This fortnightly newsletter was curated and edited by: J.W. Holloway and his Team
Synopsis
Reducing the age at the slaughter of finished cattle and the number of days that animals are on feed in the feedlot can significantly reduce GHG emissions in beef and other meat animal production systems. Improved animal health and reduced mortality and morbidity are expected to increase herd productivity and reduce GHG emission intensity in all livestock production systems. Pursuing a suite of intensive and extensive reproductive management technologies provides a significant opportunity to reduce GHG emissions. Recommended approaches will differ by region and species but should target increasing conception rates in dairy, beef, and buffalo, increasing fecundity in swine and small ruminants and reducing embryo wastage in all species. Interactions among individual components of livestock production systems are complex but must be considered when recommending GHG mitigation practices.
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
Recombinant Bovine Somatotropin
An animal management practice that can indirectly reduce emissions by improving productivity in dairy cattle is the use of rbST. Capper et al. (2008) used a mathematical modeling approach to estimate the effect of rbST use on individual cow and industry-wide scales, assuming an increase in milk production of 4.5 kg/d (an optimistic assumption according to European data; Chilliard et al., 1989). The results of the analysis suggested that rbST use may reduce CH4 output by 7.3% per unit of milk produced. However, the use of rbST for milk production is banned in Canada, Japan, the European Union, Australia, and New Zealand. Limited evidence suggests that the use of rbST may increase the risk of clinical mastitis, of cows failing to conceive, and of developing clinical signs of lameness (Dohoo et al., 2003). However, other extensive studies detected no decline in fertility using rbST but made note a reduction in the length of expressed estrus (Rivera et al., 2010).
Furthermore, in a sizeable multi-head study in the United States, rbST use did not increase the incidence, duration, or severity of mastitis nor increase the culling rate in the herds. Still, it was associated with a slight increase in foot problems not related to lameness (Collier et al., 2001). Should the use of rbST have a negative influence on fertility and animal health, then the reduction in CH4 emission estimated by Capper et al. (2008) would be smaller or even nonexistent. In addition, this mitigation practice is likely to be applicable only in intensively managed animal production systems.
Growth Promotants
Growth promotants of various types [ionophoric antibiotics (discussed in the companion paper; Hristov et al., 2013a), implants (hormones, melengestrol acetate, and trenbolone acetate), and β-agonists (ractopamine, the decrease in zilpaterol hydrochloride) are routinely used by the U.S. beef and pork industries to stimulate growth and partition nutrients, specifically energy, from fat to lean tissue deposition (Duckett and Owens, 1997). Similar to rbST, the effects of these compounds on GHG emissions from ruminants can be expected to come from increased growth rate (i.e., less time on feed to reach slaughter BW) and feed efficiency (Scramlin et al., 2010; Parr et al., 2011; Al-Husseini et al., 2013), thus reducing CH4 Ei (Cottle et al., 2011).
In monogastric species, increased feed efficiency will result in less manure excreted and, consequently, decreased GHG Ei. In beef cattle, the gains in feed efficiency can be remarkable, reaching over 15 to 20% (CAST, 2005). Assuming meat quality is not impaired (which may not be the case, according to some reports; Faucitano et al., 2008; De Almeida et al., 2012), the production and environmental benefits of these compounds are unparalleled. As with rbST, however, growth promotants are banned in many countries, and their use will heavily depend on societal perception and acceptance.
Animal Genetics
Improvements in both genetic potential and diet management can lead to a significant reduction in GHG emissions per unit of product from livestock production systems, as shown for the Australian beef industry (Henry and Eckard, 2009). Beef cattle with low residual feed intake (RFI, defined as the difference between actual and predicted feed intake) can produce up to 28% less CH4 (Nkrumah et al., 2004; Hegarty et al., 2007). According to Herd and Arthur (2009), variation in RFI can be attributed to variation in protein turnover, tissue metabolism, and stress (37%), with lesser contributions from digestibility (10%), heat increment and fermentation (9%), physical activity (9%), and body composition (5%). In an extended review of the topic, Waghorn and Hegarty (2011) concluded that there was little evidence that efficient animals have a different CH4 yield per unit of DMI. Furthermore, they pointed out the need to select high-producing animals because this reduces emissions per unit of product. Similarly, Weber et al. (2013) reported no difference in CH4 emissions between high and low RFI beef cattle.
