Glycal Forte ® the rationale for its use as a dairy-feed ingredient

Glycal Forte is a complex of glycerol supported in a solid calcium matrix. A feed ingredient, it is a free-flowing powder and is listed in the EU Feed Materials Register as Solid Calcium-Stabilised Glycerine. It is a source of by-pass energy, a rumen pH regulator and a source of bio-available calcium. Glycal Forte is produced by a unique, patent-protected process. It helps the high-yielding dairy cow avoid metabolic disorders – a nutrition-based health approach to managing transition and early lactation. Controlling ketosis, sub-acute rumen acidosis (SARA), and hypocalcaemia is the key to successful transition and lactation.

Glycal Forte – a source of by-pass glycerol

The successful metabolic transition from the “dry” period to early lactation is dependent on the increased synthesis of glucose and the optimal mobilisation of body fat reserves to meet the energy demands of a rapidly increasing milk flow. In high-yielding cows this metabolic transition is often impaired resulting in ketosis, hypocalcaemia and fatty liver syndrome. These increase the risk of conditions such as displaced abomasum, retained placenta, mastitis and metritis, which, in turn, can lead to lower milk yield and reduced fertility.

Robinson et al., (2006) reported that in high-yielding dairy cows excessive negative energy balance reduces insulin and IGF-1 concentrations and increases growth hormone leading to delays in oestrous cyclicity and impaired oocyte quality and corpus luteum function.

Buckley et al., (2003) suggest that a severe NEBAL (Negative Energy Balance) can predispose cows to metabolic disorders. Milk fever, ketosis, retained foetal membranes, metritis, displaced abomasa and increased susceptibility to mastitis primarily impact cows during this transition period. In addition, the duration and severity of NEBAL can negatively impact reproduction with a significant association between extent of NEBAL (amount of body condition lost) and decreased fertility.

Glycerol is recognized as having gluconeogenic properties which in the transition and early lactation period is vitally important in maintaining body condition and minimising the incidence of nutritional disorders. Liquid glycerol can be added to feed but this route is not without its problems:

  1. Glycerol is highly viscous and therefore difficult to handle, especially in cold weather.
  2. Its high viscosity does not allow homogenous mixing into feed –“balling” occurs.
  3. Due to uneven mixing, high doses of glycerol in the rumen can cause a rapid drop in pH adversely affecting rumen fermentation.
  4. Fermentation of glycerol in the rumen yields higher proportions of propionate and butyrate than acetate.
  5. Over 50% of fermented glycerol is lost as carbon dioxide
  6. The fraction converted to butyrate is metabolised to beta-hydroxy butyrate (BHB) and thus can be ketogenic rather than gluconeogenic

Hippen et al., (2008) reported that glycerol is an efficient glucogenic substrate because it enters the gluconeogenesis pathway at the triose phosphate level and, therefore, is not affected by two of the rate-limiting gluconeogenic enzymes. Logically, the dairy cow in negative energy balance has pathways activated for utilization of glycerol liberated from mobilization and hydrolysis of triglycerides from body fat. This activity is dependent upon absorption of glycerol rather than fermentation to propionate and butyrate, which is somewhat counterproductive due to the ketogenic nature of butyrate. If absorbed intact, glycerol is a highly efficient glucogenic substrate, but it must either be delivered in water to associate with the liquid fraction of the rumen contents or be able to “bypass the rumen in some form to be absorbed as glycerol and converted to glucose by the liver”

It is widely accepted that a significant proportion of glycerol in the rumen is fermented to propionic and butyric acids. This may not be desirable for managing the transition dairy cow. Certainly propionic acid is a useful energy source for ruminants but it is also quite a strong acid and may well exacerbate problems of SARA. DeFrain et al., (2004) concluded that feeding glycerol to transition dairy cows increased the indicators used to gauge the degree of ketosis in dairy cattle, primarily due to an increase in butyric acid production. Feeding liquid glycerol to the transition cow may in fact exacerbate problems of ketosis and acidosis.

The stabilised complex of calcium and glycerol in Glycal Forte protects it against the release of the glycerol at normal rumen pH. The glycerol passes through the rumen largely undigested, into the abomasum where it is released as the complex dissociates at the low pH, and thence into the small intestine. In other words, Glycal Forte largely by-passes the rumen. This protection allows the glycerol to escape rumen fermentation and enter the small intestine where it is absorbed directly into the portal vein and thus into the liver. Here glycerol enters the gluconeogenesis cycle and is transformed efficiently into glucose, boosting the energy supply for milk production and sparing the mobilization of body fat. This route of absorption avoids the less efficient conversion of glycerol into butyrate that would otherwise depress feed intake in an animal already with a low appetite, and raise the blood ketone levels.

