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Effects of dietary forage level and source on partial carbon footprint of milk in Holsteins and Jerseys.

M. E. Uddin




Effects of dietary forage level and source on partial carbon footprint of milk in Holsteins and Jerseys.
M. E. Uddin*1,3, H. A. Aguirre-Villegas2, R. A. Larson2, M. A. Wattiaux1. 1Department of Dairy Science, University of Wisconsin-Madison Madison, WI, 2Department of Biological Systems Engineering, University of Wisconsin-Madison Madison, WI, 3Department of Animal Science, University of California-Davis Davis, CA.

We determined the partial carbon footprint (CF) of milk for 4 diets fed to 2 breed using measured enteric methane and greenhouse gas emissions during manure storage and after field application. Emissions and animal performances were collected in companion studies with diets containing forage neutral detergent fiber at 2 levels (NDF; 19 and 24% of dry matter, referred as low forage and high forage diets, respectively) and from 2 sources [70:30 or 30:70 ratio of alfalfa silage (AS) NDF and corn silage (CS) NDF]. Measured emissions were incorporated in a modeled Wisconsin dairy farm of 117 ha of cropland with a dairy herd consisting of 122 lactating cows (all primiparous), 22 dry cows, and 119 heifers. We assumed that manure was field-applied according to a nutrient management plan, and cropland was used to produce AS, CS and corn grains fed to the cows. Purchased inputs included other concentrate feed to balance rations and chemical fertilizers necessary to fertilize the crops as recommended. The cradle-to-gate life cycle assessment was performed with SimaPro using fat- and protein-corrected milk (FPCM) as the functional unit. Emissions were allocated between milk and meat using either economic or mass allocation. Low forage-fed cows had 11% greater CF than high forage-fed cows (1.57 vs. 1.42 kg CO2-e/kg FPCM) most likely due to the increase in both DMI and milk production when cows were fed with greater content of highly digestible soyhull in the low-forage compared with the high-forage diets. Forage sources did not influence CF (1.50 kg CO2-e/kg FPCM). The CF for Holsteins was 5% greater than for Jerseys (1.55 vs. 1.48 kg CO2-e/kg FPCM). Overall, CF was 1.5 kg CO2-e/kg FPCM when using economic allocation, but 1.42 kg CO2-e/kg FPCM when using mass allocation. Under this study conditions, differences in enteric emission intensity across diets were minimal but differences in emission intensity became substantial when assessed by combining the effects of the cow, the manure, the on-farm crop rotation, and the purchased feed, highlighting the need for an integrated approach to assess the diet effects on milk CF.

Keywords: alfalfa silage, corn silage, greenhouse gas.

Biography: Speaker is currently working as a postdoctoral scholar in the field of ruminant nutrition and modeling with Dr. Ermias Kebreab in the Department of Animal Science at University of California-Davis, USA. In 2016, he completed European Master in Animal Breeding and Genetics from Wageningen University and Research, The Netherlands; and subsequently in 2019 he earned his PhD in Dairy Science (focusing ruminant nutrition and modeling) under the supersion of Dr. Michel Wattiaux from University of Wisconsin-Madison, USA.