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51.
52.
This is the first morpho-histological comparison of guanaco ovaries between reproductive (long-days) and non-reproductive (short-days) seasons, and oestrogen receptor-alpha (ERα) and beta (ERβ) detection. Different stages of follicle development were found in the cortical area, but no corpus luteum was detected. The size and frequency of antral follicles and large atretic follicles were higher in long-day ovaries than short-days, consistent with ovarian activity in this season. Differential expression of ERα and ERβ was observed in follicles at different stages of development between short and long days. These data reveal histological and molecular differences between reproductive and non-reproductive seasons of guanaco ovaries.  相似文献   
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54.
In most cases, when calculating soil water availability, only thewater content is considered. The effect of salinity on the wiltingpoint is neglected. The objective of this work is to use asimulation model (CERES-maize) in order to predict cornyields as a function of water salinity under severalenvironmental, agrotechnical, and plant characteristics. A modelis presented in which the wilting point is a function of the soilsalt content. At high salinity, the water content at wilting pointis higher than at low salinity, resulting in an insufficient amountof available water and, therefore, a reduced yield. The modelwas used to simulate several theoretical and experimentalsituations for forage corn and grain corn. Simulation resultsshowed that nitrogen fertilization increases the salinity thresholdvalue and the yield sensitivity (rate of yield reduction per unitof salinity). The also showed that forage corn is more sensitiveto salinity than grain corn. If the soil is not leached, a heaviersoil texture has a higher salinity threshold value. On the otherhand, if the soil is leached, the soil texture has no influence onthe salinity threshold value and the yield is less sensitive tosalinity in sandy soils. The determination coefficient (r2= 0.75) indicated that the results of the simulations were in goodagreement with the field data.  相似文献   
55.
Landscape Ecology - An understanding of species-habitat relationships is required to assess the impacts of habitat fragmentation and degradation. To date, habitat modeling in fragmented landscapes...  相似文献   
56.
This study evaluated the application of stable isotopes of carbon as an alternative and more accurate method to determine gastrointestinal transit time (GTT) in fish by comparing it to the inert marker method. The stable isotope method detects alterations of the normal carbon flow in a biological system by analyzing naturally occurring isotopes of carbon, contrary to studies based on conventional techniques that apply external markers to the diet to determine GTT through visual observation of the color change in feces. Therefore, 320 pacu, Piaractus mesopotamicus juveniles were reared in 32 tanks under two different temperatures (25 and 29 C). The pacu juveniles received two different diets, one based on ingredients derived from C3 photosynthetic cycle plants and the other based on C4 plant ingredients, both containing titanium oxide (TiO2) as a marker. After 40 d, the isotopic signature of the diets was changed, and the marker was replaced by chromic oxide (Cr2O3). In the isotopic technique, the feces were analyzed to determine the exchange in the isotopic ratio of carbon δ13C. Both methods found that GTT was faster (nearly 6 h) in fish at 29 C when using the C4/C3 feeding strategy and slower in fish at 25 C using the C3/C4 strategy (15 h by inert marker and 18 h by the isotopic method). In conclusion, GTT determination in pacu juveniles using the stable isotope technique exhibits the same accuracy obtained with the inert marker method at temperatures suitable (nearly 29 C) for the metabolism of these animals.  相似文献   
57.
