple regression analysis showed that last gestation length (standard partial regression coefficient = 0.54) was more influential on the present gestation length than foal gender (standard partial regression coefficient = 0.22). The present gestation length and the last gestation length were moderately positively correlated (r = 0.56, P < .01). Colt foal (n = 106) pregnancies were significantly (P < .01) longer than fillies (n = 103) (mean ± SEM: colt 337.1 ± 0.7 vs. filly 332.7 ± 0.9). According to our results, last gestation length (mare itself) and foal gender were the main factors affecting gestation length in heavy draft horses. Once several gestation lengths are known, predictions with acceptable accuracy can be made about the gestation length of that mare's following foaling.     

影响奶牛超数排卵效果因素的分析与研究

[目的]为了充分利用优良母牛遗传资源,发挥超数排卵技术对改良奶牛品种的重要作用。[方法]本试验采用CUE-MAT孕酮栓+FSH+PGF2α法和自然发情+FSH+PGF2α法对酒泉地区饲养奶牛进行超数排卵研究,重点就不同激素处理、季节、供体母牛体况、胎次等单一因素对超排效果影响进行观察,[结果]表明:春季(4.00)秋季平均可用胚数(4.86)冬季平均可用胚数(5.07)。平均可用胚率:秋季(56.04%)冬季(50.71%)春季(43.54%)。春、秋两季在可用胚率上差异有统计意义(P=0.0240.05),春、冬两季在可用胚率上差异无统计意义(P=0.2230.05),秋、冬季在可用胚率上差异无统计意义(P=0.3420.05)。经产母牛和青年母牛平均可用胚数分别为9.06和9.65,平均可用胚率分别为55.83%、56.48%。经产母牛和青年母牛可用胚率之间差异无统计意义(P=0.9020.05),但青年母牛的超排效果略高于经产母牛。[结论]为当地从事超数排卵工作提供基础性参考资料。     

Management and Genetic Factors Affecting Fertility in Sows

Contents The purpose of this article is to summarize the current knowledge on genetic and management methods for improving fertility in sows. Fertilization rate, litter size and the interval between weaning and oestrus are traits that can be monitored on farms. These traits are heritable but can also be influenced by management. Age at puberty and the interval between weaning and oestrus are genetically linked ( r _g = 0.3) and a shorter weaning-to-oestrus interval is related to a longer duration of oestrus. Consequently, selection may be used to simplify detection of oestrus but because of variation in duration of oestrus between lines/breeds, farm-specific insemination strategies are needed. The direct boar effect on fertilization is small, probably due to the superabundance of sperm cells that is available in each dose of semen. Consequently, the use of a large number of sperm cells per dose is the best management tool for avoiding fertilization problems in sows. Health status of the boars, both for artificial insemination and natural mating, is of importance in order to produce a large number of sperm cells/doses of good quality per ejaculate. It is concluded that factors that influence fertility in sows, particularly prior to and during fertilization, are mainly related to oestrus and the optimal timing of insemination. Selection for adequate symptoms of oestrus, together with farm-specific insemination strategies are needed.