Nutritive ratio of maize grain is 10.7 and DCP content is 7 %... | Agrigyan

• ME Utilization under Cold Stress: Below the lower critical temperature (cold stress), the heat increment of feeding (HIF) is not wasted; it contributes directly to maintaining homoeothermic body temperature, making the efficiency of ME utilization effectively $100\%$ for thermoregulation. (True)
• Ruminal Fermentation End Products: The molar proportions of volatile fatty acids (acetate : propionate : butyrate) dictate the biochemical pathways of metabolism, directly altering the efficiency of ME utilization ($k_m, k_l, k_f$). (True)
• ME as a Superior Nutritive Measure: Unlike DE and TDN, ME accounts for urinary energy losses and gaseous energy losses (methane), making it a far more accurate representation of biologically available energy for ruminants. (True)
• Incorrect Statements: (A) is false because NE requires calorimetry and is far more difficult and costly to obtain than ME; (D) is false because ME efficiency depends heavily on the production purpose ($k_m \gt k_l \gt k_g$).

Correct option: (2) (B), (C) and (E) only

• Invention of Open-Circuit Respiration Apparatus: The open-circuit indirect calorimetry apparatus was devised in 1862 by Max von Pettenkofer (along with Carl von Voit) in Munich.
• Operating Principle:
• In an open-circuit chamber, fresh outdoor air is continuously pumped through the animal chamber at a metered flow rate.
• The exhausted air is sampled and analyzed for $O_2$ consumption and $CO_2$ and $CH_4$ production.
• Closed-Circuit Apparatus: In contrast, the closed-circuit respiration apparatus was devised by Regnault and Reiset (1849), where oxygen is continuously recirculated and replenished while $CO_2$ is chemically absorbed.

Correct option: (1) Pettenkofer

• Assertion (A) is True: In ruminants, despite massive production of butyrate by microbial fermentation in the rumen ($10\text{--}15\%$ of total VFAs), concentration of free butyrate in portal and peripheral circulation is exceedingly low ($\lt 0.1\text{ mmol/L}$).
• Reason (R) is True: The stratified squamous epithelium of the rumen wall is metabolically active; $80\text{--}90\%$ of absorbed butyrate is extensively oxidized and ketogenized into $\beta$-hydroxybutyrate (BHBA) and acetoacetate during trans-epithelial transport.
• Relationship: (R) is the precise physiological and metabolic explanation for (A).

Correct option: (1) Both (A) and (R) are true and (R) is the correct explanation of (A)