B-vitamins Basics in Dairy Cattle Nutrition – Part I

Dr. Kirby Krogstad, Assistant Professor, Department of Animal Sciences, The Ohio State University

B-vitamin 101

B-vitamins are water soluble vitamins that are essential nutrients for metabolism of mammals. Ruminants, like dairy cattle, are provided B-vitamins by their rumen microbes. Since the rumen microbes provide B-vitamins to the animal, they are not supplemented in their rations because we assume that microbial sources meet the animal’s B-vitamin requirements. As dairy cattle continue to increase their milk production, additional B-vitamins may be helpful. Revisiting B-vitamin’s role in the dairy cow is necessary as we continue to enhance efficiency of dairy cattle.

There are 8 vitamins in the “B-vitamin complex”. They, and some of their primary functions, are listed in Table 1. Clearly, this class of vitamins is essential to some of our most critical metabolic reactions in the body. Choline is not listed but is often considered a “B-vitamin like” molecule, but it won’t be included in this discussion.

Table 1. List of B-vitamins with important functions they fulfill. Adapted from NASEM (2021).

Name of Vitamin

Function

Thiamin (B1)

Carbohydrate metabolism, energy metabolism, branched-chain amino acid catabolism, and fatty acid oxidation.

Riboflavin (B2)

Essential component of flavin adenine dinucleotide (FAD) and flavin mononucleotide. Involved in more than 100 metabolic reactions.

Niacin (B3)

Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). Involved in critical pathways like glycolysis, lipolysis, ketogenesis, and the Krebs cycle. ​

Pantothenic acid (B5)

Essential component of Coenzyme A which is involved in energy metabolism (i.e. Kreb’s Cycle). Component of enzyme required for fatty acid elongation.

Pyridoxine (B6)

AA metabolism and glycogen utilization.​

Biotin (B8)

Component of carboxylase enzymes (pyruvate carboxylase, propinyl-CoA carboxylase, others)​ involved in energy and amino acid metabolism.

Folate (B9)

DNA replication, damage, repair, and methyl donor.​

Cobalamin (B12)

Essential for two enzymes: methylmalonyl CoA mutase and methionine synthase. Critical for methyl donation, propionate metabolism, and gluconeogenesis.

Rumen Supply

How many B-vitamins do the rumen microbes supply to the cow? Very, very small amounts, which demonstrates that these molecules are very potent. For a cow eating 55 lb/day of dry matter (DM), she will be supplied between 1.3 and 6.6 g/day of total B-vitamins (Figure 1).
 

Figure 1. Estimated B-vitamin supply from rumen microbes of a dairy cow consuming 55 lb/day of DM. Estimates were calculated from NASEM, 2021. Image created with BioRender.com.

To further complicate matters, a recent meta-analysis has demonstrated that the basal diet fed to the cows will change the amount of these B-vitamins that flow out of the rumen and get taken up by the cow (Brisson et al., 2022). Generally, increasing rumen fermentable carbohydrates will increase the amounts of B-vitamins that exit the rumen. One exception to that generality is cobalamin (vitamin B12) which is reduced when increasing the amount starch in the diet. For example, a 10% increase in dietary starch would increase thiamin by 3%, riboflavin by 5%, and folate by 6%, while reducing cobalamin by 2%.

Dairy and B-vitamins for People?

Since the rumen provides cows with B-vitamins, the cows deposit some of these B-vitamins into their milk. One cup of bovine milk can provide approximately 10% of our thiamin needs, 40% of our riboflavin needs, 1% of our niacin needs, 20% of our pantothenic acid needs, 7% of our pyridoxine needs, 4% of our folates, and 50% of our cobalamin needs (Graulet and Girard, 2017). Clearly, dairy is an excellent source of these essential nutrients for humans.  

Conclusion

One of the rumen’s superpowers is to synthesize B-vitamins for the cow. We’ve long assumed that these B-vitamins meet the cow’s requirements. The diet fed to the cows changes the amounts of B-vitamins that exit the rumen each day. Increasing dietary starch increases B-vitamins except for cobalamin; increasing starch slightly reduces the amount of cobalamin that exits the rumen. Also, the B-vitamins in milk can provide a significant portion of the B-vitamins that humans require, which demonstrates some of the benefits of dairy product consumption by humans.

References

Brisson, V., C.L. Girard, J.A. Metcalf, D.S. Castagnino, J. Dijkstra, and J.L. Ellis. 2022. Meta-analysis of apparent ruminal synthesis and postruminal flow of B vitamins in dairy cows. J. Dairy Sci. 105(9):7399-7415. 10.3168/jds.2021-21656

Graulet, B., and C.L. Girard. 2017. Chapter 15 - B Vitamins in Cow Milk: Their relevance to human health. Pages 211-224 in Dairy in Human Health and Disease Across the Lifespan. R. R. Watson, R. J. Collier, and V. R. Preedy, ed. Academic Press.