Prediction of bovine ovulation by a rapid radioimmunoassay for plasma LH

Abstract

A commonly used and specific plasma LH radioimmunoassay was modified to provide reliable results for cow LH concentrations in blood within 4-5 hr. Blood samples were collected at 2- or 4-hr intervals from at least 24 hr before the expected oestrus until after its onset. Thereafter, samples were collected at intervals of 2 or 4 days until the next oestrus. For the assay, the antigen-antibody reaction took place during a 2-hr incubation at 37°C. The immune complex was precipitated by addition of rabbit anti-γ-globulin and polyethylene glycol followed by an incubation at 22°C for 30 min. The coefficient of variation between this assay and the standard assay was < 15%. From a study of 25 cycles from 12 animals, the authors obtained intervals of ≃ 27.3 hr between the beginning of the LH peak and ovulation and ≃ 17.5 hr between the end of the peak and ovulation. This modified technique can be used to predict rapidly and precisely the time of ovulation in cattle.