The Determination of Numbers of Spermatozoa in Bull Semen by Measurement of Light Transmission

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Abstract
Five different procedures for determining spermatozoan numbers by measurement of light transmission with a Cenco-Sheard-Sanford Photelometer were compared. It was concluded that the most accurate and practical method consisted of the addition of 4 cc. of sodium citrate buffer to 0.1 cc. of semen and the making of the readings with the diluted semen in a standardized tubular absorption cell 17 mm. in diameter. Haemacytometer counts and light transmission readings using this method were made with 142 samples from 50 bulls in 3 studs. A correlation of −0.97 between logarithms of Photelometer readings and haemacytometer counts was obtained. The regression coefficient was −0.28. There were no significant differences between the within-bull correlation or regression coefficients. A comparison of readings made on nine Photelometers with five semen samples in duplicate indicated that an instrument would not need to be calibrated if it were to be used in a bull stud but that it should be if maximum accuracy, such as that required in some research work, is desired. Different sources of variation when comparing haemacytometer counts with counts estimated by means of light transmission values were determined. Duplicate readings by both methods were made with 25 ejaculates from 20 bulls. It was found that the Photelometer will give more reproducible readings for any given semen sample than will the haemacytometer. The main source of error when comparing the two methods is variation in the inherent properties of the seminal plasma or spermatozoa which cause variation in light transmission readings independent of spermatozoan numbers.