利用牧草生长-消费模型优化草场放牧方案

从理论上探讨了草场生态系统牧草的生长过程和消费过程,采用数学模型方法模拟了两者的动态变化规律,分析了两者在草场生态系统生态平衡中的作用机制．运用牧草的生长和消费模型模拟特定生产周期内草场生态系统的累积牧草消费量,提出优化的草场放牧方案。为实际生产提供参考依据．     

Effect of grazing on plant patterns in arid ecosystems of Patagonian Monte

Our objective was to assess the relationship between the spatial patterning of perennial grasses (total, grazed, and non‐grazed) and shrub patches in rangelands under different grazing pressures of the Patagonian Monte. We selected three grazed paddocks with the usual stocking rate for the area, where previous studies showed that a piosphere formation is common. At each paddock, we analysed the grain of heterogeneity at sites located at two distances from the single watering point (near, far), using high‐resolution aerial photographs. At these sites, we also assessed in the field the density, size, cover, and spatial patterning of grazed and non‐grazed perennial grasses and shrub patches. The grain of heterogeneity of shrub patches was coarser in sites near the watering point than in those distant from it, as a consequence of the increase in size of both, bare soil and shrub patches. Field sampling showed that a coarse grain of heterogeneity relative to fine‐grained sites resulted from changes in species composition, increased bare soil areas and reduced perennial grass cover. In coarse‐grained sites, lower perennial grass cover resulted from lower density and/or smaller size of grass bunches than in fine‐grained sites. We did not find significant differences among sites in the proportion of perennial grazed grasses. Since the density and cover of perennial grasses was higher in fine‐ than in coarse‐grained sites, we suggested that fine‐grained sites are more important as feeding stations than coarse‐grained sites. The consequences of this differential use could lead to degradation of fine‐grained sites and to higher homogeneity in spatial plant structure and floristic composition within paddocks with respect to the condition observed at present, increasing the size of the highly degraded zone within the piosphere. At the patch level, we found that at about one third of the sampled transects, both total and non‐grazed perennial grasses were spatially aggregated with shrub patches. However, in most transects grazed perennial grasses were indifferently distributed in relation with shrub patches, showing that grazers display high selectivity of foraging sites at macro level (i.e. high and low grazing pressure sites at the paddock level), but random occupancy of vegetation units (randomness in the distribution of grazed perennial grasses at the patch level). The intensity of the positive association between non‐grazed grasses and shrub patches was higher in fine‐grained than in coarse‐grained sites and may be attributed to higher protection against herbivores associated to denser shrub patches in fine‐ relative to coarse‐grained sites. We concluded that a feedback exists between the spatial distribution of species preferred by grazers and the spatial patterning of use of these species.     

Fish larvae, growth and biomass relationships in an Australian arid zone river: links between floodplains and waterholes

1. Floodplain inundation provides many benefits to fish assemblages of floodplain river systems, particularly those with a predictable annual flood pulse that drives yearly peaks in fish production. In arid‐zone rivers, hydrological patterns are highly variable and the influence of irregular floods on fish production and floodplain energy subsidies may be less clear‐cut. To investigate the importance of floodplain inundation to a dryland river fish assemblage, we sampled fish life stages on the floodplain of Cooper Creek, an Australian arid‐zone river. Sampling was focused around Windorah during a major flood in January 2004 and in isolated waterholes in March 2004 following flood drawdown. 2. Of the 12 native species known to occur in this region, 11 were present on the floodplain, and all were represented by at least two of three life‐stages – larvae, juveniles or adult fish. Late stage larvae of six fish species were found on the floodplain. There were site‐specific differences in larval species assemblages, individual species abundances and larval distribution patterns among floodplain sites. 3. Significant growth was evident on the floodplain, particularly by larval and juvenile fish, reflecting the combination of high water temperatures and shallow, food rich habitats provided by the relatively flat floodplain. 4. Low variation in biomass, species richness and presence/absence of juvenile and adult fish across four floodplain sites indicates consistently high fish productivity across an extensive area. 5. Similarities and differences in fish biomass between the floodplain and isolated post‐flood waterholes suggest high rates of biomass transfer (involving the most abundant species) into local waterholes and, potentially, biomass transfer by some species to other waterholes in the catchment during floodplain inundation and after floods recede. 6. The high concentration of fish on this shallow floodplain suggests it could be a key area of high fish production that drives a significant proportion of waterhole productivity in the vicinity. The Windorah floodplain provides favourable conditions necessary for the spawning of some species and juvenile recruitment of the majority of species. It is also appears to be a significant conduit for the movements of fish that underpin high genetic similarity, hence population mixing, of many species throughout the Cooper Creek catchment. The high floodplain fish production in turn provides a significant energy subsidy to waterholes after floodwaters recede. 7. The identification of key sites of high fish production, such as the Windorah floodplain, may be important from a conservation perspective. Key management principles should be: maintenance of the natural flooding regime; identification of the most productive floodplain areas; and maintenance of their connectivity to anastomosing river channels and the remnant aquatic habitats that ultimately sustain this fish assemblage through long‐term dry/drought and flood cycles.     

