Effects of Insulin Administration at Weaning on Hormonal Patterns and Reproductive Performance in Primiparous Sows

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Summary Twelve primiparous sows were grouped into six pairs. One sow from each pair (T) received subcutaneous injections of porcine insulin as follows: pairs 1 and 2, 0.5 IU/kg at 07.00 h; pairs 3 to 6, 0.5 IU/kg at 07.00 and 15.00 h. Insulin administration was started one day before weaning and continued until the last day of post‐weaning oestrus. Control sows (C) received physiological saline solution as a sham treatment. Blood samples were collected every 3 h from 09.00 to 21.00 h and, additionally, at 07.00 h during the period of insulin treatment. Additional blood samples were collected at 15‐min intervals for 6 h for 2 days before and for 3 days after weaning, and for 12 h on the day of weaning (D 35 of lactation). Exogenous treatment with insulin increased plasma levels of insulin (53 v 36 mU/l, P < 0.001) and decreased plasma levels of glucose (4.6 v 5.5 mmol/l, P < 0.001) in T‐sows as compared to C‐sows. During the treatment period, the average levels of cortisol (31 v 35 nmol/l, P < 0.001) and non‐esterified fatty acids (0.13 v 0.16 mmol/l, P < 0.01) were lower in T‐ than in C‐sows. No differences in glucagon or urea levels were observed between the two groups. Plasma levels of LH were higher in T‐ than in C‐sows both before and during the treatment period. However, no differences in number of LH pulses/6 h were found between the two groups. Plasma concentrations of oestradiol‐17β were higher in C‐ than in T‐sows before the treatment started, but no between‐group difference was found during the treatment period. Administration of insulin did not shorten the interval from weaning to oestrus (T‐sows, 5.1 ± 1.0 days; C‐sows, 5.2 ± 1.0 days). The average number of corpora lutea found was lower in T‐sows (13.8 ± 3.4) than in C‐sows (20.1 ± 2.8).