Patterns of stand growth and dominance among individual trees change through stand development. We tested a prediction that large, old plantations of Eucalyptus saligna (Sm.) in Hawaii and Brazil would show a pattern of “reverse” growth dominance, with the largest trees contributing more to stand biomass than to current stand increment. This pattern might develop if the largest trees accounted for a large portion of the total resource use of the stand, but were less efficient at utilizing resources to produce stemwood. The 70-year-old plantation in Hawaii had a stem mass of 610 Mg/ha, compared with 325 Mg/ha in the 66-year-old Brazil plantation. Cumulative frequency plots for both sites showed that dominant trees comprised a very large proportion of total stand mass; the largest 20% of the trees accounted for 50% and 30% of the total stand mass in Hawaii and Brazil, respectively. Contrary to expectations, the largest trees continued to produce a disproportionately large amount of total stand growth, with the largest 20% of trees accounting for 60% (Hawaii) and 40% (Brazil) of stand growth. The frequency distributions resulted in positive growth dominance coefficients (similar to Gini coefficients) of 0.14 for Hawaii and 0.09 for Brazil, rather than negative values that would indicate that reverse growth dominance. The failure of these monoculture Eucalyptus stands to develop reverse growth dominance contrasts starkly with a variety of studies with pine species, which tend to show neutral-to-reverse growth dominance. Indeed, continued dominance of large trees suggests the trees might respond well to silvicultural treatments such as thinning or fertilization. Future work that contrasts patterns of growth dominance among species will be important as a foundation for developing generalizations about trends in growth dominance with stand development.  相似文献   
58.
New mite-borne virus isolates from rakkyo,shallot and wild leek species   总被引:2,自引:0,他引:2  
Flexuous viruses were transmitted from rakkyo (Allium chinense) and wild leek species (especiallyA. commutatum) to plants of crow garlic (A. vineale), by transfer of dry bulb mites. By electron microscope decoration tests using three antisera and by inoculations onto test plants, it was concluded that from each of the two natural host species at least two viruses were isolated. The viruses from wild leeks are both pathogenic onAllium spp. and may be of economic importance. Decoration tests on a virus mixture from shallot obtained earlier, revealed another new mite-borne virus in this species. The mite-borne viruses ofAllium spp. appear to be very common; they are largely diverse and their identification remains difficult.  相似文献   
59.
Crude protein (CP) of forages can be separated into fractions of differentiated abilities to provide available amino acids in the lower gut of ruminants. This knowledge is critical to develop feeding systems and to predict animal responses. We have measured during two growing seasons (1996 to 1997 and 1997 to 1998) the CP fractions of common vetch fresh forage with the objective being to assess the influence of maturity on concentration of CP fractions (as a percentage of total CP) and fraction yields. Fraction B2, which represents true protein of intermediate ruminal degradation rate, was the largest single fraction in common vetch forage (about 40% of CP across seasons and maturity stages). Soluble fractions (A plus B1) were less than 50% of total CP while the unavailable fraction C ranged from 4 to 8% of total CP. As a result, the remaining fraction B3 (true protein of very low degradation rate) only represented 2 to 9% of total CP. Concentration and yield of fraction B3 increased (P < 0.05) from flowering to pod-filling. Results showed that undegraded dietary protein represented a small proportion of total CP in common vetch forage. Moving the harvesting stage from flowering to the pod filling phase allowed for greater yield of undegraded dietary protein.  相似文献   
60.
A longitudinal observational study of 15 red deer farms was carried out in New Zealand for two years from March 1992. The deer were monitored for performance and health problems, and farm management practices were recorded. Numbers at risk were 4,683 hind-years, 2,459 stag-years and 3,202 weaner-years. The numbers of primiparous and adult hinds at risk of losing their progeny by weaning were 653 and 3,364, respectively. Where possible, postmortem examinations were carried out, and organs were sampled for histological and microbiological investigation. Rates of mortality varied with season with most stag and hind deaths in winter and weaner deaths in autumn and winter. Overall mortality rates were 1.77, 2.60 and 5.87 per 100 deer-years for hinds, stags and weaners, respectively. Malignant catarrhal fever accounted for 0.53 stag and 0.17 hind deaths per 100 deer-years at risk Misadventure, including broken bones, accounted for 15.4 per cent of weaner mortalities, or 0.53 weaner mortalities per 100 weaner-three months in autumn. Yersiniosis was confirmed in 18.6 per cent of weaner deaths, or 1.09 weaners per 100 weaner-years during the first six months after weaning, but was also suspected but unconfirmed in a further 41 per cent of weaner mortalities. Overall, 17 per cent of yearling hinds, and 9.2 per cent of adult hinds lost their progeny between pregnancy diagnosis in June and weaning in March. One outbreak of osteochondrosis was recorded. Mortality rates varied between farms and many mortalities were preventable.  相似文献   
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