Three synthetic
steroids were evaluated as potential
chemosterilants for rodent control. Ethinyl
oestradiol, methyl
testosterone or
Org 5933, a synthetic
gestagen, were incorporated into
paraffin blocks containing cereal grains and offered to laboratory rats and mice in addition to their standard laboratory diet. Ethinyl
oestradiol (50 mg kg-1
paraffin block) was highly unpalatable to female rats, and the amount of
steroid ingested was not sufficient to interfere with their oestrous cycles or inhibit ovulation. Methyl
testosterone (5000 mg kg-1
paraffin block), although not as palatable as untreated blocks, was effective in inducing almost immediate
infertility in female rats and mice at an ingested dose of about 35 micrograms g-1
body weight day-1. This
infertility persisted throughout the
duration of treatment, and lasted for several weeks after the
cessation of treatment. Male rats became infertile after 3 months of treatment owing to suppression of spermatogenesis. Female rats developed a specific aversion to methyl
testosterone when they were pregnant or lactating; it was therefore not possible to masculinize the brains of their female offspring. In mice, the
androgen treatment induced high levels of aggression in the females so that they fought with males and with one another. One female died of her
wounds.
Org 5933 (4 mg kg-1
paraffin block) was highly palatable to female rats and mice, and at doses of about 420 ng g-1
body weight day-1 was effective in inhibiting ovulation in rats within 3 to 4 days after the start of treatment. This
infertility persisted throughout the
duration of treatment, and the animals conceived within 5 days of
cessation of treatment. A dose of about 930 ng g-1
body weight day-1 was not completely effective in inhibiting ovulation in mice, but females that became pregnant during treatment gave birth to dead young. When the
gestagen was given to female rats and mice in the last few days of pregnancy, the duration of gestation was significantly prolonged, and most young were born dead; some of the females also died in labour. The
gestagen did not appear to inhibit lactogenesis, since the few animals that gave birth to live young reared them normally for the first 5 days of life. These results show that either methyl
testosterone or
Org 5933 in
paraffin blocks could perhaps be used as a chemosterilant for the control of rat and mouse populations.(ABSTRACT TRUNCATED AT 400 WORDS)