Hormones of reproduction and their secretory tissue origins:
FSH (Follicle Stimulating Hormone) -> Anterior pituitary gonadotropes (IV)
PGF2α -> Uterine endometrium (acts as the physiological luteolysin) (III)
GnRH -> Hypothalamic arcuate/preoptic peptidergic neurons (II)
eCG (equine Chorionic Gonadotropin / PMSG) -> Fetal trophoblast cells forming endometrial cups of the pregnant mare placenta (I).

In small animal reproduction, medical pregnancy termination protocols in the bitch employ:
Aglepristone (RU534, competitive progesterone receptor antagonist, gold standard) (A)
PGF2α / Dinoprost (natural luteolytic prostaglandin) (B)
Dexamethasone (oral high-dose glucocorticoid causing luteolysis and feto-placental disruption) (C)
Dopamine agonist (Cabergoline, which suppresses luteotropic prolactin) combined with synthetic prostaglandin (Cloprostenol) (D).
All four protocols (A, B, C, and D) are recognized and used clinically. Thus, option 3 is correct.

In stallions, while interstitial Leydig cells (A) are the paramount source of systemic androgens, the seminiferous tubules (Sertoli cells and developing germ cells) (B) and the head/body of the epididymis (C) express steroidogenic enzymes (including $3\beta$-HSD and $17\beta$-HSD) capable of local testosterone synthesis and paracrine regulation. The prostate gland (D) does not synthesize testosterone. Thus, (A), (B), and (C) only is correct.

Equine reproductive infections and clinical features:

• Equine viral arteritis (EVA virus): Causes necrotizing arteritis, fever, dependent edema, and abortion typically in the latter half of pregnancy (between 3 and 10 months of gestation) -> (II).
• Equine herpesvirus-1 (EHV-1 / Equine rhinopneumonitis): Causes late-gestation abortion storms, classically occurring during the last four months of pregnancy (7 to 11 months) without premonitory signs -> (I).
• Aspergillus spp. (Aspergillus fumigatus): The leading cause of mycotic placentitis and fungal abortion in horses -> (III).
• Taylorella equigenitalis: The fastidious Gram-negative microaerophilic coccobacillus causing Contagious Equine Metritis (CEM), a highly contagious venereal disease characterized by copious mucopurulent vaginal discharge and temporary infertility -> (IV).