Animal Genetics and Breeding- ICAR JRF/SRF 2024

• Dietary Cation-Anion Difference (DCAD) and Milk Fever Prevention:
• Parathyroid hormone (PTH) acts on bone and kidney to maintain plasma calcium homeostasis:
• Metabolic Acidosis (Acidotic state): Induced by feeding anionic salts (negative DCAD diets). Acidosis optimizes the conformation of PTH receptors, markedly increasing the sensitivity of bone osteoclasts to PTH and promoting bone calcium resorption.
• Metabolic Alkalosis (Alkalotic state): Induced by excess dietary cations ($K^+, Na^+$). Alkalosis induces a refractory state where bone receptors become insensitive to PTH, impairing calcium mobilization and precipitating hypocalcemia (milk fever).
• Therefore, the assertion that an alkalotic state increases bone sensitivity to PTH is scientifically false (not true).
• nalysis:
• Statement 1 is incorrect/not true, hence the correct answer.

• Characteristics of High-Quality Silage:
• pH: $3.8 - 4.2$ (indicates rapid lactic acid fermentation suppressing clostridia).
• Lactic Acid: $3 - 8\%$ of dry matter (predominant organic acid).
• Ammoniacal / Volatile Nitrogen: $\lt 10\%$ of total nitrogen (reflects minimal proteolysis).
• Fungal growth: Absent / negative.
• Butyric Acid: Should be virtually absent or $\lt 0.1 - 0.2\%$ of dry matter.
• butyric acid level of $\gt 0.5\%$ signifies clostridial spoilage, extensive protein degradation, and putrefaction, which is characteristic of poor-quality silage.
• nalysis:
• (Butyric acid >0.5 %): Correct (this is a sign of spoiled silage, not good quality).

Correct option: (3) Butyric acid >0.5 %

• Urea Molasses Mineral Block (UMMB) Formulation:
• UMMB blocks provide a slow-release source of non-protein nitrogen (urea), fermentable energy (molasses), and essential minerals for ruminants.
• Function of Gelling / Hardening Agents:
• Magnesium Oxide ($MgO$) and Calcium Oxide ($CaO$ / quicklime) react chemically with water and organic acids present in molasses to form insoluble hydroxides that undergo hydration hardening.
• This cements the block, achieving the necessary structural hardness so that animals can only consume it by licking, preventing bite consumption that would cause fatal urea toxicity.
• nalysis:
• (to increase hardness): Correct primary mechanical role.

Correct option: (4) to increase hardness

• Enzymology of Fatty Acid Desaturation in Mammals:
• Mammalian hepatocytes possess $\Delta^9$, $\Delta^6$, and $\Delta^5$ acyl-CoA desaturases, which can introduce double bonds between an existing double bond and the carboxyl terminal.
• Mammals completely lack $\Delta^{12}$ and $\Delta^{15}$ fatty acid desaturases:
• They cannot introduce a double bond beyond Carbon atom 9 (counted from the carboxyl terminal towards the methyl end).
• Consequently, Linoleic acid ($18:2\Delta^{9,12}$) and $\alpha$-Linolenic acid ($18:3\Delta^{9,12,15}$) cannot be synthesized de novo and are obligate dietary essential fatty acids.
• nalysis:
• (Carbon atom 9): Correct.

Correct option: (1) Carbon atom 9