Synopsis

The goal of this review was to analyze published data on animal management practices that mitigate enteric methane (CH4) and nitrous oxide (N2O) emissions from animal operations. Increasing animal productivity can be a very effective strategy for reducing greenhouse gas (GHG) emissions per unit of livestock products. Improving the genetic potential of animals through planned cross-breeding or selection within breeds and achieving this genetic potential through proper nutrition and improvements in reproductive efficiency, animal health, and reproductive lifespan are effective approaches for improving animal productivity and reducing GHG emission intensity. In subsistence production systems, reduction of herd size would increase feed availability and productivity of individual animals and the total herd, thus lowering CH4 emission intensity. In these systems, improving the nutritional value of low-quality feeds for ruminant diets can have a considerable benefit on herd productivity while keeping the herd CH4 output constant or even decreasing it. Residual feed intake may be a tool for screening animals that are low CH4 emitters. Still, there is currently insufficient evidence that low residual feed intake animals have a lower CH4 yield per unit of feed intake or animal product.

Commentary

This limited series of the occasional e-letters are comprised of (3) three articles. They will appear fortnightly and are published during January and February, though they will be accessible through our social media pages.

Analysis

ANIMAL MANAGEMENT MITIGATION PRACTICES

Enhancing Animal Productivity

An increase in animal productivity can be achieved by improving animal genetics, feeding, reproduction, health, and overall management of the animal operation. In many parts of the world, the single most effective GHG mitigating strategy is to increase animal productivity, allowing a reduction in animal numbers is providing the same edible product output with a reduced environmental footprint. The decline in animal numbers was the single most influential mitigation strategy that significantly reduced the C footprint of the United States dairy industry (Capper et al., 2009). Similarly, with the milk quota system in the Netherlands, milk production per cow increased from 6,270 kg fat and protein-corrected milk (FPCM)/yr in Kyoto base year 1990 to 8.350 kg FPCM/yr in 2008, with a concomitant decrease in CH4 production from 17.6 to 15.4 g/kg FPCM, respectively (Bannink et al., 2011). The pork industry has made similar progress. The number of hogs marketed in the United States increased by 29% between 1959 and 2009, whereas the size of the breeding herd decreased by 39%.

Feed conversion efficiency increased by 33%, feed use decreased by 34%, and the C footprint per 454 kg of hot dressed carcass weight produced been reduced by 35%. The litter size increased from 7.10 in 1974 to 9.97 piglets in 2011, and the amount of pork produced from a breeding animal increased during the same period from 775 to 1,828 kg (National Pork Board, 2012). In the global context, particular attention must be placed on mitigating GHG emissions from developing countries. Europe, North America, and the non-European Union former Soviet Union countries produced 46.3% of ruminant meat and milk energy, and only 25.5% of the enteric CH4 emissions in 2005 (O’Mara, 2011). In contrast, Asia, Africa, and Latin America produced a similar amount (47.1%) of ruminant meat and milk energy but a large proportion (almost 69%) of enteric CH4 emissions. Therefore, the Intergovernmental Panel on Climate Change (IPCC, 2007) estimated that about 70% of the global GHG mitigation potential from agriculture lies in developing countries (Smith et al., 2007).

In developing countries, however, smallholders typically rely on a more significant number of low-producing animals instead of a smaller number of higher-producing animals (Tarawali et al., 2011). As pointed out by these authors, the two constraints for increasing animal production in developing countries are the low genetic potential of the animals and the poor availability of quality feed. Undoubtedly, a significant possibility exists for increased production by better feed management and proper feeding in developing countries and intensive production systems in developed countries. Using a partial life cycle assessment (LCA), Bell et al. (2011) demonstrated that improvements in feed efficiency and milk production [in their example, from about 23 to 28 kg energy-corrected milk (ECM)/d] could significantly reduce GHG emissions and land use of the dairy herd. However, selection for high productivity should not be at the expense of other important traits, especially those traits critical for the survival of livestock in the local environment (climate, feed resources, and diseases).

