Insulin sensitivity during pregnancy, lactation, and postweaning in primiparous gilts1

The objectives were to examine changes in the insulin response during pregnancy, lactation, and postweaning in an experiment involving 10 primiparous Landrace x Large White gilts. Gilts were catheterized at 50 d of pregnancy, and tests were conducted at approximately 59 d of pregnancy (midpregnancy; MP), 106 d of pregnancy (end of pregnancy; EP), 17 d of lactation (L), and 9 d after weaning (PW), respectively. Changes in plasma glucose, insulin, and NEFA concentrations were studied after 3 different tests: ingestion of 1.3 kg of feed (meal test); a glucose tolerance test; and 2 euglycemic, hyperinsulinemic clamp tests, in which 20 and 55 ng of insulin x kg of BW(-1) x min(-1) were infused during 150 min. Fasting concentrations of plasma glucose were less during L than during the other stages (P < 0.001). Concentrations of glucose and insulin increased after ingestion of the meal and decreased thereafter. Plasma insulin returned to basal concentrations at all stages, whereas glucose reached basal concentrations before the end of the meal at the PW test only. Postprandial concentrations of plasma glucose and area under the curve for insulin were greater during L than at the other stages (P < 0.05); both tended to be greater during EP than during MP or after weaning. Concentrations of NEFA were greater during L than at other stages before as well as after a meal (P < 0.001). Glucose half-life was greatest during L, least during MP and PW, and intermediate during EP. Compared with other stages, insulin secretion during the tolerance tests seemed to be delayed during L and, to a lesser extent, at EP. Irrespective of insulin dose, glucose infusion rates during the clamps did not differ between MP and PW, and were greater than during EP and L (P < 0.001). Plasma concentrations of NEFA decreased less rapidly during L than during the other stages. Gilts from EP developed a state of insulin resistance that was further accentuated during L. Changes in insulin responsiveness at MP, EP, and L may be an adaptation that allows gilts to acclimate to the increasing demand of glucose by the growing conceptus and the even greater demands of lactation.