Digestibility, faeces recovery, and related carbon, nitrogen and phosphorus balances of five feed ingredients evaluated as fishmeal alternatives in Nile tilapia, Oreochromis niloticus L.

This study shows that alternatives for fishmeal in a fish diet affect not only fish growth but also faeces stability and nitrogen (N) and phosphorus (P) waste production. Wheat gluten diet (WGD), soybean meal extract diet (SBE), soybean meal diet (SBM), duckweed diet (DWD) and single‐cell protein diet (SCP) were evaluated as a fishmeal replacement on a 15% weight weight^?1 basis in tilapia diets. Fishmeal replacement affected dry matter (dm), protein, ash and P digestibility significantly. Faeces recovery (6.8–11.2%) was not significantly affected, although the amount of non‐recovered faeces and total faeces showed significant differences. Duckweed diet and SCP resulted in the largest amounts of non‐recovered and total faeces (199–210, 224–225 g dm kg^?1 feed dm). Compared with fishmeal diet (FMD), the WGD and SBE resulted in similar growth, but higher non‐faecal N losses (471–495 vs. 416 g N kg^?1 N). Soybean meal diet, DWD and SCP resulted in lower growth but less non‐faecal loss (409–450 g N kg^?1 N). The DWD and FMD had the highest N retention (480 g N kg^?1 N) compared with the other diets (431–451 g N kg^?1 N). Carbon retention, faecal and non‐faecal losses and P retention were similar for all diets (302–358, 142–176 and 489–523g C kg^?1 C, 606–704 g P kg^?1 P). Phosphorus faecal loss was lower for all diets (329–381 g P kg^?1 P) than for the FMD (401 g P kg^?1 P).     

Comparison of faecal collection method with high- and low-quality diets regarding digestibility and faeces characteristics measurements in Nile tilapia

The need for unbiased digestibility estimation has led to the development of a number of faeces collection methods. However, there is still a large variation in apparent digestibility coefficient (ADC) of diet/ingredients between these methods. This study investigated the impact of dietary quality on ADC and faeces recovery measurements obtained by two faecal collection methods (Choubert and settling tank). The fish were fed five diets: a control diet as high‐quality diet, two levels of dried duckweed (20% and 40%) and two levels of fresh duckweed (20% and 40%), which were added to the control diet, as low‐quality diets. Apparent digestibility coefficient estimates were highly correlated (r>0.95) between both faecal collection methods. For all diets the ADC estimates were higher when using settling tanks compared with Choubert collectors. For the control diet differences in ADC between two collectors were small, but by inclusion of duckweed these differences increased. The recovery percentage of faeces was not correlated between both faecal collection methods (r=0.22, P=0.41). The estimated recovery percentage of faeces by settling tanks was about three times higher than by Choubert. In conclusion, the differences in ADC and faeces recovery measured by two faecal collection methods depend on diet quality.     

Molasses as C source for heterotrophic bacteria production on solid fish waste

The drumfilter effluent from a recirculation aquaculture system (RAS) can be used as substrate for heterotrophic bacteria production. These bacteria can be reused as aquatic feed. In RAS drumfilter effluents are organic carbon deficient for bacteria production. This is due to nitrogen accumulation in the system water. In the present experiment, a bacteria growth reactor (3.5l) was connected to the drumfilter (filter mesh size 60 μm) outlet of a recirculation system. To counteract carbon deficiency, different supplementation levels of molasses (organic carbon) were tested (carbon fluxes of 0.0, 3.2, 5.8, 7.8, 9.7 gC molasses/l/d; C:N ratios: 3.4, 6.4, 9.4, 13.0 and 16.5). The hydraulic retention time in the bacteria reactor was 6 h. For the maximum flux, the VSS and crude protein productions were about 168 gVSS and 95 g crude protein per kg feed. The maximum conversion of nitrate and ortho-phosphate was 24 g NO₃₋N and 4 gP/kg feed. This equals a conversion of 90% of the inorganic nitrogenous waste and 98% of the ortho-phosphate-P. Furthermore the maximum substrate removal rate and the K_s for molasses were determined (1.62 gC/l/h and 0.097 gC/l respectively). The maximum specific removal rate was 0.31 gC/gVSS/h and the related half saturation constant was 0.008 gC/l. The observed growth rate reached a maximum for C fluxes higher than 8 g/l/d. The present integration of heterotrophic bacteria production in RAS represents, therefore, an innovative option to reduce waste discharge by conversion. If the bacteria are reused as feed, system's ecological sustainability increases.     

Prevalence of VTEC O157 in dairy and veal herds and risk factors for veal herds

The aim of this study was to determine the herd prevalence of veal and dairy herds and to identify risk factors for VTEC O157 positive veal herds. The study was based on monitoring data from November 1996 through July 2005 of 1051 dairy herds and 930 veal herds. The herd level prevalence (95% CI) was 8.0% (6.4–9.6) for dairy herds and 12.6% (10.5–14.7) for veal herds. Within the population of veal herds, a prevalence of 39.8% (33.9–45.6) was found for pink veal herds (n = 269) and 1.5% (0.7–2.8) for white veal herds (n = 661).Multivariable logistic regression showed that the type of veal (pink vs. white; OR = 21.6; 95% CI: 10.4–45.0), ventilation (mechanical vs. natural; OR = 0.4; 95% CI: 0.2–0.8), time between arrival in the herd and sampling (3–5 months vs. 0–2 months: OR = 2.33; 95% CI: 1.1–5.1, ≥6 months vs. 0–2 months: OR = 4.11; CI: 1.9–8.9), other feed than the 7 most common (yes vs. no; OR = 2.1; 95% CI: 1.2–3.7) and at least one dog present in the stable (yes vs. no; OR = 2.6; 95% CI: 1.5–4.6) were significantly (P < 0.05) associated with the presence of VTEC O157. The large difference in the VTEC O157 prevalences for pink veal and white veal production might have been caused by a very different management of these type of herds. However, this could not be studied with the data collected.     

