Limited amounts (approximately 1-2 lbs) of high protein supplements (> 30% CP) can be utilized with low-quality forages. Low-quality forages would be less than 8% crude protein and 45% total digestible nutrients. Protein supplementation has been shown to increase digestibility approximately 15% and increase forage intake approximately 25% (Table 15). There is no way to be sure, in every circumstance, that the expected increase in intake and digestibility actually occurs. The condition of the cow herd must be monitored.
Without supplementation, a cow can consume 18 pounds of dry matter from a low-quality forage source.
18 Forage intake without supplementation
x 1.25 Increase in forage intake with adequate protein
____
22.5 Total forage intake with supplementation
0.40 TDNb content of the forage
x 1.15 Increase in digestibility with adequate protein
____
0.46 TDN content of forage with supplementation
a Wagner and Goetz (1989).
b Total digestible nutrients.
High-protein supplements that do not contain urea or other nonprotein nitrogen sources do not need to be fed every day. Simply double the amount and feed every other day. Range cake or cubes (20% crude protein) can be utilized with intermediate quality forages. Altering body condition with supplements prior to cold weather may be more effective than waiting until cold weather occurs.
Nonprotein Nitrogen Sources Nitrogen sources, such as feed-grade urea, are an excellent supplement for high-grain diets. Urea and biruet can be utilized in range situations but utilization will not be 100%. Nonprotein nitrogen sources should be fed in small amounts and at frequent intervals. Examples of calculating the value of protein in various supplements are given in Table 17.
| Table 16. Energy and Protein Supplementation of Forage Diets | ||||
|---|---|---|---|---|
| Protein Level of Suppl. | Low Protein 14% | Intermediate Protein 20% | High Proteina 30% | Digestible Fiber |
| Forage CP: | 10% | 6-10% | 6% | 6-10% |
| When feed | Every Day | Every Day | Alternate Day | Every Day |
| a. Alternate Day programs only suitable for all natural protein sources. | ||||
| Table 17. Approximate Urea Utilizationa. | ||
|---|---|---|
| Conditions | Dry Supplement | Block/Liquid Supplement |
| Weathered grass Crop residues Poor-quality hay | 0-25 | 50 |
| Medium-quality hay Silages Summer pasture | 40-60 | 80 |
| High-energy diets | 90-100 | 90-100 |
| a Wagner and Goetz (1989). | ||
The example (on the following page) demonstrates the use of "cost per unit of protein" for comparisons of protein supplements when urea is fed once a day with medium-quality hay (approximately 50% utilization).