鸡选食行为的原理——结合生产论讨的实验

引言大量事实表明,无论是野生动物还是家养动物,它们都能在广泛的范围内按某种“食谱”进行选食以满足其维持、生长和生产所必需的全部养分。为了使其“食谱”适当,动物需要一个控制系统以使其对每一种食物都能摄取最适的量。这种控制系统也许是严格的、内在的、在该种动物的所有个体中都是同样的、是通过自然选择进化来的;但在某一具体个体中,这种控制系统也可以是可塑的、是按其自身的经验而产生的。     

Seasonal changes in bud dormancy in relation to bud morphology, water and starch content, and abscisic acid concentration in adult trees of Betula pubescens

Annual cycles of change in bud morphology, bud burst ability, abscisic acid (ABA) concentration, and starch and water content were studied in mid-crown terminal buds of short shoots and underground basal buds of Betula pubescens Ehrh. In particular, we investigated the roles of ABA and bud water content in the regulation of bud growth. Basal buds differed morphologically from terminal buds of short shoots in that their leaf initials did not develop into embryonic foliage leaves and their total size did not increase significantly during summer. Bud burst ability, measured by forcing detached short shoots and stumps under controlled conditions, was maintained in the basal buds throughout the year, whereas the terminal buds of short shoots remained dormant until October, thereafter their bud burst ability increased gradually and reached a maximum in March-April. The ABA concentration of the basal buds was relatively constant throughout the sampling period (1-3 micro g g(DW) (-1)), whereas that of the terminal buds of short shoots, which was much higher (5-10 micro g g(DW) (-1)), showed a distinct seasonal cycle with a maximum from August to November. Bud ABA concentration decreased during the first 10 days of forcing, especially in basal buds. In both bud types, the amount of starch increased toward the autumn, declined in November, and was negligible in the terminal buds of short shoots between January and March, but in April, the amount was high again in both bud types. Water content varied characteristically in both bud types, although more distinctly in the terminal buds of short shoots, with an increase in spring before bud burst and a decrease during the summer until September. The significant morphological and physiological differences between the mid-crown terminal buds of short shoots and the underground basal buds may partly explain the characteristic growth habit of the basal buds and their development into coppice shoots after cutting the tree. The results also indicate a role for ABA in maintaining dormancy of the terminal buds of short shoots and emphasize the relationship between tissue water status and ABA concentration.     

燕叔叔的灵感花园

这是一个30平方米的小院,小院的男主人燕叔叔是一位从事美术编辑多年的艺术工作者,他有两个爱好,一是绘画,另外一个就是园艺手工作品。燕叔叔的园艺手工作品有两大特点,首先他把自己的艺术素养体现到手工作品中,使其具有设计感和装饰性;另外,他对各种材料非常尊重,并对废弃材料物尽其用。放眼燕叔叔的小院,到处可见男主人的巧妙用心。     

饲料企业营销渠道存在的问题及其管理

<正>在产品、价格乃至促销方式同质化趋势均日益加剧的今天,饲料企业单凭产品的独立优势赢得市场已非常困难。本文对目前饲料企业营销渠道存在的问题进行了客观分析,并实事求是的提出了一些加强饲料企业营销渠道的管理的有效措施,以期帮助饲料企业走出困境,实现企业经营目标。现阶段,产品、价格乃至促销方式同质化趋势均日益加剧,越来越多的饲料企业明白,在竞争白热化的饲料市场上仅仅凭产品的独立优势赢得胜利已非     

Seroprevalence of and agroecological risk factors for Mycobacterium avium subspecies paratuberculosis and neospora caninum infection among adult beef cattle in cow-calf herds in Alberta, Canada

A province-wide cross-sectional seroprevalence and agroecological risk factor study of Mycobacterium avium subspecies paratuberculosis (MAP) and Neospora caninum (NC) infection among cattle in 100 cow-calf herds in Alberta was conducted. The seroprevalence of MAP in adult cattle was 1.5% across all herds. Using a widely accepted herd test cutpoint of 2 or more seropositive cows out of 30 animals tested, 7.9% of herds were estimated to be infected (95% confidence interval (CI): 2.3-23.4%). Seroprevalence of MAP differed by agroecological region; specifically, cattle and herds in areas with high soil pH (> 7.0), southern latitudes, and arid climates had a moderately reduced risk of infection (P < 0.10). Seroprevalence of NC infection was 9.7% among adult beef cattle province-wide--these levels also varied by agroecological region--with 91.0% of herds infected overall.