Lately, an article in Social Media was used to spread false information regarding the healthfulness and quality of our Canadian dairy products, namely butter. This kind of attack on our industry is powered by a plain misunderstanding of our animal production systems, saying the least. The response of our scientific community (professors, nutritionists, veterinarians, ..) has been instrumental in clarifying the facts. In this brief blog, I would like to touch on a few key-points.
Palm oil and palmitic acid are not the same. Palm oil is a vegetable oil produced mainly for human consumption. The fat profile of palm oil contains 45% palmitic fatty acid, 40% oleic fatty acid, and 10% linoleic fatty acid. It is estimated that 75 million metric tonnes are produced every year, which exceeds both soy oil and rapeseed oil productions.
The attached chart roughly outlines the refining process to produce the two edible fractions of palm oil, Olein and Stearin. The refining process produces a by-product – waste below the food-grade level – that is utilized for the production of biodiesel, candles, soaps, .., as well as animal feeds. The by-product is approximately 3-5% of the raw material input, and its percentage is declining as the refining process getting better and better. Waste products in our circular global economy are expected to have economical values, and in the case of the palm oil refining process, the by-product value is worth approximately 4% of the value of the major product.
Deforestation and its negative impact on biological diversity is a major global concern. However, Canadian companies looking to import food or animal feed derived from palm plantations can reliably source their products from a certified palm oil supplier. To my knowledge, our major sources of palm by-products in Canada are imported from certified sources that adhere to “no deforestation” policies, such as RSPO (Roundtable on Sustainable Palm Oil). Dairy producers or nutritionists can request such certification from their Canadian suppliers.
Cow’s milk is ~ 4% butterfat and palmitic acid is the primary fatty acid naturally present in the milk (~ 33% of total milk fatty acid). Also, palmitic acid is present in breast milk and is usually added to baby’s formulae (20 to 25%) to provide infants with needed energy. Therefore, the claim by “Buttergate” that feeding palmitic acid poses safety or health concerns on human health has no scientific ground. Palmitic acid is certified for use as an animal feed by the CFIA and other regulatory bodies around the world.
The main palmitic acid supplement fed to dairy cows is a purified 85% palmitic acid supplement. Farmers have the option to substitute 1-2% of their cow’s dairy ration with palmitic acid (300-500g/d). This practice increases the energy density of the diet, which is very important as cows cannot consume enough forages during the early stage of lactation. Cows that undergo prolonged or severe “negative energy balance” during early lactation are susceptible to diseases and metabolic issues.
Other sources of fats can be used such as unsaturated fats (canola or soy by-products) or grains. However, palmitic acid is considered a “friendlier” source of fat with no impact on fibre degradability in the digestive tract of the cow.
Butter hardness, cheese yield, and other milk processability parameters can be influenced by many factors, some of which are the breed of the cow, season, time since calving, milk handling, and diet of the cow. There is no available data showing any impact of current practices of feeding palmitic acid (1-2%) on butterfat quality. Some evidence suggests that feeding large amounts of palmitic acid may impact butterfat melting point, however, this is not a common practice in Canada and nor it is economically feasible to do so in most regions. Likewise, feeding a large amount of unsaturated fatty acid (such as linoleic fatty acid derived from soy- or corn-based byproducts) can have an impact on butterfat content and processability (in addition to its effect on the digestion of fibre as mentioned above). More research is required in this field. Balancing the ration of our dairy cows for fibre, protein, starch, amino acids, and fatty acids among other macro micronutrients is what our nutritionists in the industry do daily. They utilize sophisticated computer models empowered by decades of research.
In conclusion, supplementing palmitic acid to lactating cows does not impact the healthfulness of milk. Palmitic acid supplements destined for animal feed can be obtained from sustainable sources obliged to “no deforestation” policies. The Canadian dairy industry delivers one of the highest standards for dairy production in the world, but at the same time holds a massive obligation to live up to consumers’ expectations and be open and transparent. Education and communication are key to avoid the spread of false information about animal agriculture.
