Endocrine regulation of follicle-stimulating hormone (FSH):

• Genistein is a plant isoflavone (phytoestrogen).
• Follistatin is a single-chain gonadal glycoprotein that binds with high affinity to activin, neutralizing its bioactivity and thereby strongly suppressing/inhibiting pituitary FSH synthesis and secretion.
• Relaxin softens the pelvic ligaments and cervix at parturition.
• Activin stimulates FSH biosynthesis and release from pituitary gonadotropes.

Neuroendocrine feedback and photoperiodic reproduction:
Statement (I) is true: Progesterone acts on the hypothalamus and anterior pituitary to exert potent negative feedback, profoundly suppressing the frequency of GnRH and LH pulsatile release (the 'progesterone block' that prevents ovulation during diestrus and pregnancy).
Statement (II) is true: Pineal melatonin secretion during darkness directly modulates kisspeptin and RFRP-3 neurons in the hypothalamus, thereby modulating the pulse frequency and amplitude of GnRH secretion to govern seasonal reproductive cyclicity in long-day and short-day breeders.

Classification of estrous cyclicity across domestic animals:

• Mare (horse): Seasonally polyestrous (long-day breeder). Mares exhibit repeated regular estrous cycles ($21\text{ days}$) during the spring and summer months under the stimulus of increasing photoperiod, entering winter anestrus under short days.
• Cow and Sow: Non-seasonal polyestrous species that cycle continuously throughout the year regardless of day length.
• Bitch: Monoestrous species, typically exhibiting one or two distinct non-seasonal estrous cycles per year followed by prolonged diestrus/anestrus.
• Ewe and Doe: Seasonally polyestrous, but short-day breeders (cycling during autumn and winter).
  
  Option analysis:
• Non-seasonal polyestrous.
• Non-seasonal polyestrous.
• Non-seasonal monoestrous.
• (Mare): Correct. Long-day seasonally polyestrous domestic species.

Photoperiodic endocrinology of small ruminant reproduction:

• Assertion (A) is correct: Pineal melatonin secretion occurs during darkness. Administering exogenous melatonin (e.g., slow-release subcutaneous implants) simulates a short-day photoperiod during summer, stimulating hypothalamic GnRH pulse frequency and pituitary LH secretion, thereby successfully advancing the onset of the breeding season by $1\text{--}2\text{ months}$.
• Reason (R) is incorrect: Ewes and does are SHORT-DAY breeders (cycling in autumn/winter when day length decreases), NOT long-day breeders (mares are long-day breeders). In short-day breeders, high nocturnal melatonin concentrations stimulate cyclicity, whereas in long-day breeders melatonin inhibits cyclicity.