Synopsis

The utilization of fibrous feedstuffs in ruminant diets is associated with another extrinsic character of beef discussed herein as the production of methane that has been condemned for its contribution to global climate change. Details exist, as will be discussed in other sections of this text, the production of methane can be ameliorated using rumen modifiers (probiotics) that decrease the energy loss of methane, thereby increasing production efficiency.

Commentary

This limited series of the occasional e-letters are comprised of (5) five articles. They will appear fortnightly and are published during September, October, and November though they will be accessible through our social media pages.

Analysis

Direct-Fed Microbials

Direct-fed microbial (DFM), in one form or another, are commonly used as supplements in animal production. Probably the most common DFM used in ruminant nutrition is yeast-based products (YP). The notion of using YP to mitigate CH4 production has been discussed (Newbold and Rode, 2006), but except for some exciting and unconfirmed in vitro results (Chaucheyras et al., 1995), convincing animal data to support this concept are lacking. Meta-analyses reported an overall positive effect of various YP on milk yield in dairy cows (Van Vuuren, 2003; Desnoyers et al., 2009; Robinson and Erasmus, 2009; Poppy et al., 2012). The Robinson and Erasmus (2009) review reported that Saccharomyces cerevisiae YP increased milk yield by (3.6%) three-point six percent on average (over the control). The same YP did not affect feed intake or milk production and composition of high-producing dairy cows (Hristov et al., 2010b), which only emphasizes the variability and conditional effects of these products. Other DFM interventions of ruminal fermentation include inoculation with lactate-producing and lactate utilizing bacteria to promote more desirable intestinal microflora and stabilize pH and promote rumen health, respectively.

A meta-analysis by Krehbiel et al. (2003) reported a generally positive trend for improved health in young, growing dairy or beef cattle treated with various DFM (mainly based on Lactobacillus and Streptococcus and in some cases Propionibacterium spp.). Several studies have reported a successful establishment of DFM products based on Megasphaera elsdenii (one of the essential lactate-utilizing species in the rumen) in sheep and cattle, but effects on ruminal pH and fermentation have been inconsistent (Klieve et al., 2003; Henning et al., 2010). There have also been other attempts to inoculate the rumen with fungi (Candida kefyr) and lactic acid bacteria (Lactococcus lactis) along with nitrate supplementation to both control methanogenesis and possibly prevent nitrite formation. Still, no consistent animal data have been reported (Takahashi, 2011). Although fermentation of lactate to VFA would help avoid a decreased ruminal Ph. The introduction of lactate-producing DFM would require careful scrutiny in situations in which subacute rumen acidosis might occur.

Defaunation

Association and cross-feeding between ruminal protozoa and archaea have been established (Vogels et al., 1980; Lee et al., 1987; Finlay et al., 1994) and are the basis for suggesting defaunation as a CH4 mitigation strategy (Newbold et al., 1995; Boadi et al., 2004; Hristov and Jouany, 2005). However, the response in CH4 production to partial or complete defaunation has been variable. Morgavi et al. (2010) calculated an average decrease in CH4 production of about (10%) ten percent due to defaunation, but the data from that study were extremely variable. Moreover, all responses were attributed to the loss of protozoa without accounting for depressed ruminal fiber digestibility, which promotes acetate and/or CH4 fermentation pathways and typically accompanies defaunation (Eugène et al., 2004). Research from the latter group with beef cattle reported no effect on rumen methanogen abundance despite a (65%) sixty-five percent difference in protozoal numbers between a high-forage and a high-starch, lipid-supplemented diet (Popova et al., 2011).

Similarly, a (96%) ninety-six percent reduction in ruminal protozoa did not affect methanogenic archaea in dairy cows treated with lauric acid (Hristov et al., 2011b). Noticeably, with such variability and uncertainty in the response (see Morgavi et al., 2011), defaunation cannot be recommended as a CH4 mitigation practice. Apart from lauric acid and coconut oil (Sutton et al., 1983; Machmüller and Kreuzer, 1999; Hristov et al., 2004, 2009, 2011b; Hollmann and Beede, 2012). Which can severely depress DMI in cattle, and some vegetable oils with a high proportion of unsaturated fatty acids (FA) such as linseed (Doreau and Ferlay, 1995), there has been no adequate and practical defaunation agents tested comprehensively in vivo.

