Influence of seminal additives and packaging systems on fertility of frozen bovine spermatozoa

Abstract

The following recommendations and conclusions are based upon results of fertility and laboratory studies, and general trends from field investigations. Fertility results due to the addition of enzymes have been variable and contradictory. Flushing of ampules with dry, gaseous nitrogen prior to filling has become a routine practice in processing semen to be frozen. For control of Vibrio fetus and Leptospira pomona, 2,000 micrograms of streptomycin and 1,000 u polymyxin B sulfate should be added per milliliter of raw semen immediately after collection. The extender for initial dilution should contain the same concentration of antibiotics used for raw semen plus 500 u penicillin. The glycerol portion of the extender should contain 500 u penicillin per milliliter. The effect of addition of sugars on fertility has been highly variable. The primary beneficial effect is probably due to their cryoprotective properties. A myriad of concoctions have been added to bovine semen and the results have been highly variable with respect to both motility and fertility. Results of subsequent experiments have rarely proven that addition of exotic compounds or mixtures has been of value. Higher mean fertility was obtained with semen in straws in 14 of 21 comparisons with ampules. The differences in favor of straws ranged from 1.1 to 18.9; while the range in favor of ampules was .1 to 4.4 percentage points. Fertility obtained with pellets has ranged from minus 12.8 to plus 11.9 percentage points in nonreturn rate (NR), compared to the corresponding NR with semen in ampules. Fertility of semen in ampules was higher in five of eight studies. Fertility of pelleted semen has ranged from minus 9.5 to plus 6.0 percentage points compared with straws. Fertility was higher for semen in pellets in only one of five investigations. Pellets should not be used until the potential for pathogenic contamination and exchange of spermatozoa among pellets is eliminated. There is a potential for higher fertility with semen in straws as compared to other packaging systems, but the issue of liquid nitrogen (LN) entry and possible contamination of semen should be further investigated. In general, fertility obtained with semen frozen in the .25 ml straw has been equal to or higher than semen in larger packages. However, they cannot be unequivocally recommended due to other considerations. From laboratory studies, it appears that greater spermatozoan survival is obtained when semen frozen in straws is thawed in water at 35 C or above.(ABSTRACT TRUNCATED AT 400 WORDS)