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Neutering Surgery in Dogs and Cats — Fossam Technique

What is "Fossam"?

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Overview of Male Neutering (Orchiectomy / Castration)

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Anatomy Review

• Testes — housed in the scrotum, suspended by the spermatic cord
• Spermatic cord — contains the vas deferens (ductus deferens), testicular artery & veins (pampiniform plexus), lymphatics, and nerves
• Tunica vaginalis — peritoneal serous layer encasing each testis; determines open vs. closed technique
• Cremaster muscle — thin muscle layer on the cord
• Scrotal fossa (Fossam) — the anatomical depression/pouch formed by the scrotum that cradles each testis

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Surgical Approaches

1. Prescrotal Approach (Most Common in Dogs)

1. Place the dog in dorsal recumbency
2. Clip and aseptically prepare the prescrotal and scrotal region
3. Push one testis cranially through the scrotum to tent the prescrotal skin
4. Make a 2–4 cm midline incision over the tented testis through skin and subcutaneous tissue
5. Incise the subcutaneous fascia to expose the testis within its tunica
6. Closed technique: Exteriorize the testis with its intact tunica vaginalis; ligate the spermatic cord as a unit with the tunica intact
7. Open technique (via the Fossam approach): Incise the tunica vaginalis to expose the bare testis and cord components; ligate the vas deferens and vascular pedicle separately
8. Repeat for the second testis through the same or a second incision
9. Close subcutaneous tissue (absorbable suture) and skin (non-absorbable or intradermal)

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2. Scrotal Fossa (Fossam) Approach — Cats & Some Dogs

CAT — Scrotal/Fossam Technique (Most Common)

Why open healing in cats? The scrotal fossa incision is small and the highly vascular scrotal tissue heals rapidly. Leaving it open reduces fluid accumulation.

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Open vs. Closed Technique — Fossam Context

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Anesthesia Protocol

Dogs

• Pre-medication: Acepromazine + opioid (butorphanol or buprenorphine), or dexmedetomidine + opioid
• Induction: Propofol IV or alfaxalone IV
• Maintenance: Isoflurane or sevoflurane via endotracheal tube
• Analgesia: NSAIDs (meloxicam), local infiltration (lidocaine/bupivacaine into spermatic cord), opioids

Cats

• Pre-medication: Dexmedetomidine + ketamine + butorphanol (IM)
• Induction: Often mask induction with isoflurane, or continued sedation is sufficient for short procedures
• Maintenance: Isoflurane via mask or intubation depending on duration
• Analgesia: Buprenorphine (sublingual or IM), meloxicam, local block of spermatic cord

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Ligation Methods at the Fossam

Three-Clamp Technique (Cats & Dogs)

1. Place 3 hemostatic clamps across the spermatic cord sequentially
2. Pass absorbable suture (e.g., 2-0 or 3-0 Vicryl) in the groove created by clamp #1 and tie a circumferential ligature
3. Optionally place a transfixion ligature at clamp #2
4. Transect the cord between clamp #2 and #3
5. Release clamp #3 and observe the stump for hemorrhage

Figure-8 (Autoligation) in Cats

• Separate the vas deferens from the vascular cord
• Use the vas deferens itself to wrap around the vascular pedicle and tie
• No suture material required — reduces foreign body reaction risk
• Only appropriate for cats (small, pliable structures)

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Postoperative Care

• Elizabethan collar for 7–10 days (dogs especially)
• Monitor for scrotal hematoma, swelling, or wound dehiscence
• Restricted activity for 10–14 days
• NSAIDs for 3–5 days post-op (dogs); buprenorphine for 1–3 days (cats)
• Suture removal at 10–14 days (if non-absorbable)
• Cats: inspect open wound daily; small amount of swelling/discharge is normal for 48–72 hours

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Complications

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Key Points Summary

• Fossam = scrotal fossa — the anatomical point of access in the direct scrotal incision technique
• In cats, the scrotal fossa (Fossam) approach is the standard — bilateral scrotal incisions, open technique, wounds often left open
• In dogs, a prescrotal midline approach is more common in adults; scrotal fossa may be used in puppies
• Open technique (incising the tunica at the fossam) allows separate ligation of vas deferens and vascular pedicle
• Proper analgesia (local nerve block of the spermatic cord) is critical for intraoperative and postoperative comfort

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Why Rabies Vaccine is Given After 3 Months in Dogs and Cats

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1. Maternal Antibody Interference (Most Important Reason)

• Colostrum (first milk) in the first 24–48 hours after birth — this is the primary source
• Transplacental transfer (minor contribution in dogs and cats)

How MDAs Block Vaccination

If rabies vaccine is given while MDA levels are still high, the maternal antibodies bind and neutralize the vaccine antigen — the animal appears vaccinated but has no protective immunity. This is called MDA interference.

