Effects of 28% Protein Diets Differing in Quality on Channel Catfish Performance,Processing Traits,and Production Economics in a Multi-Batch System

Three 28% protein feeds (premium, standard, or a low-cost diet) were fed to channel catfish in a pond study to compare growth, production, and costs as a follow up to similar work with 32% protein feeds. Twelve 0.1-ha earthen ponds at the University of Arkansas at Pine Bluff (UAPB) Aquaculture Research Station were stocked with carryover fish (0.39 kg mean weight) at 5,860 fish/ha and fingerling catfish (mean individual weight of 15.4 g) at 12,500 fish/ha. Total yield (gross and net) did not differ between fish fed the premium as compared to the standard diet, but that of the premium diet was significantly higher than that of fish fed the low-cost diet. The feed conversion ratio (FCR) did not differ between fish fed the premium and standard diets, but was lower than the FCR of fish fed the low-cost diet. There were no differences found in processing yields among treatments. Given the lower cost of the 28% standard diet and yields equivalent to those of the 28% premium diet, the 28% standard diet was economically preferable to the other diets tested.     

Transaction costs in contract farming models for mussel and oyster farming in South Africa: Organisational and management implications

Abstract

This study examines transaction costs faced by small mussel and oyster growers to elicit the appropriate organisational design of contract institutions. The theoretical premise is that high transaction costs essentially constrain the participation of small growers in mussel and oyster mariculture. Transaction cost analysis is applied to contract farming models and this approach is first discussed conceptually. Experience with contract farming by small growers in a developing context is synthesised and used in guiding the design of contract farming models. This is followed by a brief overview of the mussel and oyster industries, which is used to gain insight into transaction costs associated with contract institutions. Contracting models and implications are assessed separately for each industry. For mussel mariculture, four farming models are examined and the appropriate model is subsequently selected. For oyster mariculture, the transaction costs of contract fanning are examined to assist in organisational design.     

A MATHEMATICAL PROGRAMMING MODEL OF YEAR-ROUND HYBRID STRIPED BASS (♀MORONE CHRYSOPS x ♂MORONE SAXATILIS) FINGERLING PRODUCTION

Year-round production of hybrid striped bass fingerlings has been limited by low survival in ponds during late summer. A whole-farm model was developed to assess economic effects of incorporating indoor tank production and mobile nursery systems to extend the fingerling production season. Mixed-integer linear programming models were constructed for six production scales with three sizes of ponds and indoor tanks and with a mobile fish nursery system. Optimal allocation of production activities was sensitive to varying survival rates of fingerlings and monthly sales patterns. Breakeven prices in winter production of hybrid striped bass fingerlings in indoor tanks were 3–4 times higher than in other months, implying that year-round production would require hybrid striped bass fingerling growers to receive higher prices to cover costs of production in winter months.     

猪肉品牌连锁店顾客忠诚度评价及其影响因素实证研究 ——基于南京市消费者的问卷调查

【目的】考察品牌猪肉专卖店顾客忠诚评价等消费者行为及其影响因素。【方法】采用结构方程模型,设置变量并对品牌猪肉专卖店顾客忠诚评价及其影响因素进行分析。【结果】品牌猪肉专卖店顾客满意具有多维度性且各维度间存在共变关系,其中,猪肉产品属性满意对顾客忠诚的总驱动效应最大,顾客关系信任对顾客忠诚的直接效应最大,转移成本对顾客忠诚的形成有正向影响。同时,顾客特征变量（年龄和收入）对顾客忠诚度的评价具有一定的调节作用。【结论】注重品牌猪肉专卖店产品质量,提高顾客满意,培育顾客关系信任,同时考虑消费者特征,如性别、年龄与收入等对市场进行细分,提高顾客转换成本,进而提高消费者对品牌猪肉专卖店的忠诚度。     

“十一五”天津市农业科技进步贡献率测算及分析

科学技术是第一生产力,科学测定农业科学技术进步贡献率,有助于把握农业科技发展水平,为政府制订农业政策提供可行的科学依据。以天津市及天津十二郊区县的时间序列和截面的混合数据为基础,采用C-D生产函数模型,测定天津市＂十一五＂期间农业科技进步贡献率为60.4%,并对结果进行了分析;最后提出进一步提高天津市农业科技进步贡献率的对策建议。     

