Lecture 1- Reproductive Drugs and Hormones

Function of progesterone

Hormone of pregnancy; predominant in diestrus; suppresses estrus; decreases myometrial contractility; closes cervix; lowers uterine immune function

Progesterone feedback

Negative feedback on LH → prevents ovulation

Progesterone effects on behavior

Suppresses estrus behavior; female not receptive to mating

Progesterone side effects

Skin absorption affects human cyclicity; prolonged use → pyometra; decreases LH; alters reproductive hormones

Progesterone formulations

Oral altrenogest; MGA; injectable progesterone in oil; repository formulations; intravaginal CIDR

Uses of progesterone

Estrus suppression; synchronization protocols; pregnancy maintenance

Estrogen function

Predominant hormone of estrus; enhances estrus behavior; primes uterus for contractility; opens cervix; heightens uterine immune function

Estrogen feedback

Negative feedback on FSH

Types of estrogens

Estradiol 17β; estradiol cypionate; estradiol benzoate; estradiol valerate; estriol (Incurin®)

Conjugated estrogens

Equilin, 17‑β dihydroequilenin; produced by placenta; secreted in urine (Premarin®)

Estrone sulfate

Major circulating estrogen; indicator of fetal viability

Estrogen side effects

Bone marrow suppression

Uses of estrogens

Synchronization; induce estrus behavior; thicken vaginal wall; jump mares; urinary incontinence treatment; interfere with unwanted breedings (not recommended)

Testosterone function

Negative feedback on LH; stops cyclicity; muscle building; appetite stimulant

Testosterone drugs

Mibolerone (Cheque Drops®); Stanozolol (Winstrol‑V®)

GnRH function

Hypothalamic decapeptide; pulsatile release; regulates FSH/LH; primarily causes LH release

GnRH drugs

Gonadorelin (Cystorelin®, Factrel®, Fertagyl®); Deslorelin (SucroMate®, Ovuplant®, Suprelorin®)

GnRH uses

Initiate cyclicity; induce ovulation; synchronization programs; treat cystic ovarian syndrome; long‑term use down‑regulates LH/FSH

FSH function

Secreted by pituitary; targets granulosa/sertoli cells; increases estrogen; stimulates follicular growth; used for superovulation

FSH drugs

Folltropin® (porcine); recombinant equine FSH; EquiPure FSH™

FSH uses

Superovulation; initiate cyclicity

LH function

Secreted by pituitary; targets theca/leydig cells; increases testosterone; stimulates ovulation

LH drugs

Recombinant equine LH; EquiPure LH™

hCG function

LH‑like activity; induces ovulation

eCG function

FSH + LH‑like activity; primarily FSH‑like; induces estrus in pigs; superovulation in small ruminants

hCG/eCG drugs

Chlorulon® (hCG); PG600® (eCG + hCG)

PGF2α function

Lyse CL; short‑cycle estrous cycle; stimulates uterine contractions (ecbolic)

PGF2α side effects

Vomiting/urination in dogs; sweating/colic in horses; dangerous for asthmatics/pregnant individuals

PGF2α drugs

Dinoprost (Lutalyse®); Cloprostenol (Estrumate®)

PGE1/PGE2 function

Smooth muscle relaxants; cervical relaxation; uterine evacuation; oviductal relaxation

PGE drugs

Misoprostol (Cytotec®); Dinoprostone gel (Primigyn®, Prepidil®)

Dopamine agonists

Pergolide (Prascend®); Bromocryptine; Cabergoline (Dostinex®)

Dopamine agonist uses

Treat equine pituitary dysfunction; induce abortion in dogs (prolactin is luteotropic)

Dopamine antagonists

Domperidone (Equidone®)

Domperidone uses

Increase prolactin; stimulate lactogenesis; treat fescue toxicosis in mares

Oxytocin function

Contracts smooth muscle; induces parturition; milk letdown; uterine evacuation; dystocia treatment

Oxytocin receptor priming

Requires estrogen priming for effect

Oxytocin additional use

Prolong CL lifespan in horses (down‑regulates receptors)

Tocolytics

Clenbuterol, Terbutaline, Buscopan®

Clenbuterol effects

Smooth muscle relaxant; bronchodilator; uterine relaxation; high doses → anxiety, ↑HR, sweating; illegal in food animals

Buscopan effects

Antispasmodic; anticholinergic; decreases peristalsis; aids rectal palpation; potential cervical relaxation

Reasons to manipulate reproduction

Induce luteolysis; induce ovulation; suppress estrus; induce cyclicity; terminate pregnancy; manage dystocia; treat uterine disease; increase milk production; superovulate; growth promotion

Growth promotants

Estradiol; testosterone; progesterone; TBA (trenbolone acetate); MGA; zeranol; anabolic steroids (stanozolol, boldenone)

Growth promotant caution

Must check species label approval

Reproductive antibiotics

Systemic or intrauterine; infusion vs lavage; need good tissue penetration; avoid irritation

Intrauterine antibiotic pros

Easy; direct treatment; accepted in horses

Intrauterine antibiotic cons

Irritating; disrupt flora; contamination risk

When to choose intrauterine

First‑time infections; good biopsy; non‑irritating drug; short‑term treatment; budget

Systemic antibiotic pros

No uterine irritation; better for deep infections; stable tissue levels; less flora disruption

Systemic antibiotic cons

Higher cost; multiple days; route limitations

When to choose systemic

Chronic infections; repeat infections; poor biopsy; fluid accumulation; mare reacts to intrauterine; drug is irritating

Case: induce ovulation in mare

Use hCG or GnRH (SucroMate®, Ovuplant®, Cystorelin®)

Case: cow 5 days post‑estrus

Use PGF2α (Lutalyse®, Estrumate®) to short‑cycle

Case: dog dystocia with inertia

Use oxytocin

Case: synchronize sow for boar arrival

Use PG600® (eCG + hCG) or PGF2α + altrenogest protocols

Case: mare with low milk

Use domperidone + oxytocin