Energy requirements of Dorper×thin-tailed Han crossbred ewes during non-pregnancy and lactation

This experiment was conducted to investigate the energy requirement of Dorper×thin-tailed Han crossbred ewes during non-pregnancy and lactation. Fifteen ewes after parturition were randomly assigned to three treatments: ad libitum (100%) feed intake and 80 or 60% ad libitum intake, and another nine non-pregnant ewes were assigned to a blank control group. Digestibility trials were performed in the non-pregnant ewes and in the lactating ewes on the 20th, 50th, and 80th d of lactation. In parallel with the digestibility trial, a respirometry experiment was conducted to determine the methane and carbon dioxide production with an open-circuit respirometry system that was equipped with respiratory chambers. The net energy (NE) and metabolizable energy (ME) requirements for maintenance and growth were calculated using the carbon and nitrogen balance method. The results revealed that the carbon (C) and nitrogen (N) excretions and energy losses at faeces and urine, as well as the output of methane and CO2, increased significantly with decreasing feed intake (P<0.01). The apparent digestibilities of C in the stages of non-pregnancy and early, middle and late lactation were 55.8–58.3%, 62.5–73.8%, 64.8–71.3%, and 61.7–65.0%, respectively, and the apparent digestibilities of N were 45.2–51.3%, 73.7–82.7%, 72.8–80.5%, and 73.6–76.5%, respectively. The corresponding energy apparent digestibilities were 52.0–56.3%, 60.7–76.6%, 61.0–68.8%, and 61.4–67.7%, respectively. The ME/DE (digestible energy) values were 79.5–85.9%, 79.4–83.5%, 81.0%–85.3% and 78.6–82.9%, respectively. The maintenance requirements of NE, ME, and the efficiencies of ME utilisation for maintenance during the stages of non-pregnancy and early, middle and late lactation were 215.5, 253.1, 247.7, and 244.7 kJ kg−1 BW0.75 d, and 372.4, 327.1, 320.9, and 362.0 kJ kg−1 BW0.75 d, and 0.58, 0.77, 0.77, and 0.68, respectively. The ME requirement for the growth of non-pregnant ewes was 31.3 MJ kg−1 BW gain.