The U.S. dairy industry has committed to lowering the carbon footprint of milk production by 25% by 2020. A key factor in meeting this goal is reducing enteric greenhouse gas (GHG) emissions which represent about 51% of the carbon footprint of a gallon of milk. Methane (CH4) is the primary GHG emitted by dairy cows. Total methane emissions represented 10.6% of the total U.S. GHG emissions in 2014. Enteric CH4 emissions were 22.5% of the total methane emissions. Methane emissions from dairy cattle were 5.7% of total U.S. methane emissions or 0.6% of all U.S. GHG emissions. The purpose of this project was to examine nutrition and management options to lower methane emissions from dairy cattle.
This project utilized a number of approaches. One was to develop a base ration using the Cornell Net Carbohydrate and Protein System (CNCPS) model to evaluate the impact of level of dry matter intake and milk production on methane emissions. A second approach was to compile a database of commercial herd rations from 199 dairy farms. This database was used to examine relationships between the feeding program and CH4 emissions. A third component was to utilize published review papers to estimate potential on-farm CH4 reductions based on research data.
A base ration developed in the CNCPS model was evaluated at milk production levels ranging from 40 to 120 pounds of milk. As milk production increased, CH4 emissions increased from 373 to 509 grams/cow/day. This is primarily due to increasing levels of dry matter intake as milk production increases. However, the CH4 emissions per pound of milk decreased from 9.32 to 4.24 g as milk production increased. The 199 commercial herd database had an average input milk of 83.7 pounds per day with a range from 50 to 128 pounds. Daily dry matter intake (DMI) averaged 51.4 pounds with a range of 35.2 to 69.8. Simple correlations were run between CH4 emissions and ration components. Dry matter intake had a positive (0.795) correlation with CH4 emissions (g/day). However, the correlation between DMI and CH4/pound of milk was -0.65. These results agree with published research on the relationship of DMI and CH4 emissions. Starch intake also had a positive correlation (0.328) while percent ration starch was negatively correlated (-0.27) with CH4 emissions. There was also a positive correlation (0.79) between the pounds of NDF intake and CH4 emissions.
A review paper indicated that the maximum potential reduction in CH4 emissions by altering rations was 15% (Knapp et. al., 2014). Projected reductions from genetic selection, rumen modifiers and other herd management practices were 18, 5 and 18% in this same paper. The reduction by combining all approaches was estimated to be 30%. A second review paper listed mitigation strategies as low, medium or high (Hristov et. al. 2013). Potential reductions for the low group was <10% while the medium group was 10-30%. The high group had >30% potential to lower CH4 emissions. Ionophores, grazing management and feed processing were in the low group. Improving forage quality, feeding additional grain and precision feeding were in the low to medium group. Rumen inhibitors were listed in the low to high group. No items were listed only in the high group. These results provide guidance in terms of items to concentrate on at the farm level to reduce methane emissions.
The number of commercial herds in the database will be expanded to increase the types of rations represented and the simple correlations run. In addition, a multiple regression approach will be used to better understand the relationships of ration components and CH4 emissions. Whole herd data will be obtained and examined to determine the proportion of the total herd CH4 emissions contributed by the various animal groups. The CNCPS program will also be used on rations at constant DMI to better understand the impact of specific ration components on CH4 emissions. These results of these will permit a more defined and targeted approach to adjusting rations to decrease CH4 emissions.
Dr. Larry E. Chase, Professor Emeritus, Dept. of Animal Science, Cornell University
Hristov A.N., J. Oh, J.L. Firkins, J. Dijkstra, E. Kebreab, G. Waghorn, H.P.S. Makkar, A.T. Adesogan, W. Yang, C. Lee, P.J. Gerber, B. Henderson and J.M. Tricarico. 2013. Mitigation of methane and nitrous oxide emissions from animal operations: I. Review of enteric methane mitigation options. J. Anim. Sci. 91:5045-5069.
Knapp J.R., G.L. Laur, P.A. Vadas, W.P. Weiss an d J.M. Tricarico. 2014. Enteric methane in dairy cattle production: Quantifying the opportunities and impact of reducing emissions. J. Dairy Sci. 97:3231-3261.
This material is based upon work that is supported by the National Institute of Food and Agriculture U.S. Department of Agriculture under award number 2013-68002-20525. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author and do not necessarily reflect the view of the U.S. Department of Agriculture.
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