Prediction of bovine ovulation by a rapid radioimmunoassay for plasma LH

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Abstract
A commonly used and specific plasma LH [luteinzing hormone]radioimmunoassay was modified to provide reliable results for cow LH concentrations in blood within 4-5 h. Blood samples were collected at 2- or 4-h intervals from at least 24 h before the expected estrus until after its onset. Thereafter, samples were collected at intervals of 2 or 4 days until the next estrus. For the assay, the antigen-antibody reaction took place during a 2-h incubation at 37.degree. C. The immune complex was precipitated by addition of rabbit anti-.gamma.-globulin and polyethylene glycol followed by an incubation at 22.degree. 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, intervals of .simeq. 27.3 h between the beginning of the LH peak and ovulation and .simeq. 17.5 h between the end of the peak and ovulation were obtained. This modified technique can be used to predict rapidly and precisely the time of ovulation in cattle.