Winning roulette

The wheel of the future spins, reserving the prize of dairy farming sustainability for those who focus on valuable strategies for controlling environmental impacts.

The demand for dairy products is expected to continue to grow along with the global population. Chase (2021) summarized the reasons why milk production will remain important for human nutrition in the coming years, including the fact that dairy products are a primary source of nutrients such as vitamins, calcium, phosphorus, and especially high-quality protein.

Dairy cattle are more efficient than non-ruminants at converting plant protein into animal protein, or non-consumable protein into consumable protein, with an average Human Edible Protein (HEP) yield of 2.1 in the United States (USA; CAST, 1999). The HEP contribution of ruminants has been discussed in recent articles (Ertl et al., 2016; Broderick, 2018). Dairy cattle contribute to environmental sustainability by recycling many of the byproducts of the food processing industry, such as distillers' grains generated from ethanol production in North America and Europe (Chase, 2021) . Tricarico (2016) speculated that feeds with more than 30% fiber (neutral detergent fiber, NDF) were unusable for humans and non-ruminants and reported that the diet commonly fed to lactating cows in the US contains approximately 33 different ingredients. Van Amburgh et al. (2019) estimated that by-products represent, on average, about 30% of the dry matter intake (DMI) of dairy cattle in the US. However, in addition to being environmentally and economically sustainable, dairy production needs to be socially acceptable to consumers. Capper (2020) stated that consumers remain very concerned about the environmental impact and global warming effects of dairy production, factors that may influence the consumption of these products.

Human activity has resulted in the production of greenhouse gases (GHGs), primarily carbon dioxide, which has accumulated exponentially in the atmosphere since the early 19th century, leading to global warming (US Global Change Program). Agriculture contributes approximately 11% of the equivalent atmospheric global warming potential (GWP). Approximately 20% of GWP is attributed to methane produced by domestic ruminants and approximately 10% to GHGs from manure (IPCC, 2014). Here, we will emphasize methane production from microbial fermentation in the rumen. Anaerobic methanogenic microorganisms reside primarily in rumen ciliate protozoa and use “excess” energy in the form of hydrogen to reduce carbon dioxide to methane (Wattiaux et al., 2019). Ruminal fermentations that favor the formation of the volatile fatty acids (VFA) acetate and butyrate generate larger amounts of methane, while fermentations that form more propionate produce lower concentrations of the gas (Ungerfeld, 2020) . Furthermore, methane formation represents a great loss of energy for the animal (Wattiaux et al., 2019).

Any nutritional or management strategy that increases milk production per cow or feed efficiency will reduce ruminal methane and eGWP from dairy production (Chase, 2021). Worldwide, per-cow production has been increasing. For example, in the US, it increased 12.2% over the past four years (Table 1; Foreign Agricultural Service/USDA Global Market Analysis). This has enabled a substantial increase in dairy production with virtually no change in cow numbers. Although increasing, per-cow production increased only 4.8% in Brazil over the same period. The figures for closed lactation also differ: in the US, it is approximately 11,000 kg/year, while in Brazil, the average is only 1,500 kg/year (Table 1).

IN ADDITION TO BEING ECONOMICALLY SUSTAINABLE, MILK PRODUCTION NEEDS TO BE SOCIALLY ACCEPTED BY CONSUMERS

However, yields per cow in different regions of Brazil range from 630 to over 4,000 kg of milk/year (US Global Change Program). Thus, we recognize that there is room to improve economic and environmental sustainability in the Brazilian dairy sector. Improved nutrition and management reduced the methane intensity (methane/kg of milk) of milk production in California (the top-ranking US state in production) by 46% from 1964 to 2014 (Naranjo et al., 2016). The same authors reported that lactating cows accounted for 67% of the GHG footprint of dairy farming, with approximately 5% and 27% coming from dry cow maintenance and heifer rearing, respectively . However, in what follows, we will emphasize strategies to reduce methane intensity from lactating cows alone.

Precision feeding

Since the publication of the Urea Fermentation Potential model by Burroughs et al. (1975), increasingly precise feeding systems have emerged to balance diets for lactating cows. Through these systems, nutritional requirements can be met more precisely, and as production per cow increases, methane production is diluted by the increased volume of milk produced.

