Abstract: 【Objective】 The purpose of this study was to explore the lactation performance of East Friesen sheep, Hu sheep and East Friesen-Hu hybrid sheep.【Method】 A total of 197, 313, 346, 364 healthy East Friesen sheep (DF), Hu sheep (H), East Friesen-Hu hybrid F1 generation (F1) and hybrid F2 generation (F2) were selected from the same farm.The daily milk yield from 2020 to 2021 was collected, the lactation curve was fitted by sixth degree polynomial, and the parameters of lactation curve were estimated.Milk samples were collected and milk fat, milk protein, lactose, total solids and urea nitrogen were determined by milk analyzer.Morphological description of dairy sheep udders was taken and nipple morphological data was measured, including nipple length, nipples spacing and nipple diameter.After anesthesia, the breast tissue was collected during the nonpregnant period, and the tissue sections were stained with hematoxylin-eosin staining (HE)and examined under microscope.【Result】 The milk yield of East Friesen sheep was significantly higher than that of hybrid F1 generation (P<0.05).There was no significant difference in milk yield between hybrid F1 and F2 generations (P > 0.05).The milk yield of the hybrid F1 and F2 generations were significantly higher than that of Hu sheep (P<0.05).The six-degree polynomial model was used to fit the lactation curves of different hybrid dairy sheep, and the degrees of fit were higher than 0.90.The peak lactation days of East Friesen sheep, Hu sheep, hybrid F1 and F2 generations were 58, 18, 45 and 47 d, respectively, and the peaks daily milk yield were 2.31, 1.27, 2.24 and 1.97 kg, respectively.The milk fat content of Hu sheep was significantly higher than that of other hybrid dairy sheep (P<0.05).There was significant difference in milk protein content between East Friesen sheep and hybrid F1 generation (P<0.05), and between Hu sheep and hybrid F2 generation sheep (P<0.05).There was no significant difference in other milk components of each hybrid dairy sheep (P>0.05).The results showed that the nipple length of Hu sheep was significantly shorter than that of other hybrid dairy sheep (P<0.05), and the nipple distance of hybrid F2 generation was significantly higher than that of other hybrid milk sheep (P<0.05).There was no relationship between nipple size and milk yield.The udders groove of Hu sheep was shallow, and the nipple orientation was parallel to the ground.The udders groove of East Friesen sheep was deep, and the angle between the nipple orientation and the ground vertical direction was less than 45°.The udder morphology and structure of the hybrid F1 generation was similar to that of the hybrid F2 generation, and the nipple oriented in an outside camber shape, which was suitable for machine milking.The mammary gland tissues of East Friesen sheep, hybrid F1 and F2 generations were well developed, and the number of acinar ducts in the breast structure was denser than that of Hu sheep.【Conclusion】 After hybridization between Hu sheep and East Friesen sheep, the milk yield of hybrid F2 generation increased significantly.The results of breast morphology and breast structure showed that hybrid F2 generation had a good lactation foundation.

Key words: East Friesen sheep; Hu sheep; East Friesen-Hu hybrid sheep; lactation trait