The bypass potential of Glycal Forte was demonstrated in in vitro gas production studies which are routinely used to assess feed ingredients for ruminants. See Figure 1

Figure 1 Cumulative gas production from fermentation of liquid glycerol and Glycal Forte.

The gas production data show that Glycal Forte was fermented much more slowly than liquid glycerol. This ensures that a large proportion of the glycerol in Glycal Forte will by-pass the rumen and not contribute to acid fermentation.

The provision of bypass glucogenic energy by feeding Glycal Forte helps reduce body weight loss, reduce blood ketone levels and, in a university trial, reduce Somatic Cell Count (SCC). All of this contributes to the farm results, but this is only part of the story.

Glycal Forte – A rumen pH regulator

Another important advantage of Glycal Forte is that it can regulate the pH in the rumen and avoid drastic reductions in pH which, according to Dijkstra et al., (2012) are so deleterious to the health and productivity of the transition cow.

Russel and Dombrowski,. (1980) commented that the rumen, although well buffered by bicarbonate, phosphate, protein, and volatile fatty acids, can vary in pH from approximately 7.0 to less than 5.0 under different dietary conditions. In vivo and in vitro observations have indicated that the relative success of rumen bacteria is correlated with pH.It seems likely that pH is an effector of overall microbial protein synthesis in the rumen. Since the rumen pH of animals fed high starch diets is often below 6.0, it is possible that the availability of microbial protein to the animal could be enhanced by a manipulation of the rumen pH

Dijkstra et al., (2012) take a similar approach. Ruminal pH is a key determinant of the profile of nutrients available for absorption. Low rumen pH of below 6.0 for prolonged periods each day can negatively affect feed intake, microbial metabolism, and nutrient degradation, and low ruminal pH is related to inflammation, laminitis, diarrhoea and milk fat depression. The primary fibrolytic bacteria are intolerant to low ruminal pH, and rumen fibre digestion rapidly decreases when pH drops below critical values and this consequently reduces the amount of nutrients absorbed from the gastrointestinal tract.

Research conducted by Bio-Energy Ingredients Ltd in conjunction with Bioparametrics Ltd has shown that rumen pH drops dramatically after calving and, unless corrected, can stay low for some time. Raising the rumen pH at this time saves energy. This is the energy that the rumen microbes would have used in attempting to counter the low rumen pH. This energy can then be used for milk production. The lower the starting point for pH change, the greater the energy saving. The research into this post-calving pH drop demonstrated that raising pH from 5.5 to 6.0 will reduce the energy required for microbial maintenance by over 9MJ per day. This is sufficient energy to fuel the production of nearly 3 litres of milk. In addition, an acidic environment can decrease the growth rate of rumen bacteria. As the ruminant is largely dependent on microbes as a protein source, the efficiency of rumen microbial growth is of critical importance to performance (Russell and Dombrowski ,1980). Bioparametrics calculate that raising pH from 5.5 to 6.0 increases microbial protein supply by 6.4% or 168g/day due to faster microbial synthesis.

Research carried out by Bio-Energy Ingredients Ltd has shown that the solubility of Glycal Forte in aqueous medium increases gradually with decreasing pH. This would imply that in the case of an acidic rumen (pH below 6.0), Glycal Forte will dissolve relatively more than in the case of a cow with an optimal rumen pH of 6-7. This will thereby provide a useful sustained-release mechanism whereby the Glycal Forte adapts to the individual cow’s rumen pH at a given time to provide a larger dose of acid-neutralizing hydroxyl ions in an acidic rumen, when and where it is most needed, to increase the rumen pH towards optimal levels.

In further work the amount of Glycal Forte required to maintain the pH of the rumen in the desirable range of 6.0-7.2 was investigated. Various amounts of Glycal Forte were added to buffered aqueous solutions in glass beakers and the mixtures stirred at room temperature whilst pH readings were taken with a calibrated pH probe at different time intervals over 24 hours as indicated in Table 1.

Glycal Forte ConcentrationTime (Hours)Buffer pH 5.5Buffer pH 6.5
0.1% (w/v) equivalent to 200g/200 litre rumen65.886.78
0.1% (w/v) equivalent to 200g/200 litre rumen245.886.68
0.15% (w/v) equivalent to 300g/200 litre rumen66.367.14
0.15% (w/v) equivalent to 300g/200 litre rumen24
0.2% (w/v) equivalent to 400g/200 litre rumen67.437.59
0.2% (w/v) equivalent to 400g/200 litre rumen247.897.27

Table 1. The maximum pH reached after addition of Glycal Forte to different buffers

Glycal Forte, at a dose rate of 300 g per 200 litre buffered liquid volume per day was able to maintain an acceptable pH in the buffered mixture even when the original starting pH was 5.5.

