Question

Ruminant animal fed on hay diet only will have higher molar proportion of which of the following volatile fatty acids

• A. Butyric acid
• B. Propionic acid
• C. Valeric acid
• D. Acetic acid

Hint:

Roughage-rich diets promote cellulolytic bacteria, yielding high acetate (needed for milk fat synthesis).
Concentrate-rich diets promote amylolytic bacteria, yielding high propionate (needed for glucose synthesis and body weight gain).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Ruminants rely on symbiotic microbes in the rumen to ferment dietary carbohydrates into volatile fatty acids (VFAs), primarily acetic, propionic, and butyric acids.
These VFAs are absorbed through the rumen wall and serve as the animal's primary energy source.
The relative proportions of these VFAs depend heavily on the ratio of roughage to concentrate in the diet.

Step 2: Detailed Explanation:
Diets consisting entirely of roughage (such as a hay-only diet) are rich in structural carbohydrates like cellulose and hemicellulose.
This high-fiber diet promotes the growth of cellulolytic bacteria (such as *Fibrobacter succinogenes* and *Ruminococcus albus*) in the rumen.
These fiber-digesting microbes ferment complex carbohydrates primarily through pathways that yield acetic acid (acetate).
On a high-roughage/hay diet, the molar proportions of VFAs in the rumen are typically:
- Acetic acid: \( 65\% \text{ to } 70\% \)
- Propionic acid: \( 15\% \text{ to } 20\% \)
- Butyric acid: \( 10\% \text{ to } 12\% \)
Conversely, feeding a concentrate-rich (grain) diet promotes amylolytic bacteria, which shift fermentation pathways to produce a higher proportion of propionic acid.

Step 3: Final Answer:
A ruminant animal fed on a hay-only diet will produce a higher molar proportion of Acetic acid.