Influence of insulin treatment and feed restriction on follicular development in cyclic gills

Crossbred gilts were used to investigate whether exogenous insulin can rest ore normal follicular growth in feed-restricted gilts. After an 18-day altr enogest treatment, the first day of oestrous behaviour was designed as day 0, From day 0 to 13, all gilts received the same amount of feed, calculated to meet 200% of the energy requirements for maintenance. On day 14, luteol ysis was induced by injection of an analogue of prostaglandin F2 alpha, All gilts were slaughtered on day 19 and their ovaries removed. In Experiment 1, gilts received a high (240% of maintenance) or low (80%) level of feedin g (n = 10/group) from day 14 to 18. The number of large follicles (greater than or equal to5 mm) on day 19 was reduced in feed-restricted gilts (16.9 versus 20.6, P < 0.05). The same protocol of feed restriction was used in E xperiment 2 (240% versus 80% of maintenance from day 14 to 18), and some gi lts received daily injections of insulin (0.6IU live weight kg(-1)). The th ree experimental groups were H 240% and no insulin (n = 8); H-I: 240% + ins ulin (n = 8) and L-I 80% + insulin (n = 7). On day 18, 4h after insulin inj ection, plasma insulin was higher in insulin-treated than in untreated gilt s and glucose concentrations were reduced more dramatically in L-I than in H-I gilts (P < 0,05). Concentrations of TGF-I were lower in L-I than in oth er gilts (P < 0.05) and plasma IGFBPs were not significantly affected by tr eatments. On day 19, the number of large follicles (<greater than or equal to>5 mm) was not significantly influenced by treatments (19.4, 17.6 and 15. 3 for H, H-I and L-I gilts, respectively). Insulin, IGF-I and IGFBP-2 level s in follicular fluids from large follicles did not differ between females whereas IGFBP-3 levels were lower in L-I than in H gilts (P < 0.05) acid in termediate in H-I gilts. Intrafollicular levels of glucose were higher in f eed-restricted than in well-fed gilts (P < 0.05), These results suggest tha t exogenous insulin does not restore final follicular growth impaired by ac ute undernutrition. (C) 2000 Elsevier Science B.V. All rights reserved.