1.9 Small animal repro

Reproductive strategies for myomorphs and lagomorphs

Quick, frequent breeding with many altricial young → r selection

Reproductive strategies for hystricomorphs

Less frequent breeding with few precocious young → k selection

Rabbit sex ID (3)

• Males - longer anogenital distance

• Genital opening - males round females slit

• Testicles (older males)

Why is the mesometrium in a doe rabbit significant?

Fat store - significant in spays

Male rabbit and rodent castration consideration

Open inguinal canal - must be closed at end of castration to prevent hernia

Main reason for rabbit spaying

Uterine adenocarcinoma

• high prevalence in old entire females

When is ovariohysterectomy not a good treatment for rabbit uterine adenocarcinoma?

Metastases

• slow metastases locally, or to lung, liver, brain, bone

Why are older guinea pigs more prone to dystocia?

Fibrocartilaginous pubic symphysis often calcifies if not breed by 6-8 months

• if completely fused - C section needed

How do you diagnose cystic ovaries in guinea pigs? 

VERY COMMON in old female entire guinea pigs

• abdomen distended, masses palpated (feels like multiple kidneys)

What are the 2 types of cystic ovaries in guinea pigs? List 3 potential signs for one of them.

• Rete cysts (more common) - no hormones

• Follicular cysts - make hormones

  • Nipple hyperkeratosis

  • Bilateral flank alopecia

  • Behavioural changes (nymphomania or aggression)

List 2 reason why draining guinea pig ovarian cysts is not ideal.

• Only pallative care as they will come back

• Risk of rupture in abdomen 

Why do most guinea pig ovarian cysts not respond to hCG and GnRH agonists?

Most are rete (not hormone producing) cysts

Prevalent mammary tumour in rats

Fibroadenomas (benign)

• but high incidence

Prevalent mammary tumours in mice

Malignant

• do not excise - spreads quickly

Why is treating mammary fibroadenomas in rats difficult? (3)

• Good prognosis only when completely resected → often come back in different site if incomplete

• Complete resection challenging due to diffuse tumour (flank, neck, perineum)

• Cannot do mammary strip in rat since too traumatic

3 ways to prevent rat mammary neoplasia

• Ovariectomy before 7 months

• Calorie restriction (no obesity)

What could happen in an unmated female ferret?

Persistent hyperoestrogen in 50% of females → if elevated for >1 month → bone marrow depression and death

6 signs of hyperoestrogenism in ferrets

• Vulval swelling

• Anorexia

• Lethargy

• Anaemia (bone marrow depression) → pale mucous membranes

  • transfusion

• Thrombocytopaenia → petechial haemorrhages and melaena

• Neutropaenia

2 benefits and 1 drawback of mating ferret with vasectomised male

• Oestrus resolves within a few days

• Vasectomies are easy and often on working ferrets

• Mating is aggressive - scruff injuries

Approach for ferret spay

Midline (like cat) 

How does long light cycle lead to hyperadrenocorticism in neutered ferrets? (4)

• More light releases more hypothalamic GnRH

• GnRH → pituitary random pulsatile FSH/LH

• FSH/LH normally act on gonads for sex hormones → -ve feedback against GnRH not present when no gonads

• FSH/LH act on adrenal glands constantly (since constant release)

Signs of hyperadrenocorticism in ferrets (5)

NOT CUSHING’S since different bit of adrenal cortex

• Alopecia

• Pruritus

• Vulval enlargement

• Prostatic enlargement → urination difficulty

• Aggression

Most ideal way to treat hyperadrenocorticism in neutered ferrets and mechanism (2)

• Deslorelin (supralorin) implant → GnRH agonist

  • only licenced in male ferrets for some reason

• Initial sudden FSH/LH surge due to surplus GnRH

  • symptoms worse in first week

• Overstimulation → adrenal receptor downregulation

3 drawbacks for deslorelin implants

• GA needed for placement

• Replacement every 1-4 years

• Expensive (company has monopoly)

When should ferrets normally be castrated?

Breeding season (spring-autumn)

• testes withdraw in abdomen during winter