Strain Differences in the in vitro Fertilizing Capacity of Mouse Spermatozoa as Tested in Various Media

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Abstract
Eggs and spermatozoa of an outbred strain (CD-1) and two inbred strains (C3H and C57BL/6) of mice were tested for in vitro fertilization. Spermatozoa from CD-1 and C3H males were capable of fertilizing large numbers of eggs (73-85 percent) from CD-1, C3H and C57BL/6 females in a modified Krebs-Ringer bicarbonate solution. In contrast, spermatozoa from C57BL/6 males were able to fertilize only small numbers of eggs (14-30 percent) from C57BL/6, CD-1 and C3H females. When gametes of F1 hybrids of all possible pairings of the three strains were tested in vitro, the rates of fertilization were high (75-95 percent). Altering the medium by increasing bovine serum albumin, decreasing sodium chloride (94.6 mM instead of 119.37 mM), or adding agamma human serum or bovine follicular fluid did not increase the rates of fertilization when using spermatozoa from C57BL/6 mice. Preincubating spermatozoa for longer times and varying sperm concentrations also failed to increase the in vitro fertilizing capacity of C57BL/6 spermatozoa. This was an indication that a majority of spermatozoa from this strain may not capacitate in a Krebs-Ringer bicarbonate solution. When spermatozoa from C57BL/6 males were suspended in a modified Tyrode's solution, with or without agamma human serum, rates of fertilization were high (94 percent) whenever less than 0.8 x 106 sperm/ml were incubated for 1-2 h before the addition of eggs. This study emphasizes the importance of selecting the proper strain of mouse and fertilization medium for in vitro fertilization.

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