Dynamics of sahelian pastures in relation to drought and grazing

Summary The dynamics of the vegetation were studied in the transition zone from the savannah to the Sahel in order to distinguish between the influence of the recent drought and the influence of overgrazing on the natural rangelands. The drought affected especially the different plant species at the northern limit of their habitat. It is, however, not well possible to speak of a sahelisation of the savannah, since the species in regression were replaced by invaders, like Borreria spp, and not by true Sahelian species. An exception was Blepharis linariifolia, which moved to the south. Grazing affected good fodder grasses like Andropogon gayanus, which were replaced by a legume with a short growth cycle, Zornia glochidiata, and an unpalatable annual grass Elionurus elegans. The species much stimulated by the drought, Borreria spp. and Blepharis linariifolia, did not occur in the intensively grazed pastures.The work was carried out with the assistance of M.M.A. Djittye and A. Sow, Centre National de Recherche Zootechnique Sotuba, N. Diarra, Ecole Normale Supérieure, M. Togola, Station du Sahel, and M.I. Cissé, A. Diallo, L. Diarra, M. Sidibé, G. Traoré, Centre Pédagogique Supérieur     

The effects of sheep grazing on invertebrate numbers and biomass in unfertilized natural pastures of the New England Tablelands (NSW)

Invertebrate components of natural pastures which were grazed continuously by sheep at three stocking intensities, were sampled each season for more than two years. Grazing resulted in a significant reduction in abundance of litter and topsoil micro-arthropods. Two samplings for nematodes and enchytraeids showed similar reductions with grazing. Grazing effects on the vertical distribution of mesofauna were not consistent but all sites had greatest numbers in the 0 – 5 cm topmost soil layer. Fresh biomass of large soil and litter dwelling invertebrates also declined with grazing, with proportionally greater reductions occurring for litter animals. Changes in invertebrate populations were associated with changes in living space, microclimate and food supply. Populations of invertebrates on natural pastures were about one-third those found on previously studied sown, fertilized pastures at Armidale.     

不同放牧率对旱黄梅衣生物量和化学元素组成的影响

对羊草草原群落中旱黄梅衣生物量和化学元素组成与放牧率关系的研究表明,轻度放牧(1.33只羊·hm^-2)时,旱黄梅衣生物量达到最大值,极重牧(6.67只羊·hm^-2)时生物量最低.旱黄梅衣体内C、N、Ca含量较高,＞1%;P、Mg、K、Fe含量介于0.1%～1%;Na、Mg、Cu、Zn、B均＜0.1%.旱黄梅衣中Ca含量明显高于维管植物,是喜Ca植物.放牧处理下,旱黄梅衣含C量下降,N含量提高,C/N比在中度、重度放牧率下较低.Ca、Mg、K、Fe、Mn、Cu含量表现为无牧处理时较低,放牧处理较高.旱黄梅衣的生物量和化学元素组成的变化对放牧强度有着很好的响应,因此可以用旱黄梅衣的生物量和化学元素组成的变化来指示草地生态系统的健康状况和生物地球化学循环特征的变化.     

Interaction of livestock grazing and rainfall manipulation enhances herbaceous species diversity and aboveground biomass in a humid savanna

Journal of Plant Research - Understanding of the interaction of livestock grazing and rainfall variability may aid in predicting the patterns of herbaceous species diversity and biomass production....     

