Serum prolactin heterogeneity in the cow and goat

Jugular blood samples were taken from Friesian cows and British Saanen goats and the serum prolactin (PRL) heterogeneity profile obtained using a 2.5 × 92 cm Sephadex G-100 column. Two PRL components were identified by radioimmunoassay in cow and goat serum from virgin, pregnant and lactating animals. Using the nomenclature developed for human serum, one component, which eluted off the column just after the void volume (Vf/Vt = 0.09), was called big-big PRL and the second component eluting at a Vf/Vt value of 0.50 was called little PRL. In two out of 5 lactating cows before milking a PRL component with a Vf/Vt value of 0.27 was observed and this component was called big PRL; no big-big PRL was observed for these two cows. After milking the latter two cows the big component disappeared and the big-big component appeared. When PRL was released in response to milking in cows there was a significant decrease (P < 0.01) in the proportion of larger molecular weight PRL forms and an increase in the smaller form as compared to the values observed before milking. No such shift in either the number or proportions of heterogeneous PRL was observed in lactating goats as a result of the milking stimulus.