The transition period -defined as three weeks before calving and three weeks post-calving- is a critical phase of the cow’s life. Proper management of nutrition and health is vitally important during this period. Cows post-calving are susceptible to a plethora of disorders/diseases due to low nutrient intake, immunosuppression, and high metabolic stress. The nutrient requirements for milk production, especially for our modern cows, are exceptionally high. Cows during the early stage of lactation cannot consume enough energy to cover their requirements. This condition is referred to as “negative energy balance,” and as most lactating mammals, cows rely on body-reserve mobilization (fat, protein, ..) to meet this deficit. However, excessive fat mobilization triggered by low intake or imbalanced/deficient rations can cause fatty liver and jeopardize cows’ health and productivity. Secondary to energy imbalance, several imbalances in nutrients and metabolically active compounds may also occur during lactation. These include amino acids, vitamins, minerals, and compounds with labile methyl groups such as choline, betaine, and Met. Indeed, methyl group metabolism has received considerable attention from dairy scientists due to its essential role in metabolic health and productivity.
Unfortunately, the dietary supply of methyl donors during the onset of lactation is limited due to low feed intake and extensive microbial degradation of the methyl donors in the rumen. Whereas, the demand for such compounds is very high to support milk production (milk choline and milk protein), liver health, immune function, and mitigate oxidative stress.
When the supply of labile methyl groups is low (i.e. early lactation), methyl groups are synthesized by the interactions of two metabolic pathways: the folate (or B9) and the Met cycles (Figure 1: methylneogeneis is highlighted in blue, folate cycle in yellow, and Met cycle in green). Within the folate cycle, one-carbon sources such as serine and folate serve as a substrate for the formation of 5-mTHF. Met synthase within the Met cycle will utilize 5-mTHF to regenerate Met from HCY. In turn, Met is used to generate SAM, which is recognized as the universal methyl donor for various metabolic processes, including AA homeostasis and PtdChol synthesis. Other processes include supporting redox defence and DNA methylation (Figure 1, the transsulfuration pathway is highlighted in pink).
Figure 1. Folate cycle, Met cycle, and transsulfuration pathway (modified from McFadden et al. 2020). Methylneogenesis is highlighted in blue, folate pathway in yellow, Met pathway in green, and transsulfuration in pink. Compounds containing methyl groups are highlighted in blue and B-vitamins in red. An “S” denotes sulphur-containing compounds. DHF = dihydrofolate, SHMT = serine hydroxymethyltransferase, 5-mTHF = 5-methyltetrahydrofolate; MTHFR = methylenetetrahydrofolate reductase; MTR = methionine synthase, PEMT = phosphatidylethanolamine N-methyltransferase, PtdEth = phosphatidylethanolamine, PtdEth = phosphatidylethanolamine; SAH = S-adenosylhomocysteine; SAM = S-adenosylmethionine (other types of methyltransferases may utilize SAM; only PEMT is shown for simplicity). MATI/III = methionine adenosyltransferase I/III (liver-specific isoenzymes), HCY = homocysteine.
B-vitamins, such as folate, B6, and B12 (Figure 1, highlighted in red), play an essential role in methylneogenesis. For example, B12 plays a critical role in “coupling” the folate and Met pathways to form Met and SAM. In this process, the methyl group is transferred from 5-mTHF (folate cycle) to the cobalt group of the B12 vitamin and then transferred to the sulphur group of HCY in the Met cycle. Consequently, B-vitamins and HCY are the main limiting factors in the synthesis of labile methyl groups. It is important to note here that homocysteinyl moiety (i.e. HCY) cannot be synthesized in mammals and is derived from Met. Therefore, it is suggested that there is a “minimal absolute requirement” for Met to ensure the cycling of HCY in the methylneogenesis (McFadden et al., 2020).
