牦牛放牧率对小嵩草高寒草甸不同植物类群地上生物量生产率的影响

2年的牦牛放牧试验表明:除不同植物本身的生理特性外,降水和地温是影响小嵩草高寒草甸两季草场不同植物类群地上生物量绝对生长率的关键因素。小嵩草高寒草甸两季草场地上总生物量的绝对生长率1999年在7月份最大;1998年,冷季草场各放牧处理的绝对生长率在8月份达到最大,暖季草场的对照组和轻牧组在7月份最大,中牧组和重牧组在8月份最大。不同植物类群地上生物量生长率的变化不尽相同。1998年,冷季草场禾草和莎草地上生物量的绝对生长率8月份达到最大,暖季草场禾草和莎草地上生物量的绝对生长率7月份达到最大,且9月份出现了营养的再次积累;1999年,冷季草场禾草地上生物量的绝对生长率在6月份和8月份出现了两个峰值,暖季草场禾草地生物量的绝对生长率在7月份达到最大。对杂草类而言,1998年冷季草场的绝对生长率6月份最大,暖季草场重牧组的绝对生长率8月份达到最大,其他各处理7月份达到最大;1999年重牧组杂草的绝对生长率在6月份达到最大,其他各处理杂草在8月份达到最大。     

饲料中蛋白质含量及养殖密度对红鳍东方鲀幼鱼生长性能、氮排泄及相关生化指标的影响

本实验以平均初始体重为15.60 g的红鳍东方鲀(Takifugu rubripes)幼鱼为研究对象,研究饲料中蛋白含量及养殖密度对红鳍东方鲀幼鱼生长性能、氮排泄及相关生理生化指标的影响。设计两因素三水平(2×3)实验,配制3种不同蛋白梯度(38.87%、45.55%和51.00%,干重)的等脂实验饲料,设置3个密度梯度为1.53 kg/m^3(0.196 m3体积的实验桶,每桶20尾鱼)、2.30 kg/m^3(每桶30尾鱼)和3.06 kg/m^3(每桶40尾鱼)。每组饲料设3个重复,养殖实验为期56 d,在室内流水系统内进行。结果显示,增重率在高、中蛋白组显著高于低蛋白组(P<0.05),但当饲料蛋白含量一定时,养殖密度对增重率没有显著性影响。饲料蛋白含量和养殖密度对鱼体常规成分没有显著性影响。当饲料蛋白一定时,高密度组的血清总蛋白和胆固醇含量显著高于中密度组(P<0.05)。血清总蛋白含量在低蛋白组显著高于中蛋白组(P<0.05)。血清碱性磷酸酶含量在低蛋白组显著高于高蛋白组(P<0.05)。饲料蛋白含量和养殖密度对红鳍东方鲀幼鱼的生长、氨氮排泄没有显著性交互作用。静水投喂3 h后,氨氮排泄率在高密度组显著高于低密度组(P<0.05)。研究表明,45.55%饲料蛋白质含量已经能够满足红鳍东方鲀幼鱼正常生长的需求。饲料蛋白含量和养殖密度对红鳍东方鲀幼鱼的生长性能和氨氮排泄没有显著性交互作用。     

天峻县北部地区畜牧业发展思考

天峻县北部地区因受气候干旱、鼠虫危害等因素的影响,畜牧业生产逐年下降,通过对存在问题的分析,提出了北部地区今后走退牧还草或休牧育草路子的设想。     

不同养殖密度对中国明对虾生长和能量代谢的影响

本研究采用网箱养殖的方法,通过室内28 d的养殖实验,在4个养殖密度G1(100尾/m3)、G2(200尾/m3)、G3(300尾/m3)、G4(400尾/m3)组中,研究不同养殖密度对中国明对虾(Fenneropenaeus chinensis)生长、能量代谢和代谢酶活力的影响.结果显示,G2组的增重率(WGR)、相...     

牦牛放牧率对江河源区混播禾草地上初级生产量及种间竞争力的影响

在江河源区2龄混播禾草草地(垂穗披碱草 星星草)上牦牛放牧试验结果表明: 随着放牧率的增加,在生长期内不同功能群地上净初级生产量和总地上初级生产量均出现了单峰曲线变化,即“S”型变化趋势; 总的地上净初级生产量和垂穗披碱草地上净初级生产量对放牧率的变化很敏感, 且随着放牧率的增加, 峰值出现日期提前; 其它禾草和星星草的峰值对放牧率的变化不很敏感;莎草类和杂草类对放牧率的变化比较敏感。随放牧率的增加, 地上现存量和总地上初级生产量的峰值下降, 且达到峰值的时间提前。在整个放牧期(植物生长期),重度放牧的RYT值均小于1,表明重度放牧使垂穗披碱草和星星草一直处于拮抗状态,其它各处理组在生长中后期也处于拮抗状态; 不同放牧率(包括对照)下垂穗披碱草的竞争力强于星星草, 垂穗披碱草因其高度和发达而较深的根系成为竞争的优胜者。     

