Effects of glycerol on chicken spermatozoa incubated in vitro at 41 C in oviducal and embryonic cell cultures

Sperm-egg penetration assay assessment of the contraceptive effects of glycerol and egg yolk in rooster sperm diluents

Glycerol (GLY) and egg yolk (EY) are good cryoprotectants of avian and mammalian sperm, but in birds, they strongly inhibit the eventual fertilization of ova. Using the sperm penetration (SP-holes) assay and fertility trials, the present study investigates (1) the possible mechanism by which this contraceptive effect occurs in chickens and (2) the maximum concentrations of GLY and EY tolerated by fresh rooster sperm. Seventy Black-Barred Andaluza hens (five per treatment) were inseminated four times (twice per week) with 0.1 mL of fresh semen from roosters of the same breed diluted 1:1 (v:v) with Lake and Ravie medium containing different concentrations of GLY or EY. No adverse effects on acrosome integrity, sperm motility, or viability were seen with any concentration of GLY or EY. The number of SP-holes on perivitelline layer samples taken from above the germinal disc became progressively lower at GLY concentrations of 1.5% or greater (P > 0.05). No holes caused by sperms were seen in unfertilized eggs. The corresponding fertility results showed similar reductions when the GLY concentration was 1.5% or greater. No changes in the number of SP-holes were seen with increasing EY concentrations (0%-7.5%), nor were any differences in fertility observed, except for a reduction when 15% EY was used. The results therefore reveal that GLY affects the transit of sperms through the oviduct in their attempt to reach the infundibulum area, limiting their access to the ovum perivitelline layer. Egg yolk had no such effect, nor did it influence acrosome reaction capacity; its mechanism of contraceptive action therefore remains unknown. The maximum GLY and EY concentrations tolerated by the rooster sperm were 0.75% and 7.5%, respectively.

Cryopreservation of poultry semen: a review

Although still in the experimental phase, the technique of freezing domestic fowl semen may prove of interest and value to the industry. Various stages of the application of this method of preservation still need to be improved. One of the most critical aspects is the choice of cryoprotectant and its use during the process of freezing and thawing. While glycerol has a better cryopreservative action than other cryoprotectants in domestic fowl semen, it exerts a widely demonstrated contraceptive action, the mechanism of which has not yet been clarified. Thus the use of glycerol as a cryoprotectant must be accompanied by its complete removal before insemination.

The fertilizing capacity of semen preserved by freezing is notably less than that of fresh (non-preserved) material and has been evaluated as 1.6% and 19.7%. Genetic influences appear to affect spermatozoan response and tolerance to thermal treatments resulting in differences in subsequent fertility. Most studies using fowl semen report final freezing temperatures between –79°C and –196°C, a cooling rate of 1–10°C/minute and a thawing rate of 50–70°C/minute.

Straws have been found to be more satisfactory containers than glass vials or ampoules for preserving semen from domestic fowl.

An effective method for improving the fertility of glycerol-exposed poultry semen

Semen cryopreservation is necessary for banking germplasm from critical poultry stocks. To date, glycerol is the most effective cryoprotectant for poultry sperm; however, the contraceptive effects of glycerol require a significant reduction of the cryoprotectant from thawed semen before artificial insemination (AI). The effectiveness of glycerol reduction by dialysis, Percoll density gradient centrifugation, or washing through 12% (wt/vol) Accudenz was evaluated by fertility trials with highly inbred chicken research lines and commercial turkey lines. Semen was extended 1:1 and then diluted with glycerolized extender to yield a final 11% (vol/vol) glycerol concentration. Glycerolized rooster semen was aliquoted for control, Accudenz centrifugation, and dialysis treatments. A total of 90 pure line and 85 F1 hybrid chicken hens were each inseminated with 100 x 10(6) sperm at 7-d intervals for 4 to 6 wk. All eggs from the glycerolized control semen treatments were infertile, and fertility rates from dialyzed semen decreased steadily from 26.4 to 0% within the first 4 wk for the pure lines. In contrast, fertility rates for Accudenz-processed semen increased from 17.9 to 37.17% during the first 4 wk. Similar fertility rates occurred with the F1 hybrid cross lines. For turkey fertility trials, the dialysis treatment was not used; glycerolized turkey semen was processed by Accudenz or Percoll centrifugation to reduce glycerol. A total of 36 hens were inseminated with 150 x 10(6) sperm at 7-d intervals for 6 wk. Similar to the chicken trials, fertility rates of Accudenz-processed semen steadily increased to 49.4% by the sixth week of insemination. The average fertility of Percoll-processed semen was only 19.1%. These data demonstrate that Accudenz centrifugation is an acceptable glycerol reduction method for nonfrozen poultry semen.

Cryopreservation of poultry sperm: the enigma of glycerol

This review summarizes recent data for cryopreservation of poultry sperm and data establishing the contraceptive effect of glycerol. Successful cryopreservation protocols for bovine sperm are compared to the requirements for rooster sperm, with emphasis on glycerol-induced alterations in avian reproductive systems. It has been shown that molar concentrations of glycerol can affect (a) physical features of the cytoplasm (cytoplasmic organization and viscosity), (b) permeability and stability of the membrane bilayer(s), and (c) noncovalent attachment of proteins to the sperm surface. Perturbing effects of glycerol on sperm metabolism and the essentiality of maintaining bioenergetic balance during the temperature changes associated with any cryopreservation protocol are discussed. Emphasis is placed on the processes in avian reproduction that may be altered by interactions with glycerol. Finally, we discuss the potential value of using available genetic models (lines of roosters differing in the capacity of their sperm to survive a freeze-thaw cycle) to clarify and overcome damage to poultry sperm induced by cryopreservation.

Contraceptive action of glycerol on chicken spermatozoa in oviducal organ-slice cultures

Chicken spermatozoa in diluent with and without glycerol were evaluated after coculture with oviducal tissues. The motility of glycerolized (G) spermatozoa was lower in the cultures of vaginal tissue than in uterine tissue. The percentage of dead, G spermatozoa increased in cultures of the vagina and uterus but not in infundibulum cultures. Glycerol significantly increased the percentage of dead spermatozoa in both vaginal and uterovaginal cultures when compared to nonglycerolized spermatozoa in the same cultures. The percentage of dead G spermatozoa was higher for semen in vaginal culture than in uterovaginal culture. Uterovaginal tissue appeared to protect spermatozoa from some of the detrimental effects of glycerol. Incubation time had a significant detrimental effect on motility and percentages of dead and abnormal spermatozoa regardless of semen or tissue treatment.