Methyl groups generated via methylneogenesis (SAM) are transferred to over a hundred different pathways, one of which is the PEMT pathway. This pathway generates PtdChol, which is utilized in the liver to create VLDL and export lipid to various tissues for utilization. This pathway works in unison with the CDP-choline pathway to support phospholipid synthesis in the liver. The inability of the liver to export lipid can lead to lipid accumulation and fatty liver. Therefore, current research is focused on enhancing the PEMT and CDP-choline pathway activation.
As mentioned, methyl groups can be synthesized via the folate cycle when dietary supply is low. However, methyl groups necessary for SAM can be donated by exogenous sources (methyl donors) such as supplemental choline, betaine and Met (Figure 2, circled in orange). However, due to their extensive degradation in the rumen, it is suggested that the folate cycle remains the primary source for endogenous methyl groups for ruminants when these supplements are fed in an unprotected form (McFadden et al., 2020).
Figure 2. A simplification of Figure 1 showing the possible contributions of exogenous methyl donors to methylneogenesis (circled in orange). BAD = betaine aldehyde dehydrogenase; BHMT = betaine-homocysteine methyltransferase, CDH = choline dehydrogenase. (Additional abbreviations explained in Figure 1)
Supplementing rations with rumen-protected (RP) methyl donors such as RP-choline is an approach to enhance dairy cow liver health and milk production. In a recent meta-analysis, RP-choline feeding showed a consistent effect on metabolic health and performance during the onset of lactation (Arshad et al., 2020). Approximately half of the increase in milk production observed with RP-choline feeding is believed to be due to direct improvements in dry matter intake. The remaining half is likely due to the ability of choline to act as a methyl donor or enhance mammary epithelial cell proliferation. It is important to note that, in addition to being a methyl donor and supporting PEMT pathway activation, supplemental choline can be phosphorylated directly via the CDP-choline pathway to PtdChol. This pathway is energetically more feasible than the PEMT pathway and likely more relevant to liver health in lactating cows (McFadden et al., 2020). However, there is little or no information concerning RP-betaine. Available studies that fed unprotected betaine to cows have attributed its ability to enhance milk production to improved fibre digestibility (i.e. benefited the microbiota).
It was suggested that the status of methyl donors and nutritional practices should be considered when evaluating the impact of any supplementation strategy. For example, B-vitamin supplementation improved Met status -likely due to improved remethylation- but only when the diet was deficient with Met (no RP-Met provided). However, co-supplementing B vitamins with RP-Met increased protein synthesis, milk yield, milk protein, and lactose yield regardless of RP-Met supplementation (Preynat et al., 2009).
High levels of SAM and an increased supply of exogenous methyl groups can promote the activity of the transsulfuration pathway and, consequently, antioxidant production. On the other hand, oxidative conditions have been shown to downregulate Met synthesis and, therefore, the generation of SAM. This proposed mechanism was to divert the sulphur-containing compound HCY towards the transsulfuration pathway and generation of antioxidants (reviewed by McFadden et al., 2020). Hence, Met is not just an essential AA but a compound containing both methyl and sulphur groups and integrally situated on the intersection of methyl and sulphur transfer metabolism.
In conclusion, methyl donor nutrition plays an important role in the health and productivity of lactating cows. However, methyl donor requirements and status are not well defined, nor the specificity of each methyl donor. The ability to determine methyl-groups balance/status and best supplemental strategy can empower nutritionists and veterinarians to revise their guidelines to fit each herd’s requirements. This topic is a rather complex one, and this complexity is exacerbated if you were to consider the methyl-group requirement of the rumen microbiota, in addition to the cow’s requirements. For example, limited studies on unprotected betaine speculate an effect on microbial growth/efficiency, as evident by improvements in digestibility.
Furthermore, B-vitamins are synthesized by the ruminal microbiota to facilitate their various metabolic processes. The washed-out microbes are expected to meet the B-vitamin requirements of the host animal. However, recent findings suggested that B-vitamins production may become a limiting factor to the microbiota and the host animal under certain conditions. More studies are needed to uncover the underlying mechanisms and improve our understanding of methyl donor nutrition.
