Effect of mating on the luteinizing hormone surge in the pig

Twenty-eight cannulated crossbred gilts were assigned to one of four treatments: natural mating, artificial insemination (AI, whole semen), AI (seminal plasma) or control (nonmated). Blood samples were collected four times daily (0800, 1200, 1600 and 2000 hr) on the day before standing estrus, the day of the onset of standing estrus and the first day after the onset of standing estrus. Thereafter, blood samples were collected once daily (1200 hr) until 15 days postestrus. Analysis of luteinizing hormone (LH) in the plasma revealed similar concentrations for all groups on the day of estrus, but higher (P less than .05) values for naturally mated gilts the following morning. Mean concentrations of LH on the first day after the onset of standing estrus were higher (P less than .01) for the mated gilts (2.75 +/- .54 ng/ml) than for gilts in the AI whole semen (.89 +/- .10 ng/ml), AI seminal plasma (1.02 +/- .13 ng/ml) and control groups (.92 +/- .11 ng/ml). Concentration of LH in the plasma of pregnant gilts tended to be higher after day 9. These results suggest that coitus may prolong the LH surge.