With dairy cows, tradeoffs between selection for high milk production and decreased productive life, increased death rate, and decline in fertility need to be avoided (Hare et al., 2006; Miller et al., 2008; Norman et al., 2009). The survival rate to parity two by Holstein cows in the U.S. declined from 77.3% in 1980 to 74.1% in 2000, and survival rates to parities 3 and 4 decreased from 56.6 in 1980 to 49.0% in 1999 and from 24.2 (in 1980) to 14.3% in 1997, respectively (Hare et al., 2006). With only 2 to 2.5 lactations, dairy cows cannot realize their production potential. As pointed out by Van Vuuren and Chilibrost (2011), the milking efficiency of dairy cows (i.e., milk energy output/feed energy input) increases exponentially up to 4 lactations. Impaired reproductive performance also has a significant impact on farm profitability. It might not be fully compensated by increased milk production, as demonstrated by Evans et al. (2006) for commercial dairy herds in Ireland.

Apart from productivity, however, management practices, such as improved animal health and fertility (Place and Mitloehner, 2010), in intensive production systems can improve overall animal performance and lifetime productivity. By some estimates, extended lactation (Van Amburgh et al., 1997; Auldist et al., 2007; Kolver et al., 2008; Grainger et al., 2009) can reduce enteric CH4 emission from dairy production systems by 10% (Smith et al., 2007). However, this may not be a feasible alternative to a 12-mo lactation cycle in some production systems (Butler et al., 2010). In intensive dairy systems, similar effects may be produced by reducing the dry period, with or without the use of recombinant bovine somatropin (rbST; Annen et al., 2004; Rastani et al., 2005; Klusmeyer et al., 2009). This practice may not be suitable for all cows and all herds (Marett et al., 2011; Santschi et al., 2011). Pinedo et al. (2011), for example, reported decreased early lactation and 305-d milk yields and increased overall culling rate when the dry period was reduced or eliminated.

Progress in reducing GHG emission intensity (Ei; GHG per unit animal product) from ruminants in the developing countries can be achieved by increasing animal productivity. Gerber et al. (2011) demonstrated a significant difference in GHG emissions depending on the milk yield of dairy cows, with as much as a 10-fold variation between countries or regions with high and low milk yields. Flachowsky (2011) estimated that a dairy cow producing 40 kg milk/d would have about 50% lower CO2–equivalent (CO2e) emissions per kilogram of edible protein than a cow milking 10 kg/d. Similarly, emissions would be about 70% lower from beef cattle gaining 1.5 vs. 1.0 kg/d, 40% lower from a growing or fattening pig gaining 900 vs. 500 g/d, and 60% lower from a laying hen with 90 vs. 50% laying performance. According to data for the dairy sector by the Food and Agriculture Organization (Gerber et al., 2011), in 2010, the annual milk production per cow for North America was approximately 8,900 kg and in South and Southeast Asia (SEA) 2,800 kg/yr for specialized dairy systems and 1,000 kg/yr for unspecialized systems.

Using the Gerber et al. (2011) relationship for GHG emissions (CO2e, kg/cow per yr = 0.8649 × milk yield, kg/ cow per yr + 3,315.5, r2 = 0.79, and assuming milk yield is as FPCM), a North American cow will produce about 11,000 kg CO2e/yr and a SEA cow about 5,700 kg CO2e/ yr, which is 1.24 and 2.05 kg CO2e/kg FPCM milk, respectively. If milk production in SEA is increased by 30%, the CO2e output will decrease to 1.79 kg/kg milk. Similarly, Blümmel et al. (2009) estimated that increasing milk yield per animal in India from the national average of 3.6 L/d to up to 9.0 L/d was possible using currently available feed resources, and this would potentially reduce CH4 production in that country from 2.29 to 1.38 Tg/yr. Another example of how increased productivity, through increased feed quality, can decrease enteric CH4 Ei was provided by Waghorn and Hegarty (2011). These authors calculated that growing lambs on higher quality pasture (20% higher ME value) would result in greater gain and about 50% lower enteric CH4 Ei.

