The productivity and nutritive value of some cultivated perennial grasses, Bromus inermis (B), Elymus sibricus (S), E. nutans (N), Agropyron cristatum (A), Poa crymophila (P) and mixtures B + N, S + A, B + S + A, S + B + N, N + S + A, B + S + N + A, B + N + A + P, B + S + A + P and S + N + A + P, in the alpine region of the Tibetan Plateau were investigated. Elymus nutans and E. sibricus and the mixtures, B + S + N + A, B + S + A + P and S + N + A + P, were most productive with yields of dry matter (DM) of between 11 000 and 14 000kg)1 of biomass annually in the second harvest year. Acid-detergent fibre (ADF) concentrations increased (P<0

Forage selection plays a prominent role in the process of returning cultivated lands back into grasslands. The conventional method of selecting forage species can only provide attempts for problem-solving without considering the relationships among the decision factors globally. Therefore, this study is dedicated to developing a decision support system to help farmers correctly select suitable forage species for the target sites. After collecting data through a field study, we developed this decision support system. It consists of three steps: (1) the analytic hierarchy process (AHP), (2) weights determination, and (3) decision making. In the first step, six factors influencing forage growth were selected by reviewing the related references and by interviewing experts. Then a fuzzy matrix was devised to determine the weight of each factor in the second step. Finally, a gradual alternative decision support system was created to help farmers choose suitable forage species for their lands in the third step. The results showed that the AHP and fuzzy logic are useful for forage selection decision making, and the proposed system can provide accurate results in a certain area (Gansu Province) of China.

天然草原退化是北方草原地区一个严重的生态经济问题，超载放牧是引起草地退化最直接的根本性原因。对甘肃省肃南县红石窝乡的草原畜牧业生产现状调查研究表明，草原产权制度与草地过度利用密不可分，产权制度设计的缺陷和制度供给的滞后性使草地的使用和保护处于一种无序状态，诱发了牧民掠夺式经营行为的发生，致使天然草原被长期过度利用。

对不同类型草地功能群多样性和组成与植物群落生产力之间的关系进行了探讨。结果表明：（1）在矮嵩草（Kobresia humlis）草甸和金露梅（Potentilla f roticosa）灌丛中，豆科植物的作用比较明显，而其他功能群植物的作用较弱。（2）在藏嵩草（Kobresia tibetica）沼泽化草甸和小嵩草（K. pygmaca）草甸中，虽然杂类草、C3 植物和莎草科植物功能群的生产力占群落初级生产力的比例较大，但二者在统计上没有显著性差异，这表明群落生产力除受物种多样性的影响外，也受物种本身特征和环境资源的影响，更主要的是受到功能群内物种密度和均匀度的影响，即功能群组成比功能群多样性更能说明对生态系统过程的影响。（3）不同类型草地群落植物功能群盖度与群落初级生产力呈显著的线性相关。（4）不同类型草地群落生产力与功能群内物种数的变化均表现为单峰曲线关系，即功能群内物种数处于中间水平时，群落生产力最高。

综述了芳香族化合物的发现过程、反刍动物饲草料、瘤胃和尿液中芳香族化合物的主要类型及存在形式。马尿酸是最早从家畜排泄物中发现的芳香族化合物。反刍动物的尿液中排出的苯甲酸几乎完全来源于日粮中的前体物。饲料日粮中芳香族化合物是酚酸、简单酚、香豆素、棉子酚、酚的生物碱、类黄酮、单宁酸和木质素。羟基肉桂酸和安息香酸是维管束植物中广泛存在的一类酚类化合物，其在禾本科牧草中的含量远高于豆科牧草，但禾谷类籽实中的含量却很低。瘤胃液和尿液中的芳香族代谢物主要是无酚的芳香酸、酚酸和苯酚，环己烷羧酸是惟一发现的脂环族酸。饲喂不同的日粮饲草料，反刍家畜以马尿酸形式排出的氮量大约占尿氮总量的6%，变化范围为1%～38%。测定尿中芳香族化合物特别是马尿酸对预测反刍家畜的采食量具有重要潜力和作用。