References:
Arshad, U., M. G. Zenobi, C. R. Staples, and J. E. P. Santos. 2020. Meta-analysis of the effects of supplemental rumen-protected choline during the transition period on performance and health of parous dairy cows. J. Dairy Sci. 103:282-300.
McFadden, J. W., C. L. Girard, S. Tao, Z. Zhou, J. K. Bernard, M. Duplessis, and H. M. White. 2020. Symposium review: One-carbon metabolism and methyl donor nutrition in the dairy cow. J. Dairy Sci. 103:5668-5683.
Preynat, A., H. Lapierre, M. C. Thivierge, M. F. Palin, J. J. Matte, A. Desrochers, and C. L. Girard. 2009. Effects of supplements of folic acid, vitamin B12, and rumen-protected methionine on whole body metabolism of methionine and glucose in lactating dairy cows. J. Dairy Sci. 92:677-689.
In the past few decades, we have learned valuable information about the rumen ecosystem, but we are still far from unveiling the complex interplay between the different microbial groups and their functions. Microbiology and the laws of kinetics and thermodynamics can explain the majority of what we’ve learned thus far, but not all. New advances in “omics” and mixed-microbe culturing techniques are expected to improve our knowledge exponentially. This blog is inspired by my recent readings, namely “The Role of Thermodynamics in the Control of Ruminal Fermentation” by Ungerfeld and Kohn (2006).
Ruminants have a unique ability to degrade fibrous materials (“poor” quality feed) that are considered indigestible by other monogastric animals, such as pigs and poultry. The ruminants’ digestive system doesn’t have the enzymatic capacity to degrade complex fibrous structures but instead relies on diverse microbial groups residing in the rumen to break down these structural carbohydrates. This symbiotic relationship between the ruminal microbiota and the host provides, synergistically, the needed energy for both the host animal and the residing microbiota. Any external factors that lead to “dysbiosis” of this ecosystem will impair the health and productivity of the ruminant animal. Complete oxidation of organic materials in living cells is only possible in the presence of oxygen. The end products of complete oxidation are CO2, water, and heat. Electrons generated from oxidation are transferred to O2 as the final electron “acceptor.” This process deems O2 as essential for energy generation (ATP generation) in aerobic metabolism. However, the rumen microbiota evolved as anaerobic microbes, where the presence of oxygen is not required but for the most toxic. Some facultative bacteria that tolerate oxygen do survive in the rumen and play a role in “scavenging” oxygen dissolved in water and feed, thus improving the anaerobic conditions of the rumen. Anaerobic microbes have evolved alternative fermentative pathways to harness energy (ATP) from substrates such as cellulose without the need for oxygen. The terminal electron acceptors in the fermentation processes are the organic compounds produced in the process itself. Electron acceptors can be metabolic intermediates of fermentation (formate, lactate, fumarate, acrylyl-CoA, acetoacetyl-CoA, crotonyl-CoA, CO2,..) and fermentation end products (short-chain fatty acids, SCFA’s).
Fermentation is considered an incomplete oxidation of substrates by the microbes. It is estimated that anaerobic metabolism is up to 15 times less efficient than aerobic metabolism at generating energy. Thus, the end products of fermentation (SCFA’s) are energy-dense and, once absorbed by the digestive system of the host, constitute the primary energy source for the host animal. Gases (mainly CO2 and CH4) and heat produced by fermentation are released and deemed “unuseful.” In addition, the microbial biomass, after being washed from the rumen, digested, and absorbed in the small intestine, makes the main source of nitrogen and protein for the host. Microbial protein is the most economical source compared with exogenous feed sources such as soybean meal. Thus, maintaining optimal ruminal conditions for carbohydrate digestion can reduce the need for expensive protein supplements. It is important to note that fermentation is one type of anaerobic respiration and that other types such as nitrate, sulphate, and sulphur respiration do exist in the rumen but will not be discussed here.
