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27 Starch Granule Test for the Evaluation of Oviductal Patency

Sofie Sitters1 and John J. Dascanio2

1 Amsterdam, The Netherlands

2 School of Veterinary Medicine, Texas Tech University, USA

Introduction

The oviduct plays a critical role during fertilization and early embryonic development. Consequently, pathologic conditions of the oviduct such as salpingitis, hydrosalpinx, and occlusion can adversely affect fertility of mares.

Blockage of the oviducts by masses of collagen, fibroblast cells, and other cellular and non‐cellular debris has been described. These oviductal masses can become a physical obstruction to both the upward passage of sperm and the downward passage of an embryo after fertilization. Diagnosis, however, of a blocked oviduct may be difficult and is sometimes suspected after exclusion of other possibilities for infertility in a mare.

This chapter describes the starch granule test for the diagnosis of oviductal patency. The starch granule test involves the deposition of a starch suspension onto the ovarian surface (through a transabdominal approach with a long needle) and the subsequent recovery of starch from the uterus or cervix. One oviduct can be tested at a time.

Equipment and Supplies

Surgical scrub, clippers, sterile soluble starch powder (1 g), sterile water (10 ml), sterile saline, 2% lidocaine, 2% Lugol’s iodine, microscope slides, coverslips, microscope, 14 gauge 5 cm (2 inch) needle, 18 gauge 12.5 cm (5 inch) spinal needle, syringes, obstetrical sleeve, obstetrical lubricant, sterile lavage tubing (optional).

Technique

The mare should be in diestrus for the procedure. Estrual mares may have a delay in oviductal transport.

A suspension of starch granules is made by mixing 1 g of sterile soluble starch powder in 10 ml of sterile water.

The flank of the mare is clipped and a sterile prep performed.

5 ml of 2% lidocaine is infiltrated subcutaneously and into deeper muscle layers in the flank area corresponding to the needle puncture for starch deposition.

As an optional procedure, one can create a puncture hole through the skin with either a small scalpel blade or a 14 gauge needle.

The ovary is held per rectum against the ipsilateral flank and a percutaneous needle puncture is made through the skin, or the previous puncture hole, with an 18 gauge 12.5 cm (5 inch) spinal needle to deposit 5 ml of starch solution on the ovarian surface.

The external cervical os and vagina are flushed with 10 ml of sterile saline beginning 24 hours after application of the starch solution (original description of the test). The fluid is recovered by aspiration back into the syringe.

Alternatively, the uterus of the mare could be lavaged with sterile saline through a catheter and inflatable cuff. The recovered fluid is allowed to sediment or is centrifuged.

An aliquot of the recovered fluid is placed onto a microscope slide and stained using a few drops of 2% Lugol’s iodine. A coverslip is then placed over the admixture.

The solution is examined with conventional light microscopy with the 10× objective for the presence of stained starch granules (dark blue granules).

The presence of starch granules in the uterine fluid suggests that the oviduct is patent.

Another option for deposition of the starch granules onto the surface of the ovary would be via laparoscopy or a transvaginal needle.

Additional Comments

The starch granule procedure is relatively easy to perform and does not require specialized equipment, technology, or training. However, the starch granule test requires individual testing of each oviduct on separate estrous cycles. The rate of transport through the oviduct is decreased significantly if the starch granules are applied at the time of ovulation. In the original report, granules were evident in the vagina of all mares by 24 hours, except when applied onto an ovulating ovary, in which case granules were not identified until at least 4 days later. The starch mixture contains granules of varying size (4–120 μm diameter), but only small granules (6–56 μm) are usually recovered from the uterus or cervix. These granules are significantly smaller than an early equine embryo (150–250 μm). There is considerable variability in the transport and recovery of all markers. As with other tests evaluating natural oviductal transport of markers, the starch granule test is not considered to be highly reliable or accurate in the detection of oviductal blockage.