The urogenital system includes the urinary and reproductive organs.
The urinary system is divided into two regions based on anatomy and function: upper (kidneys and ureters) and lower urinary (urinary bladder and urethra) tracts. The kidneys filter metabolic wastes from the blood to be excreted into the urine. The kidneys also participate in blood pressure regulation and maintenance of the delicate electrolyte and water balance within the body-keeping only what is needed. The ureters bridge the upper urinary tract to the lower urinary tract. The lower urinary tract serves as a reservoir for urine (bladder) and a pathway for excretion (urethra). Indications of a urinary tract problem can be varied: excessive urination and drinking, straining to urinate, blood in the urine, odor to urine, diarrhea, inappetance, incontinence, colic, and lethargy.
The genital system consists of the reproductive organs- uterus and ovaries. These organs produce hormones and allow reproduction. Signs associated with genital tract problems in mares include: abortions, discharge, odor, straining to urinate, colic, and lethargy. Genital tract abnormalities in stallions may manifest as: discharge, odor, straining to urinate, scrotal/penile swellings, and lethargy.
Common urogenital ailments affecting horses:
o Abortion: Equine Herpesvirus, Equine Arteritis Virus, Leptospirosis, Equine Infectious Anemia, Bacteria, Mycotic, Protozoal
o Ovarian cysts
o Perineal and Rectovaginal Lacerations
§ Placentitis: bacterial and fungal
§ Retained placenta (fetal membranes)
§ Early embryonic death
§ Infectious: Endometritis, Metritis, Pyometra
§ Inflammatory: Prolapse, Rupture, Torsion
o Venereal disease: bacterial, viral, Contagious Equine Metritis
Foals : Ruptured urinary bladder; Patent urachus; Cryptorchidism
Kidney failure : acute and chronic. Acute kidney failure can be caused by infections, kidney stones, toxins, and drugs to name a few. Aging pets may develop chronic kidney failure. Often, by the time chronic kidney failure is diagnosed, the cause cannot be determined.
Urine, produced by the kidneys, is stored in the urinary bladder before exiting the body through the urethra. The urethra acts as a channel for urine excretion; its length offers protection against infection. Urinary tract infections are uncommon in horses, unless they have a condition that causes abnormal urine flow: mares prior to foaling, recumbency, and anatomical defects (e.g.: patent urachus, ectopic ureters). Horses with urinary bladder abnormalities may strain to urinate; they may have obvious blood in their urine or evidence of urine scalding.
The horse has two ovaries, located behind the kidneys. The ovaries release reproductive hormones that regulate the estrous cycle and sustain pregnancy. Evaluation of ovarian function is done by history, physical examination, rectal examination, imaging with ultrasound, and hormonal testing. Changes in the size of the ovaries can be categorized into three broad categories:
- Enlargement of one or both of the ovaries: tumors (e.g.: granulosa cell tumor, cystadenoma), hematomas, cysts, pregnancy
- Small ovaries: hyperadrenocorticism (Cushing’s disease), poor nutrition
- Abnormal function: persistent luteal follicles, anovulatory follicles
The gestation period for horses is variable and ranges from 11-12 months. Diagnosis of pregnancy is made by rectal examination, ultrasound, and hormonal testing. As pregnancy nears full term, the mare shows more signs indicative of impending birth: enlarged abdomen, development and waxing of the mammary glands. Complications that may occur during pregnancy and birth include:
- Abortions: caused by viral (Equine Herpesvirus), bacterial, and fungal infections; twinning; and fescue toxicity
- Dystocia (difficulty giving birth)
o rectovaginal tears range in severity; surgical correction is required to restore normal anatomy
o premature placental separation: often caused by placental inflammation
During the birthing process, the foal’s feet usually come through the birth canal first. Occasionally one of the foal’s feet can tear through the top of the vagina and into the rectum. If the foot retracts back into the vagina before delivery of the foal, a hole, or fistula, is left.
During the birthing process, the foal’s feet usually come through the birth canal first. Occasionally one of the foal’s feet can tear through the top of the vagina and into the rectum. If the foot does not retract back into the vagina before delivery of the foal, the tear extends completely to the exterior.
The reproductive tract of a mare includes two ovaries and a two-horned uterus. Mares reach sexual maturity and begin heat cycles around 12 months of age. The heat cycle in horses is seasonal, ranging from April through October. The estrous cycle varies in length with the average being 21 days. The mare is receptive to breeding during the estrus period, which lasts 5-7 days. With successful breeding, the gestation length of the horse varies from 11-12 months.
In some older mares, the conformation of the vagina and vulva begins to sink back towards the abdomen because of loosening supportive tissue. This can occasionally cause a problem when urine does not completely expel from the vagina during urination and flows backwards to the front of the vagina, causing inflammation and infertility.
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