Objective:To explore the effect of postpartum fatigue(PPF) on maternal behavior in rats and its mechanisms.Methods:Sprague-Dawley (SD) rats on the first day after delivery were randomized into the control group and the PPF group using the random number table method, with eight rats in each group.The rat model of PPF was established by forcing rats to stand in a cage with water and last for seven days.To maintain galactosis and lactation, rats and pups were caged for 90 min after every 3 h of separation.The control group was separated routinely without any stimulus.The length and body mass of the pups were recorded at birth and postnatal day 7.On the seven days after modeling, the following maternal behaviors were observed via video recordings: suckling, nesting, clicking and retrieval.The morphology of neurons in the paraventricular nucleus of hypothalamus (PVH) was observed by HE staining.The expression of oxytocin in the paraventricular hypothalamus (OxtPVH) was determined by immunofluorescence and immunohistochemistry.Western blot and qRT-PCR were performed to detect mRNA and protein expression of prolactin (PRL) in pituitary gland, respectively.Statistical analysis was performed by SPSS version 22.0, normally distributed continuous variables were compared between the two groups using an independent-sample t test, and nonnormally distributed continuous variables were compared between the two groups by Mann-Whitney U test. Results:On the seventh day after modeling, the length and weight gain of pups in the PPF group ((5.82±0.17) cm, (5.33±2.54) g)were significantly lower than those of the control group ((6.24±0.36) cm, (7.92±2.54) g, t=3.199, 2.227, both P<0.05). Compared with the control group, the rats in PPF group exhibited abnormal maternal behaviors, such as gnawing cage, biting tails, turning circles, repeatedly nesting and refusal to suckling.The results from the maternal behavioral test revealed that the latency of first pup retrieval and last pup retrieval ((39.25±3.50) s, (280.75±59.16) s) in the PPF group were significantly prolonged compared with those in the control group((19.25±7.68) s, (146.00±49.62) s, t=-4.742, -3.490, both P<0.05), the duration of nesting building ((19.50±12.69) s)and clicking ((95.50±70.55)s) in the PPF group were significantly shorter than those in the control group((68.00±37.59) s, (243.00±62.07) s; t=2.445, 3.139, both P<0.05). Compared with control group, the neurons cells of PVH in the PPF group were in disordered manner and the OxtPVH content in the PPF group decreased significantly.The mRNA (0.33(0.29, 0.38) vs 0.85(0.76, 1.76), Z=-3.576, P<0.05) and protein ((1.00±0.65) vs (4.17±0.49), t=-7.726, P<0.05) levels of PRL in PPF group were significantly decreased compared with those in the control group. Conclusion:The behaviors of holding back, nesting and licking offspring are decreased in postnatal fatigued rats.This may be related to the decreased expression of OxtPVH and PRL in hypothalamus of female rats.