Postharvest water relations in cut rose cultivars with contrasting sensitivity to high relative air humidity during growth

A constant high relative air humidity (RH) during cultivation can strongly reduce the vase life in some cut rose cultivars. We studied three contrasting cultivars in their tolerance to high RH in order to analyse in detail the water relations during postharvest and better understand this genotypic variation. Plants were grown at moderate (60%) and high (95%) RH, and cut flowers were placed in water immediately after cutting. Flowers of cv. Pink Prophyta grown at high RH did not open throughout vase life, while flower opening of cvs. Frisco and Dream was not affected by preharvest RH. Cultivation at high RH resulted in about 80% shorter vase life in Pink Prophyta, whereas in Dream and Frisco the negative effect was considerably smaller (15 and 9% shorter vase life, respectively). The shorter vase life and reduced flower opening of cut roses grown at high RH was due to a higher rate of transpiration both in the light and dark periods. It was found that the leaves of Pink Prophyta grown at high RH could partly close their stomata upon lowering of the water potential or when flower stalks were fed with abscisic acid, but stomata remained far more open than in leaves grown at moderate RH. The RH during cultivation did not affect stem hydraulic conductivity and its recovery after air emboli induction. Preventing vascular occlusion largely alleviated the high-cultivation-RH effect on vase life and flower opening, showing that the effect of high-cultivation-RH becomes only important if water uptake is limited.     

Pedometric mapping of soil organic matter using a soil map with quantified uncertainty

This paper compares three models that use soil type information from point observations and a soil map to map the topsoil organic matter content for the province of Drenthe in the Netherlands. The models differ in how the information on soil type is obtained: model 1 uses soil type as depicted on the soil map for calibration and prediction; model 2 uses soil type as observed in the field for calibration and soil type as depicted on the map for prediction; and model 3 uses observed soil type for calibration and a pedometric soil map with quantified uncertainty for prediction. Calibration of the trend on observed soil type resulted in a much stronger predictive relationship between soil organic matter content and soil type than calibration on mapped soil type. Validation with an independent probability sample showed that model 3 out‐performed models 1 and 2 in terms of the mean squared error. However, model 3 over‐estimated the prediction error variance and so was too pessimistic about prediction accuracy. Model 2 performed the worst: it had the largest mean squared error and the prediction error variance was strongly under‐estimated. Thus validation confirmed that calibration on observed soil type is only valid when the uncertainty about soil type at prediction sites is explicitly accounted for by the model. We conclude that whenever information about the uncertainty of the soil map is available and both soil property and soil type are observed at sampling sites, model 3 can be an improvement over the conventional model 1.     

Genetic and QTL analyses of yield and a set of physiological traits in pepper

An interesting strategy for improvement of a complex trait dissects the complex trait in a number of physiological component traits, with the latter having hopefully a simple genetic basis. The complex trait is then improved via improvement of its component traits. As first part of such a strategy to improve yield in pepper, we present genetic and QTL analyses for four pepper experiments. Sixteen traits were analysed for a population of 149 recombinant inbred lines, obtained from a cross between the large-fruited pepper cultivar ‘Yolo Wonder’ (YW) and the small fruited pepper ‘Criollo de Morelos 334’ (CM334). The marker data consisted of 493 markers assembled into 17 linkage groups covering 1,775 cM. The trait distributions were unimodal, although sometimes skewed. Many traits displayed heterosis and transgression. Heritabilities were high (mean 0.86, with a range between 0.43 and 0.96). A multiple QTL mapping approach per trait and environment yielded 24 QTLs. The average numbers of QTLs per trait was two, ranging between zero and six. The total explained trait variance by QTLs varied between 9 and 61 %. QTL effects differed quantitatively between environments, but not qualitatively. For stem-related traits, the trait-increasing QTL alleles came from parent CM334, while for leaf and fruit related traits the increasing QTL alleles came from parent YW. The QTLs on linkage groups 1b, 2, 3a, 4, 6 and 12 showed pleiotropic effects with patterns that were consistent with the genetic correlations. These results contribute to a better understanding of the genetics of yield-related physiological traits in pepper and represent a first step in the improvement of the target trait yield.     

Abortion of reproductive organs in sweet pepper (Capsicum annuum L.): a review

Summary

Levels of abortion of reproductive organs (i.e., buds, flowers, and young fruits) in sweet pepper plants (Capsicum annuum L.) are high, and cyclical fluctuations occur in fruit set. Stages susceptible to abortion are very young buds (< 2.5 mm), buds close to anthesis, and flowers and fruits up to 14 d after anthesis. An overview of factors and processes involved in flower and fruit abortion in sweet peppers is presented. More light, higher CO₂ concentrations, and lower planting density, increase the availability of assimilates per plant, and decrease fruit abortion. The cyclical pattern in fruit set is caused by changes in demand for assimilates. High flower abortion occurs when fast growing fruit (at approx. 3 weeks after anthesis) are present, due to competition for assimilates. Fruit set increases when fast growing fruit are almost mature and have a low assimilate demand. Prior to abortion, auxin export from the reproductive organ diminishes, ethylene production increases, and lower levels of activity of sucrose-cleaving enzymes are found. Severe water stress and low nutrient supply also increase abortion levels. Low night- and high day-time temperatures hamper pollen development, causing low seed set, which can result in fruit abortion. Two theories have been used to explain abortion: unbalanced demand for and supply of assimilates, and hormonal dominance of developing fruit over young fruit. Attempts to prevent abortion or to diminish the cyclical pattern of fruit set have not yet been successful, but new suggestions are presented.