Feeding dairy cows’ liquid glycerol is a common strategy to avoid ketosis. A condition which occurs when the cow mobilises body fat to satisfy her energy requirements in volumes which exceed the capacity of the liver to convert the fat into glucose (energy).
She mobilises body fat within early lactation to satisfy her increasing energy requirements, which are largely driven by milk production. Around the point of calving feed intake is naturally depressed, so the cow is often unable to physically consume enough feed to meet her increasing energy requirements. This is a condition known as negative energy balance as illustrated in Figure 1, where her energy requirements exceed her energy intake, this condition can last up to 20 weeks. Minimising the “energy gap” is important for avoidance of ketosis and maintaining health, production & profitability.
Figure 1 Energy balance of dairy cows from gestation to lactation adapted from Hoeij, (2017).
Glycerol can be effective in aiding to alleviate ketosis because it’s a very efficient glucose precursor. The metabolic pathway of glycerol is much closer to glucose than other major precursors for gluconeogenesis, such as propionate, lactate and amino acids (McDonald et al., 2011). Compared to propionate conversion of glycerol to glucose is only a 3-step process, whereas propionate to glucose is a 6-step process as shown in Figure 2. This means that glycerol is converted to glucose at a higher metabolic efficiency, using less energy intermediates which reduces the energy cost and nutrient requirement to the cow to synthesise the glucose from glycerol. Ultimately, this increases blood glucose levels and improves metabolism.
Figure 2 Major pathways of gluconeogenesis in cattle adapted from McDonald et al., (2011).
When cattle use their body fat for energy this can also commonly reduce the cow’s appetite. Therefore, by supplying glycerol and increasing blood glucose levels this will reduce the requirement for the breakdown of fat for energy and subsequently support feed intake (Allen et al., 2003).
Whilst feeding and particularly drenching glycerol has some proven efficacy, studies have shown that delivering liquid glycerol into the rumen significantly reduces the effectiveness for several reasons.
Glycerol is rapidly fermentable within the rumen meaning that:
Within a 2015 study, Piontoni and Allen infused glycerol either into the rumen or abomasum (this simulates rumen protection). They found that infusing glycerol into the abomasum instead of the rumen was more effective in increasing blood glucose levels, indicating better energy supply when the glycerol is not released within the rumen.
It’s clear from research that feeding glycerol in a way that it remains unaltered within the rumen will offer better and more consistent results. Hippen et al., (2008) stated that to be a glucogenic precursor glycerol must be able to bypass the rumen. That’s why the glycerol in Glycal Forte® is rumen protected.
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Allen, M.S., Bradford, B.J. and Oba, M. 2009. Board-invited review: The hepatic oxidation theory of the control of feed intake and its application to ruminants. Journal of Animal Science, 87 (10), pp.3317-3334.
Hippen, A.R., DeFrain, J.M. and Linke, P.L. 2008, January. Glycerol and other energy sources for metabolism and production of transition dairy cows. In Florida Ruminant Nutrition Symposium (Vol. 605, No. 1).
Kristensen, N.B. and Raun, B.M.L. 2007. Ruminal fermentation, portal absorption and hepatic metabolism of glycerol infused into the rumen of lactating dairy cows. Publication European Association for Animal Production, 124, p.355.
Mc Donald, P., Edwards, R.A., Greenhalgh, J.F.D., Morgan, C.A., Sinclair, L.A. & Wilkinson, R.G. 2011. Carbohydrate synthesis. In: Animal Nutrition. pp. 226-234. Harrlow, England: Pearson Education Limited 7th Edition).
Piantoni, P. and Allen, M.S. 2015. Evaluation of propylene glycol and glycerol infusions as treatments for ketosis in dairy cows. Journal of Dairy Science, 98 (8), pp.5429-5439.
Van Hoeij, R. 2017. Metabolic status, lactation persistency, and udder health of dairy cows after different dry period lengths. Wageningen University and Research.