| Expreiment1:Effects of different feeding levels on digestion of nutrients and gaseous metabolism during pregnancy and lactation of Dorper×thin-tailed Han crossbred ewesUtilizing the gradient method, this experiment was conducted to investigate the effects of different feeding levels on digestion of nutrients and gaseous metabolism during pregnancy and lactation of Dorper X thin-tailed Han crossbred ewes. Fifteen healthy ewes were selected for estrus synchronization and artificial insemination, and then assigned into three groups in a complete randomized design after pregnancy tests:one group fed ad libitum (100%), and the other two fed for80%or60%of the ad libitum intake, In addition, nine non-pregnant ewes of the same age and species were used as an extra control group. Digestibility and respirometry trials were performed in the periods of the non-pregnancy,40th,100th and130th days of pregnancy,20th,50th and80th days of lactation, respectively. The apparent digestibilities of dry matter (DM), organic matter (OM), neutral detergent fiber (NDF), acid detergent fiber (ADF), nitrogen (N), carbon (C) and energy of ewes increased significantly with decreasing levels of feed intake (P<0.05). With the pregnancy progressed, the amounts of feed intake reduced, but nutrients digestibilities and methane (CH4) emissions were increased, and on the130th day of pregnancy, the ewes fed at60%ad libitum intake were in negative nitrogen balance. There was a declining trend in milk carbon with decreasing levels of feed intake (P>0.05), but it decreased significantly as lactation progressed (P<0.05). The retained nitrogen (RN), RN/NI (nitrogen intake) and RN/DN (digestable nitrogen) decreased significantly with the decreasing feeding levels during the non-pregnancy and lactation (P<0.05). The carbon in feces and urine decreased significantly with the decreasing feeding levels (P<0.05), and it was tgreater in lactation than in non-pregnancy (P<0.05). Increasing with the decreasing feeding levels significantly (P<0.05), the metabolizibility of digestible energy in the non-pregnant period and on40th,100th and130th days of pregnancy,20th,50th and80th days of lactation were78.55-82.93%,87.83-88.76%,75.48-77.59%,76.31-79.03%,79.53-85.89%,79.40-83.49%, and80.99-85.33%, respectively. The respiration quotients decreased significantly with the decreasing feeding levels (P<0.05), and were greater in non-pregnancy and on the40th day of pregnancy, ranging from0.83to0.96. Except for the100th day of pregnancy, the CH4production and its ratios to DM intake and metabolic body weight (W0.75) decreased significantly with the decreasing feeding levels (P<0.05). Feed intake significantly influenced the apparent digestibilities of dietary nutrients in Dorper X thin-tailed Han crossbred non-pregnant and lactating ewes (P<0.05). There were significant correlations between the O2, CO2, CH4or RQ and feed intake (P<0.05). The digestion and utilization of dietary nutrients, and the carbon and nitrogen output in urine were significantly increased in lactation (P<0.05).Expreiment2:Nitrogen metabolism and net protein requirement for maintenance of Dorper x thin-tailed Han crossbred reproductive ewesThis experiment was conducted to investigate the apparent nitrogen digestibility at different feeding levels and net protein requirement for maintenance during pregnancy and lactation of Dorper×thin-tailed Han crossbred ewes. Fifteen ewes after synchronous estrus and artificial insemination were assigned into three groups:one group fed ad libitum (100%), and the other two fed at either80%or60%of the ad libitum intake, with another nine non-pregnant ewes used as an extra control group. Digestibility trials was performed in the non-pregnant ewes and on the40th,100th,130th day of pregnancy and20th,50th,80th day of lactation, to determine the metabolic parameters of nitrogen and net protein requirement for maintenance. The apparent digestibilities of N in the non-pregnant ewes and on the40th,100th,130th day of pregnancy and20th,50th,80th day of lactation were45.21-51.34%,59.71～64.14%,69.98～71.91%,67.34～68.80%,73.72～82.71%,72.79～80.51%,73.57～76.47%, respectively, and differed only in the non-pregnant period, mid-and late-lactation (P<0.05). The regression equations between NI (g/kg W0.75·d) and RN (g/kg W0.75·d) in the non-pregnant period, and on the40th,100th,130th day of pregnancy and20th,50th,80th day of lactation were:RN=0.3415NI-0.2697, RN=0.4895NI-0.3037, RN=0.3845NI-0.3234, RN=0.4574NI-0.4962, RN=0.2521NI-0.3380, RN=0.2821NI-0.3136, RN=0.2863NI-0.2982(P<0.01), respectively. The net N requirements for maintenance of ewes in the non-pregnant period and on the40th,100th,130th day of pregnancy and20th,50th,80th day of lactation were269.7,303.7,323.4,496.2,338.0,313.6, and298.2mg/kg W0.75-d, respectively.Expreiment3:Energy requirements for maintenance during pregnancy and lactation of Dorper x thin-tailed Han crossbred ewesThis experiment was conducted to investigate the energy requirement for maintenance of Dorper x thin-tailed Han crossbred ewes in the non-pregnant period, pregnancy and lactation. Fifteen ewes were randomly assigned to three treatments:ad libitum (100%) feed intake, and80%or60%of the ad libitum intake, and another nine non-pregnant ewes were assigned into an extra control group. Digestibility trials was performed in the non-pregnant ewes and in the lactating ewes at the20th,50th, and80th day of lactation. In parallel with the digestibility trial, a respirometry experiment was conducted to determine the methane and carbon dioxide productions with an open-circuit respirometry system attached to respiratory chambers. The net energy (NE) and metabolizable energy (ME) requirements for maintenance and growth were calculated by the carbon and nitrogen balance method. The results revealed that the carbon excretions and energy losses in the feces, urine and methane, as well as the output of carbon dioxide increased significantly with decreasing feed intake (P<0.05). The apparent digestibilities of carbon in the non-pregnant ewes, and on the40th,100th,130th day of pregnancy and20th,50th,80th day of lactation were55.75-58.33%,56.78～60.11%,57.06～61.45%,60.82～66.83%,62.54～73.84%,64.80～71.25%, and61.73～65.03%, respectively, and the corresponding apparent energy digestibilities were52.00～56.32%,57.05～58.43%,61.26～64.53%,63.29～66.49%,60.74～76.62%,60.97～68.82%, and61.43～67.74%, respectively. The ME/DE were78.55～82.93%,87.83～88.76%,75.48～77.59%,76.31～79.03%,79.53～85.89%,79.40～83.49%, and80.99～85.33%, respectively. The maintenance requirements of NE in the non-pregnant period, and on the40th,100th,130th day of pregnancy and20th,50th,80th day of lactation were215.48,205.32,246.43,261.85,253.05,247.74, and244.68kJ/kg BW0.75·d, and the corresponding ME requirements for maintenance were372.37,331.61,427.07,498.16,327.08,320.85, and362.04kJ/kg BW0.75·d, respectively. The efficiency of ME utilization for maintenance were0.58,0.62,0.58,0.53,0.77,0.77, and0.68in the non-pregnant period, and on the40th,100th,130th day of pregnancy and20th,50th,80th day of lactation, respectively. The ME requirement for growth of non-pregnant ewes was31.28MJ/kg BW gain. |
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