Editor's note: The following answer is provided by Al Kertz, dairy field technical service and research, Milk Specialties Global Animal Nutrition.

Q: How can I better understand and manage energy status of cows?

A: While a book could be written about this topic, there are some basic principles involved.

Cows cannot defy the laws of thermodynamics (a quote from David Weakley). So, let's think of a bank account (cow) with money (energy) being the currency. The cow has a certain amount of energy needs. She can bank energy when it is in excess, but we do not want an excess for a long period of time because that indicates that she is not using her reserves well or we are not managing that currency well. Cows take energy in and use energy in various ways, which then also determines what the returns for this energy investment will be. Energy is required for body maintenance, and if energy is not adequate for this purpose, cows will deteriorate, not produce milk well, and will deplete their body condition in trying to stay alive and produce milk. Their health will be compromised; and if they survive, it will take time for them to fully recover — if they ever do.

Second, this energy currency is somewhat interchangeable and convertible. If cows need more energy for milk production than they are able to consume, either milk production decreases or they must lose body condition to maintain or increase milk production. But if cows have poor body condition, they may not be able to convert additional remaining body condition in an attempt to maintain milk production. There is a minimum balance required. In that case, milk production will decrease because staying healthy and alive has a higher priority than milk production. Likewise, reproduction may suffer when the energy account is low. And the higher milk fat and protein are, the more energy is required from the bank to produce these levels.

How to best maintain this energy bank? Particularly in earlier lactation, cows cannot eat enough to meet their energy requirements for milk production. Thus, they make withdrawals from their energy bank to provide for milk production. As managers for cows' energy bank, we need to do things to minimize how much and how long cows withdraw from this energy bank. Feeding high-quality forages helps provide for more energy from forages, and their higher rate and extent of digestibility means that cows can then eat more, too. Likewise, feeding more grain and less forage can help to increase energy intake, but only to a point before lower forage levels can impair rumen function and result in some health issues such as increased feet and leg problems from marginal acidosis.

The highest currency to use in the energy bank is dietary fat as it has 2.25 times more energy than protein and carbohydrate, as long as the fat source does not decrease DMI. In an early-lactation 15-week trial (Journal of Dairy Science. 92:6144-6155, 2009), cows fed 60-percent forage with a fat supplement (mostly saturated free fatty acids-SFA) increased NEL intake, but that went into regaining body condition. They needed that extra energy in their low bank reserves. With 40 percent forage (starch was kept lower by using byproducts), plus the fat supplement which did not decrease DMI, cows had enough reserves in the bank so they put the extra energy into more milk.

Managing those reserves is the dual charge of dairy producers and nutritionists.


60% Forage         

60% Forage 

40% Forage

40% Forage   

DMI, lb/d





Mcal/d NEL





Body condition score





Milk, lb/d