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2. Immune System Maturity

• B lymphocytes (antibody-producing cells) are present but not fully differentiated
• T lymphocytes lack full functional capacity for antigen presentation and memory formation
• Antigen-presenting cells (dendritic cells, macrophages) are not fully active

• Process rabies antigen via MHC class II pathways
• Activate CD4+ helper T cells
• Stimulate B cells to undergo class switching and produce IgG antibodies
• Generate immunological memory (long-lived plasma cells and memory B cells)

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3. The "Window of Susceptibility"

Birth ──── 6 weeks ──── 8–10 weeks ──── 12 weeks ──── Vaccine immunity established
  |              |              |               |
High MDAs     MDAs waning   "Window of    MDAs low enough
(blocks vaccine) (inconsistent)  susceptibility"  for full seroconversion

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4. Rabies Vaccine Biology

• It requires a competent adaptive immune response to generate neutralizing antibodies — it does not replicate in the host and thus cannot overcome MDA by spreading
• Compared to modified-live vaccines (used for some other diseases), killed vaccines are even more susceptible to MDA interference because they present antigen only once at the injection site
• Studies show that inactivated rabies vaccines given before 12 weeks have significantly lower seroconversion rates (some as low as 30–50%), while vaccination at ≥12 weeks achieves >95% seroconversion

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5. Regulatory and Legal Reasons

• Regulatory agencies (USDA, EMA, national veterinary authorities) license rabies vaccines specifically for use at or after 12 weeks of age
• A vaccine given before the licensed minimum age is considered off-label and may not be legally recognized for travel, import/export certificates, or local anti-rabies ordinances
• If an animal vaccinated before 12 weeks bites a human, the vaccination may be deemed legally invalid, requiring quarantine as if unvaccinated

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6. Duration of Immunity and Booster Schedule

The 1-year booster after the initial dose exists precisely because a small percentage of animals vaccinated at 12 weeks may still have had just enough residual MDA to partially blunt the first response. The booster at 1 year guarantees solid, verified immunity.

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7. Why Not Earlier (e.g., 8 weeks)?

• They use modified-live virus that can partially overcome MDA
• A series of doses (every 3–4 weeks) is designed to "catch" the animal as MDAs progressively decline

• High probability of MDA clearance
• Early enough protection before peak exposure risk
• Legal and regulatory validity

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Summary

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Detailed Heat Cycle (Estrous Cycle) in Dogs and Cats — Theriogenology

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PART I: CANINE ESTROUS CYCLE (Dog)

General Characteristics

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The Four Phases of the Canine Estrous Cycle

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Phase 1: Proestrus

• FSH (follicle-stimulating hormone) rises from the anterior pituitary → stimulates follicular development
• Estrogen (estradiol-17β) rises progressively as follicles grow → peaks just before end of proestrus
• Progesterone is at basal levels (<1 ng/mL) — no corpus luteum yet
• LH remains at baseline until the LH surge

• Multiple follicles recruited and grow under FSH stimulation
• Granulosa cells produce increasing amounts of estradiol
• Follicles are not yet ovulatory

• Vulvar swelling (edema) — turgid, firm vulva
• Serosanguineous (bloody) vaginal discharge — from uterine and vaginal diapedesis of RBCs under estrogen influence
• Male dogs are attracted to the female but she refuses mounting (lordosis absent)
• Behavioral changes: restlessness, increased urination (scent marking), tail flagging beginning toward end

• Early: predominantly parabasal and intermediate cells with many RBCs and neutrophils
• Late: progressive shift to large superficial cells; RBCs persist; neutrophils disappear as estrogen peaks
• Transition: >80–90% cornified superficial cells signals impending estrus

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Phase 2: Estrus

• LH surge → Ovulation occurs ~48 hours later
• Ovulated oocytes are primary oocytes (immature) — unique to the bitch
• Oocytes require 48–72 hours of maturation in the oviduct before they are fertilizable (become secondary oocytes)
• Fertile period: Days 4–7 after the LH surge (progesterone ~5–10 ng/mL indicates ovulation has occurred)
• Progesterone ≥5 ng/mL = ovulation confirmed
• Progesterone 2–4 ng/mL = LH surge occurred (~48 h to ovulation)