These models include the Cornell Net Carbohydrate and Protein System (Van Amburgh et al., 2019), also available in NDS Dynamics and AMTS versions (marcelohentzramos@gmail.com); the Nordic Feed Evaluation System (Volden et al., 2011), widely used in northern Europe; the French Ruminant Feeding System (INRA) (Wageningen, 2018); and the recently released 8th edition of the Nutrient Requirements of Dairy Cattle (NASEM, 2021). In addition, an updated system for feeding Brazilian beef cattle, BR-Corte (2016), is available. However, the national system for dairy cattle has not yet been published.

Garg et al. (2016) applied a nutrient requirements model available from the National Dairy Development Board of India to balance the diets of approximately 164,000 dairy cows from small farms across four Indian states. The authors observed dramatic reductions in methane intensity. Although total GHG emissions increased from 24.4 to 26.5 tons of carbon dioxide equivalent (CO2 eq.), after diet balancing, milk production increased and methane intensity decreased. White and Capper (2014) found that weekly diet reformulation, taking into account changes in concentrate ingredient composition, was much more effective than reformulation every three months or even every month.

Numerous trials have been conducted to study the effects on milk production of altering protein or amino acid supply. Olmos and Broderick (2006) added soybean meal (SM) to increase dietary crude protein (CP) from 13.5% to 19.4%. Production responded with maximum increases of 16.7% in milk yield and 17.1% in true milk protein. Using the equation of Congio et al. (2022), methane emission estimates from DMI indicated that the methane intensity produced was 10.6 g methane/kg of energy-corrected milk (ECM) lower with the intake of 15.0% CP. The protein in SM, one of the main protein supplements fed to ruminants, has methionine as the first limiting amino acid (NASEM, 2021). Nursoy et al. (2018) fed FS-based diets containing 11, 13, 15, and 17% CP, with protected methionine to maintain the 3:1 methionine:lysine ratio in the metabolizable protein of the four diets. According to the results, milk and true milk protein yields increased with each CP increment, and methane emissions estimated from DMI declined (Figure 1).

Meta-analyses of the effects of replacing SF with canola meal (Huhtanen et al., 2011; Martineau et al., 2013) indicated an increase in milk and milk protein production when the protein feed was replaced. Furthermore, Holtshausen et al. (2021) showed that replacing SF with canola meal was effective in reducing the intensity of methane production. Furthermore, supplementation with essential amino acids, identified as limiting in feed, has the potential to improve feed efficiency – protected methionine (Zanton et al., 2014; Patton, 2010) and protected lysine and histidine (Lee et al., 2013; Giallongo et al., 2017).

High energy

Like all ruminants, dairy cattle require adequate amounts of NDF in the diet to maintain rumen function. Wales et al. (2009) fed lactating cows on ryegrass pasture supplemented with 3 kg/d or 6 kg/d of a concentrate containing primarily ground barley and steamed cornflakes. The authors observed an increase of approximately 2 kg/d in milk yield and a reduction in methane intensity in response to the 3 kg/d supplement. However, with the 6 kg/d supplement, there was no response in milk production and a much less pronounced reduction in methane intensity, which the authors explained as a possible genetic limitation of the animals. Thus, the results suggested that providing more fermentable energy from starch, and less from NDF, reduces methane production.

Ensiling high-moisture corn grains is widely practiced on dairy farms in North America and Europe. When evaluating whether grinding high-moisture corn would be advantageous when fed as part of the total diet to lactating cows (Ekinci and Broderick, 1997), we observed that reducing the mean particle size from 4.3 to 1.7 mm increased milk and milk protein production by 2.4 and 0.12 kg/d, respectively, and reduced methane intensity by 12% per unit of milk and 10% per unit of protein. The reduction in rumen ammonia concentrations indicated that microbial protein formation was increased, and the reduction in methane intensity was a dilution effect of milk production. Impressive results were also obtained by Charbonneau et al. (2006), who observed that grinding corn kernels (compared to cracked corn), with or without the addition of starch, increased milk and milk protein production and reduced methane intensity per unit of milk and milk protein.