The quantity and profile of SCFA’s have a direct impact on the productivity and metabolism of the host animal and are influenced by feed intake, type of feed, feeding management, type of animal, rumen microbiome (collective genome or meta-genome), and others ecological factors. Acetate is the most abundant SCFA on a molar basis followed by propionate and butyrate during high-forage feeding. However, propionate is proportionally elevated during high-grain feeding. It is important to note that propionate as an end product retains more energy than acetate. Thus, it is energetically more useful to the host animal. On the other hand, propionate fermentation, depending on the pathway, may yield less energy (ATP) for microbial growth than acetate. Therefore, fermentation “efficiency” implied by a greater propionate fermentation should not be mixed with microbial ATP generation “efficiency” (Ungerfeld, 2020).
There are very complex kinetics and thermodynamics regulations in the rumen that dictate metabolic pathways and thus end product production and inter-conversion. Classical biochemistry and microbiology studies have revealed significant differences among microbes in substrate utilization, enzymatic activities, and fermentation end products. These studies are now being integrated with new information from metagenomic, metatranscriptomic, and proteomic to enable us to interpret results and improve our understanding of the rumen environment. There are several excellent reviews that shed light on the importance of integrating rumen thermodynamics, kinetics, and microbiology in order to improve our understanding of the rumen ecosystem. For example, “The Role of Thermodynamics in the Control of Ruminal Fermentation” by Ungerfeld and Kohn (2006) and “Metabolic Hydrogen Flows in Rumen Fermentation: Principles and Possibilities of Interventions” by Ungerfeld (2020). The readers are recommended to refer to the original articles for more information. Below, I will summarize some of the key mechanisms related to the topic discussed.
Electrons from acetate and butyrate fermentative pathways are transferred via intracellular electron carriers to form dihydrogen (H2). This process is catalyzed by H2-evolving hydrogenase enzymes, which are widely encoded by genes in fermentative microbiota. Theoretically, dihydrogen accumulation could impair fibre fermentation. However, H2 plays a role as an intercellular electron carrier where H2 generated by certain fungi, bacteria or protozoa is utilized by other microbes. Methanogens are the main H2 utilizers in the rumen (Hungate, 1967), where CO2 is reduced to CH4 as the end product. The formation of CH4 generates ATP necessary for methanogens’ growth and serves as a very important H2 “sink” in the rumen ecosystem. Methanogens have the lowest threshold for H2; therefore, they outcompete most other H2-incorporating microbes (Kohn and Boston, 2000). Methane is considered wasted energy to the animals (2-12% of ingested gross energy) (Johnson and Johnson, 1995) and a potent greenhouse gas. Nonetheless, not all fermentative pathways are associated with a net production of metabolic hydrogen. For example, fermentation of starch to propionate as the end product is associated with a net uptake of H2. Thus, propionate production competes with CH4 as a metabolic hydrogen sink (Janssen, 2010). Hence, SCFA profile is closely associated with CH4 formation (Ungerfeld, 2020). High acetate to propionate ratio and high CH4 (% of total gas) implies a lower fermentation efficiency, but maximal ATP microbial generation. However, Hackmann et al. (2017) demonstrated in their study that a number of bacterial species encoded for “incomplete” glycolytic pathways in addition to several “alternative” pathways of carbohydrate metabolism. For example, acetate formation via the Bifidobacterium pathway was not associated with metabolic hydrogen production nor incorporation.
Suppressing methanogens by chemical agents has been shown to shift fermentation pathways towards propionate formation (Janssen 2010), which in turn is energetically valuable for glucose production in the liver of the host ruminant. The efficacy of such strategies has been variable, but recent studies have shown a potential for 3-nitrooxypropanol to reduce methane emissions in dairy cattle, for example, Melgar et al. (2020). Therefore, to optimize ruminal fermentation, for the benefit of both the microbiota and the host animal, strategies should focus on investigating non-hydrogen producing fermentation pathways and/or alternative hydrogen sinks to divert away from CH4 formation. In practice, optimizing rumen function reflects positively on farm profitability and the health of both the animal and the environment. In conclusion, there is a need for more integrative studies to maximize ruminant productivity in different feeding systems and to minimize environmental impact. These studies should comprehensively and concurrently measure SCFA, gas production, and microbial parameters in addition to performance indices. These studies should employ our recent understating of ruminal thermodynamics and recent “omics” data.
