The blood-testis barrier (BTB) is formed by specialized tight junctions (zonula occludens) between the basolateral membranes of adjacent Sertoli cells in the seminiferous tubules, protecting developing haploid spermatocytes and spermatids from immune attack.

Estrus duration and detection challenges in zebu cattle:

• Statement (I) is correct: Zebu (Bos indicus) cows exhibit a significantly shorter estrus duration ($10\text{ to }14\text{ hours}$ on average) compared to European (Bos taurus) dairy cattle ($16\text{ to }20\text{ hours}$).
• Statement (II) is correct: Zebu cattle and buffaloes frequently initiate estrus behaviors during nocturnal hours (nighttime), making visual estrus detection difficult without heat-detection aids.
• Both statements are fully correct.
• Therefore, option 1 (Both Statement (I) and Statement (II) are correct) is the correct answer.

Pregnancy signs and species-specific gestation periods:

• Statement (I) is correct: Following conception, persistent progesterone inhibits cycling (cessation of estrus), the animal becomes calmer, and metabolic efficiency increases with a tendency to fatten.
• Statement (II) is incorrect: Gestation in buffaloes lasts approximately $310\text{ days}$ ($10\text{ months }10\text{ days}$), whereas $280\text{ to }285\text{ days}$ ($9\text{ months }9\text{ days}$) is the gestation period of cows (cattle).
• Thus, Statement (I) is correct but Statement (II) is incorrect.
• Therefore, option 3 is the correct answer.