An update on the nutrition of dairy sheep grazing Mediterranean pastures

In the light of recent findings in sheep nutrition and feeding behaviour, the diets of grazing dairy sheep should be based on forages encompassing a variety of complementary nutritional values and containing moderate levels of diverse plant secondary metabolites, until recently regarded as “anti-nutritional”. In lactating sheep, pastures of tannin-containing legumes like sulla (Hedysarum coronarium) and chicory (Cichorium intybus) can be integrated with annual grasses for establishing artificial pastures under rainfed conditions. Diets based on these forages, while ensuring high milking performance, can mitigate the unbalance of CP to energy ratio of grazing sheep. By grazing sulla and Italian ryegrass (50:50 by area) as spatially adjacent monocultures or in timely sequence (complementary grazing) sheep eat more and perform better than by grazing the ryegrass pasture only. Concentrate supplementation of lactating sheep should be preferably based on sources rich in digestible plant fiber (soyhulls or beet pulps), particularly from mid-lactation onwards and when supplementation levels are high. Milk urea concentration is confirmed as a useful monitoring tool to balance protein nutrition and curb the waste of N at animal and system level. Finally, challenging tasks for future research on dairy sheep grazing management and nutrition are on-farm application of recent technological advances, such as image-based estimation of pasture biomass and quality, evaluation of sheep dietary quality by faecal Near Infrared Reflectance Spectrometry, and establishment of remote control systems.     

放牧格局和生境资源对矮嵩草（Kobresia humilis）分株生物量分配和补偿性生长的影响

为研究密集型克隆植物对放牧扰动和生境资源变化的生物量分配和补偿生长响应特性,验证克隆植物的觅食模型和3个有关植物个体补偿反应的假说(①放牧优化假说,grazing optimization hypothesis,GOH;②反应连续谱假说,continuum of responses hypothesis,CRH;③增长率模型,growth rate model,GRM),在具有不同放牧利用格局和土壤养分水平的高寒矮嵩草草甸(Ⅰ.畜圈草地:重度放牧、资源丰富;Ⅱ.牧道草地:中度放牧、资源贫乏;Ⅲ.封育草地:不放牧、资源贫乏)中通过设置扣笼/无扣笼样方对其建群种矮嵩草(Kobresia humilis)进行了研究.结果表明不论当年解除家畜放牧与否,春季采摘率越高(畜圈草地),分株生物量向生长的投入越少,向贮藏器官的投入越多.繁殖分配在中度采摘下最高(牧道草地),扣笼内外分株各部分的生物量分配无差异.矮嵩草分株在中度采摘×资源贫乏条件下产生了超补偿响应,在重度采摘×资源丰富条件下为等量补偿,重度采摘导致分株密度显著减少.生物量分配格局与觅食模型的预测不符.补偿生长响应特性证实了GOH和GRM的预测,但与CRH的预测不符.这说明在研究地区放牧扰动格局对克隆植物矮嵩草分株的生物量分配和补偿生长具有重要影响,适度放牧利用更利于引起超补偿,而重度利用可能会对该种群的长期保持产生不利影响.     

Verotoxin-producing Escherichia coli in sheep grazing an irrigated pasture or arid rangeland forages

Worldwide, verotoxin-producing Escherichia coli (VTEC) have been recognized as the cause of many sporadic cases or major outbreaks of human illnesses involving consumption of contaminated meat, especially beef. Although sheep products have not been linked to reported human illnesses, their role as a food safety risk factor should not be ignored. The objective of this study was to assess VTEC prevalence in two groups of ewes (20 each) grazing an irrigated pasture or arid range in a western United States environment (Nevada) over 1 year (summer of 1999 to summer of 2000). A random sample (n = 504) of potential VTEC isolates were tested for verotoxicity and were screened for the presence (polymerase chain reaction [PCR]) and expression (VTEC-reversed passive latex agglutination assay) of the toxin genes (i.e., VT1 and VT2). Forty-one VTEC isolates (16 having only the VT1 gene and 25 having both VT1 And VT2 genes) were detected in both groups of ewes. Except for seven isolates, the genotype and phenotype data matched. All the isolates (nonmotile [H-]) were non-O157:H7 VTEC (i.e., O91:H- [n = 25], O128:H- [n = 9], and untypeable ones [n = 7]). More infected ewes (nine versus three) and different VTEC strains were found in the irrigated pasture than in the arid range. Because our ewes were shedding two VTEC serotypes known to cause human illnesses, it is beneficial to identify VTEC-positive sheep before slaughter as an initial control point before entering the food chain.     

