Effects Of Dietary NDF/NFC On Rumen Methane Emissions,Nutrient Apparent Digestibility And Production Performance Of Dairy Cows During Different Lactating Stages

By changing dietary the ratio of neutral detergent fiber and non-fiber carbohydrate（NDF/NFC）and using sulfur hexafluoride（SF₆）tracer technique,the methane emission from rumen of dairy cattle was determined in order to study the methane emission from rumen in the peak,middle and late stages of lactation.It provides a reference for improving the efficiency of dietary utilization and reducing greenhouse gas emissions.The concrete research content was divided into the following 3 Experiments.Experiment 1:Effects of dietary NDF/NFC on rumen methane emissions,nutrient apparent digestibility and production performance of dairy cows during peak lactation periodMethane emissions from lactating cows under production condition were determined by SF₆ tracer technique in order to study the effects of dietary NDF/NFC（neutral detergent fiber/non-fiber carbohydrate）on rumen methane emission,nutrient apparent digestibility and production performance of dairy cows during peak lactation period.Twelve Holstein lactating cows were selected with body weight（564.0±24.97,mean±standard error）kg,parity（1.5±0.23）parities,lactating days（88.0±15.32）d and daily milk yield（20.6±0.77）kg/d and were allocated to 3 groups with 4 lactating cows in each group.Dietary NDF/NFC was 1.14,1.30 and 1.55,respectively,and concentrate to forage ratio was 59∶41,53∶47 and 44∶56.The whole experiment lasted for 28 d with 14 d of pre-test and 14 d of test.The results showed that,（1）rumen methane emissions and methane energy（CH₄-E）were highly significant lower in low NDF group than that of high NDF group（P<0.01）,methane/DMI and methane energy/GEI were highly significant difference（P<0.01）among the 3 groups.（2）There was no significant difference（P>0.05）in nutrient apparent digestibility among the 3 groups.（3）With the decrease of NDF/NFC,there was no significant difference in milk yield and milk composition among the three groups（P>0.05）.The average daily gain of low NDF group was significantly higher than that of high NDF group（P<0.05）.In conclusion,without affecting the health and production performance of dairy cows,low NDF group with NDF/NFC of 1.14could significantly reduce rumen methane emissions during peak lactating period of dairy cows.Experiment 2:Effects of dietary NDF/NFC on rumen methane emissions,nutrient apparent digestibility and production performance of dairy cows during middle lactation periodMethane emissions from lactating cows under production condition were determined by SF₆ tracer technique in order to study the effects of dietary NDF/NFC on rumen methane emission,nutrient apparent digestibility and production performance of dairy cows during middle lactation period.Twelve Holstein lactating cows were selected with body weight（649.5±18.44）kg,parity（1.4±0.15）parities,lactating days（170.1±19.04）d and milk yield（18.5±0.89）kg/d and were allocated to 3 groups with 4 lactating cows in each group.Dietary NDF/NFC was 1.44,1.65 and 1.82,respectively,and concentrate to forage ratio was61∶39,53∶47 and 46∶54.The whole experiment lasted for 28 d with 14 d of pre-test and 14 d of test.The results showed that,（1）there was highly significant difference（P<0.01）in rumen methane emissions,methane energy,methane/DMI,and methane energy/GEI among the 3 groups.（2）The apparent digestibility of NFC in low NDF group was significantly higher than that in high NDF group（P<0.05）.（3）With the decrease of NDF/NFC,there was no significant difference（P>0.05）in milk yield,milk composition and average daily gain among the three groups（P>0.05）.In conclusion,without affecting the health and production performance of dairy cows,low NDF group with NDF/NFC of 1.44 could significantly reduce rumen methane emissions during middle lactating period of dairy cows.Experiment 3:Effects of dietary NDF/NFC on rumen methane emissions,nutrient apparent digestibility and production performance of dairy cows during late lactation periodMethane emissions from lactating cows under production condition were determined by SF₆ tracer technique in order to study the effects of different NDF/NFC diets on rumen methane emission,nutrient apparent digestibility and production performance of dairy cows during late lactation period.Twelve Holstein lactating cows were selected with similar body weight（777.5±27.31）kg,parity（1.5±0.15）parities,lactating days（243.0±15.28）d and milk yield（18.8±0.62）kg/d and were allocated to 3 groups with 4lactating cows in each group.Dietary NDF/NFC was 1.52,1.96 and 2.10,respectively,and concentrate to forage ratio was 44∶56,37∶63 and 30∶70.The whole experiment lasted for 24 d with 14 d of pre-test and14 d of test.The results showed that,（1）there was significant difference（P<0.05）in methane emissions,methane energy,methane emissions per unit of DMI,and methane energy emissions per unit of gross energy intake in lactating dairy cows,With the decrease of NDF/NFC;（2）There was no significant difference（P>0.05）in the production performance,feed conversion rate and nutrient apparent digestibility.In conclusion,without affecting the health and production performance of dairy cows,low NDF group with NDF/NFC of 1.52 could significantly reduce rumen methane emissions during middle lactating period of dairy cows.General conclusionThe purpose of this study was to study the effects of dietary NDF/NFC on rumen methane emissions,nutrient apparent digestibility and production performance of Chinese Holstein cows during different lactating stages by using SF₆ tracer technique to determine methane emissions from dairy cows during the peak,middle and late stages of lactation under production condition.The results showed that,（1）when the dietary NDF/NFC was 1.14,1.30 and 1.55,the rumen methane emission of dairy cows during peak lactation period of low NDF group was highly significant lower than that of high NDF group（P<0.01）,The daily CH₄ emissions were 325.2,347.1 and 391.9 g/d,CH₄/DMI was 15.6,18.9 and 25.4 g/kg,respectively,CH₄-E/GEI was 4.9%,5.9%and 8.2%.There was no significant difference（P>0.05）in milk yield and milk composition among the 3 groups.The average daily gain of low NDF group was significantly higher than that of high NDF group（P<0.05）.（2）When the dietary NDF/NFC was 1.44,1.65and 1.82,there was highly significant difference（P<0.01）in rumen methane emissions of dairy cows during middle lactation period among the 3 groups,The daily CH₄ emissions were 261.0,331.4 and 399.8g/d,CH₄/DMI was 17.1,24.9 and 34.5 g/kg,respectively,CH₄-E/GEI was 5.2%,7.6%and 10.6%.The apparent digestibility of NFC in low NDF group was significantly higher than that in high NDF group（P<0.05）.There was no significant difference（P>0.05）in milk yield and milk composition among the 3groups.（3）When the dietary NDF/NFC was 1.52,1.96 and 2.10,the rumen methane emission of dairy cows during late lactation period was significantly lower than that of high NDF group（P<0.05）.The daily CH₄ emissions were 241.8,329.3 and 395.6 g/d,CH₄/DMI was 15.7,20.6 and 26.2 g/kg,respectively,CH₄-E/GEI was 5.1%,8.0%and 9.2%.There was no significant difference（P>0.05）in milk yield and milk composition among the 3 groups.In conclusion,without affecting the health and production performance of dairy cows,the rumen methane emissions of dairy cows during different lactating stages could be significantly reduced by reducing the dietary NDF/NFC properly,it is suggested that the diets with NDF/NFC of 1.14-1.30,1.44-1.65 and 1.52-1.96 should be fed to the dairy cows during the period of peak,middle and late lactation,respectively.