Among women who ate more than seven beef meals a week in pregnancy, almost 18 per cent of sons had sperm counts below 20 million sperm per millimetre of seminal fluid — the infertility threshold.
But only 6 per cent of men whose mothers ate fewer than four beef meals a week had a low sperm count.
For the study, 387 men gave semen samples. Their mothers were then questioned about diet in pregnancy. Sons of high beef consumers had an average 43.1 million sperm per millimetre of seminal fluid; those of women who ate less beef, 56.9 million.
The researchers say use of growth promoters, such as testosterone, in cattle might be reducing fertility in men.