6. Winter rations – Protein or Energy?

Cattle grazing dormant mature grass, crop residues, or other lower quality forages in the fall and early winter are often unable to consume sufficient quantities to meet their energy and protein requirements particularly as temperatures fall and requirements increase. A common misconception many producers have is that since cattle are now deficient in energy, supplementation of the diet with an energy source (grain, pellets or range cubes) is the best solution.

In reality, a cow in an energy deficient situation (assuming adequate roughage is available) is caused by a forage protein deficiency. When forage protein levels decline, rumen microflora efficiency declines because their protein requirement can no longer be met by forage alone. Protein is the first limiting nutrient for those microbes in the rumen and without enough protein they can’t work to ferment and extract the energy that is tied up in the fiber. Supplementation with an energy source like grain also reduces the rumen microbial population of the forage digesters as they shift to digestion of the energy addition. This serves to further the inefficiency of forage digestion and lower the dry matter intake.  If producers focus on protein supplementation, maximizing the efficiency of rumen forage digestion will increase and impact the energy and protein status of the cow. Energy supplementation should only be considered in cases where cows are extremely thin and need to gain body condition before calving, or when requirements for fetal development and milk production (ie: calving in early spring) are more than dormant forages can be expected to supply. The following table will illustrate.

No Supplement Protein Supplement Energy Supplement
Forage Intake (dry matter) 20 lb. 23 lb. 17 lb.
Digestibility (energy) 50% 55% 45%
Energy From Supplement 0 0.75 lb. + 2.4 lb. +
Energy From Forage 10 lb. 13.4 lb. 10.05 lb.

*This example assumes a forage of 7% crude protein, an increase in  forage digestability of 5% with protein supp., and a decrease in forage digestability of 5% with energy supp. There is no real net energy gain with the addition of 3 lb. of grain or energy source. You would need to feed more than 2 times that amount to net a higher energy intake than one pound of a protein supplement will provide. The gains come from increasing efficiency of forage digestion thus increasing the dry matter intake which enables the cow to extract more energy that is bound in the fiber of lower quality feeds.

*For more information, please contact Craig at (403)-894-3147


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