| With the development of animal nutrition evaluation, it is the general trend to evaluate the energy requirement of animal by the net energy (NE) system. At present, some progress has been made in the research of the NE requirement of ruminants, pigs, chicken and so on. However, there is little known about the NE requirement of ducks, and it is also not clear that whether there are differences among the NE requirement of different duck species. The objective of this study was to establish models of NE requirement of Tianfu duck and Cherry Valley duck from 2 to 3 weeks old based on the determination of their NE requirement for maintenance (NEm) and NE requirement for weight gain (NEg) using the factorial method, and to compare the differences between the NE requirement and efficiency of energy utilization of the two duck species.300 one-day-old Tianfu ducks and Cherry Valley ducks, whose body weight were not different significantly (P<0.05), were selected and acclimated to the environment and diet for one week. After then 50 ducks were selected and randomly distributed into five feed treatments consisting of ad libitum and 15%,25%,35%,45% restriction groups for the metabolic experiment. Each treatment was replicated five times with 2 ducks per replication. The remaining 250 ducks were used for the feeding experiment and the comparative slaughter experiment. At the beginning of the experiment,10 ducks were selected and slaughtered to determine the initial body composition; The remaining 240 ducks were randomly distributed into five feeding treatments (same as the metabolic experiment), and the ad libitum group was replicated ten times, while restriction groups were replicated five times with every replication 8 ducks. At the age of 14 days old,10 ducks were selected from the ad libitum group and slaughtered to determine the body composition; at the 21 days old,10 ducks were selected from every feeding treatment to determine the finial body composition. NEg was obtained by linear regression between body energy content (BE) and body weight (BW) based on the determination of body composition and BW weekly. Metabolizable energy intake (MEI) and heat production (HP) of ducks at different feeding levels were obtained from the metabolic experiment, feeding experiment and comparative slaughter experiment. The logarithmic relationship between HP and MEI provided the NEm, as being the HP at zero MEI. The results showed as follows:① The average daily feed intake (ADFI) and average daily weight gain (ADG) of Tianfu ducks and Cherry Valley ducks of restriction groups were lower than those of the ad libitum group (P＜0.05); while feed/gain (F/G) of Tianfu ducks of restriction groups were higher than that of the ad libitum group (P＜0.05), F/G of Cherry Valley ducks of restriction groups were also higher than that of the ad libitum group, but there was no significant difference between the ad libitum group and the 15% restriction group (P>0.05), and the significant difference appeared until the 25% restriction group (P<0.05); The ADG, ADFI and F/G of Tianfu ducks were all higher than those of Cherry Valley ducks at the corresponding feeding level (P＜0.05).② The body fat content and body energy content of Tianfu ducks and Cherry Valley ducks of restriction groups were lower than those of the ad libitum groups (P＜0.05); while the body water and body protein content of Tianfu ducks of restriction groups were higher than those of the ad libitum group (P<0.05), and the body water content of Cherry Valley ducks was also higher than that of the ad libitum group (P<0.05); the body protein content of Cherry Valley ducks of restriction groups were also higher than that of the ad libitum group, but there was no significant difference between that of the ad libitum group and the 15% restriction group, nor between that of the 35% and the 45% restriction groups (P>0.05), and that of the remaining feeding levels were different significantly with each other (P<0.05); The body fat content and body energy content of Tianfu ducks were all higher than those of Cherry Valley ducks at the corresponding feeding level (P<0.05). However, it’s body protein content was lower than that of Cherry Valley ducks at the corresponding feeding level in addition to that of the 15% restriction group (P＜0.05), and Cherry Valley ducks’body water content was higher than that of Tianfu duck at the corresponding feeding level in addition to that of the 25% and the 45% restriction groups (P＜0.05).③ Energy retained as fat and as protein of Tianfu ducks and Cherry Valley ducks of restriction groups were lower than those of the ad libitum group (P<0.05), and energy retained as fat of Tianfu ducks was higher than that of Cherry Valley ducks at the corresponding feeding level (P<0.05), while the energy retained as protein of Tianfu ducks was lower than that of Cherry Valley ducks at the corresponding feeding level in addition to that of the 15% and the 25% restriction groups (P＜0.05).④ Apparent energy metabolizablity of Tianfu ducks and Cherry Valley ducks of restriction groups were higher than those of the ad libitum group (P＜0.05); Moreover, the apparent energy metabolizablity of Cherry Valley ducks was higher than that of Tianfu ducks at the corresponding feeding level (P<0.05).⑤ MEI, body energy retention (RE) and HP of Tianfu ducks and Cherry Valley ducks of restriction groups were lower than those of the ad libitum group (P<0.05); What’s more, the MEI, RE and HP of Tianfu ducks were all higher than those of Cherry Valley ducks at the corresponding feeding level in addition to the RE of the ad libitum group (P<0.05).⑥ There were significant differences between both of Tianfu duck and Cherry valley duck’s BW and BE at different ages (P<0.05); more older, and more higher of BW and BE of the two duck species; Moreover, BW and BE of Tianfu ducks were all higher than those of Cherry Valley ducks at the corresponding age (P<0.05).⑦ Through linear regression analysis, the NEm and NEg of Tianfu ducks from 2 to 3 weeks old can be calculated by the following formulas:Log10HP=2.76+0.00013MEI, BE=-768.87+10.71BW; and the NEm and NEg of Cherry Valley ducks can be calculated by following formulas:Log10HP=2.74+0.00012MEI, BE=-793.02+10.41BW.Based on these results, it can be concluded as follows:① The NEm of Tianfu ducks and Cherry Valley ducks from 2 to 3 weeks are 577.03 and 549.54KJ·kg-1BW0.75·d-1,respectively;The MEm are 646.71and 625.59KJ·kg-1BW0.75·d-1, respectively; The efficiency of energy utilization for maintenance are 0.89 and 0.88, respectively.② The NEg of Tianfu ducks and Cherry Valley ducks from 2 to 3 weeks are 10.71 and 10.41 KJ·g-1, respectively; The MEg are 15.08 and 13.88 KJ·d-1, respectively; The efficiency of energy utilization for weight gain are 0.71 and 0.75, respectively.③ A model is developed to calculate NE requirement for Tianfu ducks from 2 to 3 weeks old:NE=577.03BW0.75+10.71 ΔW, and for Cherry Valley ducks from 2 to 3 weeks old:NE=549.54BW0.75+10.41 ΔW (where, BW0.75 is metabolic body weight, ΔW is daily weight gain). |
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