• Follicles luteinize before rupture (unique in canines — progesterone rises before ovulation)
• Ovulation of primary oocytes
• Corpus luteum (CL) begins forming

• Vulva becomes soft and less turgid (estrogen decline → less edema)
• Vaginal discharge lightens in color (straw-colored to clear) or may cease
• Female actively accepts mounting — stands still, deflects tail (lordosis, "flagging")
• Playful, flirtatious behavior with male

• >80–90% anucleate or pyknotic superficial (cornified) cells
• No neutrophils (estrogen suppresses neutrophil diapedesis)
• Few or no RBCs
• "Dirty background" of cellular debris
• This peak cornification pattern persists through estrus

• Natural breeding: Days 2–5 of standing estrus
• Progesterone-guided breeding:
  • Progesterone 2–4 ng/mL = LH surge → breed in 4–5 days
  • Progesterone ≥5 ng/mL = ovulation occurred → breed within 2–3 days
  • Progesterone 10–25 ng/mL = post-ovulation, optimal fertility window
• Vaginal cytology transition (diestrus shift): Neutrophils reappear abruptly — signals end of fertile period

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Phase 3: Diestrus (Metestrus)

• Progesterone peaks at 15–90 ng/mL around days 20–30 post-LH surge
• Progesterone is maintained by the corpus luteum (CL) — NOT the placenta
• Progesterone declines gradually:
  • Pregnant bitch: Sharp drop ~24–48 h before parturition (due to luteolysis)
  • Non-pregnant bitch: Gradual decline over 60–90 days — pseudopregnancy is normal and physiologic in all bitches
• Prolactin rises in second half of diestrus (in both pregnant and non-pregnant bitches)
• Relaxin: Detectable only in pregnant bitches (produced by placenta) — used as a pregnancy test

• Corpus luteum is the dominant structure
• Progesterone-dominant phase
• No follicular activity

• Vulvar swelling resolves
• No vaginal discharge
• Pseudopregnancy (false pregnancy / overt pseudocyesis): Variable expression — mammary development, galactorrhea, nesting behavior, mothering of objects; occurs to some degree in virtually all bitches physiologically; overt signs in ~50–75%

• Abrupt return of neutrophils — hallmark of diestrus onset ("Day 1 of diestrus" = first day with >50% non-cornified cells)
• Parabasal and intermediate cells reappear
• Superficial cell percentage drops below 50%

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Phase 4: Anestrus

• All reproductive hormones at basal levels
• Low FSH, LH, estrogen, progesterone
• GnRH pulse frequency is low but gradually increases toward end of anestrus
• Prolactin declines
• Anestrus is actively maintained — not just quiescence; the hypothalamic-pituitary axis is suppressed by unknown inhibitory mechanisms

• Ovaries quiescent — small, no active follicles
• Previous CL has regressed (corpus albicans)

• No signs of reproductive activity
• Vulva small and non-edematous
• No discharge
• No male attraction

• Predominantly parabasal cells (small, round, round nucleus)
• Some intermediate cells
• Occasional neutrophils
• Very clean background

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Canine Vaginal Cytology — Summary Table

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Canine Hormonal Profile — Timeline

         PROESTRUS          ESTRUS           DIESTRUS              ANESTRUS
    |___________________|______________|__________________________|______________|
    
Estrogen  ▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼ Baseline
LH                                 ↑↑↑ (surge ~48h)
Progesterone           ▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▼▼▼▼▼▼▼▼ Baseline
Prolactin                                              ▲▲▲▲▲▲▲▲ Declines

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PART II: FELINE ESTROUS CYCLE (Cat)

General Characteristics

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The Feline Estrous Cycle — Phases

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Phase 1: Proestrus

• FSH rises → follicular development begins
• Estradiol gradually rising
• LH at baseline

• Subtle behavioral changes — increased affection, restlessness
• May assume mating posture briefly but does not allow mating
• Vocalization beginning
• Rolling behavior beginning

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Phase 2: Estrus

• Estradiol peaks (30–100 pg/mL) — drives all estrous behavior
• LH is NOT released without coital stimulation (afferent vagal/spinal stimulation → hypothalamic GnRH pulse → LH surge)
• Progesterone remains low unless mating/LH surge occurs

