RDP (Rumen Degradable Protein)
RDP — Rumen Degradable Protein — is the fraction of dietary protein in cattle feed that is broken down by rumen microbes into ammonia. The rumen microbes use this ammonia, along with carbon from rumen fibre fermentation, to build their own microbial protein. The microbial protein then flows out of the rumen into the small intestine, where it is digested and absorbed by the animal.
RDP is the fuel of the rumen microbial population. Without adequate RDP, the microbes cannot grow, fibre digestion falls, and overall feed efficiency drops. RDP is not optional — every ration needs enough of it.
RDP vs RUP
Every protein in cattle feed splits into two fractions in the rumen:
- RDP — Rumen Degradable Protein: broken down by rumen microbes; feeds microbial growth
- RUP — Rumen Undegradable Protein: passes through the rumen; digested directly in the small intestine
A typical untreated ration delivers around 60–70% RDP and 30–40% RUP of total dietary protein. The right balance shifts depending on the animal's production level.
How much RDP a cow needs
Working guidelines for a lactating cow ration:
| Production level | RDP target (% of total CP) | RUP target (% of total CP) |
|---|---|---|
| Maintenance / low yield (< 8 L) | 65–70% | 30–35% |
| Mid-yield (8–15 L) | 60–65% | 35–40% |
| High-yield (15+ L) | 55–60% | 40–45% |
| Peak lactation with bypass supplement | 50–55% | 45–50% |
Notice the pattern: as production rises, RDP percentage falls and RUP percentage rises. This is because the high-yielding animal needs more protein in absolute terms, and the additional protein needs to bypass rumen degradation (microbial protein synthesis has an upper limit).
RDP in common Indian feed ingredients
| Ingredient | RDP (% of total protein) |
|---|---|
| Untreated soybean meal | 65–70% |
| Bypass-treated soybean meal | 20–30% |
| Cotton seed cake | 55–60% |
| Mustard cake | 75–80% |
| Groundnut cake | 70–75% |
| Wheat bran | 75–85% |
| DORB | 75–85% |
| Urea (NPN) | 100% |
| Green forage | 60–75% |
| Maize silage | 65–70% |
Maize is unusual — it has a naturally high RUP fraction (40–50%) because its protein is protected within the starch matrix.
Why both fractions matter
A ration with too much RDP relative to fermentable energy in the rumen leads to excess ammonia — wasted protein that the kidneys must filter out as urea, costing the animal energy and producing surplus urinary nitrogen.
A ration with too little RDP starves the rumen microbes, slowing fibre digestion and reducing feed efficiency. Even a high-RUP "premium" ration without enough RDP will fail.
The right approach is to balance both fractions to the animal's production level and the energy density of the ration.
Practical use
For most Indian dairy operations using a typical Type-1 or Type-2 compound feed with mixed-source protein (soybean meal + cotton seed cake + mustard cake), the natural RDP/RUP balance is acceptable for moderate yields. For high-yielders, add a dedicated bypass protein supplement to shift the balance toward more RUP without sacrificing RDP.