以放牧率梯度研究内蒙古典型草原主要植物种群的生态位

对内蒙古典型草原主要植物种群在不同放牧强度下生态位分化规律进行研究。结果表明,羊草,克氏针茅的生态位,宽度相对较窄,分别为０．２９８和０．５６５,表明对放牧较敏感,属宜轻牧植物。蓿豆,冰草和菊叶委陵菜的生态位宽度适中,属宜中牧植物。而糙隐子草,冷蒿,星毛委陵菜,雨草苔,木地肤和变蒿等耐牧性较强,具有很宽的生态位宽度分别为０．９７８,０．９６９,０．９３１,０．９７０,０．９３８,０．９２４,具有很     

放牧率对土壤饱和导水率及其空间变异的影响

本文研究放牧对土壤饱和导水率及其对饱和导水率空间变异的影响。结果表明,在２ｍ及２ｍ以上相邻两点之间土壤饱和导水率相互独立,在各个方向均如此。虽自然对数正态分。放牧对饱和导水率和饱和导水率的标准差有极显著的作用,一元方差分析ｐ＝０．００３和０．００４。随着放牧率的增大,饱和导水率降低,与放牧率呈极显著的回归关系。     

Italian ryegrass establishment by self-seeding in integrated crop-livestock systems: Effects of grazing management and crop rotation strategies

We evaluated the re-establishment of an Italian ryegrass pasture by self-seeding on a no-till integrated crop-livestock systems (ICLS) in the southern region of Brazil. This work is part of a long-term experimental protocol initiated in 2003. We tested the effects of various management practices, such as summer crop systems (soybean vs. maize–soybean rotation), stocking methods (continuous vs. rotational) and grazing intensities (low vs. moderate), on Italian ryegrass pasture establishment. In addition, we tested resilience of the system by testing pasture's ability to re-establish following a year without seed head production. The experiment consisted in the rotation, on the same area, of Italian ryegrass pasture grazed by sheep during the winter and up to the end of the grass production cycle, and soybean or soybean-maize grain crops rotation cultivated during the summer. The pasture established itself by self-seeding since 2005. Data were collected in 2011 and 2012 stocking season. The soybean summer crop, continuous stocking and low grazing intensity, all positively affected the production of reproductive tillers in 2011. Grazing intensity in 2011 strongly influenced early vegetative tiller densities (before crop harvest) in 2012. However, none of the grazing intensity or the stocking method treatments affected herbage mass at the end of pasture establishment in 2011 or 2012. On the other hand, the soybean summer crop positively affected pasture establishment, both in term of tiller densities and herbage mass at the end of pasture establishment. The removal of all seed heads in 2011 (preventing seed production) resulted in the total failure of pasture establishment in 2012. Overall, Italian ryegrass establishment by self-seeding relies on the annual replacement of the soil seed bank. This experiment demonstrated that under various stocking methods, moderate grazing intensity and maize or soybean summer crop, Italian ryegrass pasture establishment by self-seeding remains successful even when the stocking periods extended up to the end of the grass production cycle. Self-seeding with moderate grazing intensity ensures successful pasture establishment, reduces labour and costs and allows to increase the stocking period and so animal live weight gain over the grazing season.     

Land degradation,stocking rates and conservation policies in the communal rangelands of Botswana and Zimbabwe

Communal rangeland management policies in Botswana and Zimbabwe are based on incorrect technical assumptions about the stability of semiarid rangeland, the nature of rangeland degradation, and the benefits of destocking. Consequently, inappropriate policies, stressing the need to destock and stabilise the rangelands, are pursued. Acknowledgement of the great instability but intrinsic resilience of rangeland would encourage the Governments to more favourably regard the opportunistic stocking strategies of the agro-pastoralists of the Communal Areas. However, degradation of rangelands is occurring, although at varying rates. This justifies the promotion of a ‘tracking strategy’, in which livestock densities are encouraged to follow, more closely that at present, variations in rainfall. The establishment of grazing territories controlled by specific ‘communities’ may be a prerequisite for the promotion of the tracking strategy, and for communal rangeland management and improvement. However, the establishment of such territories must take into account social equity, institutional problems and transaction costs, as well as spatial and temporal variation in rangeland resources.     

Effects of Stocking Density on Composition and Performance of Reared Arctic Charr (Salvelinus alpinus)

Abstract

Proximate composition and performance of Arctic charr (Salvelinus alpinus) stocked at 40, 50, and 75 kg/m³, were determined. Moisture content of fish fillets decreased while their protein and lipid contents increased during the 24 weeks of rearing period. Statistical analyses indicated that moisture, protein and lipid contents of charr flesh varied significantly among density groups while ash contents did not. While the moisture and ash contents of fish fillets were directly related to stocking density (r = +0.9435 and r = +0.9918, respectively), contents of protein and lipid did not (r = ?0.5251 and r = ?0.7038, respectively). The level of carotenoids in the flesh and skin of Arctic charr increased with duration of feeding on pigmented diets. However, no correlation (r = ?0.6053) existed between stocking density and concentration of carotenoids. The specific growth rate (SGR), feed conversion ratio (FCR), and protein efficiency ratio (PER) were significantly influenced by stocking densities but the hepatosomatic index (HSI) of fish did not. These performance parameters of fish were well correlated with stocking density (r = ?0.9368, ?0.9975, ?0.9899, and ?0.9920, respectively). Although SGR, FCR and PER of fish from different stocking densities varied significantly (p < 0.05), their final weights did not.