Prolactin in blood plasma and milk of buffalo during estrous cycle and early pregnancy

Concentration of prolactin was measured by radioimmunoassay for 11 primiparous and 16 multiparous buffalo. Prolactin concentration of blood plasma on day of insemination was about 200 ng/ml for primiparous and about 315 ng/ml for multiparous animals and fluctuated between 130 and 200 ng/ml for primiparous and between 250 and 345 ng/ml for multiparous pregnant animals. For the nonpregnant group prolactin fluctuated between 145 and 240 ng/ml for primiparous and between 210 and 310 ng/ml for multiparous animals with minor elevations 1 to 2 days before estrus. Concentration of prolactin of milk was not significantly different from that of plasma and was positively correlated .68 for nonpregnant and .93 for pregnant animals.