Digestion,Metabolism And Enteric Methane Emission Of Tan Sheep Grazing In Typical Steppe

Typical grassland is the main area for sheep meat production in northern China,grazing is one of the efficient use of grassland.In recent years,greenhouse gases emitted by agriculture,especially animal husbandry,have attracted widespread attention.The digestion,metabolism and methane emission of grazing livestock are the basic parameters of sustainable grassland management.However,related experimental studies are relatively scarce.Therefore,a Tan sheep grazing experiment was carried out at the Huanxian Grassland Agricultural Trial Station of Lanzhou University to determine the digestion,metabolism,and enteric methane emissions of livestock.The key research finding was as following:1 Effects of stocking rate and grazing season on the digestion,metabolism,and methane emission of Tan sheep.(1)Impact on dry matter intake and digestibility.The stocking rate of summer and winter gazing was negatively correlated with the dry matter intake of Tan sheep in 2018 and 2019;The dry matter digestibility and stocking rate showed a "saddle" curve,which showed the lowest digestibility(51.34%)at 5.3 sheep/ha in the summer of 2018;the dry matter digestibility decreased with increasing stocking rate in winter grazing land of 2018 and both summer and winter grazing land of 2019.The dry matter intake of Tan sheep in winter grazing land of 2018 and 2019 was significantly higher than that in the summer,increasing by 12.36%and 10.45%,respectively.In 2018 and 2019,the dry matter digestibility of Tan sheep in winter grazing land was significantly lower than that in summer by 13.27%and 15.90%,respectively.(2)Impact on energy metabolism and nitrogen metabolism.In 2018,the total nitrogen intake decreased with increasing stocking rate and had no significant effect in 2019.In the summer grazing land of 2018,the nitrogen deposition rate and stocking rate showed a "saddle" curve,and it was the lowest at 5.3 sheep/ha with 12.51%,and it was positively correlated with stocking rate in the summer of 2019 and negatively correlated in the winter of 2019.In the winter grazing land of 2018 and 2019,the total nitrogen intake of the grazing Tan sheep was significantly reduced by 27.8%and 31.7%compared with that in the summer.The nitrogen deposition rate of Tan sheep decreased by 101.3%and 100.7%in winter of 2018 and 2019 compared with summer.Stocking rate and metabolizable energy,metabolizable energy/total energy show a "saddle" curve change in the summer and winter grazing land of 2018,and a linear positive correlation in the summer of 2019,and a "hump" curve change in the winter of 2019.The metabolic energy of Tan sheep in the winter of 2018 and 2019 decreased by 17.7%and 14.5%compared with that in the summer.(3)Impact on enteric methane emission.The ratio of methane energy/digestible energy of the grazing Tan sheep showed a "hump" curve with increasing stocking rate in the summer and winter grazing seasons of 2018,and they showed a linear decline and "saddle" curve change in 2019.In the winter of 2018 and 2019,the ratio of methane energy/digestible energy of grazing Tan sheep was significantly higher than that in summer,improved by 56.7%and 36.7%.The grazing season has a very significant effect on the serum and rumen fermentation parameters of Tan sheep,but the stocking rate has no significant effect on it.The rumen fermentation parameters of grazing Tan sheep were not affected by grazing management regulation(stocking rate and grazing season).Although there were significant differences in forage nutrition levels between stocking rates and grazing seasons,the total volatile fatty acids acetic acid,propionic acid,and rumen ammonium nitrogen of all Tan sheep under the two treatments are not significantly differenceGrazing in summer,8.7 sheep/ha(2018,2019)can improve the dry matter digestibility,the efficiency of energy and nitrogen use,and reduce the daily methane emissions of Tan sheep.In winter grazing,2.7 sheep/ha(2018)and 5.3 sheep/ha(2019)have the highest dry matter digestibility,energy and nitrogen use efficiency and the lowest daily methane emissions of Tan sheep.2 Effects of grazing and feeding cellulase on digestion,metabolism and methane emission of grazing Tan sheep(1)Impact on dry matter intake and digestibility.In summer,5.3 sheep/ha,dry matter intake and digestibility of Tan sheep fed cellulase group were 10.7%and 6.3%lower than those of the control group;8.7 sheep/ha in summer,5.3 and 8.7 sheep/ha in winter,the dry matter intake and digestibility increased by 20.9%,8.0%,10.1%and 11.6%,11.7%,12.5%,respectively.(2)Impact on enteric methane emission.Under different stocking rates in winter and summer,the CH4/DMI,CH4-E/gross energy,CH4-E/digestible energy and CH4-E/metabolic energy of the tan sheep fed with cellulase were lower than those of the control group.(3)Impact on rumen fermentation parameters.In summer and winter,the total volatile acid production of rumen fluid of 5.3 sheep/ha and 8.7 sheep/ha Tan sheep were fed with cellulase increased by 10%,10.2%and 15.4%,15.8%,respectively.In summer pasture,the cellulase-fed Tan sheep had the highest digestibility and energy and nitrogen use efficiency,and the methane emission per unit of dry matter intake was the smallest at 8.7 sheep/ha.In the winter pasture,the methane emission per unit of dry matter intake was the smallest at 5.3 sheep/ha.