Within the previous article effective energy was explained. Effective energy is a concept which can be used to denote the observed energy response in cattle consuming Glycal Forte®. The energy response observed is typically far greater than the chemical composition of the feed would suggest. Potentially upwards of 36MJ whilst only consuming 250g of the total diet. This is due to both the physiological and metabolic improvements offered by the product which ultimately allows the animal to perform better. Glycal Forte® is highly functional as a feed ingredient and the benefits can largely surpass that of the rumen bypass glycerol it supplies. Being highly functional typically allows for the removal of costly dietary components which have a combined aim to supply the cow with what Glycal Forte® can supply.
The Effective Energy response of a specialty feed ingredient such as Glycal Forte® is derived from four parameters recognising the interactions with feed intake and rumen pH management. These are designated as E1, E2, E3 and E4.
E1: Glycal Forte® has a unique composition which enables it to raise and maintain rumen pH to an optimal level. This means that up to 9.0 MJ/day can be obtained from more efficient feed utilization as previously demonstrated by Fawcett (Bioparametrics). Energy which the rumen microflora would have previously used to maintain homeostasis in an acidic environment. By raising the pH, Glycal Forte® makes this energy available to the cow. Farm trials using intra-ruminal boluses have shown that 250g Glycal Forte® can have this effect on pH. Therefore, one can ascribe an Effective Energy value E1 of 9.0MJ.
Low rumen pH (<5.8) is extremely common especially after the animal has consumed a large meal (Oetzel, 2007). Low rumen pH for significant periods <5.8 for several hours a day (Li et al., 2013) is otherwise known as sub-acute ruminal acidosis (SARA), a condition which is negative for animal health and reduces herd profitability (Plaizier et al., 2014). Prevalence of SARA within milking herds is estimated to range from 11-26% (Abdela, 2016).
E2: The primary fibrolytic bacteria in the rumen are intolerant to low ruminal pH. Rumen fibre digestion rapidly decreases when pH drops, this consequently reduces the amount of nutrients absorbed from the gastrointestinal tract by some 10%. The additional energy provided to the cow by correcting the rumen pH to optimal levels and thereby optimising microbial efficacy has been shown to be 0.6 MJ/kg DM for grass silage and 0.5 MJ/kg DM for maize silage (Dijkstraa, et al. 2012). Approximately 0.5MJ/kg DM can be recovered from the feed ingredients if the rumen pH is well managed. For a cow consuming 24 kg DM/day this is an extra 12 MJ/day which is accomplished by 0.25 kg Glycal Forte® so the Effective Energy of E2 is 12.0 MJ.
E3: This is the energy derived from the glycerol (glucose precursor) content of the solid calcium glycerol complex. When the rumen pH is raised by the addition of Glycal Forte® to an optimum level the maximum bypass of glycerol is achieved meaning that it is all available for absorption from the small intestine. The Gross Energy (GE) of glycerol = 18.1 MJ/kg. In pigs and poultry, the metabolisable energy (ME) is 98% of the GE. Rumen bypass makes the cow more like a monogastric. Glycal Forte® has a 60% glycerol content, therefore E3 = 10.64 MJ/kg (18.1 x 0.98 x 0.60) which is 2.66 MJ/250g.
Rumen unprotected glycerol is fermented to volatile fatty acids (VFA), especially butyrate and propionate which decrease rumen pH and can alter the acetate to propionate ratio depressing milk fat (Kijora et al., 1998). Furthermore, unprotected glycerol is absorbed less efficiently. Kristensen and Raun (2007) fed 925g of glycerol per cow and found that only around 10% was recovered within the portal vein for use by the cow to synthesise glucose.
E4: Dry Matter Intake (DMI) is reduced in cows with a sub-optimal rumen Ph (Oetzel, 2003). By raising the pH, Glycal Forte® stimulates DMI. Farm records indicate that feeding 250g of Glycal Forte® increases DMI by 1kg per day. This adds a further 12 MJ to the Effective Energy of Glycal Forte®. The recommended daily dose of Glycal Forte® is 250g and therefore potentially the Effective Energy response is: (9.0) + (12.0) + (2.66) + (12.0) = 35.66MJ/250g.
Many traditional energy feeds fail to acknowledge the potential negative effects on rumen function, and subsequent reductions in the energy derived. However, Glycal Forte® can clearly perform greater than its book value in terms of energy, and therefore prediction of performance when feeding Glycal Forte® would be under estimated using book values. Using effective energy would allow for better estimation.
