Small animal oestrus cycle & sterilisation

When do bitches start their oestrus cycle?

6-18 months.

What type of oestrus pattern do dogs have?

Monoestrus, non seasonal, spontaneous ovulators (no need for copulation)

Give the main stages of the oestrus cycle in dogs

• Anoestrus (3-4 months)

• Proestrus (9d)

• Oestrus (9d)

• Diestrus (60 days)

Which phases of the oestrus cycle make up 'heat'?

Proestrus & oestrus.

(both typically 9 days)

What are the clinical signs of proestrus in dogs?

• Serosanguinous vulval discharge

• Vuvlal sweling

• Male attracted but rejected

• Behaviour such as urine marking & roaming

Describe the hormones involved in pro-oestrus

Follicle development —> FSH & LH, growing follicle produces oestrogen

Rising oestrogen levels, peak @ end of pro-oestrus

What are the clinical signs of oestrus in dogs?

• Reduction in vulval swelling

• Vulval discharge becomes serous/brownish

• Willing to accept male

• Movement of tail to uncover vulva ('flagging')

What are the hormones involved in oestrus?

Oestrogen peak in proestrus → LH surge (~48hrs into oestrus)

Progesterone starts to rise (about to ovulate)

Primary oocyte ovulated —> must undergo 2 meiotic divisions to mature (48hrs)

Oocyte fertile for 48-72hrs

Gradual elevation in the oestrogen produced by developing follicle → GnRH pulses → surge in LH (positive feedback) → ovulation.

After ovulation the CL produces progesterone.

This elevation is responsible for the behavioral changes we see in diestrus

What is the most common oestrus phase for pyometra?

Dioestrus.

What is the optimum phase for spay?

Anoestrus.

Describe the hormonal changes during proestrus in dogs

• Stimulation of follicle by FSH and LH pulses

• Oestrogen secreted by growing follicles

When does oestrogen peak during the proestrus phase?

End.

What signifies the end of proestrus?

Oestrus peak.

What hormonal changes occur in oestrus?

• Oestrogen peak causes LH surge (24-48 hours into oestrus)

• Progesterone starts to rise after LH surge

What causes ovulation to take place in the bitch? When does this happen?

LH surge —> occurs 24-48 hours after.

Which has the shorter ovulation period (closer to 24 hours): younger bitches and older bitches?

Younger.

How long does the oocyte remain fertile after maturation (in the bitch)?

48-72 hours

When does proestrus end?

Peak of LH.

What hormone predominates in diestrus?

Progesterone.

What hormone predominates during anoestrus?

(Basal levels) oestrogen and progesterone.

What are the hormonal signs that a bitch is in late anoestrus?

LH pulsing and FSH pulsing.

How do progesterone levels vary between pregnancy and non-pregnancy?

In pregnancy, remain higher for longer and then suddenly drop at parturition.

What would you ask during taking a history in terms of monitoring the oestrus cycle?

• Last season?

• Males showing interest? Willing to accept mating?

  • interest but refusal during pro-oestrus

  • interest & acceptance during oestrus

• Vulva swelling?

  • begins during pro-oestrus, decreases during oestrus

• Vaginal discharge?

  • seroanguinous during pro-oestrus, brown during oestrus

Which hormone assay can be done to monitor oestrus cycle?

Progesterone —> blood sample

• First sample taken and then repeated a few days later —> rise in progesterone before ovulation = ovulation in next couple days → can then mate

Describe the vaginal cytology characteristics in proestrus

• Plump round parabasal cells (& intermediate cells = not as round)

• Contain RBCs & neutrophils (due to seroanguinous discharge)

Describe the vaginal cytology characteristics in oestrus

• Almost 70-100% cornfield cell (anuclear and superficial)

• No neutrophils & very clear background

Describe the vaginal cytology characteristics in diestrus

• Abrupt drop in cornified cells from 100% to 30%

• Other 70% are parabasal cells & neutrophils

What is the point of vaginal cytology (for oestrus)?

Determines whether a bitch/queen is in oestrus or not.

Swab inside vagina, rolled onto slide

Which cell is which?

What is an expensive and rarely used method of oestrus detection in dogs?

Vaginoscopy.

Summarise the key aspects of the feline oestrous cycle

• Seasonally polyoestrus

• Induced ovulators

How often can cats cycle?

2-3 weeks.

What is required for ovulation in cats?

A male cat present + copulation

Mating → GnRH release from hypothalamus → LH surge (may need several copulations)

What are the hormonal changes of interoestrus phase in cats?

Drop in projesterone and oestrous.

(If not induced to ovulate)

What are the hormonal changes of dioestrus phase in cats?

Increased progesterone if induced to ovulate

When does seasonal anoestrus occur in cats?

September/October = reduced daylight (less than 8hrs)

What is the typical pathway of oestrus cycling for outdoor cats?

Proestrus then oestrus then ovulation (+/- fertilisation) then dioestrus or pregnancy then return to interoestrus or seasonal anoestrus (dependant on time)

Ovariectomy vs ovariohysterectomy vs “ovary sparing” spay

Ovariectomy = just removal of ovaries (done laparoscopically)

Ovariohysterectomy = removal of ovaries + entire uterus

Ovary sparing = uterine body ties (only small portion removed)

Removal of hormones otherwise risk of pyometra & pseudopregnancy

What are the benefits of neutering female dogs?

• Population control

• Prevention of pyometra (progesterone-driven)

• Reduced risk of mammary tumours (if spayed early on)

• Diabetes mellitus management

• Increased life expectancy

• Prevent pseudopregnancy

• Reduction of heat behaviour

What are the risks of neutering female dogs?

• Surgery complications (1/1000) —> haemorrhage

• Risk increased with obesity

• Urethral sphincter incontinence

• Ovarian remnant syndrome

• Transitional cell carcinoma

• Osteosarcoma

• Cruciate dx

• IVDD (intervertebral disc dx)

Why may obesity occur in neutered female dogs?

After spay, drop in basal metabolic rate (due to reduced oestrogen e.t.c.) and owner does not reduce feed (by approx 10%).

What drugs can we give for urethral sphincter incontinence?

Propalin or estriol.

What is ovarian remnant syndrome?

When functional ovarian tissue is left within the dog after the spay —> sometimes only small cells → grow into large clumps & effectively grow a new ovary (can't folliculate though).

When do we typically spay small breed dogs? What can change this?

• First season around 6mo

• Unless juvenile vaginitis / recessed vulva

When do we typically spay medium breed dogs? What can change this?

• First season around 6mo

• Unless at risk of cruciate disease (then wait till plate closure), vaginitis or recessed vulva

When do we typically spay large breed dogs? What can change this?

• After at least 1 season

• If at risk of cruciate disease/OSA then delay until growth plate closure

What are the benefits of neutering male dogs?

• Poluation control

• Reduced orchitis, testicular neoplasia, epipidmyitis

• Reduced perineal hernias

• Reduced perineal adenomas

• Possible reduced aggression (unless nervous aggressive = poss makes worse)

• Removal or cryptiorchid testicle = reduced risk of tumour development

What are the risks of neutering male dogs?

• GA risk

• Surgery risk

• Scrotal haematoma = accum of blood in dead space of scrotum

• Prostatic neoplasia

• Transitional cell carcinoma

• Obesity

• Osteosarcoma

• Worsened behaviour

What are the benefits of neutering in cats?

• Reduced fighting (FIV risk)

• Reduced roaming (RTA RISK)

• Population control

• Unwanted behaviour control

• Removes pyometra risks

• Reduces risk of mammary tumour