Sugarcane silage is commonly fed to ruminants in Brazil due to its widespread availability. However, its nutritional value is lower than that of corn silage (Mariz et al., 2013). Magalhães et al. (2004) tested whether corn silage could be replaced by sugarcane silage as the sole roughage in the diets of lactating cows (Table 2). Despite the significant decrease in DMI and milk production, milk protein production was numerically similar to that resulting from replacement with 33% sugarcane silage. Methane emissions decreased as a function of the DMI reduction, but notably, methane intensity (per unit of milk protein) was lower when the replacement was 33% corn silage. Ultimately, the authors concluded that this level of replacement was the most economically viable. Methane production per unit of milk was similar when corn silage was replaced by sugarcane at 0% to 67%, but fat-corrected methane in milk was not improved at any replacement rate (Table 2). These effects are largely driven by the reduction in DMI resulting from increased rumen filling by the NDF of sugarcane silage compared to corn silage: 52% vs. 28% indigestible NDF, respectively (Oliveira et al., 2011).

Grass forages are fed as pasture or ensiled to dairy cattle worldwide. Because they are virtually devoid of starch, replacing a portion of them with corn silage (with 25-35% starch, DM basis) can be beneficial in diets for lactating cows. Khan et al. (2015) found that replacing 50% of the DM of grass silage with corn silage increased DMI, milk yield, and milk protein. Methane emissions increased by 14% due to the increased DMI. Clearly, dietary changes that increase milk production (and milk components) will likely increase profits but will not necessarily improve the environmental sustainability of the production system.

Researchers have indicated that silage additives, particularly inoculation with lactic acid bacteria prior to ensiling, improve silage intake and energy value (Muck et al., 2018). Winters et al. (2001) evaluated Charolais steers weighing approximately 400 kg, fed ad libitum on a diet of untreated ryegrass silage (control), ryegrass silage treated with formic acid, or ryegrass silage treated with lactic acid bacteria. The treatments substantially reduced non-protein nitrogen formation in the silage, optimizing protein utilization. Additive inclusion increased average daily gain and gain/DMI, and although methane emissions increased, the intensity per unit of average daily gain was substantially reduced.

Dietary additives

Since the mid-1970s, ionophores have been fed to increase feed efficiency in beef cattle. Their purported mode of action was initially attributed to reducing methane formation, resulting in increased propionate formation, reduced acetate and butyrate formation, and improved dietary energy capture for body growth. However, researchers later indicated that rumen microorganisms adapt to ionophores, limiting their effectiveness in reducing methane production. For example, Guan et al. (2006) showed that the methane emission reduction effect diminished three weeks after adding monensin or lasalocid to the diet, although the reduced acetate:propionate ratio persisted throughout the 15-week feeding period.

Ionophores, such as monensin, approved for dairy cattle feeding, have generally been shown to increase milk production efficiency. McGuffey et al. (2001) indicated that monensin was superior in promoting increased milk production compared to lasalocid. Duffield et al. (2008) indicated that, in most studies, monensin consumption increased milk production by 2.3% and reduced DMI by the same percentage. When body weight gain was accounted for, the monensin diet resulted in a 4.3% increase in energy efficiency. Although methane emissions cannot be calculated from these data, the increased energy efficiency accompanied the lower DMI, implying that methane intensity was reduced by monensin supplementation.

Feeding fats and fatty acids is known to reduce methane emissions, partly due to toxicity to protozoa, which harbor most rumen methanogenic microorganisms (Jayasundara et al. 2016); and partly due to the physical coating of NDF, which reduces fiber digestibility (NASEM, 2021). The diversion of hydrogen from methane formation to the reduction of unsaturated fatty acids also accounts for a small portion of the effects of feeding fat. The NASEM (2021) equation developed to estimate methane emissions indicates that, in a typical diet, increasing fatty acid concentration by 4 to 5% of DMI reduces methane by approximately 7%.

Certain medium-chain fatty acids can have substantial effects on methane emissions. Machmuller et al. (2001) observed that feeding sheep a diet containing 60 g/kg DM of coconut oil reduced methane production two days after dietary inclusion. Odongo et al. (2007) reported that the addition of 50 g/kg myristic acid (a C-14 saturated fatty acid) reduced both DMI and milk yield by approximately 1 kg/d. However, methane emissions were reduced by 36%, and methane intensities from milk yield and milk protein were reduced by 29% and 30%, respectively. Eugene et al. (2021) showed a smaller effect of fat supplementation on methane emissions: on average, DMI reduced by 6.4%, but milk yield remained unchanged, so methane intensity decreased by approximately 9%.

