Hormones

Knowing when to breed is the most component for successful breeding. Ovulation timing, the telltale indicator that a brood bitch is ovulating and thus ready to breed, is the most common thing to go wrong in dog breeding. Poor timing during a bitch’s three-week heat cycle, also known as estrus, can cause a missed breeding and result in a normal female being labeled infertile.  

Progesterone testing is used to determine when a bitch ovulates and thus when to breed. A reproductive hormone, progesterone increases in the bloodstream just before ovulation. As the progesterone level increases, lutenizing hormone (LH) is released from the pituitary gland, triggering the release of eggs from the follicles.  Once the eggs are released, it takes at least 2 more days before they mature 

We currently use in-house progesterone testing using an Idexx catalyst which measures progesterone in ng/ml.  The table below indicates how determine timing using progesterone levels: 

Progesterone (ng/mL)

< 1.0 Anestrus/Proestrus

1.0-1.9 Pre-LH surge

2.0-3.0 Associated with LH surge, about 24-48 hours prior to the ovulation wave

3.1-4.9 Post-LH surge, pre-ovulation

5.0-12.0 At or near ovulation (progesterone concentration may vary with breed and size)

To determine the days of mating two factors have to be considered: ovulation and maturation. Bitches will ovulate at around 6 ng/ml (18 nmol/l). After ovulation the oocytes have to mature for a further 2 days before they can be fertilised. Once mature they will be viable for another 2 days. Spermatozoa will take 6-12 hours to capacitate and reach the oviduct.

Possible testing regime:

       Plasma progesterone levels of <1 ng/ml (3 nmol/l): retest in 4 days

       Plasma progesterone levels of <2 ng/ml (6 nmol/l): retest in 3 days

       Plasma progesterone levels of >2 ng/ml (6 nmol/l): retest in 2 days

       Plasma progesterone levels of >25 ng/mol (75 nmol/l) indicates the end of the fertile period     

Possible mating regime:

      Fertilisation period: ovulation +1 day until +4 days

      Two matings: ovulation +1 day and +3 days or ovulation +2 days and +4 days

      One mating: ovulation +2 days or ovulation +3 days

When using a laboratory the post office 'next day delivery' service is very useful. One should also consider weekends and bank holidays. Given the predictable rise of progesterone and the time available after ovulation this system normally works well.

 LH peak usually occurs when progesterone levels reach 2-3ng/mL. When this level is reached, ovulation will occur two to three days later.

At the end of the follicular phase of the estrous cycle, a marked increase in LH over usual baseline values develops over 24–48 hours, followed by a return to baseline values. This surge is thought to occur in response to the decline in estrogen levels and increase in progesterone levels. The LH surge triggers ovulation, making it the central endocrinologic event in the reproductive cycle of female dogs.

Daily serial measurement of LH to identify the exact date of the LH surge is an accurate diagnostic tool to time breedings. Affordable semiquantitative in-house kits are available to measure serum LH levels in dogs and to identify the preovulatory LH surge and thus the time of ovulation and the true fertile period. Blood samples must be drawn daily (at approximately the same time) for LH testing, because the LH surge may last only 24 hours in many dogs. The kits can be subject to variable interpretation, so the same person should run the tests if possible. Progesterone testing should always be performed concurrently in case the LH surge is missed.

The bitch will go through physical changes that corelates to the LH surge. Prior to the LH surge the bitch will have considerable edema, or swelling, and dark red bloody discharge. As estrogen drops and progesterone begins to rise at the start of the LH surge the edema will go out of the vulva and vagina. The owner may observe softening of the skin around the vulva and a change in the discharge from a dark bloody red to a more serum straw color secretion. This is variable so this may not be obvious in every bitch. If you are taking your bitch to a veterinarian for ovulation timing they will visually see a change from edematous to crenulation on vaginoscopy. Vaginoscopy is another tool a veterinarian uses to get a visual assessment where a bitch is relative to ovulation. 

The bitch will also dramatically increase in her flagging behavior.  If there are other dogs in the home, fellow house mates will start mounting but the male is not that interested yet. Male dogs usually will intensify in their interest and go off feed and cry for the female days 4,5 and 6 post LH surge. Intact females in homes where they are the only dog the owner may note that the bitch starts to walk around and whine a little, or the bitch may flag when someone bumps in to her.

This is something that is very useful for owners to record on bitches’ cycles that occur prior to breeding. Keep a record of first day of heat, day bitch starts dramatically standing and days where males are crying for them. Also good to record the first day where the female goes out or abruptly loses interest in breeding.

Generally when a bitch first starts standing she will be ready to breed starting 2-3 days later. No need for panic. When males are crying, off feed, and crazy for a female the bitch is likely in her optimum fertile period and ready to breed then.