Investigation on requirement of crude protein for maintenance in Shaoxing ducks

Abstract

A series of nitrogen (N) balance trials were carried out to investigate the requirement of crude protein (CP) for maintenance in Shaoxing Ducks. The N balance was determined for five periods from the age of 1 day to 28 weeks (0–4 weeks, 5–8 weeks, 9–16 weeks, 17–20 weeks, 20–28 weeks). Fifteen ducks were used in each period. The birds were divided into three equal groups and fed on the diets with equal metabolizable energy (ME) and different contents of CP (low, medium and high). The N requirements for maintenance were estimated from the relationship between the N retention and N intake (NI). Following the above series of N balance test, 25 ducks at the age of 10 weeks were used in an N balance test with N-free ration. The birds were divided into five groups and offered N-free ration at levels of 100, 75, 50, 25 and 0 g per day, respectively. The net protein utilization (NPU) ranged from 0.45 to 0.53 and increased with the advancing age of ducks, but no significant difference was found among different contents of the dietary CP. The estimated N requirement for maintenance was, on an average, 455 mg/kg BW 0.75 per day, which was equal to 2.8 g CP/kg BW 0.75 per day. The result from the trial in the N-free ration showed that the value of N requirement for maintenance was 467 mg/kg BW 0.75 per day, conforming the results in the series of N balance test. The lower intake of N-free ration resulted in more N excretion suggesting that protein catabolism may occur in the body of birds to meet maintenance requirements for N when the dietary NI was very low.