Early research on potential methane inhibitors indicated that, as with ionophores, rumen microorganisms adapted rapidly, and initial reductions in methane emissions dissipated within a short period (Clapperton, 1977). However, recent research has identified a chemically synthesized methane-suppressing compound: 3-nitrooxylpropanol (3-NOP), to which microbial adaptation has not yet occurred.

Hristov et al. (2015) observed that methane emissions were depressed for twelve weeks when 3-NOP was fed at 40, 60, or 80 mg/kg DM. Hydrogen emissions were elevated in the first eight weeks according to the 3-NOP inclusion levels (i.e., 80 > 60 > 40), but by the end of twelve weeks, the treatments showed the same hydrogen emission. Importantly, DMI and milk, milk fat, and milk protein yields were not altered, and methane intensity was suppressed by an average of 28% in animals receiving the three dietary inclusions of 3-NOP (Table 3). Contrary to the results of Hristov et al. (2015), Jayanegara et al. (2018) reported a linear decline in methane emissions as 3-NOP concentrations were increased in the diet, as later confirmed by Melgar et al. (2020) and Yu et al. (2021). Furthermore, Yu et al. (2021) reported that 3-NOP provides more positive effects in dairy cattle compared to beef cattle. Currently, there are no financial incentives to develop research on the inclusion of 3-NOP or other compounds that reduce methane formation.

IN RECENT RESEARCH, A CHEMICALLY SYNTHESIZED COMPOUND WAS IDENTIFIED THAT EXERCISES A SUPPRESSIVE ACTION ON METHANE

There is interest in certain red algae that substantially suppress methane emissions when added to ruminant diets. Kebreab (2021) reported that bromoform-like compounds found in the seaweed species Asparagopsis were responsible for reducing methane formation in vitro. In an in vivo trial, in which Asparagopsis algae were included at 1% of the DM in the diet of dairy cattle, methane emissions were suppressed by 67%. The author also cited studies demonstrating no microbial adaptation to seaweed fed to steers for five months. A report summarizing the results of methane suppression by Asparagopsis expressed concern about the potential toxicity of bromoform and other compounds found in seaweed, although the concentrations required to suppress methane formation appear to be quite low (Vijn et al., 2020). However, there is still much research to be done before this approach can be incorporated into dairy farms.

Individual variations

Producers disagree about which dairy breed is most efficient in terms of production and profit. Capper and Cady (2012) evaluated the environmental impacts of milk production from Holstein and Jersey cows for cheesemaking. They estimated that producing 500,000 tons of cheese would require 4.94 billion kg of milk from Holstein cows and 3.99 billion kg of milk from Jersey cows. Thus, the carbon footprint of producing 500,000 tons of cheese from Jersey milk would be reduced by 1.67 million kg of CO2 eq.

On the other hand, Olijhoek et al. (2018) evaluated Jersey and Holstein cows fed low and high concentrate diets and observed that methane emissions per DMI were lower in Holstein cows on both diets (with a more pronounced difference in the high concentrate treatment). Furthermore, the methane intensity per unit of LCE did not differ between breeds.

Prendiville et al. (2009) compared the productive efficiency on pasture, with limited concentrate supplementation, between Holstein, Jersey, and F1 Holstein x Jersey cows. Although F1 cows were 50 kg lighter, their average DMI was similar to that of Holstein and higher than that of Jersey cows, while milk production was higher in Holstein cows. Ultimately, F1 cows were more efficient in terms of product yield and less environmental damage. As summarized by Berry and Evans (2022), "the bigger the cow, the more she eats"—and the greater the challenge of reducing dairy farming's contribution to GHG emissions, as it is necessary to mitigate the effects of body size and metabolic needs without losing milk production and its components.