Ruminant production systems based on concentrate feeds are reportedly more efficient from the animal perspective and emit less GHG per unit of product (Beauchemin et al., 2010; Pelletier et al., 2010). However, this may not be the case if all inputs are included in calculating GHG Ei for dairy production systems (Rotz et al., 2009) or intensive grain-finished vs. extensive, grass-finished beef systems (Pelletier et al., 2010; Waghorn and Hegarty, 2011), particularly when soil C storage in grasslands and land-use changes are adequately considered. Improvement in animal nutrition through the strategic use of available resources such as feeding a balanced diet based on the physiological needs of the animal, reducing feed wastages, increasing concentrate feed availability, and improving animal genetics have a tremendous potential ‘to increase animal productivity in developing countries (Makkar, 2013).

Due to poor pasture quality, grazing management may not be a viable option for improving animal nutrition in many regions, in which case improvement in productivity must come through feeding preserved forages or concentrates. Because the growth in cereal grain production has generally followed the growth of the world population (Hristov et al., 2013b). Because human nutrition is expected to improve in the developing world, it is questionable if more grain will be available for feeding ruminant animals. Growing ruminants are much less efficient in utilizing grain for BW gain than poultry or swine, but dairy cows can be as efficient (depending on the level of production) as monogastric animals in producing edible protein (Flachowsky, 2002, 2011; Gill et al., 2010; De Vries and de Boer, 2010). Whether increasing the inclusion of grain in the ration of ruminants can be an economically feasible strategy to increase milk and particularly meat production and thus reduce the environmental footprint of livestock is questionable in the long term.

A challenging but more sustainable solution is to produce concentrate by strategically mixing agro-industrial by-products that are rich in energy or proteins (Makkar, 2013). Within dairy production systems, grassland-based systems have been estimated to have generally higher (by about 50%) GHG emissions per unit of FPCM than mixed farming systems. However, some grazing systems in temperate regions have low GHG emissions (FAO, 2010). Organic dairy production systems generally have higher GHG Ei than conventional dairy systems (Heller and Keoleian, 2011; Kristensen et al., 2011). This may not always be the case, depending on the amount and type of fertilizer used for crop production and the level of animal productivity (Martin et al., 2010). The environmental efficiency of pasture-based dairy production systems can be improved by a variety of best management practices (Basset-Mens et al., 2009; Beukes et al., 2010).

Including improved reproductive performance leading to low involuntary culling, using crossbred cows with high genetic merit for milk solids, and improved pasture management to increase average pasture and silage quality. Kennedy et al. (2001) investigated the response of Holstein-Friesian cows, of medium or high genetic merit, fed an adequate supply of grass to half and twice the industry norm level of concentrate supplementation and concluded that the low concentrate feeding system restricted the ability of the high genetic merit cows to express fully their genetic potential for milk production. The authors also concluded that high-concentrate supplementation systems, although yielding more milk and better utilizing the genetic potential of the animal, may not be economically feasible when milk price is low, and feed cost is high. Enhancing the genetic potential of the animal is critically essential. Still, it is equally important not to import high genetic potential animals into climates and management environments where high-producing animals can never achieve their potential.

In fact, perform worse than native breeds or crossbreeds due to management, disease, or climatic challenges. The Holstein dairy cow, for example, has a high genetic potential for milk production, which translates into low GHG emissions per unit of product. However, importing Holstein cows into regions that cannot provide the necessary nutritional, health, and physical environments to support their genetic potential for production leads to poor health, milk production, and reproduction. (Compounded with the already low genetic merit of the breed for this trait) resulting in underperformance and long-term inefficiency of the production system (Harris and Kolver, 2001; Evans et al., 2006; Madalena, 2008). As pointed out by Harris and Kolver (2001), the failure of the Holstein breed to maintain high reproductive efficiency appeared to be one of the main reasons for the reduced survival of the breed within the pasture conditions of New Zealand. Whereas in these conditions rearing the local cross-bred dairy cows has resulted in a substantial economic advantage for farmers.

Enhancing Animal Productivity by Improving the Nutritive Value of Low-Quality Feeds.

