Bovine respiratory disease in feedlot cattle: phenotypic, environmental, and genetic correlations with growth, carcass, and longissimus muscle palatability traits     

Snowder GD  Van Vleck LD  Cundiff LV  Bennett GL  Koohmaraie M  Dikeman ME 《Journal of animal science》2007,85(8):1885-1892

Bovine respiratory disease (BRD) is the most costly feedlot disease in the United States. Selection for disease resistance is one of several possible interventions to prevent or reduce the economic loss associated with animal disease and to improve animal welfare. Undesirable genetic relationships, however, may exist between production and disease resistance traits. The objectives of this study were to estimate the phenotypic, environmental, and genetic correlations of BRD with growth, carcass, and LM palatability traits. Health records on 18,112 feedlot cattle over a 15-yr period and slaughter data on 1,627 steers over a 4-yr period were analyzed with bivariate animal models. Traits included ADG, adjusted carcass fat thickness at the 12th rib, marbling score, LM area, weight of retail cuts, weight of fat trim, bone weight, Warner-Bratzler shear force, tenderness score, and juiciness score. The estimated heritability of BRD incidence was 0.08 +/- 0.01. Phenotypic, environmental, and genetic correlations of the observed traits with BRD ranged from -0.35 to 0.40, -0.36 to 0.55, and -0.42 to 0.20, respectively. Most correlations were low or negligible. The percentage of carcass bone had moderate genetic, phenotypic, and environmental correlations with BRD (-0.42, -0.35, and -0.36, respectively). Hot carcass weight and weight of retail cuts had moderate, undesirable phenotypic correlations with BRD (0.37 and 0.40, respectively). Correlations of BRD with LM palatability and ADG were not detected. Low or near zero estimates of genetic correlations infer that selection to reduce BRD in feedlot cattle would have negligible correlated responses on growth, carcass, and meat palatability traits or that selection for those traits will have little effect on BRD susceptibility or resistance.  相似文献   

Age prevalence of trypanosomal infections in female Glossina morsitans morsitans (Diptera: Glossinidae) on the plateau area of eastern Zambia     

Kubi C  Billiouw M  Van Den Bossche P 《The Onderstepoort journal of veterinary research》2007,74(3):223-229

Trypanosomal infections in female Glossina morsitans morsitans were investigated in an area in the Eastern Province of Zambia between 1992 and 1994. A total of 4416 flies were captured, aged using the ovarian ageing method and screened for trypanosomal infections in both the mouthparts, salivary glands and the midgut. Congolense-type infections were identified in 4.8% of the flies. Vivax-type and immature infections were identified in 1.8% and 6.8% of the flies, respectively. The prevalence of congolense-type, vivax-type and immature infections increased with age. For vivax-type infections the age-prevalence relationship could be described by a model assuming a constant per capita rate of infection. For congolense-type and midgut infections, a polynomial term was added to the model significantly improving the fit. The per capita at which flies become infected was significantly higher for immature compared to mature infections. Observations strongly suggest that tsetse acquire new midgut infections at any age and that maturation of these infections is not limited to those obtained during the first blood meal.  相似文献   

Managing the water balance of The Fayoum Depression,Egypt     

W. Wolters  Nadi Selim Ghobrial  H. M. Van Leeuwen  M. G. Bos 《Irrigation and Drainage Systems》1989,3(2):103-123

A study of the water balances of The Fayoum irrigated lands and Lake Qarun was made to investigate the management of the irrigation system and the efficiency of irrigation water use. The two water balances are strongly interrelated. The drainage flow to Lake Qarun and the water level of the Lake are in delicate balance. A rise in Lake level causes the inundation of adjacent land. Management of The Fayoum water balance assumes control over irrigation water flows, but this control has technical and organizational limitations. Also discussed is the influence of irrigation practices in The Fayoum on the water balance (e.g., the autumn flushing of fields and farmers' preference for not irrigating at night in winter). Notwithstanding a high overall efficiency, irrigation efficiency during the winter is low. The reasons for this are given, together with the constraints against improving system management. Improved uniformity of the division and application of irrigation water will enable a better technical control of flows and will result in better water management in The Fayoum. Abbreviations: FID — Fayoum Irrigation Department, 1 feddan (fe) — 0.4 ha, 1 mcm — 1 million cubic metres: an average annual flow of 3.17 m³/s gives 100 mcm, m³/fe.year — supplied volume (m³) per surface area (fe) per year: 1000 m³/fe.year equals 240 mm/year, MSL — Mean Sea Level  相似文献   

