Requirement of concentrate mixture for buffalo weighing 400 kg producing 10 kg milk/day will be:

Correct option is C

As per standard feeding thumb rules given in ICAR and Tanu’s Feeding Standards, concentrate requirement for buffaloes is calculated based on maintenance requirement and milk production requirement together.

For milk production, a buffalo requires 1 kg concentrate mixture for every 2 kg of milk produced, which means 10 kg milk requires about 5 kg concentrate.
Additionally, a 400 kg buffalo requires around 0.5 kg concentrate for maintenance, especially under average field conditions.
Thus, the total concentrate requirement becomes 5.0 + 0.5 = 5.5 kg per day, making option (c) correct.

Information booster:
According to ICAR (2013) Feeding Standards, buffaloes require higher concentrate allowance than cows due to higher milk fat and energy demand.
Tanu’s Livestock Feeding guidelines recommend combining maintenance requirement based on body weight with production requirement based on milk yield.
Buffalo concentrate requirement is generally higher than cattle for the same milk yield.
Proper concentrate feeding improves milk yield, body condition, and reproductive efficiency in dairy buffaloes.

Why other options are incorrect:
(a) 3.5 kg is insufficient and does not meet either production or maintenance energy requirements.
(b) 4.5 kg accounts mainly for milk production but ignores maintenance requirement.
(d) 6.5 kg exceeds the recommended allowance and may cause unnecessary feeding cost and metabolic stress.