Manipulation of Rumen Archaea and Bacteria

Significant efforts have been devoted to suppressing archaea and promoting acetogenic bacteria in the rumen. Vaccines against rumen archaea are based on the concept of a continuous supply of antibodies to the rumen through saliva. Vaccines against archaea have been successful in vitro (Wedlock et al., 2010) but not in vivo (Wright et al., 2004; Williams et al., 2009). Vaccines prepared from New Zealand and Australian methanogen strains proved unsuccessful in reducing CH4 production in ewe lambs (Clark et al., 2004). New approaches have involved identification of genes encoding specific membrane-located proteins from Methanobrevibacter ruminantium (perhaps the most essential rumen methanogen) and using purified proteins (produced in Escherichia coli) as antigens to vaccinate sheep (Buddle et al., 2011).

In another approach, antisera were generated in sheep against subcellular fractions from M. ruminantium, which reduced microbial growth and CH4 production in vitro (Wedlock et al., 2010). Sequencing the genome of M. ruminantium has opened new frontiers and opportunities for inhibition of rumen methanogens and the potential to mitigate ruminant CH4 emissions (Leahy et al., 2010). Ruminal bacteria capable of utilizing hydrogen and CO2 to produce acetate exists in the rumen (Joblin, 1999). Although these bacteria do not seem to be able to compete with methanogens for hydrogen under normal ruminal conditions (Fievez et al., 2001), they might be competitive if dissolved hydrogen concentrations increase as a result of suppressed CH4 production (Le Van et al., 1998). The model of Janssen (2010) proposes a dynamic interaction between dissolved hydrogen, passage rate, propionate production, and the growth and activity of methanogens in the rumen.

These interactions need to be acknowledged in the development of vaccines, and this is an exciting and fast-developing area of research that may produce effective CH4 mitigation technologies in the future (Wright and Klieve, 2011). Recent research has suggested that interventions in the early life of the animal can trigger differential microbial rumen colonization and development, which may result in differential rumen CH4 production. In a study by Abecia et al. (2011), kids from does treated with BCM had reduced CH4 production compared with kids from untreated dams. (Although animals were group fed and individual DMI was not reported), introducing the possibility that responses to rumen modifiers may be influenced by the mother and remain programmed in the animal’s adult life. This exciting concept may offer new opportunities for mitigating CH4 emission in ruminants but needs to be further tested and verified. Another interesting approach, using antimethanogen antibodies to suppress CH4 production, was shown to be ineffective in vitro (Cook et al., 2008).

Dietary Lipids: Vegetable Oils

There is a large body of evidence that lipids (vegetable oil or animal fat) suppress CH4 production. The effects of lipids on rumen archaea are not isolated from their overall suppressive effect on bacteria and protozoa. Several reviews have attempted to develop prediction factors for the effect of feed lipids on CH4. GigerReverdin et al. (2003) found the following relationship between CH4 production and dietary fat [as ether extract (EE)]: CH4 (L/kg DMI) = 47.3 – 0.0212 × DMI2 (kg/d) – 0.680 × EE (%) (R2 = 0.76, n = 37). Eugène et al. (2008) (9%) nine percent reduction in CH4 production in dairy cows due to lipid supplementation of the diet, but this was accompanied by a (6%) six percent reduction in DMI, which resulted in no difference in CH4 per unit of DMI. However, these authors also reported that lipid supplementation did not affect (4%) four percent fat-corrected milk (FCM), which, combined with the reduced DMI, resulted in a trend for increased feed efficiency with oil supplementation. A more recent meta-analysis of (38) thirty-eight research papers reported a consistent decrease in DMI with all types of dietary fat examined (tallow, various calcium salts of FA, oilseeds, and prilled fat), but milk production was increased (Rabiee et al., 2012).