Diagnosis of regional evaporation by remote sensing to support irrigation performance assessment     

W. G. M. Bastiaanssen  T. Van der Wal  T. N. M. Visser 《Irrigation and Drainage Systems》1996,10(1):1-23

The success of water management in large irrigation schemes with composites of soil, crop, wetness and micro-meteorological conditions is difficult to quantify. Performance assessment indicators, being among others a function of evaporation, are useful tools to evaluate the actual functioning of an irrigation system. The inevitable spatial variability of evaporation in large irrigation schemes makes its determination with conventional point measurements almost impossible. A new remote sensing evaporation parameterization algorithm has been tested with high resolution Landsat Thematic Mapper data for the Eastern Nile Delta, Egypt. Although the implementation of such an algorithm requires assumptions to be made, the current case study shows that these assumptions do not hamper the estimation of actual and potential evaporation at regional scale. The actual evaporation has been used to express the uniformity of crop water use which is related to the equity of irrigation water distribution. The coefficient of variance in actual evaporation between 53 differenent irrigation districts is 10% on average. The relative evaporation was considered to determine whether the crop was adequately irrigated. The relative evaporation was more than 75% for 48 out of 53 irrigation districts. It is concluded, that improved information on actual crop growth conditions through remote sensing provides an essential insight into the planning of real-time and seasonal irrigation water deliveries.  相似文献   

The impact of increasing farm size and mechanization on rural income and rice production in Zhejiang province,China   总被引：1，自引：0，他引：1  

M. Marrit Van den Berg  Huib Hengsdijk  Joost Wolf  Martin K. Van Ittersum  Wang Guanghuo  Reimund P. Roetter 《Agricultural Systems》2007

Economic growth in China’s agricultural sector lags behind growth in industry and services, creating an ever widening rural–urban income gap. Development of the non-agricultural sectors offers new opportunities for farmers in China’s more advanced provinces such as Zhejiang. Increased income in the urban sector creates markets for new products, and migrating farmers rent their land to those staying. Until now, the prevailing rice-based systems have been managed mainly using manual labour and animal traction, but the larger farms resulting from migration may facilitate, or even require mechanization. In this study, we use a simulation model of the farm household to analyse the effects of increasing farm size and the transition from rice to vegetable production, while also studying the effects of mechanization.  相似文献   

Using drainage systems for supplementary irrigation     

P. J. T. Van Bakel 《Irrigation and Drainage Systems》1988,2(2):125-137

The use of drainage systems for supplementary irrigation is widespread in The Netherlands. One of the operating policies is to raise the surface water level during the growing season in order to reduce drainage (water conservation) or to create subsurface irrigation. This type of operation is based on practical experience, which can be far from optimal.To obtain better founded operational water management rules a total soil water/surface water model was built. In a case study the effects of using the drainage system in a dual-purpose manner on the arable crop production were simulated with the model. Also, the operational rules for managing this type of dual-purpose drainage systems were derived.The average annual simulated increase in crop transpiration due to water conservation and water supply for subsurface irrigation are 6.0 and 5.4 mm.y^–1, respectively. This is equivalent with 520 × 10³ and 460 × 10³ Dfl.y^–1 for the pilot region (2 Dfl 1 US $). The corresponding investments and operational costs are 600 × 10³ Dfl and 9 × 10³ Dfl.y^–1 for water conservation and 3200 × 10³ Dfl and 128 × 10³ Dfl.y^–1 for subsurface irrigation. Hence, water conservation is economically very profitable, whereas subsurface irrigation is less attractive.Comparing the management according to the model with current practice in a water-board during 1983 and 1986 learned that benefits can increase with some 50 and 500 Dfl per ha per year, respectively.  相似文献   

Water balance estimates of evaporation from ponded rice fields in a semi-arid region   总被引：1，自引：0，他引：1  

T. Talsma  A. Van Der Lelij 《Agricultural Water Management》1976,1(1):89-97

Evaporation from ponded rice grown on fine-textured soils was calculated using a simple water balance equation, and compared with pan evaporation measured at a regional meteorological station. Crop/pan (E_r/E_p) evaporation ratios showed seasonal trends, with values generally exceeding unity during the mid- to late-season ponding period. Mid-summer ratios of E_r/E_p for two experimental fields were not significantly different from those reported in a previous study using a different experimental technique, but were higher on a third. On the average, evaporation over the whole ponding period equalled that from a Class A pan. The assumption that the infiltration or seepage term of the water balance may be neglected for fine-textured soils would seriously overestimate E_r on one of the three experimental sites.  相似文献   