Low-quality feeds, such as crop residues and low-quality grasses, are essential basal feeds for ruminants in developing countries (Blümmel et al., 2009; Walli et al., 2012). Devendra and Leng (2011) and Tarawali et al. (2011) argued that interventions to improve the feeding value of low-quality feeds should be considered in the whole farm system context. In developing countries, most farmers operate in smallholder mixed crop-livestock systems, and almost 3 billion people depend on such systems for their food supply (Herrero et al., 2010). Most livestock production systems typical of those areas are faced with one or more seasons with low feed availability and quality, and production during such seasons is nonexistent or even negative because animals rely solely on crop residues. During the cropping and harvesting season, more and better feeds are available, but labor limitations and grazing land availability may prevent optimal feeding (Tarawali et al., 2011; Owen et al., 2012). The importation of high quality feeds into these systems is very low (e.g., Blümmel et al., 2009).

In most smallholder mixed crop-livestock methods, the primary goal is crop production, and animals are simply a means to achieve this goal. In these systems, livestock intensification competes with crops for inputs of labor, capital, and land. Livestock in developing countries is not only valued for their production of food but also for functions such as manure production, draught, capital store, and insurance (Udo et al., 2011), which are functions supported by larger herd sizes. Reduction of the number of animals, particularly in subsistence production systems, allows for adequate feed to a herd selected for the genetic potential that can receive appropriate veterinary care (Tarawali et al., 2011), leading to an improvement in individual animal and total herd productivity. Hence, CH4 emissions will be reduced for both the entire herd and per unit of animal product. However, herd size reduction requires mechanization, artificial fertilizers, and proper banking and insurance systems to replace the importance of the animals (Udo et al., 2011).

Regulatory measures (taxes and quota) could reduce the benefits of keeping too many animals. Supplying a substantial amount of relatively good quality feed in a ration will increase individual animal productivity. Green feeds such as multipurpose leguminous fodder trees and grasses, such as Napier (Pennisetum purpureum), are promising supplements with a reasonable expectation for worldwide adoption (Saleem, 1998; Mekoya et al., 2008; Oosting et al., 2011; Tarawali et al., 2011; Owen et al., 2012). However, such fodder crops compete with food crops for land and water. A positive contribution of leguminous fodder crops to soil fertility can be expected because of N fixation. Whether polyphenols in leguminous fodder trees will positively affect CH4 emissions at the inclusion levels observed in developing countries needs investigation (Owen et al., 2012; Hristov et al., 2013b). Another kind of supplementation is the provision of relatively small amounts of nutrients that limit intake, digestion, or utilization of the ration (Oosting et al., 1994, 1995; Owen et al., 2012).

The urea molasses multi-nutrient block developed in Asia (Sudana and Leng, 1986; Owen et al., 2012) is an example of an N-providing supplement for diets low in N. The potential role of these blocks as a source of CH4 mitigating agents, that is, nitrates is discussed in our companion paper (Hristov et al., 2013a). Calcium, P, Cu, and Zn are other nutrients that improve low-quality feeds. Limitations of those nutrients mostly occur when low-quality feeds are given as the sole feed. Whenever some green feeds or concentrates are available, limitations are less pronounced. Hence, under such conditions, the direct effect of supplementation on animal productivity might below. Sarnklong et al. (2010) and Owen et al. (2012) discussed options for treating crop residues. Rice or wheat straw, the crop residue in these publications, can be regarded as a proxy for other low-quality feeds. Chemical treatments [e.g., urea, ammonia (NH3) or sodium hydroxide] and biological treatments (direct by growing fungi on the straw or by administering fungal enzymes to the straw) aim to improve straw digestibility by disrupting the cell wall structure and making hemicellulose and cellulose fractions more available for rumen digestion.

