Influence of exogenous insulin before breeding on conception rate and litter size of sows

We conducted two experiments on commercial farms to evaluate the effect of insulin administered to primiparous sows before postweaning estrus on subsequent reproductive performance. On the day after weaning in Exp. 1, 138 crossbred primiparous sows were assigned to receive saline or insulin (.4 IU/kg BW) once daily at the time of feeding for four consecutive days. Treatment did not affect interval from weaning to estrus (5.1 +/- .2 d) or percentage in estrus by 7 d after weaning (92.6%). Farrowing rate at second parity was increased by insulin (76.7 and 92.3% for saline and insulin treatments, respectively; P < .01). Litter sizes at second parity were not affected by insulin treatment. Experiment 2 was conducted on a different commercial farm using 491 primiparous crossbred sows. They were treated similarly to those in Exp. 1 with saline or insulin after weaning, except that treatment duration of 2 d of saline or insulin was included. Treatment did not affect the interval from weaning to estrus (overall, 9.2 +/- .5 d), percentage in estrus by 7 d after weaning (79.1%) or farrowing rate (90.2%). However, the number of total pigs born in the second litter for sows mated within 7 d after weaning was increased (P < .05) by one pig in sows treated with insulin for 4 d (10.3 +/- .3 pigs) compared with 2 d (9.1 +/- .3) and with saline (2 d and 4 d grouped together: 9.3 +/- .1). Third-parity litter size was not adversely affected by treatments applied before the second litter. In conclusion, manipulation with a metabolic hormone such as insulin may improve postweaning fertility by affecting aspects of ovarian follicle development or pregnancy establishment.