Abstract: 【Objective】 Nutrition supply in different physiological periods has great impact on reproduction of ewes, which determines the conception rate, birth weight, survival rate and potential growth performance of lambs. The nutrition after weaning compensate for the body reserve which was consumed during pregnancy and lactation, and is necessary for the ewes to prepare for the next reproduction cycle. The energy metabolism is essential in the study of nutrition of mutton sheep, especially during early growth period. The lack of study in related area limited the development of mutton sheep industry in China. This experiment was conducted to investigate the effect of different feeding levels on energy and gas metabolism in Dorper × Thin-tailed Han crossbred ewes during non-pregnancy and lactation periods. 【Method】 Non-experimental factors should be limited in the feeding trial, which is a common method in the research of nutrient requirement. Combined with the digestibility and gas metabolism trials, the energy balance of ewes in different physiological periods could be systemically investigated. Fifteen healthy ewes treated for estrus synchronization were assigned into three feeding levels according to the randomized block design: ad libitum, 80% of ad libitum, and 60% of ad libitum. Another nine non-pregnant ewes of the same age and species were used as a blank group. Digestibility and respirometry trials were conducted on 20, 50 and 80 d of lactation. 【Result】The apparent digestibility of carbon (C) and energy of non-pregnant and lactating ewes increased significantly with decreasing levels of feed intake (P＜0.05). Milk C decreased significantly with increasing lactation periods (P＜0.05). Fecal and urinary C decreased significantly with decreasing feeding levels (P＜0.05), and it was higher in lactation period than in non-pregnant period (P＜0.05). The metabolic rates of digestible energy increased with the decreasing feeding levels (P＜0.05), and were 78.55%-82.93%, 79.53%-85.89%, 79.40%-83.49% and 80.99%-85.33% in the period of non-pregnancy, early, middle and late lactation, respectively. The respiration quotients decreased significantly with the decreasing feeding levels (P＜0.05). However, they were similar between non-pregnancy and lactation periods, ranging from 0.83 to 0.96. The methane (CH₄) production and the ratio of CH₄ to DMI (kg) or metabolic weight (W^0.75) decreased significantly with the decreasing feeding levels (P＜0.05). 【Conclusion】 Feed intake significantly influenced the C and energy apparent digestibility of Dorper × Thin-tailed Han ewes during non-pregnency and lactation periods. There were correlations between the O₂, CO₂, CH₄, RQ and feed intake (P＜0.05). Lactation significantly improved the digestion and utilization of C and energy.

Key words: ewes, non-pregnancy, lactation, carbon metabolism, energy metabolism