Changes in testicular function? Semen quality in AI bulls over a 25-year period

A number of publications have suggested that there may be a worldwide decli ne in human sperm count over the past 50 years. If this decline is real and due to environmental contaminants, falls might also be seen in sperm numbe rs in the semen of Al bulls. Therefore, 6,918 ejaculates collected from 1,153 bulls of different breeds (Simmental, Holstein Friesian, Brown Suiss) between 1972 and 1996 at 5 Germ an AI centers were used to evaluate longterm trends in sperm output. Data w ere limited to test bulls with an age of 16 months at the beginning of the evaluation. Data were also adjusted for other effects, especially for the i nterval between semen collection and breed. Analysis of the pooled data obtained from all AI centers revealed a decreas e of the mean total sperm counts from 6.4x10(9)/ejaculate in 1972 to 3.9x10 (9)/ejaculate in 1996 as well as a decrease in the mean seminal volume (5.2 mi in 1972 to 4.05 mi in 1996) and the mean sperm concentration (1.245x10( 6)/mu l in 1972 to 0.944x10(6)/mu l in 1996). In spite of high yearly fluct uations average sperm counts of Brown Suiss bulls were significantly lower (4.7x10(9)) than in Simmental and Holstein Friesian bulls (6.9x10(9) and 7. 0x10(9), resp.). Using time series analysis for each individual AI center s ignificant changes of sperm counts during the study period could not be pro ven. It is concluded that in spite of potential exposure to environmental p ollutants there is no consistent trend towards declining sperm production i n bulls in Germany over the last 25 years.