For cows, not all energy is equal

The term metabolisable energy (ME) is often used as a proxy to indicate a ration’s value for a cow. But as a crude measure, ME doesn’t always equate to milk in the vat. 

 

Sourcing the right energy for rumen bugs

A cow’s rumen has an incredibly diverse microbial population (often referred to as bugs) capable of digesting different feeds and extracting ME from them. In a symbiotic relationship, a cow’s rumen bugs form a system within a system. Optimising bug performance is a key driver to increasing milk solids yield.

When a cow consumes a ration, the rumen bugs drive fermentation processes that produce different combinations of volatile fatty acids (VFAs). Rumen bugs in lactating cows require combinations of readily and slowly fermentable carbohydrates, in combination with fibre, proteins and minerals to influence the ratio of VFAs produced.

If we can manipulate these VFA ratios to favour increased levels of propionic acid, we supply more glucose precursors to the liver and enable lactating cows to increase blood glucose supply to the mammary gland. Simply put, this means more milk.

The importance of non-fermentable carbohydrates (NFCs)

Different supplementary feeds may appear to have similar ME values, but the way they perform in the cow can be very diverse. Propionic acid production is typically improved by increasing the levels of sugars, starch, pectin and fermentation acids in a ration, as they are more fermentable carbohydrates. A broad term that can be used to describe these carbohydrates is non-fibre carbohydrates (NFC). When it comes to evaluating supplementary feeds, the NFC value will give you a far better indication of anticipated milk production responses than ME values.

Calculating NFC values

The following table shows the equation used for calculating NFC values. It is: 

NFC= 100 – NDF – Crude Protein – Fat – Ash.

 

 

NFC Calculation

PKE

TopCow MAXUM 12

Barley

100

100

100

100

Neutral Detergent Fibre

- NDF%

- 65

- 16

-18

Crude Protein

- CP%

- 17

- 12

-12

Fat

- Fat%

- 9

- 5.5

-2

ASH (= mineral content)

- Ash%

- 4

- 7.5

-7

= NFC

 

 

= 5% (or 50g/kg)

= 59% (or 590g/kg)

=61% (or 610g/kg)

Discussion

ME specs for PKE are typically 11 – 12 MJME

ME for TopCow Maxum12 is 13.3 MJME

ME for barley is typically 12.3-12.8 MJME

Conclusion

Making purchases based on ME in isolation from NFC data can easily leave your cows underperforming

 

 

 

Balancing the system - avoid stripping condition

Researchers believe that if we could supply three grams of NFC for every gram of rumen degradable protein in a ration, we would produce more propionic acid and optimise the flow of metabolisable protein from the rumen to the intestines for absorption.

As pasture provides high levels of rumen degradable protein (RDP) and moderate levels of NFC, it makes sense to offer compound rations high in NFC to lactating cows. The best sources of NFCs are vegetative pastures, high WSC forage crops (eg fodder beet), cereal grains (wheat, barley, maize) and molasses.

Stripping condition off cows is not a sustainable source of ME for fresh cows either. Research work published by Professor Mike Allen at Michigan State University has repeatedly shown that cows losing a lot of condition early in their lactation have suppressed appetite (see ‘hepatic oxidation’ below). This feeds into the law of diminishing returns.

The take home message is to look a little deeper than ME values - supplementary feeding is a strategic investment and it literally pays to get it right.

Hepatic oxidation

This is a newly revealed metabolic mechanism that occurs in the liver of cows during the transition period and has a regulatory impact on DMI.

  • As metabolites (fuels) reach the liver they are oxidised in the process of creating energy. The combination of metabolites oxidising in the liver influence the firing rate of the vagus nerve. Any slowing in the firing rate of this nerve sends a satiety signal to the cow’s brain, so she thinks that she is full.
  • Increased levels of fat from the ration of body weight losses will increase hepatic oxidation, slowing the firing rate of the vagus nerve and reducing DMI.
  • The liver may also become overwhelmed with more fat than it can process, predisposing cows to conditions such as ketosis and fatty liver. Fat stored in the liver as a result of this essentially reduces the liver’s ability to manufacture blood glucose. Therefore, feed conversion efficiency is capped and milk output is less than optimal.

 

To find out more about getting the energy intake right for your cows talk to your local Ingham Dairy Nutrition Specialist.


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