COMPARATIVE EFFECTS OF INSULIN AND PORCINE SOMATOTROPIN ON POSTWEANING FOLLICULAR DEVELOPMENT IN PRIMIPAROUS SOWS

We compared the effects of exogenous insulin and Porcine ST (pST) on f ollicular development after weaning. Crossbred primiparous sows receiv ed saline (1.5 mt i.m.; n = 9), insulin (.4 IU/kg BW s.c.; Eli Lilly L ente Iletin II; n = 10), or PST (40 mu g/kg BW i.m.; n = 10) from d 1 to 5 after weaning(d 0). Ovaries were collected, the diameter of each follicle greater than or equal to 2 mm was measured, and fluid from th e 20 largest follicles was assessed for IGF-I, IGF binding proteins (I GFBP), estradiol, progesterone, and testosterone. The total number (27 .7, 25.3, and 29.1 for saline, insulin, and pST, respectively; SEM = 3 .2) and average diameter (4.7, 5.2, and 5.5 mm for saline, insulin, an d PST treatments, respectively; SEM = .3 mm) of ovarian follicles were not affected by insulin or PST treatment. The pST and insulin increas ed follicular fluid estradiol and testosterone in medium and large fol licles compared to fluid from saline-treated sows, but the increase wa s greater for insulin than for PST treatment (treatment x size interac tion, P < .01). Similarly, progesterone concentrations in follicular f luid were higher in medium and large follicles after insulin treatment , and pST treatment induced higher progesterone concentrations in smal l follicles and increasingly lower concentrations of progesterone in m edium and large follicles (treatment x size interaction, P < .0007) co mpared to saline treatment. Follicular fluid IGF-I was greater (treatm ent x health interaction, P < .0001) in atretic and nonatretic follicl es from PST-treated sows than in those from insulin-and saline-treated sows. Follicular fluid IGFBP-2 (tendency, P < .07) and IGFBP, possibl y representing IGFBP-5 (30 kDa) and IGFBP-4 (22 kDa), were higher in a tretic follicles than in nonatretic follicles (P < .05), whereas IGFBP -3 was not influenced by health status. The 30- and 22-kDa IGFBP were also influenced by treatment, increasing due to pST compared with sali ne or insulin treatments (P < .008). Follicular fluid IGFBP-2 and IGFB P-3 were not influenced by treatment. In conclusion, PST and insulin p ositively influenced follicular steroidogenesis and possibly follicula r development, although through different mechanisms.