绿色GDP与环境成本核算研究

从环境成本与绿色G D P的关系入手,总结了环境成本核算的一些基础理论和方法,最后提出了绿色G D P核算存在的主要问题以及推行绿色G D P核算的五大对策。     

Evolutionary analysis of herbivorous insects in natural and agricultural environments

Herbivorous insects offer a remarkable example of the biological diversity that formed the foundation for Darwin's theory of evolution by natural selection. The ability of insects to evolve resistance rapidly to insecticides and host‐plant resistance present a continual challenge for pest management. This paper considers the manner in which genetic constraints, host‐plant availability and trade‐offs affect the evolution of herbivorous insects in natural and agricultural environments, and the extent to which lessons learned from studying natural systems may be applied to improve insect resistance management in agricultural systems. Studies on the genetic architecture of adaptation by herbivores to host plants and to insecticides are reviewed. The genetic basis of resistance is an important component of simulation models that predict the evolution of resistance. These models often assume monogenic resistance, but available data suggest that this assumption may be overly narrow and that modeling of resistance as oligogenic or polygenic may be more appropriate. As omics (e.g. genomics and proteomics) technologies become more accessible, a better understanding of the genetic basis of resistance will be possible. Trade‐offs often accompany adaptations by herbivores. Trade‐offs arise when the benefit of a trait, such as the ability to feed on a novel host plant or to survive in the presence of an insecticide, is counterbalanced by fitness costs that decrease fitness in the absence of the selective agent. For resistance to insecticides, and resistance to insecticidal transgenic crops in particular, fitness costs may act as an evolutionary constraint and delay or prevent the evolution of resistance. An important observation is that certain ecological factors such as host plants and entomopathogens can magnify fitness costs, which is termed ecological negative cross‐resistance. The application of omics technologies may allow for more efficient identification of factors that will impose ecological negative cross‐resistance, thereby bolstering insect resistance management. Copyright © 2009 Society of Chemical Industry     

从双黄连口服液分析中兽药提取制剂的应用前景

和中兽药非提取制剂（主要是散剂）相比,虽然中兽药提取制剂具有明显优点,但片面于讲究现代化制剂工艺和指标性质量标准,导致生产成本增高,失去了经济动物应用价值。针对经济动物临床应用特点,中兽药提取制剂应遵循中兽医药客观特点及发展规律,既要满足药剂学要求,又要保持中兽医药特色,即要充分利用现代先进制剂技术,还有保持制剂成本符合经济规律。     

Effects of Weed-Free Periods on Organic Romaine Lettuce Production

Weed management in Romaine lettuce (Lactuca sativa L. var. longifolia) is an economic challenge for organic farmers. This study evaluated the effect of weed-free durations on crop yield and quality, weed densities and biomass, and weeding time in two growing seasons. Treatments included weedy entire-season; weed-free for 7 days after transplanting (DAT), 14 DAT, 21 DAT, 28 DAT, 35 DAT, 42 DAT; and weed-free entire season (49 DAT). Weeds were removed by hand-hoes and the time taken to weed each plot was recorded. Weed densities were recorded prior to each weeding and weed biomass was recorded at crop harvest. Total and marketable lettuce heads were recorded and crop quality was estimated. Weed interference up to 21 DAT resulted in approximately 45% total and 58% marketable yield loss. Weed control beyond this period did not result in significant (p < 0.05) increases in crop yield and quality. However, weed densities at the end of the season were 4- to 15-fold and weed biomass approximately 18-fold greater in plots kept weed-free only for 21 DAT compared with plots kept weed-free season-long. This suggested that weed seed-return may be a concern if late-season weeding is not conducted. To minimize weed seed-return, the plots would have to be kept weed-free for about 35 DAT. However, labor costs must be taken into consideration because the time required to hand-hoe was approximately 87 hr ha^?1 person^?1 greater in plots kept weed-free for 35 DAT compared with plots kept weed-free for 21 DAT.