| Objective: To investigate the effect of estradiol(E2) and progesterone(P4) in milk from pregnant cow on the endocrine metabolism and pubertal development in young male rat.Methods: Forty eight male SD(Sprague-Dawley) rats aged 19 days old were randomly assigned to four groups of twelve animals each and fed with quantitative milk from postpartum cow, milk from pregnant cow, commercial whole milk and artificial milk respectively. The body weight, body length, tail length and the time of preputial separation were observed, and the urinary estriol(E3), P4, testosterone(T), follicle-stimulating hormone(FSH) and luteinizing hormone(LH) concentration was assayed by ICMA in all groups. All rats were sacrificed at their fifty three days old. The serum P4 and T concentration was assayed, the reproductive organs weight were measured, the testes were analyzed with quantitation pathoimage apparatus, the bone mineral density(BMD) of left tibia was detected by dual energy X-ray absorptiometry (DEXA).Results: (1) There were no statistically significant difference in body weight, tail length, body length, the time of preputial separation , organ indices (for testes, epididymis and ventral prostate) between postpartum cow milk, pregnant cow milk, commercial whole milk and artificial milk groups. The seminal vesicle index in pregnant milk group[(1.80±0.40)mg/g] was higher than that in postpartum milk group [(1.44±0.33) mg/g](P<0.05) , with no difference among other groups. (2) In aforesaid groups, the seminiferous epithelium areas to the seminiferous tubules areas ratios were 0.83±0.03, 0.91±0.02, 0.91±0.03 and 0.84±0.03 respectively. The seminiferous epithelium areas to the visual field areas ratios were 0.72±0.06, 0.83±0.03, 0.82±0.04 and 0.77±0.04 respectively. The number of cells in seminiferous tubules to the seminiferous tubules areas (piece/μm2) ratios were (7.29±0.94)×10-3, (10.08±1.81)×10-3, (10.73±0.87)×10-3 and (7.23±0.76)×10-3 respectively. The above three indexes in pregnant milk and commercial whole milk group were all higher than those in postpartum milk and artificial milk group (P<0.05). (3) In aforesaid groups, the serum P4 concentration(ng/ml) was (19.02±5.51), (18.26±5.94), (17.87±6.57), (20.02±7.86) respectively, the BMD (g/cm2)was (0.15±0.02), (0.15±0.02), (0.16±0.02) (0.16±0.03) respectively, and the adjusted BMD(cm-2) was (0.53±0.11)×10-3, (0.53±0.08)×10-3, (0.55±0.09)×10-3, (0.53±0.10 )×10-3 respectively with no statistically significant difference among all groups. (4)The difference of the first(3335 days old) 24-h urinary FE3, P4, T, FSH and LH concentration adjusted by Cr was not as statistically significant as the second(48～50days old) ,respectively. (5) The serum T concentration in postpartum cow milk group[(7.14±6.48)ng/ml] was higher than that in commercial whole milk group [(2.35±1.44) ng/ml](P<0.05), with no difference among other groups.Conclusions: The female sex hormones in milk from either pregnant cow or commercial whole milk mainly from pregnant cow might have no significant effect on the body growth, BMD, the time of preputial separation, the reproductive organ indices (except for seminal vesicle), the serum P4, the gonadotropin and sex hormones levels in urine in young male rat in this study. But they might affect the development of seminiferous epithelium of testes and seminal vesicle ,and perhaps affect the level of serum T.
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