Study On Rule Of Methane Emission Of Dairy Cows In Different Physiological Stages And Methane Emission Of Calves Under Heat Stress

Trial one:This study examined the rule of methane emission of dairy cows in different physiological stages. Twelve cows in three different stages, which were calves (BW,130±2.8kg), heifers (BW,400±20kg), and dry cows (with permanent rumen fistulas, BW,550±50kg), were selected. Four animals in each stage were placed in four environmental control chambers randomly, and fed with the TMR diets, which reached the physical requirement. The temperature of environmental control chamber was25℃, and humidity was40%(THI=70.7). Experimental period for each stage lasted for9days. The results showed that methane emission increased significantly as age and body weight gain of cows increased. The ratio of energy loss via methane emission to total energy intake was the highest in the heifers, and higher than the calves (P<0.01) and dry cows (P<0.05). The rumen fluid pH in dry cow was significantly higher than heifers (P<0.05). The concentration of tVFA in rumen fluid of heifer was significantly highers than calves and dry cows (P<0.01). The proportion of acetic acid and propionic acid in the young bovine was significantly higher than the calves (P<0.01) and dry cows (P<0.05). In conclusion, as age and body weight gain increased in different physiological stages of cows, methane emiss on increased very significantly; the ratio of methane energy to gross energy is the highest in the heifer cows group.Trial two:To differentiate between the effects of heat stress (HS) and decreased dry matter intake (DMI) on health, Blood biochemical parameters and methane emissions in dairy calves. we conducted an experiment in which a thermoneutral control group (n=4,) was pair fed (PF) to match nutrient intake with heat-stressed Holstein bull calves (n=4). Calves (114±6.2d old,130±2.8kg, BW) housed in environmental controlled chambers were subjected to2experimental periods:P1(Temperature:25℃, humidity:40%) and ad libitum intake for10d, and P2(cyclical daily temperatures ranging from33℃to37℃, humidity:40%) and ad libitum intake or PF (in P1conditions) for10d. During each period, blood was collected at1,3,6,9d, and rumen fluid was collected at10d during the trial. The gas data was Real-time monitored during the trial. Compared to PF, HS increase (P<0.01) rectal temperature and respiratory ratebasal. HS tended (P=0.09) to decrease CH4emissions. The rumen pH was no significant difference (P>0.05) between PF and HS, but HS was able to derease (P<0.05) tVFA, acetic and butyric concentration, and tend to decrease propionic, isobutyric and valeric concentration. Plasma T3and GLU concentrations was decreased (P<0.05) under HS, but neither HS nor PF altered plasma T4, BUN and NEFA concentrations (P>0.05). In conclusion, HS had serious affected the respiratory rate and rectal temperature of calves, a little affected the CH4emission and a greater affected the serum T3and GLU under the same of DMI.