Ovary

The ovary – in everyday language usually simply called the ovary – is a paired female reproductive organ that is at the centre of reproduction in dogs. The ovaries not only provide the egg cells released during ovulation, but also produce oestrogen and progesterone. These two sex hormones control the cycle, shape the female dog’s behaviour and accompany the development of her sexual characteristics – from first oestrus to old age.

Structure and location of the ovaries

Those who have seen the ovaries on an ultrasound image are often amazed at how small they are: almond-shaped organs, hardly larger than a strawberry, sitting deep in the abdominal cavity near the kidneys to the right and left of the uterus. They are directly connected to the uterus via the fallopian tubes. Every female dog has two of these organs, symmetrically on both sides of the body – and they contain, since birth, the entire supply of immature egg cells.

Function of the ovaries

The ovaries fulfil two basic tasks:

Production of egg cells (oogenesis): At birth, every female dog carries all the egg cells she will ever have. During the ovarian cycle, some of them mature and are released from the ovary during ovulation. From there, they travel through the fallopian tubes towards the uterus – where, upon mating, they can meet sperm and be fertilised.

Hormone production:

The ovaries are also an important hormonal control centre. Two hormones dominate here:

Oestrogen: During pro-oestrus and oestrus – i.e. during heat – oestrogen levels reach their peak. This hormone prepares the uterus for a possible pregnancy, triggers ovulation and noticeably influences the female dog’s behaviour.

Progesterone: After ovulation, progesterone takes over. It keeps the uterine lining in a receptive state and is simply essential for maintaining a pregnancy.

Role of the ovaries in the ovarian cycle

The ovarian cycle of the female dog is divided into four phases, the course of which is hormonally directed by the ovaries: prooestrus, oestrus, metoestrus and anoestrus.

1. Prooestrus: The oestrogen levels rise and stimulate the growth and maturation of egg cells. The female dog shows interest in males, but is not yet fertile.
2. Oestrus: Now ovulation occurs – the mature egg cells leave the ovaries. The female dog is fertile and receptive to mating.
3. Metoestrus: The ovaries switch to progesterone production to support a possible pregnancy. In this phase, the female dog is no longer receptive for further mating.
4. Anoestrus: The resting phase. No new egg cells, minimal hormonal activity – the ovaries are, as it were, regenerating for the next cycle.

Diseases of the Ovaries

When the ovaries fall out of rhythm, this usually has rapid effects on the entire cycle – and on the well-being of the female dog. An overview of the most common diseases:

1. Ovarian cysts: Fluid-filled cavities that can form in or on the ovaries. Depending on their size and location, they disrupt the hormonal balance, interrupt the cycle or lead to infertility.
2. Ovarian tumours: Fortunately comparatively rare – but when they do occur, they can trigger serious hormonal changes and, in the worst case, spread to other organs (metastases).
3. Inflammation (oophoritis): Oophoritis – i.e. inflammation of the ovaries – is usually caused by infections or injuries. Pain, infertility and further complications can be the result.
4. Hormonal disorders: If the ovaries produce too much or too little, the entire system loses its balance. An overproduction of oestrogen, for example, can noticeably influence behaviour and health; hormonal imbalances sometimes manifest as delayed oestrus, persistent oestrus or delayed ovulation.

Ovariohysterectomy – Removal of the Ovaries

In an ovariohysterectomy – colloquially often simply called spaying – the ovaries and uterus are surgically removed. The procedure is primarily recommended to prevent unwanted pregnancy and to reduce the risk of uterine infections (pyometra) or mammary tumours. With the removal of the ovaries, the ovarian cycle ends permanently, and the female dog no longer produces female sex hormones.