References
Hackmann, T. J., D. K. Ngugi, J. L. Firkins, and J. Tao. 2017. Genomes of rumen bacteria encode atypical pathways for fermenting hexoses to short-chain fatty acids. Environ. Microbiol. 19:4670-4683. Hungate, R. E. 1967. Hydrogen as an intermediate in the rumen fermentation. Arch. Mikrobiol. 59:158-164. Janssen, P. H. 2010. Influence of hydrogen on rumen methane formation and fermentation balances through microbial growth kinetics and fermentation thermodynamics. Anim. Feed Sci. Technol. 160:1-22. Johnson, K. A. and D. E. Johnson. 1995. Methane emissions from cattle. J. Anim. Sci. 73:2483-2492. Kohn, R. and R. Boston. 2000. The role of thermodynamics in controlling rumen metabolism. in Modelling Nutrient Utilization in Farm Animals J.P. McNamara, J. France, and D. E. Beever, ed. CAB International. Melgar, A., K. C. Welter, K. Nedelkov, C. M. M. R. Martins, M. T. Harper, J. Oh, S. E. Räisänen, X. Chen, S. F. Cueva, S. Duval, and A. N. Hristov. 2020. Dose-response effect of 3-nitrooxypropanol on enteric methane emissions in dairy cows. J. Dairy Sci. 103:6145-6156. Ungerfeld, E. and R. Kohn. 2006. The Role of Thermodynamics in the Control of Ruminal Fermentation. Pages 55-85 in Ruminant physiology: Digestion, Metabolism and Impact of Nutrition on Gene Expression, Immunology and Stress. K. Sejrsen, T. Hvelplund, and M. O. Nielsen, ed. Wageningen Academic Publishers, Wageningen, the Netherlands. Ungerfeld, E. M. 2020. Metabolic hydrogen flows in rumen fermentation: Principles and possibilities of interventions. Front. Microbiol. 11.
Credits: Image used under permission from Sheri Amsel (www.exploringnature.org)
Vitamin B12 is an essential nutrient in human nutrition. It is synthesized by bacteria and archaea, in the rumen. Therefore, dairy and beef products are considered the main source of vitamin B12 in the human diet (Martens et al., 2002). Vitamin B12 acts as a co-factor for several enzymes involved in carbohydrate, amino acid, and fatty acid metabolic pathways in humans and other mammals. Vitamin B12 deficiency can cause pernicious anemia, cognitive disabilities, neuropathy, and sustained spinal cord degeneration (Hoffbrand, 2015). According to USDA (2012), a 250-ml glass of milk provides 46% of the daily requirements of vitamin B12 (2.4 µg for humans above 13 years old). However, vitamin B12 levels in the milk of individual cows have been shown to vary significantly (Duplessis et al., 2019). The main known factors that influence the microbial synthesis of B12 in the rumen are genetics and dietary composition (the effects of season or stage of lactation are likely confounded with dietary composition). Apparent ruminal synthesis of vitamin B12 was shown to be positively associated with dietary cobalt, neutral-detergent fibre (NDF) and sugars, and negatively associated with dietary non-fibre carbohydrate (Schwab et al., 2006). According to Beaudet et al. (2016), apparent ruminal synthesis of vitamin B12 was 3-fold greater for cows receiving a high-forage diet compared with a high-starch diet. It is important to note that the metabolism of vitamin B12 is highly interconnected with the status of other B vitamins, such as Biotin. However, in this short review, I will focus on vitamin B12 for simplicity.
Similar to mammals, most bacteria require vitamin B12 for critical metabolic functions but, at the same time, lack the ability to synthesize their own vitamin B12. It is unknown which groups of ruminal bacteria are able to synthesize B12, however, based on a human study (Degnan et al., 2014), only 25% of the commensal microbiota in the intestine can synthesize vitamin B12, and the rest are considered vitamin B12 utilizers.