This combination of decreased DMI and maintained or increased milk production (assuming no decrease in milk fat) results in increased feed efficiency and, consequently, decreased CH4 Ei. The greater inhibitory effect of unsaturated vs. saturated FA on rumen microbial activity reported by Palmquist and Jenkins (1980) and Nagaraja et al. (1997) does not appear to apply to CH4 production in most studies (Beauchemin et al., 2007b; Van Zijderveld et al., 2011a; Sauvant et al., 2011) although a greater mitigating effect of polyunsaturated FA was observed in the analysis by Doreau et al. (2011). Biohydrogenation of unsaturated FA can also serve as a hydrogen sink. Still, it has been suggested that only (1) one to (2%) two percent of the metabolic hydrogen in the rumen is used for this purpose (Czerkawski and Clapperton, 1984; Jenkins et al., 2008). Meta-analyses by Moate et al. (2011) and Grainger and Beauchemin (2011) documented a consistent decrease in CH4 production with fat supplementation.

Moate et al. (2011) reported the following relationship between dietary fat and CH4 production per unit of DMI: CH4 (g/kg DM) = 24.51 (±1.48) – 0.0788 (±0.0157) ×  fat (g/kg DM). Grainger and Beauchemin (2011) analyzed 27 studies and concluded that within a reasonable feeding rate of less than (8%) eight percent fat in the diet, a (10) ten g/kg increase in dietary fat would decrease CH4 yield by (1) one g/kg DMI in cattle and (2.6) two-point six g/kg in sheep. However, all these studies either scale CH4 per unit of DMI (i.e., disregarding the likelihood of an increased need for replacement animals if DMI and subsequent milk production are depressed) or included DMI as a variable (i.e., assuming that DMI can be maintained or predicted accurately). Prediction equations could account for these effects by substituting the response of fat on DMI into a subsequent equation relating the effect of fat on CH4, as done for RDP’s responses on DMI and milk protein production (Firkins et al., 2006).

The critical question of the persistence of the effect of lipids on CH4 production has not been adequately addressed. In a study with dairy cows on pasture, Woodward et al. (2006) examined the effect of vegetable and fish oils on milk production and CH4 emission after (14 d) fourteen days and again after (12 wk) twelve weeks. Lipids significantly decreased CH4 production in the short term. Still, this effect was not observed after (11 wk) eleven weeks of feeding lipids. These authors concluded that lipids were not beneficial for milk production and emphasized the need for long-term studies when developing on-farm strategies for CH4 mitigation with grazing animals. Grainger and Beauchemin (2011) examined (6) six long-term studies (6 to 36 wk), six to thirty-six weeks mostly with dairy cows) and concluded that the effect of dietary fat on CH4 production persists but the result is not consistent among studies.

Persistence of the mitigating effect of dietary oil was also observed in the study of Martin et al. (2011) with flaxseed in dairy cows. However, it was not supported by another study from the same group with young bulls (Eugène et al., 2011). In some studies, lipids had a significant and negative impact on DMI (e.g., Martin et al., 2008). This factor must be carefully considered both in the prediction of mean responses and for risk assessment by those choosing to adopt these mitigation strategies. Another essential factor to take into account with lipids is that mitigation of CH4 tends to correspond with an increased likelihood of depressing milk fat and protein concentration, potentially with enhanced responses when combining lipids with other strategies such as ionophores (Mathew et al., 2011).

Some fats such as coconut oil, for example, can severely depress feed intake, fiber digestibility, and, consequently, milk production and cause milk fat depression in dairy cows (Hristov et al., 2004, 2009, 2011b; Lee et al., 2011; Hollmann and Beede, 2012) although they may be still beneficial as CH4 mitigating agents (Machmüller and Kreuzer, 1999; Machmüller, 2006; Hristov et al., 2009). Even a blend of mostly saturated long-chain FA (C16:0, C18:0, and C18:1) was found to cause a significant drop in feed intake and milk production and a marked decrease in milk fat percentage (from (3.10)  three-point one to (2.51%) two-point-five one percent; a clear indication of milk fat depression although not statistically significant; Hollmann and Beede, 2012). Lipids causing this kind of production effects cannot be recommended as mitigation agents.

