Ram Management

The artificial vagina is used most commonly for collection of ram semen. It is prepared for collection by the introduction of warm water (100°–130°F [40°–55°C]) and air between the outer casing and soft inner sleeve, lubrication with petrolatum in the end where intromission of the penis occurs, and attachment of a graduated collecting glass at the opposite end. Rams quickly learn to mount a restrained ewe, and intromission and ejaculation are extremely rapid.

The second method of semen collection is by electroejaculation, for which the ram may be restrained on its side. The lubricated bipolar electrode is inserted into the rectum. The withdrawn penis is held with a piece of gauze to facilitate insertion of the glans into a 10- to 15-mm diameter graduated collecting tube. Ejaculation usually occurs after a few short electrical stimulations; “stripping” of the urethra may be helpful when expulsion of semen seems incomplete. Electroejaculation is less reliable than the artificial vagina; specimens vary in quality and can be contaminated with urine.

The volume of semen collected with the artificial vagina is 0.5–1.8 mL, and the concentration of the spermatozoa is 2.5–6 × 10⁹/mL. Semen obtained by electroejaculation generally is of larger volume but lower concentration.

Immediately after collection, the semen is assessed for contamination, volume, concentration of spermatozoa, and sperm motility (wave motion and sperm progression).

Semen can be processed by extending or diluting, packaging, and storing. Semen may be extended 5-fold, depending on the initial concentration, the processing and storage method, and whether the semen will be used fresh, chilled, or frozen-thawed. Most semen extenders or diluents are based on Tris, egg yolk, and additional cryoprotectants such as glycerol. Commercial extender concentrates contain cryoprotectants and require the addition of egg yolk and double-distilled water. These extenders can be used for either fresh or frozen semen.

Extenders for fresh and chilled semen include whole, skimmed, or reconstituted cow’s milk that has been heated to 92°–95°C for 8–10 min in a water bath to inactivate toxic factors, egg yolk/glucose/citrate (15% egg yolk, 0.8% glucose [anhydrous], 2.8% sodium citrate dihydrate in glass-distilled water). The addition of Tris or glycerol improves the sperm survival of frozen-thawed semen. The reconstitution of frozen-thawed semen with fresh seminal plasma improves its fertilizing ability when used for intracervical insemination but not for intrauterine insemination. The number of motile spermatozoa and the volume of an insemination dose for the ewe depends on the site of insemination and the method of processing. For vaginal insemination, 0.3–0.5 mL with 300 million motile spermatozoa is used; for cervical insemination, 0.05–0.2 mL is used with 100, 150, and 180 million spermatozoa of fresh, liquid-stored, and frozen-thawed semen, respectively. Intrauterine insemination by laparoscopy requires 0.08–0.25 mL (with a total of 20 million motile spermatozoa) into each uterine horn.

Ram semen may be stored for up to 24 hr by cooling the extended semen to 2°–5°C over 90–120 min and by holding at this temperature. Fertility decreases rapidly and is low by 48 hr.

Freezing and storage of ram semen in 0.25–0.3 mL, three-dose pellets or in 0.25 mL, single-dose synthetic straws at liquid nitrogen temperature (196°C) is successful in maintaining sperm viability, but there may be a range in motility after thawing and in fertility between rams or processing batches. Use of frozen-thawed semen may result in lambing rates of 50% with cervical insemination and 50%–80% with intrauterine insemination.

Freeze-thawing reduces the numbers of motile sperm. Chilling results in membrane changes that reduce the longevity of sperm. The membrane changes are similar to capacitation and acrosome reactions, and affected sperm are thus ready to fertilize oocytes. Fresh seminal plasma mitigates the effects of some of the capacitation changes.