The extent to which CH4 can be reduced by selection for RFI depends on the heritability of the trait, dispersal of efficient animals through all populations, and their resilience in a production system. Selection for individual animals that have a lower than average CH4 yield requires that 1) the host animal controls its microflora and that the trait is heritable 2) selection for low CH4 producers is more important to animal producers than other traits (e.g., productivity, fertility), and 3) the effect is persistent and applicable to all levels of production. Therefore, the immediate gain in GHG reductions through RFI is quite uncertain. De Haas et al. (2011) estimated heritability of RFI in dairy cattle of 0.40. Genetic variation suggests that a reduction in CH4 production in the order of 11 to 26% is theoretically possible. Type of diet fed and forage or pasture quality have an essential role in selecting low-CH4 emitters through selection for RFI. Jones et al. (2011), for example, concluded that the hypothesis that low-RFI cows produce less CH4 was not supported on low-quality summer pasture but was supported when cows were grazing high-quality winter pastures.
McDonnell et al. (2009) concluded that differences in digestive capacity for some dietary fractions—but not rumen CH4 production—may contribute to differences in RFI between cattle. In the McDonnell et al. (2009) study with Limousin × Friesian heifers, DMI and CH4 emission did not differ between low and high-RFI animals, but CH4 expressed per unit feed DMI was significantly higher for the low-RFI (i.e., more efficient) animals. Modern molecular techniques have revealed much greater diversity in the ruminal microbiota than previously known. Significant collaborative efforts are underway to understand the interactions between the host animal and its microbiome and potentials for selecting more efficient animals or animals, producing less CH4 (McSweeney and Mackie, 2012). These authors indicated that, based on the analysis of global datasets, the majority (>90%) of rumen methanogens are affiliated with genera Methanobrevibacter (>60%).
Methanomicrobium (approximately 15%), and a group of uncultured rumen archaea commonly referred to as rumen cluster C (approximately 16%; recent data have indicated that these methanogens produce more significant amounts of CH4 relative to Methanobrevibacter). Animal species, breed, and environmental conditions affect rumen microbial diversity, which could be used to select animals with lower CH4 emitting potential or manipulate the rumen ecosystem to raise animals producing less CH4 per unit of digested feed (Abecia et al., 2011). Permanent inoculation of the rumen with foreign microbes is rare but has thrived under certain conditions (Jones and Lowry, 1984; Jones and Megarrity, 1986) and maybe a possible mitigation approach in the future. As indicated earlier, RFI selection is a promising technology but with uncertain returns. In addition, the current system for estimating RFI requires significant investments in animal identification and accurate measurements of feed intake and animal production unlikely to take place in developing countries in the short term (Waghorn and Hegarty, 2011).
The concept of genetically modified animals, designed to have a lower environmental footprint (primarily by having higher feed efficiency), although not universally accepted, may offer an opportunity for more efficient animal production (Niemann et al., 2011). Breeds may differ in their efficiency of feed utilization, which may be explored as a long-term GHG mitigation option. Breeds have different maintenance requirements and efficiency of energy use for maintenance. A long-term study by Solis et al. (1988) concluded that maintenance energy requirements for weight and energy balance were lower and the efficiency of ME use was higher in beef breeds and their crosses than in dairy breeds and their crosses, which was explained by differences in body composition associated with altered nutrient partitioning. In dairy cows, selection for gross feed efficiency (i.e., milk per unit of feed) may not be advantageous because of the high genetic correlation between gross feed efficiency and milk yield (Korver, 1988; Østergaard et al., 1990).
