| Grassland is a main landscape in China.As an important pastoral area in China,Tibetan plateau is named as the"roof of the world"and the"third pole".It is the largest and highest plateau in the world,with an area of nearly 2.5×10~6 km~2.Grassland husbandry is an indispensable part of animal husbandry in China.However,in the past 50 years,due to the influence of human and unfavorable natural environment factors,the grassland has been largely degraded.The grassland ecological environment is declining.Grassland desertification,vegetation degradation and sand dune activation occurred much often in Qinghai-Tibetan plateau,mainly due to human activities such as overgrazing,excessive reclamation and deforestation.Two main reasons are responsible for the grassland degradation:one is the decline of grassland productivity caused by natural climate.The other is that the grazing amount of grassland animal husbandry is far beyond the carrying capacity of grassland,resulting in the decline of grassland production,grassland degradation and even desertification.Based on this,if we fully understand the livestock grazing mode,herbage nutritional value,livestock carrying capacity and explore a simple method to estimate the weight of major livestock in Tibetan plateau,it will be feasible for local farmers to reasonably manage their herd by knowing the quantity and quality of pasture,and the nutrition requirement of the livestock.Interview of 135 herdsmen on their herd structure and current management strategies was carried on in Guinan county,Yushu city and Maqu county.The current study explored yak bodyweight estimation method by analyzing the yak photos.This study was carried out in July 2017(summer),November 2017(winter)and April(spring)2018.At the same time,the forage samples of different months from natural grassland were collected to evaluate the comprehensive nutrition value of grassland.So as to provide scientific basis for the balance of forage and livestock and the grazing method in this area.The main research results are as follows:Part?:Research on livestock structure and grazing management(1)The proportion of yak and Tibetan sheep is similar in taxiu village,guinan county.Jiashan village is mainly composed of Tibetan sheep.The livestock structure of the two places is more reasonable,with Tibetan sheep aged between 1 and 3 years account for a large proportion in Jiashan and Taxiu village.The reason is that herdsmen quickly fatten and sell Tibetan sheep aged between 1 and 3 years to accelerate the production cycle and reduce economic losses.Banning grazing in summer will lead to great grazing pressure in autumn and winter and serious degradation of grassland for a long time.Therefore,it is suggested to implement a round of bans on grass and livestock.(2)The proportion of female yak in yushu city is relatively low,the proportion of old and old animals is relatively high,and the livestock structure is too simple.It is suggested to sell older animals and increase the number of young ones by increasing the number of females.(3)A survey of Anmao Village and Hequmachang in Maqu County,Gannan Province found that the Hequmachang was limited by water sources,there is no rotation in the year,excessive use of grassland grazing leads to serious degradation and serious damage to grassland rats.However,the survey results showed that the livestock herd structure in the region was relatively reasonable.Part?:Yak weight was estimated by photosThe results used photos of yak,and the body measurements of yak was obtained:withers height(WH),body side area(BSA),and Body diagonal length(BDL),which can accurately estimate grazing yak weight in different seasons.The linear equations for estimating the weight of yak in different seasons are:LBW=-160.6+3.38 WH,LBW=-93.3+392.6 BSA,LBW=-148.01+32.15 BDL.The optimal estimation model of yak body weight are summer:LBW=-174.68+0.82 BDL+2.17 WH+51.3 BSA,winter:LBW=-181.8+1.62 WH+281.6 BSA,spring LBW=-231.18+1.74 WH+1.41BDL.Part?:Evaluation of nutritive value of natural grassland and balance of herbage and livestockThere were significant differences in nutrient content,ground biomass,48h gas production,dry matter digestibility,organic matter digestibility and metabolizable Energy of natural grassland in different months(P<0.05).In July,natural pasture has the highest gas production,dry matter digestibility and organic matter digestibility,while the neutral and acidic detergent fiber content are the lowest.Therefore,natural pasture has the highest nutritional value in July.In terms of capacity carrying,the DCP carrying capacity in autumn grassland is the highest,and the amount carrying capacity in winter and spring pasture is the highest.According to the theory of minimum factor limitation,the winter and spring grassland should be grazed with ME carrying capacity,and the autumn grass field should be grazed with DCP carrying capacity,supplementing the digestive energy and digestible protein by supplementing the feeding.In annual grazing,grazing management should be carried out according to energy carrying capacity. |
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