Study On The Regularity Of Methane Emission And Nutrient Digestibility In Holstein Reserve Cows At Different Physiological Stages

This trial set up 18-,21-,24 month old three group Holstein reserve cows to determine methane production versus carbon dioxide production in the rumen of three month old staged reserve cows using the internationally advanced greenfeed system.Studies focusing on the regulation of methane emission,methane emission factors and their related prediction models in Holstein cows at different physiological stages in China are not perfect,and there is a lack of basic emission data,based on our previous study,we systematically investigated the growth performance,apparent digestibility of nutrients and ruminal methane production of 18-,21-and 24 month old Holstein reserve cows,aiming to explore the regulation of methane emission in reserve cows,Basic data and scientific support are provided by R&D mitigation regulation strategies.The content of the trial is divided into the following three parts.Test one:Study on the apparent digestibility and methane emission patterns of Holstein reserve cows aged 18,21,and 24 monthsThis experiment was conducted to study the growth performance,nutrient digestibility,and rumen methane（CH₄）emission of Holstein heifers at the age of 18,21 and 24 months under the natural conditions by Green Feed system.Forty Holstein heifers with good body condition were selected and divided into three treatment groups（10 in each group）according to age and weight:18-month-old group（weight=512±11.9 kg）,21-month-old group（weight=548±6.6 kg）,24-month-old group（weight=608±6.0 kg）.The experiment lasted for 28 days,including 7 days of pre-feeding period and 21 days of trial period.The body weight of each cow was measured on the 1,14 and 28 day of the experiment.Feed samples and fecal samples were collected on the 26,27 and 28 day for routine nutrient analysis and nutrient digestibility calculation.On the day 7 of the experiment,the rumen CH₄and CO₂emissions of each cow in the three treatment groups were measured by Green Feed measurement system.The results showed that:（1）The daily gain,dry matter intake and total energy intake of Holstein cows at 18,21 and 24 months of age were significantly different（P<0.01）.The daily weight gain was 0.50,0.24 and 0.23 kg/d,respectively.The average dry matter intake of 18 months,21 months and 24 months were 9.59 kg/d,10.23 kg/d and 12.18 kg/d,respectively.（2）The apparent digestibility of dry matter（DM）of 18-,21-and 24-month-old Holstein heifers was significantly different（P<0.01）,which was 69.58%,74.07%and 75.38%,respectively.（3）With the increase of month age,the CH₄emissions,CO₂emissions,the proportion of CH₄to CO₂,the CH₄emissions per unit metabolic weight,the CH₄emissions per unit dry matter intake,the CH₄energy,and the proportion of CH₄energy to total energy were significantly different（P<0.01）.18.The average CH₄emissions at the age of 21 and 24 months were 207.8 g/d,275.1 g/d and 321.1 g/d.The average CO₂emissions are 5636.33 g/d,6559.34 g/d and 7267.67 g/d.CH₄accounts for 3.74%,4.19%and 4.42%of CO₂.In summary,the amount of CH₄emissions varies with the age of the cow.As the age of the cow increases,the dry matter intake of the cow increases,as well as the CH₄emissions and the ratio of CH₄energy/total energy.Test two:Study on the Prediction Model of Methane Emissions from Holstein Reserve Cows at 18,21,and 24 Months of AgeThey was divided into three treatment groups（10 heads）:18-month group（weight=512±11.9 kg）,21-month group（weight=548±6.6 kg）,and 24-month-old group（weight=608±6.0 kg）.Sample collection and analysis were consistent with the test.The results showed that:1)the dry material intake of 18,21 and 24 months was 6.67,7.57 and 9.18 k g/d respectively.The feed intake of organic matter was6.42,7.26,and 8.63 k g/d.The feed intake of neutral washing fiber was 3.45,3.88 and4.55 k g/d.Food intake of non-fibrous carbohydrates was 2.95,2.50,and 2.15 k g/d.18,21,24,60.23,70.90,and 70.57 g CH 4.3)Ruminal CH4 emissions were significantly positively correlated with body weight,DMI and dietary NDF content of Holstein reserve cows.CH4（g/d）=12.66×NDFI2（kg/d）-71.22×NDFI+278.48（R2=0.90）;CH4（g/d）=42.25×OMI（kg/d）-54.68（R2=0.88）;CH4（g/d）=37.07×DMI（kg/d）-30.07（R2=0.88）;CH4（g/d）=-46.98×NFCI2（kg/d）+193.49×NFCI+125.58（R2=0.94）。In addition,methane energy was positively correlated with NDFI and GEI.And showed a negative correlation with the NFCI.General conclusion18,21,24 months had significant intake and daily weight gain（P<0.01）.Daily weight gain is 0.50,0.24,and 0.23 k g/d,respectively.The average dry material feed intake at 18 months,21 months and 24 months was 9.59 k g/d,10.23 k g/d and 12.18kg/d,respectively;（2）The apparent digestibility of dry matter（DM）in the 18,21and 24 months was significant（P<0.01）,69.58%,74.07%and 75.38%,respectively;The apparent digestibility of acidic washing fiber（ADF）is 54.37%,56.56%,58.63%,The difference was significant（P<0.05）;（3）According to the change of month age,CH4 Emissions,CO2 emissions,CH4/CO2,CH4/metabolic body weight,CH4/dry material feed intake,methanane energy,methanane energy/total energy differences（P<0.01）.The mean CH4 emissions at 18,21 and 24 months were 207.8g/d,275.1 g/d and 321.1 g/d,respectively.The average CO2 emission equivalent was11 454.73 g/d,14 262.14 g/d,and 16 258.47 g/d,respectively.The CH4/CO2ratio was 3.74%,4.19%,and 4.42%,respectively.DMI and NDFI had the highest coefficient of determination（0.90）and（0.94）.In conclusion,CH4 emissions are different in cows by age,increasing dry material feed intake with age,while also increasing CH4 emissions and methane energy/total energy ratio.