It is recognized that intensive selection for one genetic trait can lead to losses in other traits with negative correlations. Breeding for milk yield, for example, comes at the expense of beef traits, such as ADG and carcass quality, and secondary traits, such as reproduction, animal health, etc. (Østergaard et al., 1990). A Dutch study comparing Jersey cows against a group of Holstein, Dutch Friesian, and Dutch Red and White cows found that the biological efficiency for milk production (energy in milk divided by net energy in feed) was 57 and 69% (all forage and 50:50 forage: concentrate diets, respectively) for the Jersey group vs. 56 and 61% for the Holstein-Friesian group of cows (Oldenbroek, 1988). Similar higher efficiency for the Jersey breed was reported earlier by the same author with first lactation cows (Oldenbroek, 1986). Grainger and Goddard (2004) performed a comprehensive review of experimental data for feed efficiency of various dairy breeds (Holstein, Friesian, Jersey, and Holstein-Friesian × Jersey crossbred cattle) and locations (New Zealand, United States, and Europe).
The authors concluded that Jerseys appear to have a higher feed conversion efficiency measured as milk solids per unit of DMI (from about –7 to about +19% more efficient than Holstein-Friesian cows). The authors also indicated that crossbred cows might have an advantage over purebreds due to improvements in feed efficiency, health, and fertility—partly due to heterosis. However, a more recent comparison between Holstein, Danish Red, and Jersey cows did not find a clear advantage of Jersey vs. Holstein (Halachmi et al., 2011). These authors reported lower peak milk yield, comparable lactation fat yield, and lower protein yield for Jersey vs. Holstein and Danish Red cows. Feed efficiency (kg DMI needed to produce 1 kg of milk) was lower for the Jersey breed (0.95 kg) than the Holstein (0.77 kg) and the Danish Red (0.84 kg) cows. Efficiency for the production of milk fat, however, was more significant for the Jersey cows (15.4 vs. 18.8 and 19.6 kg, respectively). Jersey cows were about 172 kg lighter than the other two breeds.
Bodyweight is an essential factor contributing to GHG emissions through energy requirement for maintenance. Smaller breeds may have a smaller C footprint per head due solely to smaller BW. Capper and Cady (2012) estimated that the C footprint per 500,000 t of cheese produced would be 1,662 kt of CO2e lower for Jersey vs. Holstein cows, partly due to a greater cheese yield mostly due to a smaller BW of the Jersey cows. The debate on the importance of milk component yields compared with milk volume in relation to GHG emissions from the dairy industry is an interesting one. According to USDA Dairy Herd Information 2011 records (USDA, 2011), the average milk yield and milk fat and protein concentration for Ayrshire, Brown Swiss, Jersey, and Holstein herds in the United States was 7.020 kg/lactation with 3.84 and 3.14% fat and protein, 9,998 kg/lactation with 3.97 and 3.31% fat and protein, 8,638 kg/lactation with 4.70 and 3.62% fat and protein, and 11,812 kg/lactation with 3.67 and 3.04% fat and protein, respectively.
Fat and protein yields per lactation can be calculated: 319 and 261 kg, 397 and 331 kg, 406 and 313 kg, 434, and 359 kg, respectively. Thus, the Holstein breed has an advantage in milk volume and milk fat and protein yields in the United States. The dairy industry well recognizes the importance of milk components even to the extent that total milk solids are considered (including lactose, which is closely related to milk volume and does not contribute to cheese and butter yields). Fluid milk consumption in the United States represented 32% of all dairy products consumed in 2012 (USDA, 2012) The proportion of milk consumed as fluid milk is much more significant in regions with high population density such as the Northeast and Mideast). In these regions, there is not much demand for milk with fat (or even less protein) concentration more generous than the standard fat content of milk sold in the grocery outlets.