Effects of cover crop quality and quantity on nematode-based soil food webs and nutrient cycling     

S. Tianna DuPont  Howard Ferris  Mark Van Horn 《Applied soil ecology》2009,41(2):157-167

Soil food webs cycle nutrients and regulate parasites and pathogens, services essential for both agricultural productivity and ecosystem health. Nematodes provide useful indicators of soil food web dynamics. This study was conducted to determine if nematode soil food web indicators and crop yield can be enhanced by combinations of cover crops in a conservation tillage system. The effects of three cover crop treatments (vetch/pea, oat/wheat and oat/wheat/pea/vetch) with low, medium and high C:N and a bare fallow control were investigated in Davis, CA. Nematode fauna, soil properties and plant productivity were measured. Soil food web indices, including the Enrichment Index (EI), Structure Index (SI), Basal Index (BI), and Channel Index (CI), based on the composition of nematode assemblages, were calculated to infer soil food web condition. Cover cropped tomato/corn rotations had twice the number of enrichment opportunist bacterial feeding nematodes, active participants in nitrogen mineralization, than fallowed tomato/corn rotations (opportunist bacterial feeders = 163 versus 98). In winter fallowed plots food webs were basal, common in disturbed, nutrient-poor conditions (BI = 37). Total number of enrichment opportunist nematodes, soil NH₄-N levels, and inferred nitrogen mineralization, were higher in cover crop treatments with low to mid C:N ratios. Omnivore and predator nematodes were scarce, averaging less than 6 nematodes 100 g^?1 in all treatments. In year one, plant productivity was highest after fallow. In contrast, in year two productivity was highest after cover crops with high nitrogen content and productivity significantly correlated with the structure of the soil fauna. Monitoring the abundance of enrichment opportunists may provide managers with a new tool to evaluate soil food web nitrogen mineralization and plant productivity.  相似文献   

Determining soil organic carbon for agricultural soils: a comparison between the Walkley & Black and the dry combustion methods (north Belgium)     

J. Meersmans  B. Van Wesemael  M. Van Molle 《Soil Use and Management》2009,25(4):346-353

Mapping soil organic carbon (SOC) and establishing any change over time are important because of CO₂ fluxes between soil and atmosphere and cropland decreases in SOC. The latter is one of the main causes of soil fertility decline and increased erodibility. As most analytical methods underestimate total SOC content, correction factors are needed to avoid methodological bias when comparing SOC data from sampling campaigns using different analytical procedures. The traditional method for SOC analysis used to be, and in most cases still is wet oxidation in potassium dichromate, better known as the Walkley & Black method. In this study, we aim to estimate correction factors for the classic and modified version of the Walkley & Black method for different land use and soil type combinations for agricultural soils in north Belgium. General correction factors of 1.47 for the classic Walkley & Black method and 1.20 for the modified Walkley & Black method are proposed. The results show that sandy grassland soils are characterised by lower recoveries than silt loam grassland soils. Furthermore, the correction factor appears to increase with soil wetness.  相似文献   

Chronology of plaggic deposits; palynology,radiocarbon and optically stimulated luminescence dating of the Posteles (NE-Netherlands)     

J.M. Van Mourik  R.T. Slotboom  J. Wallinga 《CATENA》2011,84(1-2):54-60

Plaggic agriculture was the dominant land use system on Pleistocene sandy soils in Northwest Europe before the introduction of chemical fertilizers. In the today's landscape plaggic deposits are still recognizable as characteristic soils and landforms, related to this historical land use system. They are also important constituents of the soil archives in Northwest Europe. In preliminary studies of plaggic anthrosols, the reconstruction of the development of the plaggic deposits was based on palynological and historical data and radiocarbon dates. Disagreement appeared between palaeopedological and historical explanation of the evolution of plaggic anthrosols. Application of OSL dating improves the knowledge of chronology of plaggic deposits. The soil organic matrix, including pollen grains, consists of a complex mix of compounds of different ages and sources. Pollen diagrams of plaggic anthrosols show a palynological registration of the Late Holocene landscape evolution, but the palynological signal is not consequently correlated with the age of the plaggic sediments. An older soil organic matrix is suspended in the voids of a younger mineral soil skeleton.  相似文献