Dietary Lipids: By-Products

Although supplementing animal diets with edible lipids for the sole purpose of reducing CH4 emissions is debatable, high-oil by-products from the biofuel industries [dry (DDG) or wet (WDG) distillers grains alone or with solubles (DDGS and WDGS, respectively) and mechanically extracted oilseed meals] can naturally serve as a CH4 mitigating feed, if included in the diet to decrease feed cost. McGinn et al. (2009), for example, reported up to (24%) twenty-four percent less CH4 emissions when DDG replaced barley grain in the backgrounding diet of beef cattle by supplementing an additional (3%) three percent lipid to the dietary DM. However, the effects of distiller’s grains on CH4 production are not consistent and might depend on the rest of the diet. Hales et al. (2013) fed diets containing (0) zero to (45%) forty-five percent WDGS (substituting steam-flaked corn) to Jersey steers and observed a linear increase in CH4 emission per unit of DMI (up to (64%) sixty-four percent increase with the highest inclusion rate), due primarily to increased NDF intake. However, the EE content of the diet increased from (5.9) five point nine to (8.3%) eight point three percent.

High-oil by-product feeds might have the same suppressive effect on feed intake as free lipids, so caution must be exercised to prevent adverse impacts on animal productivity or milk fat depression in lactating cows (Schingoethe et al., 2009). Hales et al. (2013), for example, reported about an (11%) eleven percent decrease in DMI with the highest WDGS inclusion rate compared with the control. Inclusion of (12 to 13%) twelve to thirteen percent mechanically extracted canola or rapeseed meals with various FA compositions (replacing traditional, solvent-extracted canola meal) depressed DMI and, consequently, milk production in high-producing dairy cows (Hristov et al., 2011a). These feeds also contain higher total N (but less digestible than N from the original seeds) and P, which may present an environmental challenge due to high N and P content of manure and, consequently, more elevated ammonia and N2O emissions. Spiehs and Varel (2009) reported a linear increase in urinary N and total manure P excretion with increasing WDG inclusion (0 to 60%) zero to sixty percent in the diet of beef steers.

Similarly, Hales et al. (2012) reported that the inclusion of (30%) thirty percent WDGS in the diet of feedlot cattle increased total N excretion by (18%) eighteen percent but also increased urinary N losses by (35%) thirty-five percent. In contrast, dietary N intake was (23%) twenty-three percent higher compared with the control (0% WDGS). Distillers grains are also inherently variable in composition (Spiehs et al., 2002) and particularly in intestinal digestibility of ruminally undegraded protein and lysine limiting production in ruminants (Boucher et al., 2009). Therefore, a new trend in the bioethanol industry to partially extract oil from distillers’ grains will decrease the energy value of the product and is likely also to reduce the CH4 mitigating effect discussed above. Biodiesel by-products provide high-oil feedstuffs for livestock feeding. Biodiesel can be made from various feedstocks with relatively small capital investment. With high oil yield per hectare, canola (or rapeseed) is the preferred feedstocks for biodiesel production.

Mechanically extracted canola and rapeseed meals can have markedly high residual oil content (up to (17%) seventeen percent, DM basis) and might depress DMI and milk production in dairy cows (Hristov et al., 2011a). The oil in these meals has a high proportion of monounsaturated FA and can impair rumen function if included at levels exceeding (6 to 7%) six to seven percent total dietary fat. Another product of the biodiesel industry, glycerol, has been shown to promote CH4 production during ruminal fermentation in vitro (Czerkawski and Breckenridge, 1972).

Conclusion

Research has been carried out for at least a decade following systematic measurements of methane production in studies of energy metabolism in ruminants, which began in the 1970s.

The main factors studied are:

• • Type of forage (botanical nature, vegetation stage, grass silage vs. corn silage, temperate vs. tropical fodder)
  • Rations very rich in concentrate, nature of the concentrate
  • Rations enriched in lipids, nature of lipids
  • Plants rich in tannins (temperate or tropical)
  • Natural food additives (saponins, garlic extract, essential oils)
  • Chemical food additives (nitrates, 3-NOP, etc.)
  • Contribution of exogenous microorganisms (yeasts, bacteria) or products of their metabolism

These methane emission reduction routes have been tested in vivo on sheep, dairy cows, fattening bulls and heifers, sometimes over the long term, sometimes by combining two agents, recently studying the residual effect of the application of these techniques in the young age. To do this, INRA teams have three measurement techniques: respiratory chambers, the use of the SF6 gas tracer, the Greenfeed discontinuous measurement system. These studies are often preceded or supplemented by in vitro measurements. In the next E-letter, we will present you with additional solutions!

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