Topics:
Animal Nutrition, Animal Refresher
Optimum Starch to Urea Ratio
Starch: urea ratio in diet should be:
- 10:1 — Correct Answer
- 15:1
- 20:1
- None
Explanation:
Correct Answer: 10:1
The optimal Starch : Urea ratio in a ruminant diet is 10:1 — meaning 1 kg of starch is required for every 100 g of urea fed. Rapidly fermentable starch provides the energy (carbon skeletons + ATP) that rumen microbes need to efficiently assimilate the NH₃ released from urea hydrolysis into microbial protein.
Key Ratios in Urea Feeding
| Ratio | Value | Purpose |
|---|---|---|
| Starch : Urea | 10:1 | Energy for NH₃ assimilation by rumen bacteria |
| N : S ratio | 10:1 | Microbial amino acid synthesis |
| Water : Urea (straw treatment) | 10:1 | Uniform distribution during UTES |
Consequences of Incorrect Starch:Urea Ratio
- Too little starch (high urea) → excess NH₃ accumulates → rumen NH₃ > 80 mg/100 ml → urea toxicity (hyperammonaemia).
- Too much starch (low urea) → N is limiting for microbial protein synthesis; wasted starch energy.
- Rumen bacteria unable to use NH₃ effectively if diet CP > 13% or rumen NH₃ > 5–8 mg/100 ml.
Why Other Options Are Wrong
- 15:1 → too much starch relative to urea; safe but wasteful.
- 20:1 → excessive starch; not optimal.
- None → 10:1 is the established standard.
📚 About this Topic — Animal Nutrition
This multiple choice question is from Animal Nutrition, Animal Refresher. It has 4 options with a detailed explanation of the correct answer. Practice more MCQs from Animal Nutrition to strengthen your preparation.
