Introduction on Dairy sustainability.
Dairy production is considered a major societal asset globally due to its economic and nutritional benefits.
Despite not being the world’s top milk producer, the dairy business generated $628.27 billion in revenue in 2018 (O’Keefe, 2018). This indicates that the industry has a significant economic impact. As of 2019, the United States is home to 9,336,000 dairy cows that yield an average of 10,610 kg of milk annually, or approximately 99,056,409 kg (USDA, 2020).
California produces over 20% of the nation’s milk, while the top five states that produce the most are Wisconsin, Idaho, New York, and Texas (Sumner and Matthews, 2019; USDA, 2020). Due to the dairy industry’s significant economic contribution, California’s milk production and processing in 2019 generated an estimated $57.7 billion in economic effect and supported over 179,900 employment (Sumner and Matthews, 2019). Approximately 13% of the $49.9 billion in cash revenues generated for the top-ranked agriculture-producing state of California come from the production of dairy, making it the main agricultural commodity in the state (CDFA, 2019). The dairy business not only contributes significantly to economic growth, but its products also provide a significant nutritional advantage to the world’s expanding population.
In addition to being a full, premium protein, milk and dairy products are well-known sources of calcium, vitamins, and other specific minerals. Dairy products have been shown to have numerous nutritional advantages for maintaining healthy bones, including the prevention of osteoporosis and other bone disorders. Specifically, milk’s calcium increases children’s bone mass, and when combined with vitamin D—found in fortified milk products—it helps older people avoid osteoporotic fractures and bone loss. Studies have demonstrated that supplementing with dairy products increases vitamin B-12 plasma concentrations significantly and enhances growth, activity, and cognition in low-income nations where children suffer from nutritional inadequacies (Allen, 2003; Siekmann et al., 2003). Furthermore, a baby’s birth weight and subsequent bone mineral content in infancy are favourably correlated with the amount of milk consumed by the mother during her pregnancy. Due to their antibacterial and immunomodulatory qualities, bioactive peptides found in milk’s whey component have been demonstrated to have positive effects on the immune system. Dairy products have been linked to improvements in glucose homeostasis and a lower incidence of type-2 diabetes, which suggests an inverse relationship between dairy consumption and cardiovascular disease. Despite the relatively high saturated fat content of milk, studies have shown that drinking milk does not raise the risk of cardiovascular disease. In addition, milk consumption was linked to a lower incidence of juvenile obesity as well as better adult body composition and weight loss.
It has also been demonstrated that dairy consumption is inversely linked to the incidence of certain cancers, including colorectal, bladder, stomach, and breast cancers; no other cancer types have been linked to dairy consumption. Despite the fact that the manufacturing of dairy products promotes human health, the economy, and general nutrition, environmental concerns over dairy products are growing.
Impact on Dairy sustainability.
The previous 30 years have seen the warmest period on record, with the earth’s surface experiencing enormous temperature increases, mostly in the recent three decades (IPCC, 2014). Apart from this rise in temperature, the climate has also undergone significant changes due to rising sea levels, increasing ocean temperatures, and a significant rise in greenhouse gas emissions (IPCC, 2014).
The previous several centuries have also seen an increase in the ocean’s absorption of CO2, which has led to ocean acidification, a drop in the pH of surface water, and a sharp decline in the number of glaciers and ice sheets worldwide. The primary source of these significant climate shifts is the anthropogenic (caused by humans) emissions of greenhouse gases, which have been rising consistently since the 1750s, when the industrial revolution first got underway (Place and Mitloehner, 2010). With over 78% of these CO2 emissions coming from industrial activities and the burning of fossil fuels, atmospheric concentrations of CO2, CH4, and N2O are likewise at their highest points in at least the last 800,000 years (IPCC, 2014).
Numerous research studies have demonstrated that the raising, transportation, processing, and consumption of cattle all contribute significantly to global warming (de Vries and de Boer, 2010; Milani et al., 2011). It has been demonstrated that dairy cattle, in particular, have an adverse effect on the air, water, and land (Naranjo et al., 2020). Over time, the US dairy business has witnessed significant advancements in environmental protection. Specifically, there has been a significant rise in milk output, mostly as a result of sharp increases in milk production per cow, an increase in the average number of cows per farm, and a general decline in the total number of animals (Wolf, 2003; Barkema et al., 2015).
Through the use of total mixed rations calibrated for nutritional and energy requirements accounting for each animal’s age and stage of lactation, the nutrition of dairy animals has also enabled a significant improvement in production (National Research Council, 2001). Further lowering the environmental impact per unit of milk produced, genetic selection has also been a significant factor in the productivity, lifespan, and efficiency gains of dairy cows (Pryce and Haile-Mariam, 2020). From the mid-1940s to 2007, milk productivity increased fourfold due to advances in herd management, mainly achieved by increasing density on dairy farms, as well as improvements in nutrition and genetics (Von Keyserlingk et al., 2013).