The concept of residual feed intake (RFI), a feed efficiency metric initially developed to evaluate beef cattle (Koch et al., 1963), was incorporated into dairy cattle production. The RFI value is calculated as the difference between observed and predicted intake (based on feeding models) for a given individual at a given stage of lactation. Because it represents the difference between actual and predicted intake, lower or negative RFI values are ideal. Estimates can be made retrospectively using accurate and robust data from previous nutritional studies (e.g., Liu and Vandehaar, 2020). The variation found between animals indicates that RFI can be a parameter for genetic selection, as there is evidence of "moderate" heritability (Connor et al., 2015). Using data from 166 cows between 50 and 130 days in milk, Liu and Vandehaar (2020) determined that the best (i.e., lowest) energy RFI values were well correlated with the best (i.e., lowest) protein RFI values: when consuming diets differing only in CP level, cows in each group were classified as high, medium, and low RFI. As RFI decreased (or improved), indicating greater energy efficiency, milk protein production efficiency (milk protein/CP intake) and methane intensity improved at both dietary CP levels (Table 4).

Milk methane/protein production was lower when the 18% CP diet was consumed, indicating better protein utilization. This finding suggests that the metabolizable protein supply was insufficient in the 14% CP diet. Finally, the results indicate that selection for RFI in dairy cattle holds considerable promise for the environmental and economic sustainability of milk production systems.

RESIDUAL FEED CONSUMPTION (RFI) IS A METRIC WITH THE POTENTIAL TO SELECT THE MOST EFFICIENT ANIMALS IN CONVERTING ENERGY AND NUTRIENTS CONSUMED INTO HIGH-VALUE-ADDED MILK PRODUCED

Additional tools

In addition to the above approaches, parallel tools are emerging to reduce methane intensity and GHG emissions. Feed additives include fibrolytic enzymes (Arriola et al., 2017), yeast cultures (Poppy et al., 2012), and direct-fed microorganisms (McAllister, 2011). Similarly, the incorporation of "essential oils" into the diet demonstrates potential to suppress methane emissions (Belanche et al., 2021; Klop et al., 2017), as do dietary blends of tannins and essential oils (Rodrigues et al., 2019). For example, replacing conventional forage legumes with legumes containing condensed tannins can improve feed and protein efficiency (Hymes Fecht et al., 2013) and possibly reduce methane intensity in milk production (Kelln et al., 2021). Through summaries of published research, authors pointed out improvements in feed efficiency and reductions in GHG emissions in cows that received biweekly doses of bovine somatotropin (Capper et al., 2008; Capper and Bauman, 2013).

On average, US dairy cows have only 2.5 lactations, and approximately 28% of GHG emissions are attributed to heifers (Capper and Cady, 2020). Therefore, any measure capable of increasing the number of lactations per cow will contribute to reducing the carbon footprint associated with dairy farming. Some of the dietary strategies adopted to improve lactation efficiency, such as ionophore supplementation, can also improve growth efficiency in heifers, thereby reducing GHG production.

Although not mentioned, the storage of manure that is later used in agriculture should also be discussed in the proposal to reduce the carbon footprint. In this context, balancing diets and using other methods that improve feed efficiency can reduce the production of solid and liquid manure—in this regard, Benchaar and Hassanat (2019) described interesting management approaches.

The turning point

Global warming caused by the accumulation of GHGs in the atmosphere is one of the most threatening problems facing humanity today and in the coming decades. Enteric methane produced by domestic ruminants, including dairy cattle, is one of the sources of GHGs from agricultural activities. Aware of this, we recognize that any nutritional or management practice that increases cow production efficiency will reduce the GHG footprint associated with dairy production.

Since the last century, much progress has been made in the productivity of lactating cows worldwide. Brazil has made progress in milk and solids production per animal, but much remains to be done. The ongoing genetic evolution of dairy cattle has increased the need to adopt nutritional models that accurately and accurately meet the energy and metabolizable protein requirements of lactating females. Accurately balancing lactation diets boosts productivity by reducing methane intensity.

Furthermore, methane derives more from NDF fermentation than from starch in the rumen. Therefore, supplementing with starch-rich feeds and strategies to improve the quality of forage included in the diet will reduce methane formation. Furthermore, the inclusion of fats and chemical additives, such as 3-NOP, show potential to directly suppress methane synthesis.

Finally, future genetic improvement may be guided by selection for nutrient use efficiency, as already indicated by the metric that classifies the CAR of individuals.

The wheel of the future is spinning. With each spin, the chance to get the strategy right and win the grand prize of business sustainability is renewed. This moment calls for transformation, and the time to turn things around has to be now.

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