母猪的窝产仔数取决于胚胎早期存活率

窝产仔数是决定养猪场盈利的关键因素之一,通常以窝初生仔数或者窝断奶仔猪数表示。遗传和营养因素在窝产仔数上起着很大的影响,且主要于妊娠的最初25d发挥作用,妊娠25d后则影响不大。因此,深入了解影响早期胚胎存活率的因素及其作用机理对提高母猪生产率有着重要的意义。     

能提高动物生产性能的靶向释放酸化剂

<正>据饲料原料的供应情况、消费者的担忧、法律法规的约束和收益性分析等改变动物的营养和家畜的生产,已促使养猪生产者重新探讨饲料的组成。不幸的是,还出现了多种肠道疾病(如肠炎、腹泻、痢疾、大肠杆菌病以及沙门氏菌病等)联合爆发的情况,这种情况在以前是很少见的。养猪生产者目前面临着新的挑战,如饲料的重新配制、无抗生素生产体系的建立,同时要保持低成本的生     

Does synergized pyrethrin applied over wetlands for mosquito control affect Daphnia magna zooplankton or Callibaetis californicus mayflies?

BACKGROUND: Public health agencies may apply aerosolized synergized pyrethrin over wetlands repeatedly to control mosquitoes. This concerns wildlife managers because studies have shown the accumulation of pyrethroids, which are chemically similar to pyrethrin, in sediments in amounts that can be toxic to invertebrates. The authors tested whether repeated applications of synergized pyrethrin over wetlands caused mortality of two aquatic invertebrates: the zooplankton Daphnia magna Straus and a mayfly, Callibaetis californicus Banks. Fifteen wetland mesocosms were either exposed to repeated pyrethrin sprays or were protected by lids. Invertebrates in screened cages were placed in mesocosms before the fifth and eleventh spray, and directly into wetlands before spray 11. Six mesocosms were exposed to spray deposition. Caged adult mosquitoes were used to verify that sprays drifted over mesocosms. Sediments were analyzed for insecticide residues.RESULTS: There were no detectable effects of synergized pyrethrin on 36 h survival of Daphnia or mayflies, but most exposed adult mosquitoes died. Some exposed sediments yielded pyrethrin (< or =34.5 ng g(-1)); most showed piperonyl butoxide (PBO) (< or =14.9 ng g(-1)).CONCLUSIONS: Deposition of aerosolized 25% pyrethrin + 5% PBO may contaminate wetlands, but its application at rates used for mosquito control did not produce detectable effects on indicator species.     

Characterization and plant expression of a glyphosate-tolerant enolpyruvylshikimate phosphate synthase

BACKGROUND: Glyphosate tolerance is a dominant trait in modern biotech crops. RESULTS: A gene encoding a glyphosate-tolerant EPSP synthase (aroA(1398)) from bacterial strain ATX1398 was cloned and characterized. The protein is initiated at a GTG translational start codon to produce a protein that provides robust glyphosate resistance in Escherichia coli (Mig) Cast & Chalm. The aroA(1398) protein was expressed and purified from E. coli, and key kinetic values were determined (K(i) = 161 microM; K(m)(PEP) = 11.3 microM; k(cat) = 28.3 s(-1)). The full-length enzyme is 800-fold more resistant to glyphosate than the maize EPSP synthase while retaining high affinity for the substrate phosphoenol pyruvate. To evaluate further the potential of aroA(1398), transgenic maize events expressing the aroA(1398) protein were generated. T(0) plants were screened for tolerance to glyphosate sprays at 1.3x commercial spray rates, and T(1) plants were selected that completely resisted glyphosate sprays at 1x, 2x and 4x recommended spray rates in field trials. CONCLUSION: These data suggest that aroA(1398) is a suitable candidate for conferring glyphosate tolerance in transgenic crop plants.     

A baseline classification of riparian woodland plant communities in the Okavango Delta,Botswana

In the Okavango Delta information on the riparian woodland vegetation community composition and distribution is generally lacking. Past studies in the Delta were mainly focused on the quantitative classification of seasonal floodplain herbaceous vegetation communities. The aim of this study was to determine riparian woodland vegetation communities in the Okavango Delta. Vegetation sampling was conducted in 20?m × 50?m randomly placed plots. The plots were placed along a gradient from the main water body to the drier fringe of the riparian zone. Plant species present in each plot were recorded with their estimated percentage cover using the Braun–Blanquet cover abundance scale. Hierarchical cluster analysis was used to determine vegetation communities. Indicator species analysis was used to calculate indicator values for species groups defined from the cluster analysis. Plant species and diversity were determined for each vegetation cluster. Multi-response permutation procedures (MRPP) were used to determine significance of differences between communities. The Kruskal–Wallis test was used to compare species diversity and richness between vegetation communities. Four vegetation communities were identified: Croton megalobotrys– Hyphaene petersiana, Vachellia erioloba–Diospyros lycioides, Syzygium cordatum–Phoenix reclinata and Garcinia livingstonei–Senegalia nigrescens. In this classification, the Syzygium cordatum–Phoenix reclinata and Garcinia livingstonei–Senegalia nigrescens plant communities are found in frequently flooded regions, whereas the Croton megalobotrys–Hyphaene petersiana and Vachellia erioloba–Diospyros lycioides are in occasionally flooded regions. Total number of species was highest in the Garcinia livingstonei–Senegalia nigrescens and lowest in the Syzygium cordatum–Phoenix reclinata vegetation communities. The MRPP showed that there was significant (p < 0.05) differences between vegetation communities. Species diversity and richness were significantly (p < 0.05) higher in the Garcinia livingstonei–Senegalia nigrescens vegetation community. This study provided an inventory of riparian woodland plant communities, which can be used as a vital monitoring tool of vegetation change in the Okavango Delta.     

Small-Scale Spatial Variability of Plant Nutrients and Soil Organic Matter: An Arable Cropping Case Study

Soil properties can vary spatially due to differences in topography, parent material, and land management practices. For site-specific management within the field, information on spatial variation of soil properties is essential. This case study was conducted to quantify the spatial variability of available plant nutrients and organic matter under arable cropping in New Zealand. Within a 10.4-ha paddock that had a long-term history of arable cropping, 91 samples (0–7.5 cm) were collected in a grid pattern for determination of mineral nitrogen (Min N), anaerobically mineralizable N (AMN), Olsen P, total carbon (TC), and total N (TN). The data were evaluated using geostatistical and classical statistical methods. Although the paddock had a flat topography and had been managed uniformly for many years, nutrient concentrations exhibited substantial variability. All measured variables except mineral N showed moderate positional dependence. Autocorrelation distances were 400 m for Olsen P, 293 m for AMN, and 347 m for TC. Soil C showed a strong, positive correlation with the amount of clay plus fine silt (<5 µm fraction) and a negative correlation with sand content. These results suggest that textural variation was a major factor influencing within-field variability in soil organic matter. Using the spatial data, zones with different plant nutrient requirements were identified (four for N; two for P). An application strategy that accounts for fertility differences between zones may improve fertilizer use efficiency and contribute to better environmental outcomes; P inputs could be reduced by 50% by avoiding application to the high Olsen P zone.