Kim Mullenix

Extension Beef Specialist and Associate Professor / Auburn University

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Decreasing temperatures and often increasing rainfall in the Southeast in the winter influence energy demands for the herd during the cooler months of the year.

Energy needs of beef cattle are commonly expressed as total digestible nutrients (TDN) or net energy for maintenance. In the Southeast, most forage and feed analysis reports express energy values for these sources as TDN. Depending on where a cow is in the production cycle will determine how much of her daily energy need is allotted toward maintenance, lactation, gestation and/or growth.

The energy needs of cows can be classified as follows:

• Maintenance – Cows require nutrients to digest food, move, maintain body temperature and weight, expel waste and repair tissues on a daily basis. Maintenance requirements can be impacted by the environment. For example, increased activity (distance walking to water, forage, etc.) and climatic conditions (hot/humid; cold/wet) influence daily energy needs.
  
  
• Lactation – The energy requirement of lactation is largely a function of milk yield, fat and protein percentage. Energy needs for lactation are the greatest during the first 60 days after calving. During the 60 days prior to calving, cow lactation energy requirements begin to increase in preparation for the arrival of the calf. There are also differences between and within breeds that affect milk yield and composition and energy needs for lactation. The greater milk production potential, the greater energy demand on the cow.
  
  
• Gestation – Realistically, the energy requirement for gestation is almost always part of the daily energy demand for a mature cow. The gestation length of a cow is 283 days – which equates to almost 10 months out of the year. By one month prior to calving, energy demand for gestation increases to 56% of her daily energy requirement.
  
  
• Growth – For a mature cow, we often don’t think about growth as being a key factor influencing energy demands. “Growth” refers to the energy needed for a mature cow to recover body tissue energy during different times of the year. For example, after weaning and during the first six months of pregnancy represents a time period where bodyweight gain can be most economically and effectively added to cattle. This coincides with a time period where gestation and lactation demands are low to minimal, meaning the cow can use her daily energy allotment better for maintenance and bodyweight gain.