The efficiency of milk production has increased up to 2014, when 1 kg of California’s energy and protein corrected milk (ECM) released 1.12–1.16 kg of CO2 equivalents (CO2e) as opposed to 2.11 kg in 1964, a 45% decrease in CO2e (Naranjo et al., 2020). These advancements have been furthered by the dairy sector. In 2017, dairy production systems used 25.2% less water, 17.3% less feed overall, 20.8% less land, and 30.5% less feed per million metric tons of energy-corrected milk than they did in 2007. This contributed to the industry’s remarkable productivity gains and environmental advancements (Capper and Cady, 2020).
Dairy systems still have an impact on the environment despite these significant advancements over the past century. These include: greenhouse gas emissions from enteric fermentation, manure management, and feed production; water use for milk processing and feed production; water quality contamination from manure’s nitrogen (N) and phosphorus (P); and the need for land for feed production (Naranjo et al., 2020). There are environmental effects connected to dairy processing and subsequent production in addition to the direct effects of cattle, such as N and P as a result of dairy production methods.
Manure Emissions From Dairy Cattle
There’s a chance that dairy manure will harm the ecosystem. The animal will release nitrogen in its urine and feces if it is not kept by it or released in milk (Hristov et al., 2019). Compared to feces, urine is more vulnerable to nitrogen losses from animal waste to the environment. When applied to land in excess of crop requirements, dairy manure is a substantial source of N and P that can contaminate surface water (Knowlton and Cobb, 2006). The rapid expansion of algae populations that consume dissolved oxygen in water due to excess N and P in the water is known as eutrophication, and it lowers the amount of dissolved oxygen that is available for aquatic animal life to grow (Knowlton and Cobb 2007)
Along with having an impact on the environment, air quality also has an impact on the health of people and animals. Dairy cattle have been linked to poor air quality. NH3 is one such substance that dairy animals create and that has an impact on air quality. When urease found in feces combines with N in urea from the animal’s urine, ammonia is created (Place and Mitloehner, 2010). The amount of urea in the urine, pH, temperature, and the urease enzyme’s activity all affect how much ammonia is produced from dairy waste (Muck, 1982; Sun et al., 2008). Volatilization can happen during the application of waste to soil as a fertilizer, as well as during the long-term habitation and storage of manure, in addition to NH3 losses from fresh waste (Bussink and Oenema, 1998).
The amount and content of animal waste, the environment, and the management practices of the manure storage facility all affect the total amount of nitrogen lost, which can range from 0.82 to 250 g NH3/cow/day (Bussink and Oenema, 1998; Hristov et al., 2011). Strategies for managing dairy waste have a significant impact on NH3 air emissions. The manure management techniques, such as separated liquid and solids, aerated, covered, untreated straw, and finally anaerobic digestion, result in the highest NH3 emissions after field application (Amon et al., 2006). Through the synthesis and volatilization of nitrous oxide (N2O), nitrogen in trash can also contribute to the generation of greenhouse gases.
N2O emissions can result from the long-term storage of manure in lagoons and the land application of dairy dung on fields. The amount of N and carbon in the manure determines how much N2O is released during storage (Amon et al., 2006). Management and the surrounding environment have an impact on the formation of nitrous oxide and its subsequent volatilization. While anaerobic environments, like those found in lagoon systems, have reduced N2O emissions, higher temperatures and surface coverings also lead to increased emissions (Dustan, 2002). When compared to land application, the process of storing manure for an extended period of time appears to also contribute a greater percentage of greenhouse gas emissions; emissions from aerated, separated, digested, and untreated manure contribute progressively less.
Effect of Nutrition on Emissions From Dairy Cattle
It has been demonstrated that the intestinal emissions of dairy cattle contain a range of gases. For instance, the GHG that contributes most to climate change is CO2, which is released by dairy cattle as a consequence of aerobic cellular respiration (Place and Mitloehner, 2010). But because the CO2 was previously recycled from the atmosphere via fixation during photosynthesis in plants, which are then fed by the cattle, this gas is not thought to represent a net contributor to the growth in GHGs (Steinfeld et al., 2006). As a result of the NO3 redaction process that is carried out by the bacteria in the rumen, dairy cattle can also produce N2O from intestinal emissions (Kaspar and Tiedje, 1981).
CH4 is by far the most important intestinal emission component from dairy cattle. Methanogenic archaea reduce CO2 to produce methane, which functions as a hydrogen sink in the rumen (Janssen and Kirs, 2008). By eliminating this hydrogen, which can be hazardous to some bacterial communities and result in the illness condition rumen acidosis, methanogens play a crucial role in the health of the rumen (Beauchemin et al., 2009). Apart from being a strong greenhouse gas, CH4 also causes an approximate 2–12% reduction in the animal’s potential energy that may be utilized for growth, gestation, or lactation, among other productive uses (Moe and Tyrrell, 1979).