Digestibility Of Natural And Cultivated Grasslands By Yaks In Alpine Pastoral Region

Abovegmund pliytornass and nutrient contents of natural Cyperaceae Elymus nutans Kobreua capil4folia1 Polygonum vzviparwn. Rhododendran+ Polygonwn viviparum pastures of cold and humid type on the alpine pastural area and cultivated Vcia sat駫a Ejytmss sibirzczss B. inermis grasslands were determined at different stages and three cannulated yaks were used to study tempemture pHNH3-N content in rumen, disappearance rate of each nulnent at various periods, grazing intake, forage digestibility of natural grasslands and outflowing rate of the whole digestive tractResults showed tbat,green , diy mattei(DM) had single climax throughout the growth period with highest value lii August to September and lowest in mid-April. With climax at mature stage, green and DM yields of three cultivated grasslands increased with growth. Changes in nutrient contents of five natural grasslands showed that,slight differences in DM concentrations between stages, increasing tendency in organic matter(OM) contents, having one climax in crude protein(CP) contents with highest value in Jimeuly and lowest at withered period, changes in contents of acid detergent fiber(ADF), just opposite to CP contents, showing curve . Throughout the growth penod, disappearance rates of each nutrient on five natural grasslands were higher during green other than withered period. Degradability of DM and OM increased, then decreased with dxne.That of CP showed the highest value at regreening stage as with high CP content . However, degradation characteristics of ADF indicated lower value with higher concentration . As for each tamed grassland , date of highest disappearance rate of each nutrient overlapped , not at early green stage. DM contents of three cultivated grasslands showed slight differences and no obvious pattem.Contents of OM and CP, opposite to ADF , increased with growth stage , so did the disappearance rate of each nutrient did . Mean values of temperature, pH, NH3-N contents in rumen of yaks were 39.0C, 6.69, 28.5 mg/L at 8:00 and 39.6 C, 6.32, 17.1 mg/L at 20:00, respectively. Compared with 20:00 , temperatures were significantly(P<0.0l) lower and pH values were notably(P<0.01) higher at 8:00 , but NH3-N contents bad no diffences . PH values had two peaks during the whole day at 6:00 and 10:00 , respectively. Temperatures were higher in the daytime than at night , with highest value at 12:00. Fluctuating NH3-N contents bad several peaks and higher value in the daytime than at night,with highest value at 12:00. Air-dried matter disappearance rates in rumen of yaks increased from 12 to 48 h , then changed flatly . Optical lagtime in rumen was decided on 48 h . Mean grazing intake of yaks was 4599.24~49.0 g/head.d . After grazing,outflowing didn't occur at 12h and began at 24W 0.36 % of the total), then increased to the climax at 60h( 32.38% of the total) . More than Sd were required to flowout completely. Mean forage digestibility (DM) of natural grassland was 69.39?.87 %.