SUMMARY

A radioimmunoassay for bovine FSH has been developed using a rabbit antiserum against highly purified bovine FSH (160 \m=x \ NIH-FSH-S1)and a 125I-labelled tracer of the same preparation. The sensitivity was 0\m=.\25ng/ml for purified bovine FSH or 25 ng/ml with reference to a crude bovine FSH (NIH-FSH-B1) standard. Purified bovine LH and TSH showed cross-reactivities of less than 1%, while their subunits and other purified protein hormones showed no significant inhibition at concentrations up to 100 ng/ml. Ovine FSH cross-reacted significantly but in a non-parallel manner; human and rat FSH cross\x=req-\ reacted only slightly. The concentrations of FSH (means \m=+-\s.e.m.) in the sera of cows (n = 12), cows at oestrus (4), bulls (7) and steers (9) were measured as 25\m=.\4 \m=+-\4\m=.\7,58\m=.\4 \m=+-\12\m=.\6, 45\m=.\7 \m=+-\ 9\m=.\5 and 120\m=.\2 \m=+-\36\m=.\0ng/ml respectively. The FSH content of bovine pituitary glands varied greatly between individuals, from 2 to 25 \g=m\g/mgtissue. The inhibition curves of pituitary and serum FSH were parallel to that of the bovine FSH standard