Therefore, dairy breeds with higher milk yield but a lower concentration of milk components, such as the Holstein breed (outperforming the other dairy breeds in the United States), would have a clear advantage in terms of intensity of GHG emission and C footprint per unit of milk (cheese manufacturing has a greater environmental impact, primarily through energy consumption than fluid milk; Milani et al., 2011) in areas where dairy products are consumed mostly as fluid milk. Increased protein and fat content of milk would be an essential breed quality in areas where most of the milk is processed into cheese. Even in developing countries where feed resources may be limited, introducing genes for high production may be beneficial. An extensive survey of smallholder dairy farms (average milk production was 1,425 L/lactation) in the “drier transitional zones” of Kenya showed that exotic dairy breeds (Friesian, Ayrshire, Guernsey, and Jersey) adapted to the conditions of the survey regions and were economically more efficient than the indigenous breeds (Sahiwal, Boran, Zebu, and Zebu cross; Kavoi et al., 2010).
A 3-yr study in Switzerland investigated the performance of New Zealand Holstein Friesian cows under Swiss grazing conditions (60 to 65% of the diet was grazed pasture) in comparison with indigenous Swiss breeds. The New Zealand cows were more efficient than the Swiss cows, with ECM per metabolic BW being 49.7 to 55.6 vs. 44.2 to 46.6 kg/kg, respectively (Thomet et al., 2010). Another possibility for faster genetic improvement in some production systems is gender-selected or “sexed” semen technology. The application of this technology in the dairy industry could allow producers a more flexible selection to produce dairy replacement heifers from only the genetically superior animals in their herds (De Vries et al., 2008). Having more genetically superior animals in the herd is expected to increase milk production per animal and reduce GHG Ei. Still, it may increase replacement rates and temporarily increase the total milk supply (De Vries et al., 2008).
The sexed semen technology for producing heifers is of exceptionally high importance in reducing the number of dairy animals in countries such as India, where cattle are not slaughtered due to religious reasons (Harinder P.S. Makkar, unpublished data, 2012). Higher cost and lower conception rates are limitations to adopting the use of sexed semen (Weigel, 2004). Animal genetics can also have a significant effect on GHG emissions from swine and poultry. As relatively little enteric CH4 is emitted from these animals, the majority of the GHG from swine and poultry operations (excluding feed production) are attributed to manure in housing facilities and storage and following land application. Therefore, improving animal feed conversion efficiency, reducing the volume of manure produced while maintaining animal productivity, becomes an effective strategy for mitigating CH4 and nitrous oxide (N2O) emissions from these farm species.
Animals from genetic lines predisposed to high feed efficiency excrete fewer nutrients in urine and feces. Healthy herds also use feed efficiently and can reduce N excretion by 10% compared with unhealthy herds. Split-gender feeding enables producers to feed each gender closer to its nutritional requirements; for example, turkey hens require fewer nutrients due to their smaller size than male turkeys (Pennsylvania State University Extension, 2013). A study with 380 Duroc boars from 7 generations and 1,026 Landrace pigs from 6 generations showed that measures of feed efficiency (feed conversion ratio and RFI) were moderately heritable (Hoque and Suzuki, 2008). Genetic and phenotypic correlations between ADG and measures of RFI were close to zero, which, according to the authors, indicated that selection for reduced RFI could be made without adversely affecting animal growth. A study with the French Large White reported considerable improvements in development, feed efficiency, and lean carcass content of this breed between 1977 and 1998 (Tribout et al., 2010).
Another study from France investigated four pig breeds between 2000 and 2009 for estimates of genetic parameters for RFI, production traits, and excretion of N and P during growth (Saintilan et al., 2012). Residual feed intake had moderate h2 for all breeds (h2 from 0.22 ± 0.03 to 0.33 ± 0.05) and was positively correlated with feed conversion efficiency. There was a significant breed effect on N excretion. The authors concluded that a selection index, including RFI could be used to improve feed conversion efficiency, which would also lead to lower nutrient losses and, consequently, decreased GHG emissions from manure.
