Effect of diet composition and frequency of feeding on postprandial insulin level and ovarian follicular development in prepubertal pigs

Several studies have shown that insulin is positively related to reproductive processes. The objectives of the present study were to investigate the effect of three diets, consisting of different major energy sources (starch, glucose or fat) given in 2, 3 or 4 portions daily on postprandial glucose and insulin levels, and to assess the influence of 3 times a day feeding on follicular development in prepubertal gilts. In Experiment 1, Polish Landrace gilts aged 142 days (n=l 8) were randomly divided into three equal groups (n=6) fed with starch, glucose and fat diet. The same animals received their diet in three frequencies (2, 3 or 4 times daily). Each period started with three days of adaptation to the of the same diet. On day 4, blood samples were taken before, during and after feeding. The next day the frequency of feeding was changed without change of diet. The plasma glucose and insulin concentrations were detennined by enzymaticand radioimmunoassay, respectively. In Experiment 2, forty-four 140 day old gilts were divided into three treatment groups and given starch, glucose and fat diets in three equal portions at 8.00, 13.00 and 18.00h. After 25 days of experimental feeding gilts were slaughtered the day after treatment to assess: ovarian weight, follicular development and the total number of LH receptors in one ovary. Basal plasma glucose concentrations were similar for the three diets given 3 and 4 times a day (3 times daily: 50.8±4.9, 56.814.0, 56.317.4 mg/dl; 4 times daily: 53.311.7, 65.815.9, 58.317.5 mg/dl), but differed (PO.05) for the three diets given twice daily (71.4110.4, 40.813.9, 53.618.6 mg/dl, starch, glucose, fat, respectively). The basal plasma insulin concentration was similar for the three diets and different frequency of feeding (2 times daily: 7.811.4, 9.311.0, 9.510.9 uiU/ml; * Supported by the State Committee for Scientific Research, Grant No. P06D 007 16 and partly by the International Atomic Energy Agency (IAEA) technical co-operation fund, POL/5/010 472 INSULIN LEVEL AND OVARIAN FOLLICULE IN PIGS 3 times daily: 6.2+1.4,10.3+1.0, 8.6+1.0 ulU/ml and 4 times daily: 8.5+1.6,7.9+0.8, 8.2+2.7 ulU/ml, starch, glucose and fat, respectively). After feeding, the insulin concentration in gilts fed the glucose or starch diet showed a faster increase compared with the fat diet in all studied periods of feeding. The area under the total curve for the plasma insulin level was greater (PO.05) for the glucose diet than for fat diet (6870+656 vs 4028+751 arbitrary units, respectively for twice daily feeding; 6314+718 vs 3274+472, respectively for three daily feeding), whereas the starch diet was intermediate (6104+762 and 3855+729, respectively) and not significantly different from the other diets. Four daily feeding diet not caused significant differences for starch, fat and glucose diets in area under curve for insulin level. Feeding the starch, glucose and fat diets for 25 days (in three equal portions) did not affect the weight (g) of the ovary (2.8+0.1,2.8+0.2 and 3.0+0.1, respectively), the number and size of healthy and atretic follicles nor LH receptor concentration (9.0+1.2; 10.5+1.7 and 9.6+1.2 fM/mg protein, respectively). The results confirmed earlier observations that the dietary energy source affects the postprandial plasma insulin concentrations when the diet is divided into two parts. A similar effect was observed when the diet was given in three, but not four, equal portions each day. However, three times daily increase of insulin concentration in blood samples for 25 days did not affect ovarian and follicular development in prepubertal gilts of pure Polish Landrace breed.