Nora-Nyanko: May 2010

Since ringo is on heat..

Let's talk a bit bout "canine estrous cycle" =)

Female dogs normally come into heat every 5-9 months & is different for each individual.

The estrous cycle is divided into 4 stages: anestrus, proestrus, estrus & diestrus, each corresponding to the principal hormonal influence governing that stage. The combination of proestrus & estrus, which is the heat period, is averagely 21 days.

Proestrus

The initial stage of the heat cycle lasts an average of 9 days (ranging from 3-17 days). The 1st sign is a discharge of blood, might b light pink/yellow at early stage, from the vulva. There is firm swelling of the vulva along v it.

During proestrus the females discharge pheromones, substances that attract the males. During the 1st 4-5 days of proestrus, the female show no interest in breeding.

Estrus

During estrus, the blood-tinged discharge become thicker & clearer. Estrus lasts 7-9 days (the range is 2-20 days). Ovulation usually happens on the 2nd day of esturs, or about the 12th day of the heat cycle as measured from the 1st day of proestrus.

A more accurate method is to measure serum progesterone levels. It remains low during early proestrus (< 2 ng/ml). It rises as ovulation is approaching. Luteinizing hormone stimulates progesterone to raise, and LH peaks rapidly & drops precipitously during ovulation. The LH surge triggers ovulation, which occurs 2 days after peak. As LH peaks, the serum progesterone rises above 2 ng/ml. thus, whn the progesterone measures above 2 ng/ml, one cn predict that ovulation will occur within the next 24-48 hours.

Figure 1: Hormone Levels During Estrus and Pregnancy

Picture taken from Purebreed Pedigree, "Determining Breeding Times and Whelping Dates"

http://purebredpedigree.com/videos/read_blog/17/determining-breeding-times-and-whelping-dates

Diestrus

This is the stage which successfully bred bitches r pregnant. Most species hv a mechanism in place for maternal recognition of pregnancy such that non-pregnant females cut this stage of the cycle short and return to proestrus & estrus repeatedly unless that cycle is broken by pregnancy, disease, or season. Bitches do not recognize pregnancy but instead all bitches that go through estrus continue through a prolonged diestrus whether they were bred or not and whether they r pregnant or not.

A milky, odorless discharge may b seen very early in diestrus but, in general, vulva discharge should cease during this stage, because all the hormonal changes of pregnancy take place, even non-pregnant bitches may show mammary development & lactation late in diestrus. Diestrus lasts about 60 days.

Anesturs
This is the stage of reproductive quiescence. Underlying hormonal change during this stage r characterized by increasing frequency & amplitude of gonadotropin secretion, mediated by dopamine. Anestrus lasts about 4.5 months in the avg bitch but may vary widely. The avg bitch begins a new proestrus every 7 months.

Reference:

1. Eldredge DM, Carlson LD, Carlson DG, Giffin JM. Dog owner's home veterinary handbook. Howell Book House; 1992.

2. Kustritz MR. Clinical canin and feline reproduction: evidence-based answer.