Sperm counts in semen of farm animals 1932-1995.

In some countries, sperm counts in normal human semen seem to have declined over the last 50 years. If this decline is real and due to environmental factors, falls might also be seen in sperm numbers in the semen of farm animals. Sperm counts are available for bull, boar and ram from the early 1930s, obtained using techniques similar to those used for human semen. Data have been obtained from the literature between 1932 and 1995 from 137 studies involving bulls, 76 involving boars and 130 involving rams. All were normal adult animals, from which semen was collected regularly but at a frequency which would not be likely to cause a fall in sperm counts. The references were obtained systematically from Animal Breeding Abstracts, and where possible the original articles were consulted to obtain mean values for each study; where the original reference was not easily obtainable, values were taken from the abstract. The bull data showed no correlation of sperm count with year of publication (r2 = 0.000), for the boars there was a slight but non-significant positive correlation (r2 = 0.041), and for the sheep there was a slight, but significant, rise in sperm counts with time (r2 = 0.124 for sperm counts and 0.126 for total sperm per ejaculate; not all authors gave both values). It would appear that, if the fall in human sperm counts is real, then it must be due to something which is not affecting farm animals.