Animal Health and Mortality
Improving animal health and reducing animal morbidity and mortality to enhance the efficiency of the animal production system offer opportunities to reduce both CH4 and N2O from enteric fermentation and animal manure. Although connections among animal health, mortality, and productivity are apparent, few studies have examined their implications on GHG emissions (Hospido and Sonesson, 2005; Bell et al., 2008; Dourmad et al., 2008; Stott et al., 2010). The GHG emissions produced during the period the animal is grown to the productive stage are a net loss if the animal dies before its productive value is harvested. Its value is greatly reduced when the productive potential is reduced due to poor health. The opportunities to reduce GHG emissions from animal manure through improving animal health and reducing mortality are especially crucial in places where the livestock production system is rudimentary or the manure application, and dissemination technologies are unavailable or difficult to implement. As livestock industries change and consolidate over time towards fewer farms with more massive herds, the practice of veterinary medicine also changes its focus.
The primary focus of veterinary medicine for livestock production systems that rely on small herds is the eradication of clinical infectious diseases, with the emphasis on individual animal treatment. However, as herd size and animal productivity increase, the focus shifts towards preventive veterinary medicine. A greater emphasis is placed on subclinical disease and systematic health management programs that target increased productivity (LeBlanc et al., 2006). Regardless of the developmental stage of a livestock production system, reduced mortality and morbidity lead to greater saleable output, diluting GHG emissions per unit product. Taking the dairy industry as an example, lameness or injury (20.0%), mastitis (16.5%), and calving problems (15.2%) represent the major reported causes of mature cow death in the United States (USDA, 2007). Both lameness (Warnick et al., 2001) and mastitis (Wilson et al., 1997) also reduce milk output, increasing GHG emissions per unit of product.
Similarly, reproductive problems (26.3%), mastitis (23.0%), poor production (16.1%), and lameness or injury (16.0%) are significant reasons for permanently culling cows from the United States dairy herd (USDA, 2007). According to LeBlanc et al. (2006), 75% of disease occurs within the first month after calving. In addition, 26.2% of dairy culls were reported to occur from 21 d before to 60 d after calving in a study of all Pennsylvania cows with at least one dairy herd improvement test in 2005 (Dechow and Goodling, 2008). Metabolic disorders related to calving also lead to culling and reduced milk production (Berry et al., 2007; Duffield et al., 2009). Mathematical modeling approaches, including LCA and Markov chain simulation methods, were used to examine the effects of reduced incidence of mastitis on non-CO2 emissions (Hospido and Sonesson, 2005). These authors predicted a reduction in the environmental impact of 2.5 (global warming potential) to 5.8% (depletion of abiotic resources) if the clinical mastitis rate decreased from 25 to 18%, and the subclinical mastitis rate dropped from 33 to 15% in Spain.
Conclusion
Several studies have shown that the initial and overall tenderness, juiciness, residue in the mouth, and flavor differ less between meat breeds of French origin than between muscles. The quality of a muscle is not related to that of another muscle from the same carcass. The type of muscle is the predominant factor in explaining the variability in the quality of beef. Indeed, this variability of genetic origin is undoubtedly sufficient to consider selecting on criteria of meat quality. This is all the more relevant as genetic progress can be cumulated from one generation to the next. In other words, even if the changes in the quality of the meat induced by genetic selection are slight, they will be transmitted to the next generation. They will be added to the progress made on this second generation. However, the absence of easily achievable routine measures at low cost on many animals is a significant obstacle to this type of selection. This leads to consider exploiting the polymorphisms of specific genes capable of explaining this variability.
It, therefore, appears that the bovine sector is still looking for methods of routine measurement of muscle characteristics known to play a role in the determinism of tenderness or flavor (i.e., the characteristics of muscle fibers, connective tissue, and intramuscular lipids). At the same time, a better knowledge of muscle biology is necessary to identify new muscle characteristics, which would explain the essential part of the variability in the quality of meat, still unknown. In the following e-letter, we will finally talk about the last aspect of this study which is animal fertility! See you next month! We want to proceed further, more in-depth on this controversial subject. Therefore, please follow us on social media and join us on the (15th) fifteenth of the month for Part (2!) two to learn more about the environmental impact of beef production.
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