Trend analysis of plasma insulin level around parturition in relation to parity in Saanen goats

The present study investigated the effect of parity on plasma insulin level around parturition in Saanen goats. On d -14, -7, 0, 3, 7, 10, and 14 from parturition, plasma glucose, NEFA, free AA, cortisol, and insulin concentrations were analyzed in 10 primiparous and 10 multiparous goats. At parturition, BW of primiparous goats was about 75% of that of multiparous ones (P < 0.001) and then their milk production was lower than that of multiparous ones (P < 0.001). At parturition, glucose increased (P < 0.01) in both primiparous and multiparous goats and then decreased (P < 0.01) on d 3 of lactation, remaining higher (P < 0.01) in primiparous than multiparous goats until the end of the study period. In both groups, free AA decreased (P < 0.01) at parturition, returning to prepartum levels (P < 0.01) on d 3 of lactation without difference between groups. Only in multiparous goats, plasma NEFA increased at parturition (P < 0.01), returning to prepartum levels on d 14 (P < 0.01). Changes in glucose and AA could have been caused by cortisol, which increased (P < 0.01) at parturition in both primiparous and multiparous goats, returning to prepartum levels (P < 0.01) on d 7 of lactation, without difference between the parity groups. In multiparous goats, insulin decreased soon after parturition (P < 0.05), remaining at low levels until the end of the study period, whereas in primiparous goats, insulin did not vary until d 14 of lactation, when it decreased (P < 0.05) also in this group. Therefore, between d 3 and 14 of lactation, insulin was higher in primiparous than multiparous goats (P < 0.05). Only in primiparous goats, at kidding, insulin was negatively correlated to BW (P < 0.01), and after parturition it was negatively correlated with milk yield (P < 0.05) and plasma NEFA (P < 0.05). We hypothesize that higher insulin levels in primiparous Saanen goats, which are still immature at their first breeding season, acted to limit both the mobilization of bodily reserves and the capture of nutrients by the lactating mammary gland, thus providing nutrients for their own physical and physiological development.