放牧对小嵩草草甸生物量及不同植物类群生长率和补偿效应的影响

基于小嵩草(Kobresia parva)草甸连续2 a的牦牛放牧试验,研究了暖季和冷季放牧草场地上地下生物量及其分配规律、不同植物类群的绝对生长率生长率,探讨了放牧制度和放牧强度对不同植物类群补偿效应的影响。结果表明,随着放牧强度的增加地上总生物量呈减小趋势,放牧强度对暖季草场地上总生物量的影响极显著（P?0.01）,对冷季草场地上总生物量的影响不显著（P?0.05）;两季放牧草场各土壤层地下生物量随放牧强度的增加呈明显下降趋势,放牧强度对暖季放牧各土壤层地下生物量的影响显著（P?0.05）,对冷季放牧各土壤层地下生物量的影响不显著（P?0.05）;冷季放牧草场牧草生长季地下生物量与地上生物量的比值随放牧强度的增大而减小,暖季放牧草场对照区地下生物量与地上生物量的比值低于轻度放牧和中度放牧、高于重度放牧;暖季放牧草场各放牧处理不同植物类群均存在超补偿生长,但莎草科和禾本科植物的超补偿生长在8月份,阔叶植物的超补偿生长发生在6月和7月份,禾本科植物的超补偿生长效应强于莎草科植物和阔叶植物,轻度和中度放牧的补偿效应更明显;冷季放牧下不同植物类群也存在超补偿生长,但补偿效应不明现。因此,暖季适度（轻、中度）放牧利用更有利于产生超补偿生长,而重度利用对植被的稳定产生潜在的不利影响。     

Effect of herbivory on the growth and photosynthesis of replanted Calligonum caput-medusae saplings in an infertile arid desert

Replanted Calligonum caput-medusae saplings in the Tarim River watershed face short-term and frequent herbivory by goats, which can result in either growth inhibition or stimulation. The effects of herbivory on shrub saplings are unclear. We simulated herbivory with clipping to test two hypotheses. We hypothesized that (1) moderate herbivory may positively affect replanted shrub saplings due to overcompensatory growth and compensatory photosynthesis and that (2) high amounts of defoliation may change water availability and impair photosynthesis and growth of saplings. We applied four defoliation treatments (0, 30, 50, and 70 %) to 2-year-old C. caput-medusae saplings to test the effects of herbivory. Moderately defoliated (~30 %) saplings grew faster and had higher photosynthetic performance than controls; however, defoliation of 50 % or more reduced growth due to undercompensatory photosynthesis and reduced water availability. Non-photochemical quenching by thermal dissipation provided photoprotection when absorbed light energy used in PSII photochemistry was inhibited, reducing excess excitation energy and allowing saplings with high amounts of defoliation to maintain adequate photosystem functioning. This suggests that moderate herbivory of replanted shrubs used as forage in arid ecological restoration projects is feasible, but that uncontrolled grazing should be forbidden.     

Adjusting homestead feeding to requirements and nutrient intake of grazing goats on semi-arid, subtropical highland pastures

Intensive livestock grazing can largely deplete the natural fodder resources in semi-arid, subtropical highlands and together with the low nutritional quality of the pasture vegetation limit the growth and production of grazing animals. To evaluate the contribution of homestead feeding of grazing goats to rangeland conservation and animal nutrition, two researcher-managed on-farm trials were conducted in a mountain oasis of Northern Oman. Goats' feed intake on pasture in response to four rations containing different levels of locally available green fodder and concentrate feeds was determined in six male goats each (35 ± 10.2 kg body weight (BW)). Total feed intake was estimated using titanium dioxide as external fecal marker as well as the diet organic matter (OM) digestibility derived from fecal crude protein concentration. The nutritional quality of selected fodder plants on pasture was analyzed to determine the animals' nutrient and energy intake during grazing. The pasture vegetation accounted for 0.46 to 0.65 of the goats' total OM intake (87 to 107 g/kg0.75 BW), underlining the importance of this fodder resource for the husbandry system. However, metabolizable energy (7.2 MJ/kg OM) and phosphorus concentrations (1.4 g/kg OM) in the consumed pasture plants were low. Homestead feeding of nutrient and energy-rich by-products of the national fishery and date palm cultivation to grazing goats increased their daily OM intake (R2 = 0.36; P = 0.005) and covered their requirements for growth and production. While the OM intake on pasture was highest in animals fed a concentrate-based diet (P = 0.003), the daily intake of 21 g OM/kg0.75 BW of cultivated green fodder reduced the animals' feed intake on pasture (R2 = 0.44; P = 0.001). Adjusting homestead supplementation with locally available feedstuffs to the requirements of individual goats and to the nutritional quality of the pasture vegetation improves animal performance and eases the grazing pressure exerted on the natural vegetation. This management strategy therefore appears to be a valuable alternative to intensive livestock feeding in zero-grazing systems and may contribute to sustainable livestock production in ecologically fragile, semi-arid mountain regions.     

