Soluble Crude Protein % (SCP%)
Definition
Soluble crude protein (SCP%) represents the proportion of total crude protein in a feed that dissolves rapidly in rumen fluid. This fraction is broken down into ammonia very quickly and is closely linked to rumen degradable protein (RDP), particularly the portion available within two hours of feeding (RDP 2h). The higher the SCP%, the faster protein becomes available for microbial utilisation in the rumen.
Importance
- Rumen synchronisation: Adequate SCP ensures that rapidly fermentable carbohydrates are effectively utilised for microbial growth.
- Feed efficiency: Balancing SCP with energy supply improves digestion and animal performance.
- Ration formulation: SCP% is widely used in ration optimisation to coordinate protein and carbohydrate breakdown rates at rumen level.
Factors influencing SCP%
Several factors affect the percentage of soluble crude protein in forage:
- Crop type: Grass silage typically contains 40–60% of its total protein in the soluble fraction.
- Stage of growth: Younger forage has higher SCP%.
- Fertilisation: High nitrogen doses increase SCP%.
- Dry matter content: Lower dry matter often correlates with higher SCP%.
- Weather conditions: Temperature and rainfall influence protein solubility.
- Time of mowing: Early mowing generally results in higher SCP%.
Practical considerations
- Minimum requirement: A certain level of fast protein is necessary to match the availability of rapidly fermentable carbohydrates.
- Excess SCP: If SCP% is too high, excess ammonia is converted to urea and excreted in urine and milk, leading to inefficiencies and potential environmental impact.