In a recent trial rumen pH was monitored using intra-ruminal boluses. Glycal Forte was fed at 250g/cow/day and pH in these cows was compared with that from cows with no Glycal Forte added to their feed.

Figure 2 post-calving hours spent below pH 5.8

The intra-ruminal boluses used in the trials measure rumen pH every 15 minutes. The bar chart in Figure 3 shows that cows fed Glycal Forte spent fewer than half the hours with a pH below 5.8 compared to the control cows.

Glycal Forte – A source of highly-available calcium

Sub-Clinical Hypocalcaemia can be defined as low blood calcium concentrations without clinical signs of milk fever. Subclinical hypocalcaemia affects about 50% of second and greater lactation dairy cattle fed typical pre-fresh diets (Garrett and Oetzel, 2012). Hypocalcaemia has been linked to number of secondary problems. This happens because blood calcium is essential for muscle and nerve function – particularly functions that support skeletal muscle strength and gastro-intestinal motility. Problems in either of these areas can trigger a cascade of negative events that ultimately reduce dry matter intake, increase metabolic diseases, and decrease milk yield (Goff, 2008).

Supplementation with oral calcium is the preferred approach for supporting cows that are exhibiting early signs of milk fever but are still standing (Oetzel, 2011) . The source of calcium in an oral supplement and its physical form greatly influence calcium absorption and blood calcium responses. Calcium chloride has the greatest ability to support blood calcium concentrations (Goff and Horst, 1993). This can be explained by its high calcium bioavailability and its ability to invoke an acidic response in the cow, which causes her to mobilize more of her own calcium stores. Providing a typical amount of calcium chloride (e.g., 50 grams of elemental calcium) in a small oral dose provided the best absorption (Garrett and Oetzel, 2012)

Glycal Forte is a great source of highly-available calcium. When it reaches the abomasum where the pH is 3 or lower, Glycal Forte not only releases its glycerol, but the calcium in the matrix reacts with hydrochloric acid in the abomasum to form water-soluble calcium chloride. Fed at 250g per cow per day Glycal Forte provides the cow with around 60g of elemental calcium.


Glycal Forte is a nutrition-based health approach to help the farmer to manage transition and early lactation. It is a source of by-pass glycerol and can also regulate the pH of the rumen to keep it at an optimum level for good health and productivity of the cow. Feeding Glycal Forte improves milk production, health and fertility through effective management of rumen pH, the provision of by-pass gluconeogenic energy and an optimum quantity of bioavailable calcium.


Buckley, F., O’Sullivan, K., Mee, J.F., Evans, R.D. and Dillon, P. (2003) . Relationships among milk yield, body condition, cow weight, and reproduction in spring-calved Holstein-Friesians. Journal of Dairy Science 86: 2308-2319

DeFrain, J. M., Hippen, A. R., Kalscheur, K. F. and Jardon, P. W. (2004). Feeding glycerol to transition dairy cows: effects on blood metabolites and lactation performance. Journal of Dairy Science, 87: 4195-4206

Dijkstraa, J., Ellis, J .L., Kebreabb, E., Stratheb, A. B., Lópezc, S., Franced, J. and Bannink, A. (2012). Ruminal pH regulation and nutritional consequences of low pH. Animal Feed Science and Technology, 172: 22–33.

Garrett, R. and Oetzel, G. R. (2012). An update on hypocalcemia on dairy farms. School of Veterinary Medicine, University of Wisconsin-Madison

Goff, J. P. and R. L. Horst. (1993). Oral administration of calcium salts for treatment of hypocalcemia in cattle. Journal of Dairy Science, 76:101-108.

Goff, J. P. (2008). The monitoring, prevention, and treatment of milk fever and subclinical hypocalcemia in dairy cows. Veterinary Journal, 176: 50-57

Hippen, A. R., DeFrain, J. M., Linke, P.L. (2008). Glycerol and other energy sources for metabolism and production of transition dairy cows. Florida Ruminant Nutrition Symposium Best Western Gateway Grand Gainesville, Florida, USA.

Oetzel, G. R. (2011). Non-infectious diseases: Milk fever. Encyclopedia of Dairy Sciences Vol. 2. Academic Press, San Diego, California, USA.

Russell, J. B. and Dombrowski, D. B (1980). Effect of pH on the efficiency of growth by pure cultures of rumen bacteria in continuous culture. Applied and Environmental Microbiology, 39: 604-610

Robinson, J, Ashworth, C. J., Rooke, J. A., Mitchell, L. M., McEvoy, T. G. (2006). Nutrition and fertility in ruminant livestock. Animal Feed Science and Technology, 126: 259-276.