A recent collaborative study lead by McGill University in QC, Canada (Franco-Lopez et al., 2020) examined the correlations among the levels of vitamin B12 in the rumen, milk, and feces. The concentrations of B12 in the rumen and plasma were positively correlated with the yield of vitamin B12 in the milk (concentration of B12 X milk yield). However, these correlations, although significant, were considered weak (r < 35), likely due to variation among different individual animals and herds.
Further, the study investigated the bacterial communities in the rumen, milk, and feces and the correlations between these communities and the abundance of vitamin B12 in the bovine rumen, milk and feces. It is important to note here that correlation studies cannot imply causation (cause and effect); thus, we cannot determine if a particular microbial group was driven by B12 or was the driver. The genus Prevotella was more abundant in animals with high vitamin B12 concentration. It is interesting that Prevotella does not produce vitamin B12 but rather takes the opportunity of the presence of vitamin B12 in the rumen to grow and proliferate. Provetella metabolizes sugars, amino acids, and small peptides for growth and is considered a major propionate producer in the rumen (Strobel, 1992). Our research (AlZahal et al., 2017) showed that Prevotella dominated during high-forage feeding (42% phylum Bacteroidetes), and its abundance was increased to 65% when cows were switched to high-grain. This increase in dominance was associated with an increase in ruminal propionate concentration. It is important to note that Provetella is a very diverse genus with a large number of newly discovered species, the functions of which are widely unknown.
On the other hand, Franco-Lopez et al. (2020) showed that the phylum Bacteroidetes, the family Succinivibrionaceae, and the genera Ruminiclostridium, Butyrivibrio, and Succinimonas were more abundant with animals with low vitamin B12 concentration. The relationship between these bacterial groups, which are considered as important degraders in the ruminal community, and vitamin B12 abundance is not clear. The authors in this study aimed to explore the connection between bovine microbial communities and vitamin B12 abundance in the rumen and milk and to highlight gaps in our knowledge regarding vitamin B12 metabolism. It is, indeed, a complex topic given that vitamin B12 is critical to the growth and function of the gastrointestinal microbiome, the productivity and health of the ruminant animal, and the health of consumers.
Although the supply of B12 vitamin (and other B vitamins) from dietary sources and microbial synthesis in the rumen can generally be sufficient to avoid deficiency, Girard and Matte (2006) and others suggested that these supplies were “insufficient for optimizing metabolic efficiency, production, composition and the nutritional quality of milk in high-producing dairy cows.” Supplementation of B vitamins to high-yielding cows and during the transition period showed a tangible potential to improve cows’ health and healthfulness of ruminant products. Nonetheless, more integrative research is needed to understand conditions under which B vitamins apparent synthesis in the rumen becomes limiting.
References
AlZahal, O., F. Li, L. L. Guan, N. D. Walker, and B. W. McBride. 2017. Factors influencing ruminal bacterial community diversity and composition and microbial fibrolytic enzyme abundance in lactating dairy cows with a focus on the role of active dry yeast. J. Dairy Sci. 100:4377-4393.
Beaudet, V., R. Gervais, B. Graulet, P. Noziere, M. Doreau, A. Fanchone, D. D. S. Castagnino, and C. L. Girard. 2016. Effects of dietary nitrogen levels and carbohydrate sources on apparent ruminal synthesis of some B vitamins in dairy cows. J. Dairy Sci. 99:2730-2739.
Degnan, Patrick H., Michiko E. Taga, and Andrew L. Goodman. 2014. Vitamin B12 as a modulator of gut microbial ecology. Cell Metab. 20:769-778.
Duplessis, M., D. Pellerin, R. Robichaud, L. Fadul-Pacheco, and C. L. Girard. 2019. Impact of diet management and composition on vitamin B12 concentration in milk of Holstein cows. Animal. 13:2101-2109.
Franco-Lopez, J., M. Duplessis, A. Bui, C. Reymond, W. Poisson, L. Blais, J. Chong, R. Gervais, D. E. Rico, R. I. Cue, C. L. Girard, and J. Ronholm. 2020. Correlations between the composition of the bovine microbiota and vitamin B12 abundance. mSystems. 5.
