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  • Calcium: The Multifunctional Nutrient for Dairy Cows

    Calcium (Ca) is an essential nutrient for the dairy cow. It is the major mineral in the body and about 98% of body Ca is present in bones and teeth. However, dairy cows excrete a large amount of Ca during lactation due to the high Ca content in milk. One litre of milk at 4.0% milkfat contains approximately 1.22g of Ca. Consequently, high producing dairy cows may secrete more than 45g of Ca daily in milk, and this Ca flow suddenly and notably increases during early lactation as milk yield increases.

    During the first few months of lactation, the dietary Ca intake is generally lower than the amount of Ca excreted in milk, faeces and urine and this can lead to the onset of subclinical hypocalcaemia (SCH) or even full-blown hypocalcaemia (Milk Fever), (Gaingon et al., 2019). If dietary Ca is inadequate or unavailable, depletion of Ca from bone reserves occurs. Therefore, the amount and the availability of dietary Ca is important, not only for maximum milk production and avoidance of hypocalcaemia, but also for maintenance of bone integrity in high producing cows.

    The impact of calcium levels on negative DCAD diets

    A common preventative strategy to control hypocalcaemia around calving is to induce the pregnant cow into a state of compensated metabolic acidosis, achieved by feeding a negative dietary cation-anion difference (DCAD) diet within the 4 weeks before calving. This negative DCAD is achieved by an acidification of the diet. A fully acidified pre-calving diet formulated with a higher Ca concentration (DCAD -24 mEq/100g of DM with high dietary Ca (226.60 g Ca/day, 2.0% DM) has been shown to improve reproductive performance and uterine immune function in the post-calving period through the decrease of days to first ovulation and a tendency to decrease service per conception rate (Ryan et al., 2020).

    Furthermore, a fully acidified pre-calving diet that does not provide enough Ca can have as many negative impacts on reproduction post-calving as a pre-calving diet with a positive dietary cation-anion difference. This indicates another crucial role of Ca.

    The impact of calcium on rumen microbial biomass

    There is also evidence that dietary Ca has an impact on the activity of rumen microbial biomass in addition to effects on the cow’s metabolism. The rumen microbial biomass is a consortium of bacteria, protozoa, fungi, amoebae and bacteriophages. The bacteria accounts for about 50%, protozoa 40% and fungi about 8% of the total microbial biomass. This rumen microbial biomass is responsible for digestion of feed ingredients producing volatile fatty acids and microbial protein which then feeds the cow (Thirumalesh and Krishnamoorthy, 2013). Therefore, an optimum function of the rumen biomass is essential for good feed utilization and to maintain high productivity by the dairy cow.

    A major activity of the rumen biomass is to digest cellulose in the TMR and convert it into volatile fatty acids which are an important source of energy for the cow. Ca in the form of free ions (Ca2+) appears to be required by the three predominant species of rumen cellulolytic bacteria; Fibrobacter succinogenes, Ruminococcus flavefaciens, and Ruminococcus albus. No cellulose degradation occurred without Ca2+ in cultures of F. succinogenes and increases in the extent of cellulose degradation occurred with all strains of ruminococci as Ca2+ concentration increased (Morales and Dehority (2009).

    In another study however, in situ ruminal neutral detergent fibre (NDF) degradation of maize stover and crude protein (CP) degradability of a concentrate mixture were improved with increasing levels of Ca propionate. This suggests an increase in rumen microbial production. Ca propionate seems to modulate the digestive microorganisms or enzymes in a dose-dependent manner. It is not clear whether this effect was due to the Ca or the propionate, but it certainly indicates that a Ca source can influence the rumen microbial biomass (Liu et al., 2009).

    The impact of Glycal Forte on rumen microbial biomass

    Glycal Forte® is also a good source of dietary Ca and the Ca is in the form of Ca ions (Ca2+). A significant improvement in microbial biomass production with Glycal Forte® added to rumen cultures fed a TMR has been independently confirmed using a gas evolution technique. The same study was also conducted with rumen available glycerol (Table 1).


    Table 1. Digestibility of a TMR with Glycal Forte® or glycerol.

    Treatment Graph


    Moreover, the inclusion of Glycal Forte® to cultures fed the TMR increased the efficiency of the ruminal fermentation by reducing the total gas production (Table 1). Reduced gas production during rumen fermentation in the cow may result in improved fermentation efficiency with less gas eructated as waste.

    How Glycal Forte can help

    It is quite clear that Ca is not only an essential nutrient but has many functions ranging from bone composition, milk production, support of immune function, improvement of fertility and supporting the rumen microbial biomass. Glycal Forte® is an effective way of increasing dietary Ca intake by providing a source of bioavailable Ca.

    Whilst supporting Ca intake Glycal Forte® acts as a source of negative DCAD, alongside stimulating good rumen function and supporting feed intake; making Glycal Forte® a good addition to negative DCAD close up diets. Alongside this, it’s well established that Glycal Forte® will also benefit the cow in the fresh period via it’s multifunctionality provided by rumen pH optimisation, rumen protected glycerol and bioavailable Ca all in one feed ingredient. 




    Gaignon, P., Le Grand, K., Laza-Knoerr, A.-L., Hurtaud, C. and Boudon, A. (2019). Effect of calcium intake and the dietary cation anion difference during early lactation on the bone mobilization dynamics throughout lactation in dairy cows. Plos One, DOI: org/10.1371/journal.pone.0218979.


    Liu, Q., Wang, C., Guo, G., Yang, W. Z., Dong, K. H., Huang, Y. X., Yang, X. M. and He, D. C. (2009). Effects of calcium propionate on rumen fermentation, urinary excretion of purine derivatives and feed digestibility in steers. Journal of Agricultural Science, 147: 201–209, DOI: 10.1017/S0021859609008429.


    Morales, M. S. and Dehority, B. A. (2009). Ionized calcium requirement of rumen cellulolytic bacteria. Journal of Dairy Science, 92: 5079–5091, DOI: 10.3168/jds.2009-2130.


    Ryan, K. T., Guadagnin, A. R., Glosson, K. M., Bascom, S. S., Rowson, A. D., Steelman, A. J. and Cardoso, F. C. (2020). Increased dietary calcium inclusion in fully acidified prepartum diets improved postpartum uterine health and fertility when fed to Holstein cows. Theriogenology, 142: 338-347.


    Thirumalesh, T. and Krishnamoorthy, U. (2013). Rumen microbial biomass synthesis and its importance in ruminant production. International Journal of Livestock Research, 3: ISSN 2277-1964.