Effect of genetic type, lactation and management on helminth infection of ewes in an intensive grazing system on irrigated pasture.

A survey of helminth infection was conducted in a flock of 290 ewes distributed into Romanov (R), Merinos d'Arles (M) and Romanov x Merinos (R x M) genetic types, grazing irrigated pasture in the south of France. Faecal egg and larval counts were done seven times per year from 1981 to 1984 on homogeneous groups of ewes and then individually once to four times every autumn from 1985 to 1988. Helminth fauna was diverse and more abundant during autumn. High levels of strongyle infection occurred in the ewes that remained on the same irrigated pastures during summer. Moving to Alpian pastures during the summer lowered autumnal infection. Significant differences between genotypes in intensity of infection were observed in the order R > R x M > M for strongyles (Teladorsagia circumcincta and/or Trichostrongylus vitrinus, Chabertia ovina and/or Oesophagostomum venulosum, Nematodirus spp.), Moniezia spp. and Dictyocaulus filaria. The hierarchy was reversed for Fasciola hepatica infection and not consistent from one year to another for protostrongylid infections. The effect of lactation intensity on the postparturient rise was studied by equilibrating number of ewes according to reproductive status (zero, one or two lambs in lactation). Merino ewes with two lambs in lactation, as well as primiparous Romanov ewes, had significantly higher strongyle infections than the others. The repeatabilities of the larval and egg counts between the four trial years were 0.24, 0.23 and 0.16, respectively, for protostrongyles, Nematodirus and strongyles, with higher intra-annual values for protostrongyles and inconsistently significant results for strongyles due to the presence of several species.     

Effect of grazing system on fetal development in Nellore cattle

Intensive grazing systems for beef females, based on abundant availability of high quality forages and supplementary concentrates, may affect fetal development. The objective of this study was to determine the effect of grazing system on length of gestation, fetal development, and characteristics of the calf at birth. Twenty-four pregnant (bred to Nellore bulls) Nellore females were allocated into two groups. The control group (G1) grazed Brachiaria decumbens (signal grass) in a traditional (extensive) grazing system and the second group (G2) were managed on Panicum maximumcv. Tanzania 1 (Tanzania grass) in an intensive grazing system. Fetal development was evaluated by ultrasonography on days 31, 45, 59, 94, 122, 220, and 255 of gestation. The diameter of the amniotic and allantoic cavities, crown-rump length, circumference, and diameter of the head and ocular orbit were determined. At birth, calves were weighed and height, length, thoracic circumference, and ocular orbit and bi-parietal diameters were measured. There were no differences (P > 0.05) in fetal development. The G1 cows had a longer gestation period (4.5 days; P<0.05) and their calves had greater (P<0.05) weight, height, length, and thoracic circumference at birth. In conclusion, Nellore females raised under intensive pasture management conditions, had significantly shorter gestation and smaller calves at birth than those raised under extensive pasture management conditions. Therefore, adoption of new management practices (e.g. intensive pasture management), should take into consideration animal behavior and productivity.     

Effect of growth rate and hydrophobicity on bacteria surviving protozoan grazing

Measurements were made of the predation by Tetrahymena thermophila on several bacterial species in media containing heat-killed Escherichia coli cells to serve as an alternative prey. If grazing pressure was initially not intense on a mixture of bacterial species, the species that survived protozoan feeding at greater densities were those that grew quickly before the onset of active predation. If members of several species were incubated individually at similar initial densities with actively grazing T. thermophila, some species survived at ca. 10(4)/ml, some survived at ca. 10(2)/ml, and others were eliminated. Members of the first two groups but not the third group were able to multiply in the medium in the absence of the protozoan, but the growth rates in the protozoan-free medium did not correlate with the number of survivors. However, the species that persisted at the higher densities possessed highly hydrophobic cell surfaces. The size of the surviving population of four bacterial species whose growth was prevented by chloramphenicol correlated with the initial cell density that was incubated with T. thermophila. It is concluded that the individual species surviving predation on a mixture of species is related to the capacity of the bacterium to grow, the hydrophobicity of its cell surface, and the population density of the species before the onset of intense grazing.