• Multiple follicles develop and produce estrogen
• Without LH surge → no ovulation
• Follicles eventually regress (luteinize incompletely or simply atresia)
• → Returns to interestrous in 7–21 days

• Coital stimulation (penis with penile spines → cervicovaginal stimulation) → afferent nerve impulses → hypothalamus → GnRH pulse → anterior pituitary → LH surge within 4 hours
• LH surge: Peak at 4 hours post-coitus; sufficient for ovulation with ≥3–4 matings
• Ovulation: 24–36 hours after LH surge
• Corpora lutea form

• Loud, persistent, yowling vocalization ("calling") — can be mistaken for pain
• Lordosis posture: Chest down, hindquarters elevated, tail deflected laterally
• Rolling and treading (rhythmic movement of hindlimbs)
• Rubbing head and body on objects and people
• Increased affection or agitation
• Crouching and presenting to male
• Appetitie decrease

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Branching Pathways After Estrus

                         ESTRUS
                            |
            ________________|________________
           |                                 |
     NO MATING                          MATING OCCURS
           |                                 |
    Follicles regress              LH surge → Ovulation
           |                                 |
   INTERESTROUS                    __________|___________
   (7–21 days)                    |                      |
           |               FERTILIZATION?          NO FERTILIZATION
    Next estrus               YES                        |
                               |               PSEUDOPREGNANCY
                          PREGNANCY              (35–40 days)
                         (63–65 days)                    |
                                               Progesterone declines
                                                         |
                                               Return to estrus

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Interestrous Period

• Occurs between estrous periods when no ovulation has taken place
• Estradiol low, progesterone low
• No behavioral signs
• Follicles begin re-recruiting for next wave

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Phase 3: Pseudopregnancy (Post-coital without fertilization)

• Corpora lutea form after LH-induced ovulation
• Progesterone rises to 15–90 ng/mL
• Falls at day 35–40 due to luteolysis
• Queen returns to estrus after pseudopregnancy resolves

• Minimal — much less dramatic than in dogs
• Mild mammary development possible
• Behavioral changes subtle

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Phase 4: Pregnancy (if fertilized)

• Duration: 63–65 days (from ovulation/LH surge)
• Progesterone maintained by CL until approximately day 40, then by placenta (in cats, unlike dogs where CL is required throughout)
• Relaxin produced by placenta — detectable from day 20–25

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Seasonal Anestrus

• Short days → melatonin rises → hypothalamic suppression of GnRH
• No follicular development, no estrogen, no behavioral signs
• Queens housed under artificial light (>12–14 hours/day) may cycle year-round

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Comparison: Canine vs. Feline Estrous Cycle

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Feline Vaginal Cytology

• The queen shows minimal cell type changes between phases
• Cornification of vaginal epithelium does occur during estrus but is less dramatic
• Cytology can confirm estrus but not predict ovulation (since ovulation is induced)

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Hormonal Control Summary — Both Species

HYPOTHALAMUS
    ↓ GnRH (pulsatile)
ANTERIOR PITUITARY
    ↓ FSH → Follicle growth → Estrogen production
    ↓ LH → Ovulation trigger (spontaneous in dogs; coitus-induced in cats)
               ↓
          CORPUS LUTEUM
               ↓ Progesterone → Maintains uterus for pregnancy
                              → If no pregnancy: luteolysis → New cycle

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Clinical Applications in Theriogenology

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Key Theriogenology Points to Remember

1. The canine LH surge precedes ovulation by ~48 hours, and ovulated oocytes need another 48–72 hours to mature → total fertile window begins ~4 days after LH surge.
2. Progesterone begins rising in the bitch BEFORE ovulation due to premature luteinization — a unique feature among domestic species.
3. The queen will NOT ovulate without coital stimulus — spontaneous ovulation is rare and limited (some queens in intensive social housing may ovulate spontaneously).
4. Diestrus in the non-pregnant bitch is hormonally identical to pregnancy — progesterone levels, duration, and prolactin profiles are the same, explaining why pseudopregnancy is universal.
5. Canine anestrus is not passive — it is actively regulated; interventions like GnRH agonist implants exploit this to control cycling.
6. Feline seasonal anestrus is photoperiod-driven via melatonin — catteries can maintain year-round breeding with artificial lighting (>14 hours light/day).