Girard, C. L. and J. J. Matte. 2006. Impact of B-vitamin supply on major metabolic pathways of lactating dairy cows. Can. J. Anim. Sci. 86:213-220.
Hoffbrand, A. V. 2015. Megaloblastic Anaemia. Pages 53-71 in Postgraduate Haematology.
Martens, J. H., H. Barg, M. J. Warren, and D. Jahn. 2002. Microbial production of vitamin B12. Appl. Microbiol. Biotechnol. 58:275-285.
Schwab, E. C., C. G. Schwab, R. D. Shaver, C. L. Girard, D. E. Putnam, and N. L. Whitehouse. 2006. Dietary forage and nonfiber carbohydrate contents influence B-vitamin intake, duodenal flow, and apparent ruminal synthesis in lactating dairy cows. J. Dairy Sci. 89:174-187.
Strobel, H. J. 1992. Vitamin-B12-dependent propionate production by the ruminal bacterium prevotella-ruminicola-23. Appl. Environ. Microbiol. 58:2331-2333.
One of the articles that I read a while ago was “Maximizing efficiency of rumen microbial protein production” written by T. Hackmann and Jeffry Firkins. The article reignited my interest in the topic of ruminal microbial protein efficiency and its impact on overall production efficiency. Here, I would like to share my thoughts and findings with you. The authors did a great job in discussing the topic despite the obvious lack of data from the ruminant side. I invite you to give it a read. (https://www.frontiersin.org/articles/10.3389/fmicb.2015.00465/full)
The rumen is a magnificent organ that host a very complex microbial eco system, which contains manly bacteria, protozoa, fungi, and archaea. The role of which – form the host’s perspective – is to ferment forages and feedstuffs mainly into short chain fatty acids (SCFA), which in turn constitute most of the energy sources to the host animal. In addition, the microbial cells passing through the rumen to the small intestine provide the major source of AA to the host animal (60-85% of AA reaching the small intestine). The fermentation is a process utilized by microbes to generate the necessary ATP for growth (SCFA is simply a by-product of this process). However, only 1/3 to 2/3 of the generated ATP is directed towards growth and the rest for maintenance functions, synthesis of reserve carbohydrates, or energy spilling (futile cycles where energy is released as heat). As the authors indicated, it is very interesting that the microbial growth is an inefficient process, and under some conditions, only a 1/3 of ATP is directed towards microbial growth. The microbial protein is a significant source of metabolizable protein (MP) to the animal and it ideally should make 50% of total MP (microbial + dietary) reaching the small intestine. The amount of microbial MP can exceed 1 kg per day for high producing cows. Therefore, it is important to consider the factors that can affect the efficiency of microbial growth. The optimization of microbial growth can have a significant effect on farm economy.
The authors, using available data, explained some of the factors that affected microbial growth efficiency, which included: Excess carbohydrate supply, recycling of microbial protein, branched chain-short fatty acids, ammonia-N vs. peptides or AA supply, asynchrony of carbohydrate and nitrogen sources, ruminal SCFA interconversion, and supplemental fat. It is interesting that microbes respond in different ways to excess carbohydrates, one of which is by shifting to catabolic pathways that yield less ATP. In general, rapidly fermentable carbohydrate can lead to a drop in ruminal pH (<6), which inhibits fibre digestion (depressed adherence of cellulolytic bacteria to cellulose and reduced cellobiose transport across membrane).
In conclusion, this review highlights the potential inaccuracies in predicting microbial protein production in the rumen and explains several factors that can influence its efficiency. The authors suggested using mechanistic models (rather than conventional models) to improve the prediction of microbial protein in the rumen, however, there is a significant lack of data and more trials are needed. This is a very exciting opportunity to improve ruminant production efficiency!
Ousama AlZahal
(Image credit: Rigobelo and de Ávila, 2012. DOI: 10.5772/50054)
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