 Urea treatment is the most widespread treatment advocated in developing countries. Low-quality feeds are mixed with an equal weight of a 0.5 to 3.0% urea solution and stored airtight for at least 1 wk. Ammonia is formed from the urea, and the alkaline conditions compromise cell wall conformation and improve intake and digestibility. An additional benefit is the provision of N for further improvement of feed value. Economics, labor needs, and practical feasibility have led to poor adoption of these techniques (Schiere, 1995; Owen et al., 2012) despite decades of research and outreach on the subject (Sundstøl and Owen, 1984). Roy and Rangnekar (2006) described one successful case of urea treatment adoption in India, where treatment helped farmers overcome storage problems under humid conditions. Even if socioeconomic circumstances benefited crop residue treatment, it is uncertain whether this would mitigate CH4 emissions per unit of animal product. Of course, if forage digestibility and concomitant animal productivity are increased, CH4 production per unit of product will decrease.

Fungal treatment is promising on a laboratory scale, but process control is difficult in piles of material because of the heat from fermentation (Walli, 2011). Moreover, in feeding experiments, nutrient availability and animal utilization were not improved, explaining why this technology was not adopted (FAO, 2011b). The loss of digestible DM and the decrease in the feeding value of the crop during this treatment can be dramatic, rendering the process unfeasible (Lynch et al., 2012). Many farmers in extensive production systems recognize and consider straw quality in their decisions for crop cultivation (Parthasarathy Rao and Hall, 2003; Schiere et al., 2004; Parthasarathy Rao and Blümmel,2010).

Coarse straws (of millets, sorghum, and corn) have better feeding quality than slender straws (of rice, wheat, and barley). But also within crop species, genetic variation exists concerning straw yield and quantity and breeding, and selection can improve straw quality and yield without compromising grain yield (Subba Rao et al., 1993; Grando et al., 2005; Blümmel et al., 2010). An advantage of breeding and selection overtreatment is that no additional input of capital or labor is required. Increased use of crop residues for feeding may, however, reduce soil OM content (Tarawali et al., 2011). Breeding straw for improved feeding quality has already shown promise for increased production and reduced CH4 intensity in southern India (Blümmel et al., 2010).

Conclusion

Extrinsic factors such as ecological issues in beef production are essential in consumer perception of beef and branded beef products, though they must be addressed. The global human population is predicted to grow to 9.5 billion by 2050 (US Census Bureau, 2008), with a widespread increase in milk and meat requirements per capita conferred by increased global affluence (Keyzer et al., 2005). The Food and Agriculture Organization of the United Nations has projected that food production must increase by 70% to fulfill the nutritional requirements of this increase in the global population. Because of the competition for energy, land, and water will accelerate as urban areas encroach upon agricultural land, this production must occur on ever decreasing land areas (Capper et al., 2011). These forces will challenge livestock producers to produce sufficient amounts of safe, affordable, savory red meats to meet consumer demand employing a shrinking resource base.

Since 88% of the greenhouse gas emissions in beef production are accrued on the farm, cattle production must bear most of the burden required to reduce greenhouse gas emissions from beef production (Hyland et al., 2017). Environmentally sustainable food supply can only be achieved by adopting integrated systems that make the most efficient use of available resources and concurrently reduce the environmental impact (Capper et al., 2008, 2009, 2010, 2011, and Hyland et al, 2017). The role of efficiency in improving U.S. beef system sustainability has been called into question by certain groups and agencies promoting a social or political agenda as opposed to animal agriculture (Nierenberg, 2005; and Koneswaran and Nierenberg, 2008). Capper et al (2009), however, concluded that improved resource use per unit of food output considerably reduced the environmental impact of a unit of milk produced by U.S. dairies from 1944 to 2007.

The next E-letter will tackle the genetic aspect and the interlinks with cattle health! We want to proceed further, more in-depth on this controversial subject. Therefore, please follow us on social media and join us on the (15^th) fifteenth of the month for Part (2!) two to learn more about the environmental impact of beef production.  Thereafter, please join us on the (1^st) first and (15^th) fifteenth of each month for our fortnightly delivery of insightful, informative must-reads from some of the world’s scientific thinkers. Selected by our editors is a collection of current topics with a profound ability for beneficial improvements, guidelines, and process practices. Thank you for reading our publication entirely; please share it with others who also care. We look forward to your comments and having you with us again fortnightly; we will be thrilled in having you with us; thus, we will take your trust in us with great honor and appreciation.