Symposium review: Defining a pathway to climate neutrality for US dairy cattle production.

The US dairy industry has made substantial gains in reducing the greenhouse gas emission intensity of a gallon of milk. At the same time, consumer and investor interest for improved environmental benefits or reduced environmental impact of food production continues to grow. Following a trend of increasing greenhouse gas emission commitments for businesses across sectors of the economy, the US dairy industry has committed to a goal of net zero greenhouse gas emissions by 2050. The Paris Climate Accord's goal is to reduce warming of the atmosphere to less than 1.5 to 2°C based on preindustrial levels, which is different from emission goals of historic climate agreements that focus on emission reduction targets. Most of the emissions that account for the greenhouse gas footprint of a gallon of milk are from the short-lived climate pollutant CH4, which has a half-life of approximately 10 yr. The relatively new accounting system Global Warming Potential Star and the unit CO2 warming equivalents gives the industry the appropriate metrics to quantify their current and projected warming impact on future emissions. Incorporating this metric into potential future emissions pathways can allow the industry to understand the magnitude of emissions reductions needed to no longer contribute additional warming. Deterministic modeling was performed across the dairy industry's emission areas of enteric fermentation, manure management, feed production, and other upstream emissions necessary for dairy production. By reducing farm-level absolute emissions by 23% based on current levels, there is the opportunity for the US dairy industry to realize climate neutrality within the next few decades.

Technical note: valuation of an enteric methane emissions measurement system for cattle.

Through the process of enteric fermentation, cattle produce methane (CH), a potent greenhouse gas (GHG). Growing public concern about climate change has increased the need for accurate methods of measuring CH emissions from cattle directly to improve emission inventories and evaluate emissions mitigation techniques. The present study evaluated a ventilated head box system capable of measuring CH and carbon dioxide (CO) emissions, and oxygen (O) consumption from cattle. Six Holstein heifers were used to measure CH and CO emissions and O consumption from 2 ad libitum intake measurement periods (ADAPT and ADLIB) and 1 measurement period (RESTRICT) with intake restricted to 2% of BW on a DM basis. Methane emissions during RESTRICT were significantly lower ( < 0.0001) than both ad libitum periods. Daily CH4 emission rates per animal were 235.0 ± 6.19 L/d, 228.3 ± 6.18 L/d, and 193.2 ± 8.88 L/d for the periods ADAPT, ADLIB, and RESTRICT, respectively. Carbon dioxide emission rates were 3627 ± 90.72 L/d, 3632 ± 90.47, and 3184 ± 104.79 L/d for the ADAPT, ADLIB, and RESTRICT periods, respectively. Oxygen consumption rates were 3391 ± 99.77 L/d, 3454 ± 99.57 L/d, and 3002 ± 111.36 L/d for the periods ADAPT, ADLIB, and RESTRICT, respectively. The head box system evaluated provides an accurate method of measuring emissions from cattle and can provide information about daily variations and peaks in emissions.

Growth promoting technologies reduce greenhouse gas, alcohol, and ammonia emissions from feedlot cattle.

Increased animal productivity has the potential to reduce the environmental impact per unit of consumable product and is believed to be the most promising and sustainable mitigation technique to meet increasing demand for high quality protein. The feedlot industry uses ionophores, antibiotics, growth implants, and ß2-adrenergic agonists to improve health and growth performance of cattle. These technologies not only increase productivity but also alter microbes in the rumen and increase nitrogen retention in the animal, which may lead to changes in greenhouse gas (GHG), volatile organic compound (VOC), and ammonia (NH3) emissions from feedlot cattle. The present study investigated GHG, VOC, and NH3 emissions from 160 Angus crossbred steers. Steers were blocked by weight in a randomized block design and assigned to 16 pens of 10 animals each. Treatments applied were 1) control (CON; no technology application), 2) monensin and tylosin phosphate (MON), 3) monensin, tylosin phosphate, and growth implant (IMP), and 4) monensin, tylosin phosphate, growth implant, and zilpaterol hydrochloride (fed during the last 20 d of the feeding period; BAA). Cattle were on feed for an average of 107 d. Performance variables (DMI, BW, ADG, and G:F) and carcass traits (HCW, dressing percent, KPH, LM area, fat thickness, marbling score, yield grade, and quality grade) were measured. Gaseous emissions were measured during the last 10 d of the feeding period when animals were housed in 4 totally enclosed identical cattle pen enclosures. To quantify gaseous emissions a 4×4 Latin square design (n=4) was used. Gaseous emissions were analyzed using Proc Mixed in SAS and reported in grams per kilogram HCW per day and grams per kilogram per animal per hour. Treatment with IMP and BAA increased (P<0.05) ADG, final BW, and HCW. Cattle on BAA had greater HCW and LM area (P<0.05) and had lower (P<0.05) CH4, methanol, and NH3 emissions per kilogram HCW than cattle on the remaining treatments. Methane emissions were similar for CON and IMP treated cattle. Nitrous oxide emissions were similar across CON, MON, and IMP treated cattle and were higher in BAA treated cattle (P<0.05). The present study provides a better understanding of how application of growth promoting technologies to feedlot steers affects GHG, VOC, and NH3 emissions per kilogram of product.

Invited review: Contemporary environmental issues: a review of the dairy industry's role in climate change and air quality and the potential of mitigation through improved production efficiency.

Environmental concerns involving the dairy industry are shifting from an exclusive focus on water quality to encompass climate change and air quality issues. The dairy industry's climate change air emissions of concern are the greenhouse gases methane and nitrous oxide. With regard to air quality, the dairy industry's major emission contributions are particulate matter, volatile organic compounds, and ammonia. The emissions of these compounds from dairies can be variable because of a number of factors including weather conditions, animal type, management, and nutrition. To evaluate and compare emissions across the diverse operations that comprise the US dairy industry, emissions should be reported per unit of output (e.g., per kg of 3.5% fat-corrected milk). Accurately modeling emissions with models that can predict the complex bio-geochemical processes responsible for emissions is critical to assess current emissions inventories and develop mitigation strategies. Improving the dairy industry's production efficiency (e.g., improvements in management, nutrition, reproduction, and cow comfort) is an effective way to reduce emissions per unit of milk. With accurate process-based models, emissions reductions due to improved production efficiency could be reported per unit of milk and predicted on a farm-to-farm basis.