In the alpine region of the Qinghai-Tibetan Plateau four indigenous perennial grass species Bromus inermis (BI), Elymus sibiricus (ES), Elymus nutans (EN) and Agropyron cristatum (AC) were cultivated as three mixtures with different compositions and seeding rates, BI + EN, BI + ES + AC and BI + ES + EN + AC. From 1998 to 2001 there were three different weeding treatments: never weeded (CK); weeded on three occasions in the first year (1-y) and weeded on three occasions in both the first and second year (2-y) and their effect of grass combination and interactions on sward productivity and persistence was measured. Intense competitive interference by weedy annuals reduced dry matter (DM) yield of the swards. Grass combination significantly affected sward DM yields, leaf area index (LAI) and foliar canopy cover and also species composition DM and LAI, and species plant cover. Interaction between weeding treatments and grass combination was significant for sward DM yield, LAI and canopy cover, but not on species composition for DM, LAI or species plant cover. Grass mixture BI + ES + EN + AC gave the highest sward DM yield and LAI for both weeding and non-weeding treatments. Species ES and EN were competitively superior to the others. Annual weedy forbs must be controlled to obtain productive and stable mixtures of perennial grasses, and germination/emergence is the most important time for removal. Weeding three times (late May, late June and mid-July) in the establishment year is enough to maintain the production and persistence of perennial grass mixtures in the following growing seasons. Extra weeding three times in the second growing year makes only a slight improvement in productivity.

The present study was conducted to determine the effects of supplementary feeds, oat hay (OH), highland barley straw (HBS) and multi-nutrient blocks supplementation (UMMB) on reducing liveweight losses of both yak cows and calves grazed on low quality pastures during cold season. The trials of OH and HBS supplementation were conducted by using completely random design on 104 yak cows between 6 and 12 years of age as the following treatments: pure grazing (41 animals, body weight 230F67kg) as control (CK); grazing+1.5kg DM of OH per head daily (30 animals, body weight 216F28kg); grazing+1.5 kg DM of HBS per head daily (33 animals, body weight 221F34kg). The trial of UMMB was conducted on three types of yaks, 1-year calves (8-12 months old, body weight 61.1F6.9kg), 2-year calves (18-24 months old, 98.0F11.3kg) and yak cows (164.5F27.1 (S.D.)kg) with 20 animals in control group (CK) and 20 animals in supplement group for each type by using completely random design as the following treatments: pure grazing for CK group; grazing+150, 250 and 500g UMMB per day averagely for 1-year calf, 2-year calf and cow at night. The results indicate that the animals supplemented with oat hay received body weight gain (32F20.7g day1), while those supplemented with highland barley straw still suffered from body weight loss (56.7F39.3g day1); UMMB supplementation can decrease the body weight loss by 109.7%, 86.6% and 63.4% for the 1-year calves, 2-year calves and yak cows, respectively, as compared with pure grazing. Around US$1.60 output can be achieved on the basis of US$1 input for UMMB supplementation in the farming systems of the 1-year calves, 2-year calves and yak cows, while US$1 input can produce US$1.55 and 1.14 output for OH and HBS supplementations, respectively, in yak cows' farming system. It can be preliminary concluded that UMMB supplementation was the most economic way to alleviate body weight loss of grazing yaks over cold season, and the higher productive returns were obtained from OH supplementation for grazing yak cows during winter/spring months.

In the alpine region of the Tibetan Plateau, five perennial grass cultivars, Bromus inermis (B), Elymus nutans (E), Clinelymus nutans (C), Agropyron cristatum (A), and Poa crymophila (P) were combined into nine communities with different compositions and ratios, B+C, E+A, B+E+A, E+B+C, C+E+A, B+E+C+A, B+C+A+P, B+E+A+P and E+C+A+P. Each combination was sown in six 10

A feeding trial was conducted at the farm of Qinghai Academy of Animal and Veterinary Science, Xining, China during 1996-1997 with three dry yak cows (initial body weight 163-197kg, age 5-6 years) by using 33 Latin Square Design to determine the effect of levels of feed intake on digestion, nitrogen balance and purine derivative excretion in urine of yak cows. The animals were fed oat hay (nitrogen 13.5g/kg dry matter (DM), metabolisable energy 8.3MJ/kg DM), i.e., 0.3, 0.6 and 0.9 of voluntary intake (VI). Each intake treatment lasted for 17 days and the samples (feeds, faeces and urine) were collected during last 7 days of each period. The results indicate that digestibility of dietary DM, OM, NDF and ash declined when intake levels increased from 0.3 to 0.9 VI [DM, from 66.1% to 59.1% (P<0.05); OM, from 68.1% to 59.9% (P<0.05); NDF, from 62.1% to 54.3% (P<0.05); and ash, from 33.9% to 11.8% (P<0.05)]. Around 0.10g N/kg W0.75 was deficient daily in yak cows at 0.3VI, and positive N balances were observed at 0.6 and 0.9VI. Intake levels significantly (P<0.05) affected total PD excretion in yak urine. The proportion of allantoin increased (P<0.05) and uric acid decreased (P<0.05) as intake level of feed increased.