Abstract: 【Objective】 The purpose of this experiment was to investigate how long-term cold exposure affect ewes’ weight changes,serum biochemical indicators,antioxidant indicators,non-specific immune indicators,as well as fetal development,and oxidative damage to the liver of ewes and fetal sheep in late pregnancy.Meanwhile,the regulatory role of N-carbamylglutamate (NCG) was also investigated. 【Method】 24 healthy Mongolian sheep in late pregnancy,aged 3-4 years,with similar body weight (48.53 kg± 3.64 kg),were randomly divided into 3 groups,with 8 replicates in each group and 1 sheep in each replicate.The control group (group C) was raised in a warm house (average temperature 3.60 ℃),while the two experimental groups (groups L and LN) were out of the house (average temperature -12.20 ℃).In addition,each sheep in LN group was orally administered 10 mL of distilled water and 2.5 g of NCG suspension per day,while each sheep in groups C and L was orally administered 10 mL of distilled water per day.The pre-feeding period was 10 days,and the normal test period was 62 days.During the experiment,the weight of the ewes was recorded on the 1 st,30th,and 60th day.At the beginning and end of the trial period,the jugular vein blood of ewes was collected to measure serum biochemical indicators,antioxidant indicators,immune indicators,and hormone levels in the hypothalamic pituitary adrenal axis (HPA) and hypothalamic pituitary thyroid axis (HPT).At the end of the experiment,the experimental sheep were slaughtered and sampled to measure the fetal sheep’s body weight,organ index,as well as the oxidative damage indicators of 8-hydroxydeoxyguanosine (8-OHdG),4-hydroxynonaenoic acid (4-HNE),advanced oxidative protein products (AOPP),3-nitrotyrosine (3-NT) content,and superoxide dismutase (SOD) activity in the liver of ewe and fetal sheep. 【Result】 ①The average daily weight gain (ADG) of ewes in group LN was significantly higher than group L in the later and whole stages of the experiment (P＜0.05),while there was no significant difference between groups L and C in the early,late,and entire stages of the experiment (P＞0.05).Fetal sheep weight in group L was significantly lower than groups C and LN (P＜0.05),while there was no significant difference between groups LN and C (P＞0.05). Except for the lungs,the visceral organ weight of fetal sheep in group L was significantly lower than groups C and LN (P＜0.05).②At the end of the experiment,the serum NEFA content of ewes in group LN was significantly higher than groups C and L (P＜0.05),and the serum β-HB content of ewes in group L was significantly lower than groups C and LN.③The serum T₄ content of ewes in group L was significantly lower than group C (P＜0.05),while the group LN was between them,with no significant difference (P＞0.05).④For hepatic oxidative damage indicators,the content of 8-OHdG of ewes in group L was significantly higher than group C (P＜0.05),while group LN was higher than group C and lower than group L (P＞0.05).The SOD activity of ewes in group L was significantly lower than groups C and LN (P＜0.05),and group LN was lower than group C (P＞0.05).There was no significant difference in the oxidative damage indicators of fetal sheep liver among the three groups (P>0.05). 【Conclusion】 Cold exposure in late pregnancy of ewes reduced their ADG,abnormal serum metabolism,and oxidative damage to the liver.Supplementing NCG could improve the adverse effects of cold exposure on ewes and fetal sheep.

Key words: late pregnancy; NCG; long-term cold exposure; oxidative damage