The Changing Nutrient Needs of the Spring-Calving Cow
Spring-calving cows typically give birth before grass greens up. In fact, many of them are six to eight weeks into lactation before grass growth is sufficient for them to be turned out to graze without supplementation.
Providing a protein supplement to late-gestation cows grazing dormant range or fed low-quality hay is usually sufficient to maintain cow performance. At this stage of production the cow has a fairly low energy requirement (9-11 lb total digestible nutrients or TDN per day). Supplying a protein source provides nitrogen to the microbes in the rumen and allows them to digest the low-quality forage to provide the needed energy for the cow. So providing 2 lb/d of a 20-25% CP protein cube to cows grazing dormant native range would likely meet the needs of a 1200 lb cow in late gestation, provided the cow has access to as much grass as she can eat.
After a cow gives birth and lactation starts, the energy needs of the cow increase considerably. Depending on the level of milk production, weather conditions, and cow maintenance requirements, that same 1200 lb cow now needs 14.5-16.5 lb TDN/d.
If the producer increased the protein cube to 7 lb/d it would still only provide 14 lb TDN per day. Increasing the amount of protein supplement fed, does not typically meet a cow’s energy needs after lactation starts unless that protein source is also very high in energy.
Distillers grains is an example of a supplement that can be fed at low levels to meet protein needs and higher levels to meet energy needs. In this example, 5 lb of dried distillers grains supplemented on dormant range would supply 15 lb of TDN. However, some producers do not have access to distillers grains. If producers fed high-quality hay ad libitum that was at least 56% TDN and 12% crude protein it would supply 15 lb TDN/d.
All producers need to calculate the cost of their supplements on cost per unit of protein and cost per unit of energy basis to determine the most economical sources for their operation. Submitting forage and supplement samples to a commercial lab for analysis helps producers determine how much supplement is needed.
For assistance with ration balancing, producers can contact their local extension personnel.
Karla H. Jenkins
UNL Cow/Calf, Range Management Specialist